You're My Hero!
you just love a happy ending? I know
I do. Picture this.
Princess Andromeda, a helpless damsel in distress, chained to a rock as a
ferocious sea monster loomed nearby.
Just when all appeared lost, our hero -- Perseus! -- plunges out of the sky,
kills the monster, and sweeps up our maiden in his arms.
Together, they fly off into the sunset on his winged horse to live
happily ever after.
the stuff of myths and legends. That
story, the legend of Perseus and Andromeda, was recounted in last month's column
when we visited some binocular targets within the constellation Cassiopeia.
In mythology, Queen Cassiopeia was Andromeda's mother, and the cause for
her peril in the first place.
Above: Autumn star map adapted from the book Star
Watch by Phil Harrington
month, we return to the scene of the rescue, to our hero, Perseus.
He stands in our sky to the east of Cassiopeia and Andromeda, should the
Queen's bragging get her daughter into hot water again.
constellation's brightest star, Mirfak
(Alpha Persei), lies about two-thirds of the way along a
line that stretches from Pegasus to the bright star Capella in Auriga.
Shining at magnitude +1.8, Mirfak is
classified as a class F5 white supergiant.
It radiates some 5,000 times the energy of our Sun and has a diameter 62
times larger. Measurements show it
to be about 590 light years away.
Above: Finder chart for this month's Binocular Universe.
Chart adapted from Touring the
Universe through Binoculars Atlas (TUBA), www.philharrington.net/tuba.htm
Mirfak through binoculars shows that it is surrounded by dozens
of fainter stars scattered in small clumps and knots.
While most of the stars
appear white or blue-white, a few might show subtle hints of
yellow or orange. For
instance, the star Sigma Persei, one of three suns forming a small triangle south of Mirfak,
shines with a distinctly orangish hue.
stars gathered into this football-shaped area form the
Alpha Persei Association. A
stellar association contains mostly blue-white and white
(spectral types O, B, and A) stars, like most open star
however, the stars in an association are more loosely gathered
than those in open clusters. In
the case of the Alpha Persei group, some 50 suns are bound by
their mutual, though weak gravitational grip.
All are about the same
distance away as Mirfak, having formed from a common cloud of
interstellar gas and dust an estimated 51 million years ago.
Eventually, they will
scatter as their gravitational embrace continues to weaken.
Alpha Persei Association is also known as the Per OB3 Association and Melotte
20. The latter
refers to its listing in Philibert Jacques Melotte's catalog of
245 open star clusters. The
Melotte catalog is a great resource for binocularists, since it
contains many targets that are too large to be easily detectable
in the narrow fields of telescopes.
Persei Association is a beautiful sight through even with the
smallest pocket binoculars, as is our next target, open cluster
M34. M34 is located
roughly midway between Algol (Beta Persei) and Almach (Gamma Andromedae). Algol and M34 are separated by 5°, so depending on the
span of your binocular's field, both may just squeeze into the
binoculars, M34 looks like a hazy patch of light about as large
as the Full Moon.
Look for the brightest of its hundred or so stars twinkling in
the soft glow of fainter, unresolved suns.
If distance estimates of 1,400 light years to M34 are
correct, then the cluster spans about 14 light years edge to
Interestingly, M34’s discovery predates Messier’s first
encounter by more than a century.
Giovanni Batista Hodierna, an Italian astronomer in the
court of the Duke of Montechiaro, was the first to spot it,
probably before 1654.
Messier independently rediscovered it in 1764.
Left: The Alpha Persei Association (Melotte 20) as sketched through the author’s vintage extra-wide field 7x50 binoculars. North is up.
are in the area, be sure to pay a call on
Algol, the famous “Demon Star.”
Algol is a fun variable star to follow through binoculars, but in the past, it
was viewed with fear and dread. In
the Iliad, Homer described Algol as “a ghastly sight, deformed and
dreadful, and a sight of woe.”
Homer looked more carefully, he might have noticed an even more dreadful sight –
that Algol was actually winking at him.
That’s because every 2 days, 20 hours, 49 minutes, the star’s brightness
drops from magnitude 2.1 to magnitude 3.4.
Algol is not actually winking at us, of course.
These apparent fluctuations are the
result of an unseen companion star passing in
front of the binary system’s primary star.
Each eclipse lasts about 10 hours.
As the companion moves off the primary,
Algol returns to peak brightness.
minor dip in brightness occurs as the companion
passes behind the primary.
The apparent brightness of Algol keeps it
well within naked eye and binocular range across
its entire cycle, making it an ideal star for
fledgling variable star observers to follow.
To track Algol, compare it periodically with
stars of known brightness in its immediate
Use Gamma Andromedae to the west of Algol at magnitude 2.1, Epsilon Persei to its east at magnitude 2.9, and Kappa
Persei to its north at magnitude 3.8.
All are labeled on the chart above, while
the table here lists the dates this month when
Algol will be at minimum brightness.
Finally, let's close this month with a pair of
open clusters that are more challenging than the
objects discussed above.
Both lie east of the Alpha Persei
Association, near a double-triangle asterism
formed by Lambda, Mu, 48, and 53 Persei.
Algol Minima: December 2010
easier of the pair to spot is NGC 1528.
Under dark skies, my 10x50 binoculars show a perfectly round smudge of
distant starlight just beyond a tiny Y-shaped asterism of stars.
is a tough catch, even through large binoculars.
All I can make out is a very subtle hint of its existence around the
faint stars SAO 24556 and SAO 24554.
My 25x100 giant binoculars add only a few additional dim points within.
readers who would like to delve deeper still, here is a list of some additional
binocular targets plotted on this month’s finder chart.
Try your luck with each and report your results in this column’s
month, we will kick off 2011 with one of my favorite winter targets, the Hyades.
Until then, let me wish you and yours a very merry Christmas, happy
Hanukah, happy holidays, and a cloud-free new year.
And if you have any comments or suggestions for future columns, please
e-mail me at
always, remember that, when it comes to stargazing, two eyes are better than
About the Author:
Harrington is the author of Touring the Universe through Binoculars.
Visit his web site at www.philharrington.net
for a preview of his new book, Cosmic Challenge, from Cambridge University Press.
Phil Harrington's Binocular Universe
is copyright 2010 by
Philip S. Harrington. All rights
reserved. No reproduction, in whole
or in part, beyond single copies for use by an individual, is permitted
written permission of the copyright holder.