Saturday: How
do you study the life cycle of a dog? Easy. Get a dog from the animal shelter,
care for it for 15 years and study it. How do you study the life cycle of a
star? Easy. Pick a star, watch it for a few billion years, and…. Wait a minute.
Astronomers can’t observe something for a few billion years. Instead, they
study stars that are at different points in their long life cycle and piece
together the information from those different stars. What they do is like
studying a one-year-old dog for a few minutes, then studying a different
two-year-old dog for a few minutes, and so on. The sky in and near the
constellation Orion provides an example of four objects at different points of
star life.
First, find
Rigel, the bright star in the lower right corner of the constellation Orion.
This star, rapidly burning its fuel for a high energy but short-lived
existence, is three and a half fists held upright and at arm’s length above due
south at 10 p.m. It was not, is not, and never will be like our Sun. However,
about one fist up and to the left are the three objects of Orion’s sword
holder. The middle “star” is really a star-forming region called the Orion
nebula. There you’ll find baby Suns. Now, look about two fists to the right and
one fist down from Rigel. You should be looking at a star that is about one
tenth as bright as Rigel but still the brightest in its local region. The third
star to the right of that star is Epsilon Eridani, the most Sun-like close and
bright star. Betelgeuse, in the upper left corner of Orion, is a star at the
end of its life that started out life a bit larger than the Sun.
Sunday: Jupiter
and Mars are neighbors in the morning sky all this week. Look two and a half
fists above the south-southeast horizon at 7 a.m. Jupiter, the brighter planet,
is about the diameter of the full Moon above Mars. For an added challenge, look
for Mercury and Saturn low on the southeast horizon. Mercury is a half a fist
above the horizon and Saturn is about a thumb width above the horizon at 7 a.m.
As the week goes on, these two planets will move closer together in the sky.
Monday: A
new year leads us to contemplate our future. Let’s take some time to
contemplate the Sun’s future. The Sun has spent a few billion years as a stable
star fusing hydrogen into helium. Once that easily fusible hydrogen is gone,
the Sun’s outer layer will puff up like a hot air balloon, getting larger,
cooler, and redder. The star Aldebaran, in the constellation Taurus looks like
what our Sun will look like in a few billion years. Hear more about Aldebaran
and the Sun’s future at https://stardate.org/radio/program/moon-and-aldebaran-25.
At 9:30 p.m., Aldebaran is almost exactly 60 degrees, or six fists, above due
south.
Tuesday: January
is the coldest month of the year so it is time to turn up the furnace. Fornax
the furnace is one fist above due south at 7 p.m.
Wednesday: Have you ever looked down on the ground and spotted a penny? In
Yakima? While you were standing in Ellensburg? If you have, then you may be
able to see the star Hamal as more than just a point of light. It has an
angular diameter that can be directly measured from Earth. Hamal, the brightest
star in the constellation Aries the ram, has the same angular diameter as a
penny 37 miles away. (For comparison, the moon is about half the diameter of a
penny held at arm’s length.) Hamal is three and a half fists above due west at
11 p.m.
Thursday: This morning, the Moon joins Jupiter and Mars in the
south-southeastern sky. The two planets are less than a half a fist to the
lower right of the Moon at 7 a.m.
Friday: Mercury
and Saturn are side by side in the morning sky; about a half a fist above the
southeast horizon at 7 a.m. Mercury is the brighter of the two planets and is
on the right.
The
positional information in this column about stars and planets is typically
accurate for the entire week. For up to date information about the night sky,
go to https://nightsky.jpl.nasa.gov/planner.cfm.
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