Distant Open Cluster M103
Bright blue stars highlight the open cluster known as
M103.
The
gas clouds
from which these stars condensed has long dispersed.
Of the stars that were formed, the
brightest, bluest, and most massive have already used up their nuclear fuel and self-destructed in
supernova explosions.
A 20 million-year age for M103 was
estimated by finding the brightest
main-sequence stars
that still survive and theoretically computing their lifetimes.
In fact, a formerly blue star has recently
evolved off the
main sequence and is
visible above as the
red giant star near the cluster center.
In general, yellow stars like our
Sun are usually less
bright and hence less prominent in
open clusters
than their massive blue cousins.
Light takes about 14
years to cross
M103.
Although visible with binoculars toward the
constellation of
Cassiopeia,
M103's great distance of 8000 light years
makes it appear four times smaller than a
full moon.