Relive the Discoveries of Galileo September 2014 | Page 9
The Durham Region Astronomical Association
larger is because its orbit brings the planet closer to
us (check the Copernican model in the illustration on
the previous page and you will notice how Venus
comes closer towards Earth as it moves counterclockwise from position B).
On August 17, 2010, Venus is 50% illuminated.
Each following evening, Venus becomes more
crescent-shape while continuing to grow in size. By
late-September, early-October 2010, Venus appears
in a telescope as a pencil-thin crescent. (On
October 9, 2010, an equally-thin crescent moon sits
only 3º above Venus, a must see event!).
Venus then passes between the Sun and Earth, and
in November 2010, re-emerges from the Sun’s glare
to appear as the “Morning Star”, rising in the East in
the early morning before sunrise. From November
2010 to August 2011, Venus will run through the
same phases in reverse order — from crescent to full
— while shrinking in size as the planet moves
towards position A in the Copernican model.
The cycle of Venus’s phases will then repeat itself as
the planet orbits the sun. For the following four
years...
in East before sunrise, shrinking from a large
crescent to a small round circle.
May 2013 through January 2014: Evening star again.
How to observe and record Venus
When Venus is an evening star, you will need a clear
view to the west, especially to see the full and verythin-crescent phases. When a morning star, you will
need an unobstructed view to the east.
The best time to observe Venus’s phases is during
twilight, just after sunset (or just before sunrise if a
morning star). The contrast between the very bright
Venus and the background sky is not as severe
during twilight, resulting in less glare, and making it
easier to study Venus’s phase.
Use your highest-power eyepiece (smallest mm
number) in your telescope. In the squares provided,
enter the date of your observation, and above it,
draw the phase of Venus. Be sure to catch Venus
when it is at its full phase...
September 2011 through May 2012: Evening Star,
visible in the west after sunset, growing from a small
full circle to a large thin crescent.
July 2012 through March 2013: Morning Star, visible
...to relive the exci ѕ