RE: The Great Melbourne Telescope (slightly peripheral to the List)

[Roger W. Sinnott]

There is a fascinating seven-page article about the history of the GMT and its 
restoration effort in the current (October) issue of Sky & Telescope, now on 
newsstands.  It was written by well-known science writer Trudy E. Bell.

   Roger S.

-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of 
john.pick...@bigpond.com
Sent: Thursday, September 13, 2018 7:53 PM
To: Sundial List
Subject: The Great Melbourne Telescope (slightly peripheral to the List)

Good morning,

I received this news piece from another group I’m on, and thought it might 
interest List members.

***
The Great Melbourne Telescope

The Great Melbourne Telescope (GMT) is being restored after sitting 
ingloriously out in the weather in Canberra for several years.

The Great Melbourne Telescope was built in Dublin in 1868 and erected at 
Melbourne Observatory in 1869. At the time it was the second largest 
telescope in the world and the largest in the southern hemisphere.

When Melbourne Observatory closed in 1944, the telescope was sold to the 
Commonwealth Observatory at Mount Stromlo, Canberra. At Mount Stromlo the 
telescope was given a new 50-inch glass mirror and became an integral part 
of Mt Stromlo’s work from 1961 into the 1970s. In the 1990s the telescope 
was rebuilt with two large-scale digital cameras for the search for evidence 
of dark matter. Then in January 2003 a bushfire swept across Mt Stromlo, its 
firestorm destroying the majority of the telescopes and buildings. Only the 
large iron castings from the GMT, bent metal and broken glass remained.

Unloved and broken it sat in the extreme cold of Canberra’s weather for at 
least four years until members of the Astronomical Society of Victoria (ASV) 
embarked on a mission to rescue it in 2008. Lacking plans or drawings and 
missing at least 180 parts, a team of ASV volunteers has been painstakingly 
dismantling it in a large restoration area in Melbourne.  Every available 
working part has been identified, numbered, restored or rebuilt.

The GMT was built with a speculum mirror lens and is the last of the great 
mirrored telescopes. An unforgettable moment for the restoration team came 
in 2010 when a staff member found a box in the museum’s store and called for 
expert help to confirm the contents. The box contained the original 
flotation system for the telescope’s one-ton white bronze mirror. It was a 
joyous day for the GMT reconstruction team who had long wondered what had 
happened to this item of 19th century engineering which provides a balanced 
bed of 48 steel balls to support the back surface of the mirror evenly, 
keeping distortion of the mirror surface to less than a 1/10,000th 
millimetre.

The dollar value of the ASV work is incalculable, unlike the restoration 
costs. Funding for the project is an ongoing challenge. The replacement 
mirror alone, is likely to be in excess of $200,000. Many parts of the GMT 
can be repaired or remade in the restoration area by the combined efforts of 
Museum Victoria staff and the ASV volunteers. When larger equipment is 
required, it is manufactured by the staff at Scienceworks.

A 2-metre high photograph of the telescope from 1885 is a key reference for 
the group as they establish which parts are original and which were replaced 
at Mt Stromlo Observatory. The ASV team hope to have the GMT back home at 
Observatory House in 2019 to coincide with the 150th anniversary of its 
arrival in Melbourne. Everyone interested in following the progress of the 
GMT restoration or wanting to donate to this great cause can do so through 
www.greatmelbournetelescope.org.au

Written from information at www.greatmelbournetelescope.org.au and an 
article written by Liz Clarkson (also on the GMT website).

*


Cheers, John

John Pickard
john.pick...@bigpond.com

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RE: Blank subject line

[Roger W. Sinnott]

I agree with Helmut!  

When I see a blank subject line, I become suspicious and often just delete
the message without opening it.

Roger


-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Helmut
Haase
Sent: Tuesday, May 22, 2018 10:11 AM
To: sundial@uni-koeln.de
Subject: Blank subject line

Hallo gnomonicist,
It seems to become a trend here to send mails without subject information.

Is it difficult to write a subject line?

Regards

Helmut Haase



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RE: Analemma intersection

[Roger W. Sinnott]

Roger (and others),

 

A slight correction concerning the motion of Earth's perihelion with respect to 
the seasons. Owing to precession, the equinoxes and solstices drift slowly 
westward along the ecliptic in a cycle of about 26,000 years. But at the same 
time perturbations by the other planets cause the Earth's perihelion point to 
drift slowly eastward along the ecliptic.  The net effect is that the 
perihelion migrates all the way around the ecliptic (with respect to the 
seasons) in about 21,000 years.

 

Bernard M. Oliver wrote a classic article about the changing shape of the 
analemma for Sky & Telescope (July 1972, pages 20-22). He gave A.D. 1246 as the 
year when perihelion and the winter solstice coincided.  Among the other 
effects he noted, in A.D. 6489 the two lobes of the analemma will be 
essentially equal in size and perihelion will coincide with the vernal equinox.

 

(Full disclosure: I remember that article well, because one of its diagrams was 
the very first one I prepared after joining the magazine staff!)

 

Roger S.

 

 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Roger Bailey
Sent: Thursday, April 12, 2018 6:13 PM
To: Dan-George Uza; Sundial List
Subject: Re: Analemma intersection

 

Hi Dan, 

To me the value of the EQT at the intersection is an indication of the 
asymmetry of the analemma caused by the difference between the solstice and 
perihelion dates. The tilt of the earths axis is one parameter that defines the 
analemma. This is shown at the extremes, the summer and winter solstices. The 
eccentricity of the orbit is the other parameter that defines the analemma. 
This is indicated by the perihelion. If the date of the perihelion is the same 
as the solstice, I would expect the curve would be symmetrical and the EQT at 
the intersection would be equal to zero. Perihelion was 2 Jan 2018 and the 
winter solstice was 21 Dec 2018. This 12 day difference defines the offset of 
the intersection of the analemma loops. When was the perihelion on the winter 
solstice? The perihelion changes in a cycle of 25,800 years. So 12 days gives 
12/365.25x25,800 or 878 years ago. In 1140 AD I would expect a symmetrical 
analemma.

 

Of course there is more to this than this simple approximation of orbital 
dynamics. What was the actual date when the perihelion and solstice were the 
same? I offer this as quick answer to the question on the significance of the 
analemma curve intersection.

 

Regards, Roger Bailey

Walking Shadow Designs

 

From: Dan-George Uza   

Sent: Thursday, April 12, 2018 3:46 AM

To: Sundial List   

Subject: Analemma intersection

 

Hello,

 

Tomorrow the Sun will have reached the point of intersection in the analemma 
8-curve. How do you compute the exact time of intersection (i.e. when both the 
hour angle and the solar declination match for two days)? And does it have any 
special significance?

 

Dan 

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RE: Gnomon of Saint-Sulpice

[Roger W. Sinnott]

Dan,

 

I’m just guessing, but maybe the two holes and two spots are placed so that, no 
matter what the Sun’s declination is, at least one of the spots will fall on a 
smooth, uncluttered part of the floor.

 

 Roger

 

 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Dan-George Uza
Sent: Sunday, April 03, 2016 3:23 PM
To: sundial@uni-koeln.de
Subject: Gnomon of Saint-Sulpice

 

Hello,

 

Last week I visited the meridian line of Saint-Sulpice in Paris which dates 
back to 1743. After the French Revolution the Republicans chiseled out all 
references to royalty from the inscriptions. I don't know why but they also 
erased some of the zodiac signs. Could it have something to do with the new 
Republican Calendar? Also, there are two holes for the light to enter with two 
spots forming on the ground and I don't understand exactly why...

