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As
the earth and Venus go around the sun, the relative position of Venus
with respect to the sun changes. At certain times of the year, Venus
is a morning star, being visible before the sun rises. In other months
it is an evening star. From September 18th 2003 Venus appears as an
evening star.
- We measure
the angle which Venus makes with the horizon at the moment when
the Sun sets. This angle increased from September to the end of
March. Venus reached maximum height towards the end of March 2004.
- We can measure
the angle directly with our angle-dangle
meter. It turns out to be approximately 45 degrees
, towards the end of March 2004. (See B.5)
- Another
way to measure the angle is to measure the time between the setting
of the sun and the setting of Venus. The maximum time turns out
to be approximately three hours.
- Since the
earth rotates once in 24 hours, the stars and the sun appear to
move through an angle of 360 degrees in 24 hours. They appear
to move through 15 degrees (360 degrees divided by 24 hours) in
one hour. The maximum three hours time difference between the
two setting times means that the maximum angle between the Sun
and Venus is approximately 45 degrees
- From these
measurements, and a few plausible assumptions, (like the assumption
that the earth and Venus go around the sun in circles with the
sun at the center), we can calculate that the sun - Venus and
the sun - earth distance are approximately in the ratio 1 :
1.414. (See B.5)
- What this
means is that at the time of transit the Earth-Venus distance
and the sun earth distance are in the ratio 0.414 : 1.414.
From the properties of similar triangles we calculate that Venus
appears to be magnified by a factor of 1.414/0.414, which
is approximately 3.4.
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