Download The Ursa Major Moving Cluster, Collinder 285

Constellation: Ursa Major
Designation
Proper
Name
 (alpha)
 (beta)
 (gamma)
 (delta)
 (epsilon)
 (zeta)
 (eta)
Dubhe
Merak
Phekda
Megrez
Alioth
Mizar
Alkaid
Apparent
Magnitude
m
1.81
2.34
2.41
3.32
1.76
2.23
1.85
Which star appears brightest?
Which star is hottest?
Absolute
Magnitude
M
-1.09
+0.41
+0.36
+1.33
-0.22
+0.33
-0.6
Distance
lyrs
124
79
84
81
81
78
101
Dimmest?
Coolest?
Which star is the most luminous?
Least luminous?
Why does Alkaid appear so dim given that it is very luminous?
Which stars are main sequence stars?
Why does Duhbe appear so bright? (two reasons)
Spectral Type
Luminosity
Class
K0III
A1 V
A0 V
A3 V
A0 p
A1 V
B3 V
Single or
Multiple
Star System
visual binary
single
single
single
spec. triple
visual binary
single
The Ursa Major Moving Cluster, Collinder 285
Open Cluster Collinder 285, the Ursa Major Moving Cluster, in and around Ursa Major
Right Ascension
12 : 03: (h:m)
Declination
+58: (deg)
Distance
0.076 (kly)
Visual Brightness
0.4 (mag)
Apparent Dimension 1400 (arc min)
http://www.seds.org/messier/Pics/Jpg/bigdipper.jpg
Brighter stars known pre-historically. Cluster nature
by R.A. Proctor 1869 and Huggins 1872
100,000 AD
discovered
Most of the stars making up the Big Dipper show a
common
proper motion, as R.A. Proctor has found as early as 1869 (see e.g. Burnham). When W. Huggins, in
1872, determined their radial velocities from their spectra, it became apparent that they move
approximately in the same spatial direction, and thus drift commonly through their cosmic neighborhood - a property typically found for members of a physical star cluster. The cluster is currently approaching us
at 10 km/sec, and its spatial velocity relative to our Sun is about 46 km/s.
This cluster is centered at a distance of about 75 light years from us (i.e., our solar system). As it is spread
over a volume of 30 light years length and 18 light years width, it covers an enourmous portion of the
sky, and probably includes the outlying member Alpha Coronae Borealis, which is 30 degrees off. The
stars are similar to those found in the Hyades and Praesepe (M44), indicating that this cluster is of
roughly the same age (700-800 million years) as the other two.
Studies of the motions of nearby stars have revealed that a considerable number of conspicuous stars in
our neighborhood show motion in about the same direction in space, i.e. drift together with the Ursa
Major cluster, although they are spread over the whole sky. These stars include Sirius (alpha Canis
Majoris), Alpha Ophiuchi, Delta Leonis, and Beta Aurigae, together with about 100 fainter stars. It seems
that these stars are lost "former" cluster members which have their origin in the Ursa Major cluster, but
escaped due to mutual encounters, tidal forces of the Milky Way, or encounters with large interstellar
clouds and other clusters. Now as they have left the cluster, their orbits around the Milky Way Galaxy's
center is still similar to that of the cluster so that they have a common motion. All these stars are
sometimes referred to as the Ursa Major Stream, which reaches out to more than 100 light years from
the cluster's center.
Our Solar System is currently located in the outskirts but within the extent of this stellar stream, but it is
clearly not a member of this stream. Instead, it is a chance encounter, because
1. the cluster stars are much younger than the solar system's age of about 4.6 billion years,
2. the stars have a common proper motion, which our Sun doesn't share, as they pass us at about 46
km/s.
Very Cool Movie of the changing shape of the Big Dipper at http://www-astronomy.mps.ohiostate.edu/~pogge/Ast162/Movies/proper.html