 

Dan Uza

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RE: No decision on future of leap seconds

[Roger W. Sinnott]

Wolfgang,

Thanks very much -- I was ignoring real-world details.

Roger


-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Wolfgang R. 
Dick
Sent: Monday, November 30, 2015 11:14 AM
To: Sundial Mailing List
Subject: RE: No decision on future of leap seconds

Dear Rudolf and Roger,

The leap second comes from the fact that the Earth's rotation rate has 
decreased since the definition of the second. Currently each day is 1 
millisecond longer than 24 hours in the mean. One has to regard the Earth as a 
clock, which is too slow compared to a precise clock (= UTC running in parallel 
to atomic time TAI).
After one day the difference in time which the two clocks display is 1 ms, 
after two days 2 ms, ..., after 1000 days 1 second. This is the leap second.
UTC clocks are stopped for one second, so that after this the two clocks (Earth 
= UT1 and precise clock = UTC) are showing the same time again. 1000 days is 
about 3 years - currently a leap second is introduced each 3 years in the mean.

When the mean "length of day" (LoD, one day = 24 h + LoD)) was 2 ms in 1990s, 
we had a leap second each 1 1/2 years in the mean (= 500 days). Since then the 
Earth rotation has speeded up due to decadal fluctuations (core-mantle coupling 
in Earth). But it will decrease again due to the Moon.

After the next 100 years, LoD will be about 3 ms in the mean. Then a leap 
second will be needed every 333 days. And so on. This is a quadratic function 
with time, i.e. the frequency of leap seconds increases quadratically with 
time. This will be a big problem for our grandgrandgrand...children.

Best regards,
Wolfgang


Gesendet: Montag, 30. November 2015 um 12:18 Uhr
Von: "Roger W. Sinnott" <roger.sinn...@verizon.net>
An: sundial@uni-koeln.de
Betreff: RE: No decision on future of leap seconds

Rudolf,
 
If the day length starts at 86400 seconds and grows by 0.17 second each 
year, it would indeed reach 86401 seconds in about 6 years.  But if this 
rate is uniform, the tiny fractional increases would accumulate to 1 second in 
just 343 years, so I think that's when the first leap second would be needed.
 
  Roger
 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Rudolf 
Hooijenga
Sent: Monday, November 23, 2015 5:18 PM
To: 'Brooke Clarke'; sundial@uni-koeln.de
Subject: RE: No decision on future of leap seconds
 
. . . In fact, the Earth does slow down – and not just lately –, but this 
effect amounts to about 17 microseconds each year on average, and would only 
necessitate an extra leap second every sixty thousand years or so. The 
day-to-day fluctuations are much larger than this.
 
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RE: No decision on future of leap seconds

[Roger W. Sinnott]

Rudolf,

 

If the day length starts at 86400 seconds and grows by 0.17 second each 
year, it would indeed reach 86401 seconds in about 6 years.  But if this 
rate is uniform, the tiny fractional increases would accumulate to 1 second in 
just 343 years, so I think that's when the first leap second would be needed.

 

  Roger

 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Rudolf 
Hooijenga
Sent: Monday, November 23, 2015 5:18 PM
To: 'Brooke Clarke'; sundial@uni-koeln.de
Subject: RE: No decision on future of leap seconds

 

. . . In fact, the Earth does slow down – and not just lately –, but this 
effect amounts to about 17 microseconds each year on average, and would only 
necessitate an extra leap second every sixty thousand years or so. The 
day-to-day fluctuations are much larger than this.

 

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RE: due east

[Roger W. Sinnott]

Brent,

 

The "small circle" route is the one that takes you on a curved path, always
toward due east.

 

You could also start out going due east on a "great circle" route, and in
that case, as you note, the path would gradually veer southward.

 

Both of these routes start out perpendicularly from the north-south line.

 

 Roger

 

 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of David Patte
?
Sent: Tuesday, September 15, 2015 12:34 PM
To: sundial@uni-koeln.de
Subject: Re: due east

 

They are east-west lines, but they are not straight. They are circles.



On 2015-09-15 12:30, Brent wrote:

If I was in halifax at sunrise on the equinox and the earth stopped rotating
and I walked due east (towards the sun) across the ocean
I would end up in Southern Spain and not on my same latitude which is in
Southern France.

So I conclude that latitude lines are not east-west lines.

Correct?

thanks;
brent



On 9/15/2015 9:01 AM, Frank Evans wrote:

Hi Brent and all,
Compass directions that are pursued make spiral curves towards the poles, if
north of east-west then towards the north pole, if south of east-west then
towards the south pole. If east or west then they do neither but continue
east-west. Try Googling "loxodromic curve". It's what you draw on a chart.
Sailors call it a "rhumb line".
Frank 55N 1W

On 15/09/2015 15:10, Brent wrote:

I'm confused maybe.

I live in the northern hemishpere and anticipating the equinox on the 23rd.

Supposedly the sun will rise due east.

So if due east is a right angle from north south and I traveled due east I
would not follow my line of latitude.
I would get further and further south of my latitude the further I traveled.

So either the lines of latitude are not east west lines or due east is not a
straight line but curved.
I suspect lines of latitude are not east west lines?
They would work fine if the earth was not tilted, but it is.

Wouldn't it make sense to coordinate the globe so lines of latitude (or call
them something else) are straight and a right angle
from north south?

brent







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RE: Calculating azimuth of sunrise and sunset from present back 25, 000 years

[Roger W. Sinnott]

Hi Brad,

 

It seems that your listing uses the Julian calendar before year +1600, as it
should.  But the Julian calendar is not a perfect fit to the tropical year,
and the same problem that necessitated the Gregorian calendar reform would
also apply, in reverse, when going backward in time.  In fact, if the error
is on the order of 10 days per 1000 years, it would grow to more than half a
year in 25,000 years!  On top of that, there is the additional need to
convert TDT dates to civil dates by applying the delta-T correction.  (Even
just 2000 years ago, delta-T was a correction of 2 or 3 hours, so it would
grow to a number of days, as well, by the time you went all the way back
25,000 years.) 

 

So I don't think it is possible to give meaningful calendar dates for
solstices in the remote past.  The solstice date tends to drift slowly in
any calendar based on a fixed average number of days per year.  Presumably,
after a number of centuries had passed, people would notice that their
summer solstice was drifting away from the month they identified with
summer, and they would make an adjustment to their calendar to bring things
back into line.

 

Fortunately, for determining astronomical alignments in prehistoric times,
we don't need to know anything about what calendar was being used.  The
obliquity alone determines the extremes of sunrise and sunset azimuths.  So
everything boils down to finding a reliable expression for the obliquity up
to 25,000 years ago.  (I don't know if even that is possible with current
knowledge.)

 

Then too, as has been mentioned, there's plate tectonics. (But that effect
is probably much smaller than the other effects.)

 

   Roger



 

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Brad Lufkin
Sent: Tuesday, June 26, 2012 3:25 PM
To: John Pickard; Sundial Mailing List; Roger Bailey
Subject: Re: Calculating azimuth of sunrise and sunset from present back 25,
000 years

 

Dear John:

attached is the table you've asked for. It includes the astronomical year,
the month, day, and time of the event, and azimuth (in degrees) of sunrise
and sunset. Azimuth is measured from North towards East (so North = 0
degrees, East = 90, South = 180, West = 270).

