This month we feature the northern sky about 8:00 PM on February 5 from
the Little Dipper through Perseus, Cassiopeia, and Andromeda. The
Double Cluster in Perseus consists of two open, or galactic, clusters each
subtending about 30 arcminutes, the angular diameter of the full moon.
At mag 4, these clusters are visible to the naked eye under reasonably
dark skies. Each cluster has about 300 or 400 stars located about
7,400 light years from the earth. The clusters are about 57 deg above
the horizon, and about 32 deg from Polaris.
You can easily estimate visual angles using your hand. The angular
distance across your fist at arm's length is about 10 deg. The distance
across your fully extended hand at arm's length, from the tip of the thumb
to the tip of the little finger, is about 25 deg.
The Andromeda Galaxy is a pale patch of light, mag 3.5, about 15 deg from
the lower angle in the "W" of Cassiopeia (Cassiopeia is an "M" in the summer).
This galaxy is about 3 million light years away, and is the most distant
object the human eye can see under ordinary conditions. Check it
out. And see if you can estimate the angles above.
You can print a copy of this star chart so you
can take it outside.
