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
Greetings, fellow dialists
Slawek Grzechnik wrote that you can measure the sun's diameter with a
marine sextant but that you should try to avoid a mistake when reading
negative angles off the vernier.
The mistake here is that Slawek has not yet sold his vernier sextant for
a large profit.
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.
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
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.