The table is based on VSOP87D for the position of the Sun. I used a
combination of Lasker and Borger for the obliquity of the ecliptic. And the
assumed latitude of the site is 34 degrees South. Many thanks to all who
contributed to the discussion, in particular to Roger Bailey for pointing to
the Borger reference. Roger solved the azimuth problem with his spreadsheet
and charts. The attached table includes the dates as well as the azimuths.

Brad

On Thu, Jun 21, 2012 at 12:55 AM, John Pickard john.pick...@bigpond.com
wrote:

Good evening on a chilly Winter Solstice in Sydney,

 

As part of my research on fences, I need to calculate the azimuth of sunrise
and sunset back to 25,000 y ago. The question arises from the disputed
origins of some dry stone walls found in southern New South Wales. A local
historian has suggested that they are an astronomical alignment built by
Aborigines, but they were recorded as fences on survey plans in the late
19th C. The locations suggest to me that the walls were built as fences on
terrain too steep for the log fences of the time.

 

What I would like to is calculate the azimuths of sunrise and sunset at
Winter Solstice back 25,000 y (about the length of time Aborigines occupied
the area) in annual increments (or decrements to be pedantic!). I know that
I can do this for any specific date in a number of excellent programs, but I
don't relish the notion of that many calculations. Even if I increase the
interval to 100 y, I would still have 250 calculations.

 

My question is: does anyone know of a way of automating this to generate a
table of the dates and the azimuth of sunrise and sunset? 

 

 

Many thanks, John

 

John Pickard
john.pick...@bigpond.com 


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RE: Re: Re: RE: R: Where it wil be equinox, at noon

[Roger W. Sinnott]

Brad,

 

Are you sure you are using the full VSOP87 theory?  I don't think it has
been published in print form, anywhere.  The appendix in Jean Meeus's
Astronomical Algorithms gives an abridged form of VSOP87, and this could
explain your discrepancies with Table 27.E.

 

Roger

 

 

On Thu, Sep 29, 2011 at 2:24 PM, Brad Lufkin bradley.luf...@gmail.com
wrote:

Gian:
Continuing my investigation, I tried to reproduce Table 27.E of Meuus's
Astro Algorithms, 2nd Edition. The table shows the time, to the nearest
second, of the solstices and equinoxes for the years 1996-2005. The table is
based on the full VSOP87 theory.
I too am using the full theory, along with the corrections for aberration
and nutation (though I'm using the simpler version of the nutation model
described in chapter 22 of Meuus--this may be significant).
In any case, the following histogram shows the difference in seconds between
my results and Meuus's table:

-4 x
-3 
-2 
-1 x
 0 x
+1 xx
+2 
+3 xx
+4 x

So what the histogram shows is that we have exact agreement in 5 out of 40
cases, +1 second difference in 10 out of 40 cases, -1 second difference in 5
out of 40 cases, and so on. In no case is the difference greater than 4
seconds (which corresponds to a difference of one-sixth of an arcsecond).
The histogram seems fairly normal, with no clear evidence of systematic
bias.
I plan on implementing the more accurate nutation model. I'll let you know
what happens.
Regards, Brad

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RE: Re: Re: RE: R: Where it wil be equinox, at noon

[Roger W. Sinnott]

Ø  The full version is available from. . .

 

Brad,

 

So it is! – Thanks very much for letting me know about this.

 

But VSOP87 is about of the same vintage as the older JPL ephemeris DE200,
about 25 years ago.  JPL is now up to DE421, and calculations consistent
with DE421 are available from the free computer program SOLEX, written by
Aldo Vitagliano:

http://chemistry.unina.it/~alvitagl/solex/

 

I just tried Solex 11.0, using DE421 with aberration and nutation turned on,
and found that the apparent geocentric ecliptic longitude of the Sun will be
0deg 00’ 00.00” at 5h 15m 32s Dynamical Time on 2012 March 20.  So in this
case it does agree to the second with Meeus’s Astronomical Tables of the
Sun, Moon, and Planets (2nd ed., 1995).

 

 Roger 

 

From: Brad Lufkin [mailto:bradley.luf...@gmail.com] 
Sent: Friday, September 30, 2011 8:25 AM
To: Roger W. Sinnott
Cc: sun.di...@libero.it; Sundial Mailing List
Subject: Re: Re: Re: RE: R: Where it wil be equinox, at noon

 

Roger:
I'm pretty sure I am using the full theory. I'm definitely not using the
abridged form from Meuus's Appendix.

The full version is available from an FTP server. But I found (I confess I
don't remember where) an ASCII text file that, based on a more than cursory
examination, seems to be an exact match to the version available from the
FTP server.
You can find a link to the FTP server at the end of the wiki article on
VSOP.

The wiki article is at:
http://en.wikipedia.org/wiki/Secular_variations_of_the_planetary_orbits

The FTP server is at:
ftp://ftp.imcce.fr/pub/ephem/planets/vsop87/

Regards, Brad

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RE: Azimuth calculation

[Roger W. Sinnott]

Andrew:

 

I think your numbers make sense.

 

You didn’t mention the date, but I suspect your calculation was for July 30, 
2011.  For this date at 11:18 a.m. EDT, and the lat/long of Boston, I find the 
following values ---

  

   Sun’s declination:   +18.5 degrees

   Sun’s azimuth:133.4 degrees (from north through east)

 

When you say the wall “declination” is 20 degrees east (from due south), this 
is the same as saying that the normal to the wall faces azimuth 160 degrees 
(measured from north through east).

 

Then, you measured the Sun’s azimuth to be 26.8 degrees (east) with respect to 
the wall, implying that the Sun’s azimuth is 160 – 26.8 = 133.2 degrees.  This 
is rather close to the 133.4 that I got independently above. 

 

Some reference books define azimuths as the angle from due south, while others 
define it as the angle from true north, so it is important to keep these 
straight.

 

Roger 

 

 

From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On 
Behalf Of Andrew Theokas
Sent: Sunday, July 31, 2011 9:57 AM
To: sundial@uni-koeln.de
Subject: Azimuth calculation

 

Fellow dialists:

 

I am using the following well known formula to calculate the sun’s azimuth for 
a particular time and location:

 

Azimuth= tan-1(sin H/(sin φ*cos H – cos φ*tanδ)

 

where 

H= Sun’s hour angle

φ= the latitude - 42.3 degrees

δ is the sun’s declination - 18.62 degrees

 

The location is in Boston, USA or 42.3 degrees N and 71.04 degrees west

 

I am using the azimuth-azimuth approach to find the declination of a wall found 
here:

 

http://www.mysundial.ca/tsp/wall_declination.html

 

the time the measurement was made was 11:18 am (daylight savings time is in 
effect)

 

I can easily calculate that the azimuth with respect to the wall is 26.8 
degrees.

 

Here is the problem: using two other independent methods I find that the wall’s 
declination is 20 degrees East.

 

So 26.8 degrees – Sun’s Azimuth should equal about twenty degrees.

 

But, using the above equation I cannot get an Azimuth value to work. One place 
where I might be in error is the value of the Hour angle which I compute to be 
about –16 degrees.

