accuracy 0.1' or 0.2' depending on the intrument and skills of the observer
though the measurement is relatively easy. The measurement should be done
both ways, that is with reflected Sun above and below the "true" Sun and
the result should be averaged. You should try to avoid a mistake when
reading negative angles off the vernier.
Calculating the distance to the Sun by its apparent diameter is of course
rough estimate but may be amusing
Slawek Grzechnik
At 01:51 PM 1/2/01 -0800, Luke Coletti wrote:
I haven't tried to measure the variation of sub-tended arc of the
Sun's
disk but have read (URL below) of it being done for the Moon, an approx.
14% variation. However, with an enlarged solar image, via a Heliostat,
perhaps the 3% variation (mentioned below) could be be teased out.
Hmmmm...
http://www.fourmilab.ch/earthview/moon_ap_per.html
-Luke
Jeff Adkins wrote:
>
> It is true, however, that the difference is observable in page-size
photographs that
> lie side by side on a table. There is an old project physics activity
that has the
> student plot the distance to the sun based on changes in the apparent
size of the
> sun; and from this data you can computer the shape of the earth's
elliptical orbit
> to some degree of accuracy. You can also get the perihelion and
aphelion distances
> and dates from this sort of data.
>
> Jeff Adkins
>
> "Richard M. Koolish" wrote:
>
> > >From the web
page: http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/SEgeometry.html
> >
> > "Eclipse geometry is complicated by the fact that Earth's orbit
around the Sun
> > is elliptical. As a result, the Sun's apparent semi-diameter varies
from 944
> > arc-seconds at aphelion to 976 arc-seconds at perihelion. This 3%
range in
> > apparent size is, of course, quite indistinguishable to the naked eye."
