upergiant – and it’s almost 60,000 times as bright as the Sun! If placed at the
position of the Sun, Betelgeuse would reach past the orbit of Mars. However, since
it’s over 400 light years away, it appears not as bright as Sirius.
Now, look below the “belt” of Orion, at the grouping of stars which make up the
“sword.” With the naked eye, do you see anything unusual about the middle star?
Look with binoculars – what do you see? This is the Orion Nebula, a relatively nearby
star forming region. The distance to the nebula is about 1500 light years. The hot
blue stars that you see illuminating the nebula are less than a million years old.
Above Orion, almost at zenith, is the planet Mars. If you compare its appearance
with Betelgeuse, you’ll probably notice that it doesn’t “twinkle.” This is because
the planet actually shows a disk while the star is so far away that it appears as
a point. A bit toward the east from Mars, still not far from zenith, you’ll find
the bright pair Castor and Pollux, in the constellation Gemini. Castor is the upper
star, with Pollux below it. They’re sometimes called the twins, but they couldn’t
be more different. Castor is actually a complex system of six stars, but its two
brightest components are separated by only a tenth of a degree. It’s unlikely that
you will be able to resolve them, even with binoculars. We can barely resolve them
from the Keeble Observatory. Pollux is a single star, but it is known to have at
least one planet, about 2.5 times the mass of Jupiter.
Above and to the right of Orion you will find the asterism known as the Pleiades.
(In Japanese, this cluster is called Subaru, which is why you see seven stars on
the grill of that brand of car!) This cluster is about 400 light years away, and
only a few tens of millions of years old. The faint bluish haze surrounding the
cluster is dust, reflecting the starlight of the hot blue stars in the cluster.
To the northeast, you’ll eventually make out the familiar shape of the “Big Dipper,”
part of Ursa Major (the Big Bear). It will appear inverted, with the “handle” pointing
down. The two stars at the end of the bowl mark a line which should carry your eyes
up and to the right, encountering Polaris, the Pole Star. The middle star in the
handle of the dipper is actually a pair, known as Mizar and Alcor. Can you see the
pair with the naked eye? How about with binoculars?
Towards the east, you should be able to discern the familiar sickle shape of the
constellation Leo. The brightest star in the constellation is Regulus. It lies about
77 light years distant, and is 150 times brighter than the Sun. Below Regulus, you
will find the planet Saturn. With binoculars you may enable you to see its distinctive
For your own monthly star chart, you can direct your web browser to
http://www.skymaps.com. You will find extensive descriptions of what's worth
looking for, and you can download and print a single copy for your personal use.