 

But you can also find the Hour Angle on line here at 
http://pveducation.org/pvcdrom/properties-of-sunlight/sun-position-calculator

 

Where might I be going wrong?

 

Many thanks for a reply!

 

Andrew Theokas

 

 

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RE: OBASIC on a 64 bit Windows 7 PC?

[Roger W. Sinnott]

Mac,

I encountered exactly the same problem in December.  I bought a PC that came
with Windows 7 Home Premium and tried to run Turbo Basic (very similar to
QBasic).  I have literally hundreds of programs I've written over the years
in Turbo Basic and absolutely had to be able to run them.  

The way I solved the problem was to upgrade to Windows 7 Pro (which cost
about $100), and then to download  the free software from Microsoft for
setting up a virtual PC (a separate partition of my hard disk) and running
another free download that launches Windows XP.  Windows 7 Home Premium does
not support XP mode, but Windows 7 Pro does.

I don't use QBasic, but I do have it, and I just verified that I can run it
in XP mode.  The only thing that does *not* work in this XP mode is to open
a full-screen DOS window (which was possible on my previous PC, running XP).
Instead, I have to run all my programs in a small window.  This is mildly
annoying, but at least they all do run this way.

Roger
 

-Original Message-
From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On
Behalf Of Mac Oglesby
Sent: Thursday, April 14, 2011 7:06 PM
To: Sundial Mailing List
Subject: OBASIC on a 64 bit Windows 7 PC?


Hello Friends,

I've just bought a PC which runs Windows 7 (Home Premium) 64-bit. 
Despite what the sales Tech said, it doesn't seem to deal with QBASIC at
all.

There were some postings a while ago about using sundial software with
Windows 7, but looking through the archives I didn't find anything about
QBASIC and Windows 7.

If anyone knows of a reasonably simple way to use QBASIC on a 64-bit Windows
7 PC, please let me in on the secrets as soon as possible, for the PC is
still returnable for full refund.

Thanks,

Mac

P.S. It would also be very useful to hear from anyone who knows (or is
pretty sure) that there is no hope of running QBASIC on my new PC.

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Moscow sundial?

[Roger W. Sinnott]

All,

I am trying to find a YouTube video that was linked to from this list
several years ago.

It shows a large analemmatic sundial located in a public park in Moscow (I
think).  Various passersby tried to figure out how it worked, where to
stand, etc., and it was pretty funny.  This could not have been before 2005,
the year YouTube started.

Anyone have the link?

Roger


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RE: Moscow sundial?

[Roger W. Sinnott]

Hi Reinhold,

 

Yes, that’s it!!  Many thanks.

 

When it was first posted, I remember a comment by someone on this list:
Most of the people  stood on the label of the month, rather than on the
point on the centerline to which the label referred.  (I’m not sure what
point the pigeons went to.)

 

Roger

 

Direct link:  http://www.youtube.com/user/AleksandrBoldyrev?gl=RU
http://www.youtube.com/user/AleksandrBoldyrev?gl=RUhl=ru hl=ru

 

 

From: Reinhold Kriegler [mailto:reinhold.krieg...@gmx.de] 
Sent: Wednesday, March 09, 2011 5:47 PM
To: 'Roger W. Sinnott'; 'Sundial List'
Subject: AW: Moscow sundial?

 

 

Dear Roger,

 

it might well be you are looking for the very beautiful sundial-YouTube-film
which you can easily find within this link:

 

http://www.ta-dip.de/sonnenuhren/sonnenuhren-von-freunden/r-u-s-s-l-a-n-d/al
eksandr-w-boldyrev.html 

 

Have a look!

The beautiful young Russian women enjoy this sundial, made by Aleksandr W
Boldyrev as well as the pigeons and the little children… and some men!

Enjoy!

 

Best regards!

Reinhold Kriegler




* ** ***  * ** ***

 

Reinhold R. Kriegler

 

Lat. 53° 6' 52,6 Nord; Long. 8° 53' 52,3 Ost; 48 m ü. N.N.  GMT +1 (DST +2)
www.ta-dip.de

 

http://de.youtube.com/watch?v=XyCoJHwzzjU
http://de.youtube.com/watch?v=XyCoJHwzzjUfmt=18 fmt=18

 

http://www.ta-dip.de/dies-und-das/r-e-i-n-h-o-l-d.html

 

 

-Ursprüngliche Nachricht-
Von: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] Im
Auftrag von Roger W. Sinnott
Gesendet: Mittwoch, 9. März 2011 22:44
An: 'Sundial List'
Betreff: Moscow sundial?

 

All,

 

I am trying to find a YouTube video that was linked to from this list

several years ago.

 

It shows a large analemmatic sundial located in a public park in Moscow (I

think).  Various passersby tried to figure out how it worked, where to

stand, etc., and it was pretty funny.  This could not have been before 2005,

the year YouTube started.

 

Anyone have the link?

 

Roger

 

 

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RE: Fwd: [Flags] (pt) Canedo Commune (Ribeira de Pena Municipality, Portugal)

[Roger W. Sinnott]

Frank,

The Wikipedia article does not say proper motion, and I'm sure that was
not the reason for correcting the stars' positions on the flag of Brazil.
Rather, the stars may have been carelessly plotted on the original flag
(even if shown more accurately than on the flags of many other countries).

On this flag the star with the highest proper motion is Alpha Centauri,
which moves 3.71 arcseconds per year.  This is 0.1 degree since 1889 --
hardly noticeable at the flag's scale.

Roger S. 
 

-Original Message-
From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On
Behalf Of Frank King
. . . 

   http://en.wikipedia.org/wiki/Flag_of_Brazil

This article describes the current flag in great detail.  It is dominated by
a representation of the night sky over Rio de Janeiro at 08:37 on the
morning of 15 November 1889.

In an intriguing note, the article explains that the positions of the stars
were altered slightly in 1992 to account for proper motion since 1889.

The Brazilians are to be commended for their insistence on precision but
this alteration means that the flag no longer represents the night sky in
November 1889.  As such the current flag is a bit of an iconoclast.

I do hope that Instruction on the Design of the National Flag is in the
school curriculum in Brazil.  No wonder the country is doing well!

The only detail that I would like explained is just what projection is used.

Can James Morrison comment please?

Frank King
Cambridge, UK.


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RE: 360 degree clock

[Roger W. Sinnott]

It's also possible to think of degrees, arcminutes, etc., as a cryptic
notation, given the long history of timekeeping.  I have a set of 7-place
trig tables, published in 1958 by H.M. Nautical Almanac Office, with the
argument in time.

For example, this book lists the tangent of 1h 38m 13s as 0.4568685 (because
that amount of time is the same as 24.5541666... degrees).

Roger  


-Original Message-
From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On
Behalf Of Brent
Sent: Tuesday, January 18, 2011 3:03 PM
To: Sundial List
Subject: 360 degree clock

Hello;

If you think about it, hours, minutes and seconds are an awkward system for
using time.

My idea would be to switch to a 360 degree clock.
The earth is round and makes one complete revolution per day, 360 degrees.
So why not measure time based on what angle of degree the earth happens to
be at your location.

Midnight could be 360 degrees
6AM 90 degrees
Noon 180 degrees
6PM 270 degrees

For conversions:

Each hour would equal 15 degrees.
Each degree would equal 4 minutes.
Each degree would equal 240 seconds.

