PS. It seems to me that the Moon method, even if you get it working, is an awfully slow process. You'll only get two data points per night and you'll never get any data points outside a certain band centered on the east and west headings. I think it is easier to go outside with any old camera, even one on your cellphone, and take a sequence of pictures to make a panorama. There is free software for assembling such a sequence into a single panorama (Autostitich). Photoshop also will do it for you. I think some new cellphones have this capability built right into them. Anyway, just load your panorama into your favorite image processing program (MaximDL, AstroArt, Photoshop, whatever), measure how high the highest point is above what you think the horizon is in pixels. Figure out what you have to scale that number by to convert it to what you think the correct value should be in degrees (the Moon measurement might help with this step), and then write a program or set up a spreadsheet to scale all of the values and you're done.
On Jul 22, 2010, at 10:58 AM, luzius.thuerlemann wrote: > Thank you Robert for this post. The last lines describe my project well. I > tried to measure the time when the moon is just completely above or below the > horizon and then look in the Alt/Az-coordinates for the information I need in > the horizon creation file. Then I'd subtract the radius of the moon - about > 15' - from the moons altitude (probably it's center) to get the horizon > altitude where he just rose above. And it's the other way round to find out > the altitude of the horizon where he just set - meaning adding the moons > radius to the moons center altitude to get the horizon 15' above the moon. Of > course it's not that precise - especially when it's waxing moon and I can't > see when he just rises above or sets below the horizon. But with wanning moon > or better full moon it works. And also it's not that precise because of the > changing distances of the moon, and because one can only simulate whole > altitude degrees instead of minutes and even seconds. But within the range of > whole altitude degrees this measuring method should really do - I mean, a > degree is twice the moons diameter or four times the moons radius! It really > should work. > But it doesn't. > Can I send you some print screens? > > > > --- In [email protected], Robert Vanderbei <r...@...> wrote: >> >> I'm not sure I understand your questions. Do anomalies you describe apply >> only to the Moon (and planets)? Or, are you asking about all celestial >> objects including remote things like stars, galaxies, etc.? >> >> If you are only talking about nearby things, such as the Moon, then perhaps >> all that needs to be said is that locating the Moon's position on the sky in >> a computer program is complicated by the fact that the Moon orbits the >> Earth. Its orbit is a little bit eccentric and is tilted somewhat relative >> to the ecliptic plane. So, the Moon's position is constantly even in >> equatorial coordinates. >> >> If you are asking about all celestial objects including stars, then let's >> talk about stars. The equatorial coordinates of the stars do not change >> significantly over, say, 100 years. For practical purposes we can think of >> them as fixed. But, of course, their alt-az coordinates change moment to >> moment because the Earth is rotating. For example, Vega rises in the >> northeast about 6 hours later is overhead and then 6 hours after that is in >> the northwest. When it rises, depends on the time of the year and how far >> north of east depends on ones latitude. In other words, given a particular >> location on the celestial sphere, i.e., given particular RA and Dec >> coordinates, it is fairly straightforward to compute the corresponding >> Alt-Az coordinates. But, this calculation depends on the latitude and >> longitude of the observer as well as the time of day and the date. >> >> The horizon is given by Alt=0. The various values for Az determine the >> direction you are looking. Since CdC already knows how to compute Alt/Az >> coords for any location/time, providing a local horizon is easy. You just >> need to say how high the horizon is in each direction (for each Az). >> >> More comments below... >> >> On Jul 21, 2010, at 11:57 AM, luzius.thuerlemann wrote: >> >>> Thanks Robert for this answer. >>> Ok, than the world is again as it should be :) . Yes, the ecliptic changes >>> with precession and nutation over 25800 years, right. >>> But WHY does ist pretend to do a daily 25800-cycle? I mean, what needs to >>> be different from the polar projection except the coordinates which would >>> be given in Alt-Az instead of Ra/Dec? Why this tumbling around. >>> >>> Ok, here my problems: >>> 1. when I want to see if there are other coordinate data in the information >>> board for the moon in Alt-Az and Ra-Dec, and let the software search for >>> the moon in the toolbar, the coordinates are centered +00°00' and >>> 24h00m00,0s (in polar projection). But the moon is on the other end of the >>> sky. How to fix this. >> >> I don't understand this question. I just now fired up CdC and I typed Moon >> into