The Sky This Month
Welcome to our night-time sky.
Please enjoy this monthʼs tidbits of
knowledge. We are lucky to live in a
dark-sky area where the heavens can
shine through. I hope you enjoy the
sky and perhaps learn a thing or two.
Happy star gazing!
Second Solar Eclipse – If you
missed the 2017 solar eclipse, here is
your chance to see another one – albeit a little less exciting
and a little further away. On August 21, the Moon occulted
the Sun, blocking its rays from reaching the Earth. On
the morning of September 12, the star Aldebaran will be
eclipsed by the Moon. Starting around 4:48 am, Aldebaran
will disappear behind the Moon. The Moon will continue
its rotation around the Earth and Aldebaran will reappear
about an hour and fifteen minutes later around 6:02 am.
The Sun rises at 6:10 am, so you should be able to see the
star reappear before it gets too bright. You might need to
use binoculars if the brightness obscures the star. Other
than binoculars, you do not need special eyewear to see
this eclipse. You only need to wake up early. For reference
Aldebaran is near the base of one of the bullʼs horns in the
constellation of Taurus and The Pleiades are also nearby.
Why Not Every Month? – The Moon passes between
the Earth and the Sun every month. When the Moon
has its back to the Sun, the Moon appears dark. This
is called a new Moon. The new Moon is blocking the
Sunʼs rays, making it more difficult to see (although
Earthshine illuminates the new Moon enough to make
it visible). So, if the new Moon is blocking the Sunʼs
rays, then why isnʼt there a solar eclipse every month?
The answer is that the Moonʼs orbit is inclined about
five degrees from the ecliptic, which is the path that
the Earth orbits around the Sun. Only when the Moonʼs
orbit passes through the ecliptic is there a chance for
an eclipse. This passage actually occurs several times
per year. However, most of those passages occur when
the Moon is neither full nor new, so the eclipses that do
occur are typically partial. When a full Moon passes
through the ecliptic, we get a total lunar eclipse. When
the new Moon passes through the ecliptic, we get a to-
tal solar eclipse. However, since the Moon is compara-
tively small, it only obscures the Sun from a very small
portion of the Earth. In the August eclipse, that portion
was a 70 mile wide swath through the US.
—Brian Biggs
Amateur Astronomer
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September 2017 pccnews