So instead of saying it's 6:34am and 28 seconds it would be:
6x15 = 90
34/4 = 8.5
28/240 =.117
The time would be 98.617 degrees

Of course you wouldn't do conversions, you would just look at your new 360
degree watch.

If I came to work at 98.617 degrees and left at 187.786 degrees I have
worked:

187.786 - 98.617 = 89.169 degrees

Makes more sense to me.

Did anyone ever tell time this way?
It seems like it would work nicely with sundials.

brent




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RE: Dialist's Companion

[Roger W. Sinnott]

Tracy,

 

I am facing similar problems.  Two weeks ago I got a new desktop computer
with Windows 7 Home Premium on it.  I quickly discovered that when I try to
run any of the old DOS programs I get the same error message you are
reporting.  I tried opening a command-line window, which works, but when I
try to run the programs in that window I still get the error message.  This
was puzzling, because last spring I bought a notebook computer with Windows
7 Starter on it, and all my old programs *do* run properly on it, as they
had on an earlier computer running Windows XP.

 

So I put some of my programs on a flash drive and went to the local computer
store.  It seems I will have to upgrade from Windows 7 Home Premium to
Windows 7 Professional.  There is a free download available for Windows 7
Professional that lets it run XP-compatible programs in a DOS Window.  I
verified that it will do this on a couple of machines at the store.

 

Another option is a freeware program, Dosbox.  I have downloaded that from
the web, and it will run the old programs as well.  The only problem is that
with Dosbox  you have to execute a number of steps and clicks each and every
time you want to run an old program.  This is a nuisance.  I want to be able
to have icons on my desktop that I can click on and run my programs
immediately, as I could do on my old XP machine.  So I am about to upgrade
to Windows 7 Professional (which will cost about $100).

 

Roger

 

 

From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] On
Behalf Of Tracy
Sent: Sunday, December 19, 2010 8:14 PM
To: sundial
Subject: Dialist's Companion

 

Hello Everyone
I got a new computer and it has Windows 7 on it. I tried to use the
Dialist's Companion program with it, and it won't work. The error message
that comes up when I try to run the program states that the program is not
compatible with my version of Windows, and that I should check my computer
system information to see if I need a 32-bit or a 64-bit version of the
program. Can anyone help me? I tried downloading the latest version straight
from the website itself, but it still doesn't work :-(
Thank you in advance.
Tracy

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Re: stop the earth

[Roger W. Sinnott]

Brent,

Yes, I think you *could* determine your longitude by observing a 
geosynchronous satellite whose location was known.  There would be some 
uncertainty if it wanders a little.  Much more important, however, is 
figuring out which geosynchronous satellite you are looking at.  You'd 
probably have to aim a dish at it and see what TV stations you get.


   -- Roger

- Original Message - 
From: Brent bren...@verizon.net

To: Sundial List sund...@rrz.uni-koeln.de
Sent: Thursday, December 09, 2010 3:17 PM
Subject: stop the earth


I have been wondering why I can determine my latitude using simple tools 
but not my longitude? The earth is a sphere, I would think if you can 
determine one you can determine both.


The problem with calculating longitude seems to be the earth is rotating 
on its' axis. If the earth stopped spinning, the sun would not rise and 
set but stay put, and then I could determine the angle of the sun from my 
horizon and thus determine my longitude.


Well that's not going to happen anytime soon. But if I could see a 
geostationary satellite I could essentially do the same thing don't you 
think?


I have seen orbiting satellites at dusk many times but does anyone know if 
you can see geostationary satellites with the naked eye?


thanks;



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Re: Light Based Geolocation

[Roger W. Sinnott]

Brent,

I think you could determine your latitude this way, but not your longitude. 
For the longitude, you would need some way to relate your local sunrises and 
sunsets to the local time at some known longitude, such as that of 
Greenwich.

In other words, the geolocation tagging gadget must carry a time-of-day 
clock from a known longitude. This is the same as the age-old longitude 
problem that all mariners faced.

   -- Roger


- Original Message - 
From: Brent bren...@verizon.net
To: Sundial List sund...@rrz.uni-koeln.de
Sent: Tuesday, October 12, 2010 5:05 PM
Subject: Re: Light Based Geolocation


 So I am marooned on a island with nothing but I might be able to
 determine a few things that I could write on a message in a bottle
 that would help my rescuers determine my exact location.

 By careful sunrise observation I could determine the solstices.
 Now I have a calendar.

 I know dawn to dawn is 24 hours so I could make a clock with a washed
 up bottle filled with sand and measure/mark what comes out in one day.

 Then I could cut that sand in half for 12 hours and half again for 6
 hours and half again for 3 hours and then thirds for one hour.
 Now I have an hour clock.

 Now I can measure the hours of daylight from dawn to dusk on the
 solstice and send that in the bottle and my rescuers will be able to
 determine my latitude and longitude.

 Of course I would have to say northern or southern solstice but that's
 easy because we know the sun rises in the east.

 Would this be enough information?

 thanks again;
 brent

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Re: Photo etching sundials on thick metals.

[Roger W. Sinnott]

Tony,

These are fascinating, well-made videos!  I am curious:  How deep are the 
recesses etched by this technique?

-- Roger

- Original Message - 
From: Tony Moss t...@lindisun.demon.co.uk
To: Sundial Mailing List sundial@uni-koeln.de
Cc: Jack Aubert j...@chezaubert.net; Mike Tomlinson 
gman...@tiscali.co.uk
Sent: Wednesday, June 23, 2010 7:59 AM
Subject: Photo etching sundials on thick metals.



Now that I have retired from commercial dial making perhaps the time has
come to pass on some of my 'trade secrets'. The video was slightly too
long for YouTube but with some help from Tom Laidlaw in splitting it
into two 5-minute parts, the process has been transferred for all to see
on YouTube  at

http://www.youtube.com/watch?v=ML37yRmAsOA

http://www.youtube.com/watch?v=PAW0q6i7aqg

Have Fun!

Tony Moss




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New type of clock

[Roger W. Sinnott]

All,

A friend of mine (Joe Rao of New York City) just sent me this neat link. 
Check it out!

-- Roger

-

A different way to display time on the green time line.

This is a real cool clock! I  believe it comes from a Dutch web site.

Here is what you will see when you look at this clock. Don't do anything.
It's automatically adjusted to your time zone.  It gives you the EXACT TIME
of the DAY in seconds, minutes, hours, the day, month and year. Just read
the green line. Everything's  there.

Remember these definitions:

  1st Line is Seconds
  2nd Line is Minutes
  3rd line is Hours (0 to 23)
  4th Line is Days
  5th Line is Months
  6th Line is Years

I think you'll  find this interesting. Here is the  URL:
http://home.tiscali.nl/annejan/swf/timeline.swf

-- joe  rao

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Re: Nasa website

[Roger W. Sinnott]

Brad,

No, Meeus's Elements of Solar Eclipses book does not tell how to calculate 
the Besselian elements.  Rather, it LISTS these elements for all solar 
eclipses from 1951-2200.  Its real strength is that it provides detailed 
numerical examples of how to USE these elements to calculate the path of 
totality (northern and southern edge), as well as the appearance, magnitude, 
contact times, and limit curves of the partial phases.  It also explains how 
to determine the circumstances of the eclipse at any specific latitude and 
longitude.