the search box on the toolbar. The Moon has just set here and so CdC >> shows me the SW horizon and the center of the field of view is slightly >> below the horizon (I have CdC configured to start in Alt-Az mode). I >> currently have CdC configured to by default hide things below the horizon so >> I don't see the Moon. To see it, I click "Configure the >> Program-->Observatory" and check the "Horizon" tab followed by the "Show >> Object below Horizon" box. Okay, now I see the Moon. I click on its label >> to see "Details". The RA/Dec coords are 16h59m, -25d34m. The Alt/Az >> coords are -11d30m, +246d34m. The Alt/Az coords are completely consistent >> with the reality that the Moon has set in the SW about an hour ago. >> >> I'm not sure what you mean by "the coordinates are centered +00°00' and >> 24h00m00,0s (in polar projection)". I guess you mean that you are in >> Alt/Az mode looking straight up, right? If I click on the "Z" to give the >> zenithal view, I don't see the Moon in the default zoom level. But, if I >> zoom out, the Moon appears in the SW a bit below the horizon exactly where >> it is expected. >> >>> 2. on the 21. July 2010 at 00:15.00 the moon completely disappeared below >>> the south-western mountain-horizon. When I simulate this time then the moon >>> in Alt-Az-projection (because in polar alignment I can't see the >>> mathematical horizon) is already displayed below the mathematical horizon. >>> What is wrong here? >> >> It is not possible to simulate your what you see without also knowing your >> latitude/longitude. >> >>> >>> The difficulty is that I can't imagine to create a proper local horizon >>> with these obstacles - I mean, one evening the moon rises above a mountain >>> and on the following night the moon rises above the same horizon but is >>> displayed much below or above the already created horizon line from the >>> previous night. >> >> Could it be that you have not set your longitude/latitude and/or timezone in >> the "Observatory" window? >> >> Lastly, I should point out that the Moon is currently about 4 degrees from >> the closest point on the ecliptic. >> >>> >>> Thanks very much for help! >>> >>> Luzius >>> >>> >>> >>> --- In [email protected], Robert Vanderbei <rvdb@> wrote: >>>> >>>> The ecliptic does not move with respect to the celestial sphere (the >>>> background stars) over short time scales. Hence in equatorial mode it >>>> remains fixed. But the ecliptic and the stars do move from moment to >>>> moment and from day to day (at a given time of day). Hence, in alt-az >>>> mode you will see changes. Not sure if this is the source of confusion. >>>> Hope. It helps. >>>> >>>> Sent from my iPhone >>>> >>>> On Jun 28, 2010, at 11:05 AM, "luzius.thuerlemann" <luzius.thuerlemann@> >>>> wrote: >>>> >>>>> Hi John >>>>> >>>>> Yesterday I realised that the ecliptic moves during a single day. Sounds >>>>> stupid, but I've never realised that before. I thouhgt that it changes >>>>> only during long periods over months and seasons etc. But over a single >>>>> day?! I know the change of the seasons and the motion of the sun over a >>>>> year etc., but I really cannot explain this motion over 24 hours. When I >>>>> animate the daily motion it looks to me as if it was an exaggerated >>>>> motion of the earth's precession. I just don't get it. >>>>> The seasonal changes etc. are no problem, but these not obvious >>>>> short-term-things seem to be. >>>>> >>>>> But this should not affect the creation of a local horizon in CdC. When I >>>>> write down the time when the moon just rises above or sets below the >>>>> horizon, and subtract the moon's radius from the local altitude, then I >>>>> should get the horizon altitude at the moon's azimut at that time and I >>>>> can simulate the horizon altitude there. >>>>> But my problem is that the setting moon was displayed much closer to the >>>>> mathematical horizon compared to the already simulated >>>>> rising-horizon-mountain in the south-east (it was as if the western >>>>> south-mountain is half or a third as high as the south-eastern one) - >>>>> although the two mountain's altitude would not have created such an >>>>> obvious difference...they're pretty much of the same height, and the >>>>> observing position was also the same. >>>>> >>>>> It's really strange. And all because of this strange >>>>> daily-eliptic-precession. I don't get it. >>>>> >>>>> >>>>> Thanks for your help! >>>>> >>>>> Luzius >>>>> >>>>> >>>>> >>>>> ------------------------------------ >>>>> >>>>> Yahoo! Groups Links >>>>> >>>>> >>>>> >>>> >>> >>> >>> >>> >>> ------------------------------------ >>> >>> Yahoo! Groups Links >>> >>> >>> >> >> Robert J. Vanderbei >> Princeton University >> http://www.princeton.edu/~rvdb >> "I'd trade all my tomorrows for a single yesterday." -- K. Kristofferson >> >> >> >> >> [Non-text portions of this message have been removed] >> > > > > > ------------------------------------ > > Yahoo! Groups Links > > > Robert J. Vanderbei Princeton University http://www.princeton.edu/~rvdb "And you may ask yourself... How did I get here?" -- Talking Heads [Non-text portions of this message have been removed]
