A good idea. On the other hand the Heliostat allows an enlarged image to be viewed (projected) thus making the apparent size much easier to measure. The Heliostat is as well an excellent tool for viewing sunspots. I'll give the Sextant a try though.
Luke "Slawek K. Grzechnik" wrote: > > You may measure Sun's apparent diameter using a decent marine sextant with > 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."