To calculate the Besselian elements themselves, if you want to, first you 
need a source of highly accurate ephemerides for the Sun and Moon (such as 
from the Astronomical Almanac, NASA's Horizons, or Aldo Vatagliano's Solex 
shareware program).  Then you need the algorithms for deriving the elements. 
These are given is such places as the Explanatory Supplement to the 
Astronomical Almanac (either the 1992 or 1961 edition), or William 
Chauvenet's Manual of Spherical Astronomy (various editions, 1863 to 1891; 
also reprinted by Dover in 1960).  Calculating the elements is actually more 
straightforward than using them to get accurate local preditions and curves 
for an eclipse.

   -- Roger


- Original Message - 
From: Brad Lufkin bradley.luf...@gmail.com
To: Sundial Mailing List sundial@uni-koeln.de
Sent: Tuesday, December 22, 2009 3:07 PM
Subject: Re: Nasa website


 Speaking of Meeus, does anyone know if his Elements of Solar Eclipses
 includes algorithms for calculating the Besselian elements of eclipses or
 just presents tables of results? Also, does the book present algorithms 
 for
 calculating the paths of eclipses? It's not clear from the description on
 the bookseller's website.
 Regards, Brad

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Re: no analemma

[Roger W. Sinnott]

All,

A bronze sundial of this type was designed James Hartness of Springfield, 
Vermont, and patented in 1917.  It is on display in the underground museum 
at the Hartness House, which sits on a hill in the center of town.

Two pictures of it are here:
http://stellafane.org/history/early/museum-scopes.html
(Scroll about 3/4 of the way down the page, and click on the pictures to see 
them larger.)

The dial can wobble around its polar axis just enough to correct for the 
equation of time.  To control this wobble (through a cam), you set the 
calendar wheel to the desired date.

Does anyone know of an earlier sundial of this type?

  -- Roger



- Original Message - 
From: Edley McKnight e...@dcwisp.net
To: fer de vries ferdevr...@onsneteindhoven.nl; 
sund...@rrz.uni-koeln.de
Sent: Tuesday, October 06, 2009 3:10 AM
Subject: Re: no analemma


 Fer, Dialists,

 Thanks! That is a very nice dial and adjustable just as desired.

 I also wanted to remind others that rotation around some other nearby axis 
 that parallelled the
 earth's axis would work as well as with horizontal, vertical, etc. dials. 
 I don't have any idea how
 many designers have made use of an auxiliary axis in this way.  It allows 
 designs that were not
 at first designed to be adjusted to become so fairly easily.  Besides, 
 living in rainy Oregon I
 believe in tilting dials so that the rain runs off, leaves, snows slide 
 off, etc. :-)

 Edley


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Re: Direct reading

[Roger W. Sinnott]

I have to agree with Robert, who appears to have constructed an amazing 
instrument!

Surely, there is room in this world for *two* types of sundials:

   (1) Those that stay true to the concept of time before mechanical clocks, 
when local apparent solar time was the real time, no matter what time was 
used anywhere else.

   (2) Those that include various corrections (like equation of time, local 
longitude versus time-zone meridian, and standard/summer time) and are 
intended to show exactly the same time that would be indicated by accurate 
civil clocks.

   -- Roger


- Original Message - 
From: Robert Bargalló bargallorob...@gmail.com
To: sundial@uni-koeln.de
Sent: Sunday, September 27, 2009 11:57 AM
Subject: Direct reading


Dear Willy,

My long experience to persons outside the sundials is as follows: A). Too
complicated analemmatic figures or the necessary use of algebraic
calculations to know the time that they consider the real one; for this
reason, these people think the solar quadrant as an obsolete object. B). The
same persons in front my sundial of direct reading increase the interest in
gnomonics to consider these instruments as a “scientific precision
apparatus”. Thus, direct reading encourages people towards our passion: the
solar quadrants.






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Re: Sundial compass on eBay

[Roger W. Sinnott]

- Original Message - 
From: The Thurstons thurs...@hornbeams.com
To: 'Peter Mayer' peter.ma...@adelaide.edu.au; 'Sundials' 
sund...@rrz.uni-koeln.de
Sent: Friday, July 03, 2009 12:45 PM
Subject: RE: Sundial compass on eBay


 Folks,

 Alerted by Peter's message below, I have just bought an ex-Air Ministry
 Astro Compass MkII from eBay. I have wanted one of these for a while so
 thanks to Peter for posting about it. The instrument seems to be in pretty
 good condition but the LHA mechanism is stiff to turn and I am wondering
 about attempting to free it. Before I blunder in, I should be grateful for
 any advice on:
 - what lies inside the LHA mechanism
 - whether I can just apply some WD-40 and hope it finds its way to the
 critical parts
 - whether I could disassemble it with any hope of putting it back together

 Best Wishes,

 Geoff


 -Original Message-
 From: sundial-boun...@uni-koeln.de [mailto:sundial-boun...@uni-koeln.de] 
 On
 Behalf Of Peter Mayer
 Sent: 23 June 2009 10:33
 To: Sundials
 Subject: Sundial compass on eBay

 Hi,

   There's an interesting-looking RAF sun compass for sale on EBay:
 Collectables  Militaria  World War II (1939-1945)  RAF

 best wishes,


 Peter

 --
 Peter Mayer
 Politics Department
 The University of Adelaide, AUSTRALIA 5005
 Ph: +61 8 8303 5606
 Fax   : +61 8 8303 3443
 e-mail: peter.ma...@adelaide.edu.au
 CRICOS Provider Number 00123M
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Re: Sundial compass on eBay

[Roger W. Sinnott]

Geoff (and others),

Sorry about the accidental blank message just sent.

I have an AstroCompass (but not readily accessible at the moment).  If I 
remember correctly, one main knob (possibly the LHA mechanism you mention) 
operated very stiffly until I PUSHED IN ON THIS KNOB.  It is spring loaded 
to prevent turning by mistake.

   -- Roger

- Original Message - 
From: Roger W. Sinnott rsinn...@post.harvard.edu
To: thurs...@hornbeams.com; 'Peter Mayer' peter.ma...@adelaide.edu.au; 
'Sundials' sund...@rrz.uni-koeln.de
Sent: Saturday, July 04, 2009 12:34 PM
Subject: Re: Sundial compass on eBay



 - Original Message - 
 From: The Thurstons thurs...@hornbeams.com
 To: 'Peter Mayer' peter.ma...@adelaide.edu.au; 'Sundials'
 sund...@rrz.uni-koeln.de
 Sent: Friday, July 03, 2009 12:45 PM
 Subject: RE: Sundial compass on eBay


 Folks,

 Alerted by Peter's message below, I have just bought an ex-Air Ministry
 Astro Compass MkII from eBay. I have wanted one of these for a while so
 thanks to Peter for posting about it. The instrument seems to be in 
 pretty
 good condition but the LHA mechanism is stiff to turn and I am wondering
 about attempting to free it. Before I blunder in, I should be grateful 
 for
 any advice on:
 - what lies inside the LHA mechanism
 - whether I can just apply some WD-40 and hope it finds its way to the
 critical parts
 - whether I could disassemble it with any hope of putting it back 
 together

 Best Wishes,

 Geoff

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Re: Google Earth's geographic grid

[Roger W. Sinnott]

Doug,

I'm in complete agreement with all the excellent points you make!  A 
GPS-derived bearing can't be accurate to 0.1 arcsecond -- that's absurd.  I 
just meant that the latitudes and longitudes of an accurate GPS fix agree with 
Google Earth's coordinates (on the WGS84 datum) to roughly that level, in my 
experience.

For several years I've been trying to determine azimuths of distant landmarks 
as seen from choice (unobstructed) observing locations.  So if a neat planetary 
conjunction, comet, eclipse, thin crescent Moon, etc., is going to be visible 
low in the sky on a certain date, I can use my azimuth notebook to pick a 
spot, in advance of traveling there, where a certain landmark (lighthouse, 
distant cliff, or tall building) will be correctly located to be included in a 
dramatic photograph of the event.  Using spherical trigonometry and the GPS 
coordinates of the end points, an azimuth calculated using spherical trig 
should be accurate to better than 0.2 degree or so, since the landmarks are 
usually at least a half mile away.

If you are trying to get the azimuth of the wall of a building, then an 
astronomical method (such as measuring the Sun's shadow on the wall) should be 
much better than looking at a fuzzy image on Google Earth -- or the GPS 
coordinates of the building's corners!

You're right about the danger of relying on a printed map, where grid north may 
differ from true north.  This seems to be especially true of plot plans 
prepared by land surveyors of house lots, at least in the USA.

  -- Roger
 

At 09:49 AM 1/27/2007 +, Douglas Bateman wrote:
Dear Roger,

I have been following this thread for some time when questions were 
raised last year about finding north-south.

Like John C, with my own house as the test object, I have used plumb 
lines, slot-in-a-card methods, and large scale plans.  The latter uses 
our acclaimed Ordnance Survey, but even at the 1:1250 scale the house 
on the plan is only 12mm long.  Against the grid system and correcting 
for geographic north (convergence) I obtained 9.5 deg west of north 
(bearing 350.5 deg).

Google map gave me 8.5 deg with a printed image length of 25mm, and 
aligning against the eaves.  I did another print out and used the ridge 
line, and got 9.0 deg.  To me, this stresses the point that the way the 
light and shadows fall can change the appearance and choice of best fit 
for the protractor.  Further enlargement only brings more blurring.  As 
an aside, I am lucky with my Google map - a mere 10km away the area has 
yet to be photographed at the customary high resolution and one can 
barely make out the streets, let alone buildings.

Pursuing optical methods with an old theodolite on the sun and Polaris 
(at its transit) I obtained 9.28 and 9.20 deg.  I am still working on 
this method, which requires more practice to eliminate 'operator 
error'.

I am therefore interested in the GPS method and how to obtain the 
extraordinary precision of 0.1 arc sec.  For example, I cannot believe 
that a single hand held device can be pointed to this accuracy, and 
what I have seen of the screens of such receivers, the compass effect 
is crude.  Similarly, what base line is used to get the high precision? 
  If we take a building 100 feet long and the corners can only be found 
to within 10 feet, this is not much better than finding the moss on the 
north side of a tree.  I jest, because if the readings at each end are 
taken close together in time, then the same cluster of satellites will 
be in view, then the RELATIVE positions should be found to, say 10, 
times the accuracy.  Even so, this gives a bearing from one end to the 
other to an order a degree.  Incidentally I did some experiments with a 
very good magnetic compass that could be read to 0.2 deg; with care and 
the current (website derived) deviation you can achieve better that 0.5 
deg.

What then, is the secret of such alignment precision, and neglecting 
survey GPS equipment or differential GPS against precise pre-surveyed 
locations?

Or, am I misunderstanding the point being made, for I do assume that, 
at worst, the global Google 'grid' converges on the sub-north and south 
polar points to within a few metres.

Doug



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Re: Google Earth's geographic grid

[Roger W. Sinnott]

At 11:01 AM 1/26/2007 -0500, J. Tallman wrote:
I guess I am not entirely willing to automatically accept their output 
as 100% perfect...and I wonder if anybody on the list has any 
interesting thoughts or practical experience re: Google Earth and the 
accuracy of their geographic grid.

Jim,

I've found the Google Earth grid to be incredibly accurate when compared to a 
GPS receiver, provided the GPS unit is set to the WGS84 datum. They agree to 
0.1 arcsec (about 10 feet), the resolution of my GPS.  What is amazing is to 
look at a Google Earth picture of hilly terrain.  The grid lines would be 
essentially straight if you were looking straight down on them from above, but 
the Google Earth images were taken from either an aircraft or a satellite that 
generally viewed any specific spot on a slant.  So, you'd expect to see minor 
distortions whenever a grid line crosses a hill -- and you do!

For this same reason, it might not be accurate to measure bearings on a Google 
Earth image with a protractor.  But if you figure out the bearing using the 
exact latitude and longitude of the end points (trigonometrically), the result 
should be orders of magnitude better than that measured with a magnetic compass.

  -- Roger
 

  

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Re: Perpendicular Gnomon Options

[Roger W. Sinnott]

At 11:52 AM 9/1/2006 -0700, John Carmichael wrote: 
Hello Roger (Sinnott):   Humm...  I read your concerns that a threesided pyramid and a 3 sided post are problematic gnomons. And I tried tounderstand your reasoning, but for the life of me, I can't understand theproblem you mention.   I can't see any problems with either ofthese.  ...  The tip faces north and casts abeautiful shadow all day long.   Do you still think there is a problem with thesetwo types of perpendicular gnomon's.  If so, could you maybe try torephrase your explanation in a different way so that I might understandyou?  I really want to understand!   thanks Roger,   John  



John,

If you are *only* concerned with the very tip of the gnomon, then you can probably ignore my earlier comments!  In many designs, the shadow of the pyramid or post will be irrelevant, since people are supposed to be looking at the shadow of the tip instead.  In yours, as you say, the tip faces north and casts a beautiful shadow all day long.

All I meant to call attention to is that the centerline of the shadow of a post or pyramid does not necessarily pass through the shadow of the tip. I was thinking of vertical gnomons in which the tip is precisely centered over the cross section that tapers up to it, like the Washington Monument.  If the post has a circular, elliptical, square, or rectangular cross section, then everything is fine.  But if the cross section is triangular, the centerline of the post's shadow will not necessarily extend through that of the tip.  (I'm about to leave on a trip for the weekend, but I can try to post a drawing of what I'm getting at next week!)

-- Roger

PS:  This problem came up in the gnomon design for the sundial at the entrance court of Texas Instruments' Forest Lane Facility in Dallas, for which I was the astronomical consultant in 1996.  In that case, the gnomon is a 20-foot-long stainless-steel needle that points to the north celestial pole.  They wanted the centerline of the gnomon's shadow to indicate the time (rather the shadow edge, which serves this purpose in the fat triangular gnomon of a garden sundial).  The architectural firm originally proposed a 20-foot-long gnomon that had a sleek triangular cross section.  But I persuaded them that this would not work. They could go with a tapered cylinder (like a turned aluminum flagpole, inclined) or a rectangular cross section, but not a triangular one.  They thought the first option was not very elegant (and I totally agree!), so they chose the latter.



 
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Re: Perpendicular Gnomon Options

[Roger W. Sinnott]

John (and Larry),

I think there may be a problem with two of the seven designs.  Numbering them 1 through 7 from left to right in your illustration, the problematic ones are No. 3 (the three-sided pyramid) and No. 4 (the three-sided pointed post).

All the others have the shadow axis of the pole, post, or pyramid passing directly through the shadow of the point at the top.  But in these two, because the cross section is triangular, the shadow axis of the post or pyramid sometimes will NOT pass through the end point.  (Whether it does or not depends on the Sun's azimuth.)  So, someone reading the time might be biased or misled by the deviation of the shadow axis from that of the end point.

-- Roger



At 02:07 PM 8/31/2006 -0700, John Carmichael wrote: 

Hi Larry: Since you are interested in drawings that show the  different possibilities for sundial design, I thought you might like to have  this for your educational presentations.  I made this for a client so he could see the many  options for a perpendicular gnomon. These, I think, are the best  perpendicular gnomons for face designs that require very long shadows produced  from low solar angles.  For that reason I have not included an aperture  nodus.I'm not real thrilled with a long shadow cast by a ball  on a rod, but I included it anyway just because it is so popular and  traditional.  Of course, these drawings can be modified as needed by a  sundial designer to make the points sharper or fatter (the apex angles of  the points, cone or pyramids) or the ball and rods bigger or smaller.   These are just type samples.  John 
Attachment Converted: c:\eudora\sky\attach\GNOMON OPTIONS (perpendicular).pdf 
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Re: Google Earth accuracy

[Roger W. Sinnott]

List:


I'm sure Mike meant that the Greenwich Meridian Line is about 5 west, not 5' west, of where it is shown on Google Earth.  (I just looked to confirm this!)

This discrepancy is simply due to Google Earth's adopted geodetic datum, WGS84.  GPS receivers can often be set to show coordinates for other datums (data?) as well (for example, GB36, the Ordnance Survey of Great Britain 1936, on which the Greenwich meridian line is *much* closer to 0 longitude).

The datum choice probably explains the equator discrepancy in Ecuador as well.  It's simply that each country, historically, conducted geodetic surveys that are internally consistent to high accuracy. But they don't join up perfectly with those done in other countries. The WGS84 datum is intended to apply to the entire world.  We had a brief discussion of this issue in Sky  Telescope for August 2005, page 110.

I learned this lesson the hard way.  When I went to find the gravestone of telescope maker Russell W. Porter in Port Clyde, Maine, I had GPS coordinates from a friend.  After an hour and a half, no luck -- so I gave up. Only later did I learn that his receiver was set to WGS84 while mine was set to NAD27.

-- Roger




At 08:27 AM 7/23/2006 +0100, Mike Shaw wrote: 

Bill G. said: There is a large monument in Ecuador that  marks the exact location of the equator, so they claim.  Google Earth puts  it about 780 feet south of the equator.  Any thoughts on who is more  accurate:  Google Earth or the Ecuadorian surveyors?   >> I have also noticed that, according the Google  Earth, the meridian line at the Greenwich Observatory (surely correct) is  at 5.26 minutes West. Mike Shaw  53.37N
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Re: EOT + Longitude Correction Table

[Roger W. Sinnott]

All,

I realize this is not the question John Carmichael originally asked, but I 
decided to find out how much the Equation of Time varies over several years on 
the SAME month and day. I used Jean Meeus's Astronomical Algorithms, chapter 27 
(actually, the method is attributed to W. M. Smart) and adopted noon in the 
middle of North America as the test location.

For the years 2000, 2001, 2002, and 2003, here are the dates of greatest and 
least spread in EoT values:

DateAve. EoTSpread in EoT values
==
Feb. 11   -14m 16s 0 sec
Mar. 27 -5m 17s   13 sec
May 14+3m 40s 0 sec
June 19 -1m 22s9 sec
July 25  -6m 31s0 sec
Sept 17+5m 34s  16 sec
Nov. 2 +16m 28s   0 sec
Dec 22 +1m 17s  22 seconds (the max for the year)

What this means is that you can incorporate the AVERAGE value for EoT (for 
example, 1m 17s on December 22nd) in a sundial's design or auxiliary table, and 
the reading will never be off more than half of 22 seconds, or 11 seconds. 
That's pretty good!

 -- Roger
  

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Re: EOT with Longitude correction?

[Roger W. Sinnott]

John and others,
Maybe I'm being dense, but isn't the variation of the equation of time
with longitude masked (or at least complicated) by the similar variation,
from one year to the next, due to our use of a 365-day calendar and
occasional leap year?
It's hard for me to imagine that the longitude deviation would ever need
to be included in a sundial design. (But if one is observing a noon
transit of the Sun in a specific year and calendar date for establishing
a true north-south line, then it *would* be helpful.)  
 -- Roger

At 01:39 PM 7/5/2004 -0700, John Carmichael wrote:
Hello
All:

Does anybody know if there is a program,
spreadsheet or website that will calculate EOT values corrected for
specific longitudes in either a graph or a
table?

RE: accuracy

[Roger W. Sinnott]

At 08:25 AM 12/21/01 +1100, David Pratten wrote:
Dear Walter,

Greetings.  

There is another factor which limits sundial accuracy to about +/-22
seconds.  This is the variation in the value of Equation of Time from
year to year within a leap cycle.  See
www.sunlitdesign.com/infosearch/sundialaccuracy.htm

David and others,

This might be true if the equation-of-time correction is obtained from
a look-up table by date.  But if the sundial includes the EoT correction 
in the shapes of its curves, or in the shape of the gnomon, the declination
of the Sun is what controls the value of the correction being applied. In 
that case, I think the error would be *much* smaller than +/- 22 seconds.

-- Roger

  

Re: Equinox discrepancy

[Roger W. Sinnott]

At 10:48 AM 8/12/01 EDT, Bill Gottesman wrote:
Hello All,
I know Fred must be right about the declination being non-zero at the 
equinoxes, but I can't figure out why.  As I understand, solar celestial 
right ascension must equal solar ecliptic longitude (Lambda) on the equinoxes 
(0 degrees spring and 180 degrees fall).

Bill,

The Sun's ecliptic latitude can amount to a full arcsecond (although
it is usually much less), and this can also cause the Sun's declination
to be slightly different from zero at an equinox. The main reason 
is the pull of the Moon, whose orbit is inclined to the ecliptic.

The Earth's center is not precisely at the Earth-Moon barycenter, 
but is orbiting around the barycenter. This also explains why the 
dates of the Earth's aphelion and perihelion dates jump around by 
several days from year to year.

-- Roger
 

Re: Last Lunar Harrah - Astro trivia

[Roger W. Sinnott]

At 11:23 PM 12/11/99 -0500, Larry Bohlayer wrote:

In lay-mans terms it will be a super bright full moon, much more than the
usual AND it hasn't happened this way for 133 years! Our ancestors 133
years ago saw this.  Our descendents 100 or so years from now will see this
again.

 Dr. Robert E. Murphy

The combination of a full moon, lunar perigee, and winter solstice on the
same date is unusual, but it *almost* happened in other two recent years
at the following dates and Universal Times:

 Dec 1999  Dec 1991  Dec 1980
Full Moon 22, 18h   21, 10h   21, 18h 
Perigee   22, 11h   22, 9h19, 5h
Solstice  22, 8h22, 9h21, 17h

Also, the moon was closer to earth on 1912 Jan 4 and 1893 Dec 23 than in
*either* 1866 or 1999. This is covered in Jean Meeus's Astronomical
Algorithms, page 332.

   -- Roger at ST