Expert: Tom Whiting - 11/21/2008

Question
I'm doing a project for science, and we have to study a constellation. My constellation is Pegasus, and I'm having trouble finding how many major stars ar in it, and their names. I've seenn many different answers, and I just have no idea which ones are correct. I was hoping you could help me?

Answer
Hi Maddie,
Yes, Pegasus is a very prominent Autumn constellation (area of sky
as are all constellations) which is located high in the south,
due south at around 7:45 pm local time right now, about 70 degrees
above your southern horizon (for 40 degrees N. Latitude, higher the
farther south you are of 40 North Latitude).  Another easy way to
find it is a line from Polaris (North Star drawn through the western
side of Cassiopeia (The Big "W" -inverted this time of the year
and nearly overhead at that time) and extended southward an equal
distance.
This will bring to the famous asterism the "Great Square" of Pegasus
consisting of 4 average bright stars, which actually looks like
a baseball diamond in a dark sky. We are "viewing the game" sitting
down the First Base line, with homeplate the southeastern most star
of the Square, First Base is to the lower right (southwestern star),
and on around to second base and third base.  The Third base star
is the brightest in the GREAT SQUARE at 2nd magnitude, and is actually on the Andromeda/Pegasus border so it's astronomical name
is Alpha Andromedae (common name Alpheratz)....all the rest of the
stars of the Great Square are slightly dimmer 3rd magnitude stars
of "average" brightness.  There are no prominent 1st magnitude stars
in Pegasus, but the square in the sky itself, is very obvious being
nearly devoid of stars with the slightest light pollution, except for
2 dim 5th magnitude stars, representing the "Pitcher's Mound" inside
the square, but closer to the second base star instead of home plate.

The First Base star is named Alpha Pegasi, the second base star is
Beta Pegasi, and the home plate star is Gamma Pegasi...common names
Markab, Scheat, and Algenib respectively....although most astronomers
prefer the Greek letter system of names as they are far easier to
memorize...Oh, and those are ALL lower case Greek letters.
(Us astronomers know all the lower case Greek letters, but none of
the upper case!) A joke, of course, but basically true!

Ok, the rest of Pegasus are two parallel lines of average bright stars off of Second Base off to the Northwest...the first line is
directly away from homeplate/second base, and in order are Eta
Pegasi (Matar), and Pi Pegasi. The other line jogs 90 degrees southwestward, then back Northwestward, and are the stars Mu, Lambda,
Iota, and Kappa Pegasi in order away from second base.  These can
be pretended to be the second baseman, short center fielder, and
center fielder...take your pick which star represents which player.
Now a final line 4 stars come off of First Base toward the Southwest
with an end jog of 90 degrees; this line is Xi, Zeta, Theta, and
Epsilon Pegasi (common name Enif, or 'fine' backwards)....all these
stars are rather dim 4th magnitude stars, except Epsilon Pegasi is
a brighter 2nd magnitude star, representing the Right Fielder playing
well off the homeplate/first base line, actually in foul territory
for some strange reason.  {Enif is a beautiful double star in a
small telescope, and the only prominent star in Pegasus that is an
easy double for small amateur scopes.
Other than lots of faint NGC galaxies, there is only one prominent
Deep Sky Object in the area of Pegasus, and that's Messier number 15
(M-15)....a beautiful globular star cluster (tied for third in it's
brightness and beauty of all the fine Globular star clusters in our northern night sky), and located on a line from Theta to Enif, and extended 50% of it's length, just below naked eye at 6.5 magnitude, but an easy binocular fuzzy spot in the sky. For the advanced
amateur, Pegasus is a fertile hunting ground for fine but very faint
NGC (New General Catalogue) galaxies.

Notice I have not referred to Pegasus as the "flying horse" as all
constellations now are simply areas of the sky, like states of the
USA.  (since 1930 when the IAU - International
Astronomical Union) designated specific areas of the sky as constellations, making it much much easier to learn and memorize them; as easy as learning and memorizing our states of the USA).

So long gone are the days of 'picturing' men or animals in the
night sky...they are just simple areas now.  And all the borders run
either N-S or E-W...there are no diagonal lines or irregular lines
like the Mississippi River dividing our states. So basically with
the area of Pegasus, just picture a big rectangle around all those
stars discussed above, and there you have it.

Oh, a word about magnitude (brightness) of stars in case you are
fairly new to astronomy...it's a REVERSE scale. The lower the magnitude number, the BRIGHTER the star. Stars of first magnitude
are the brightest in our sky, then second magnitude are slightly
dimmer, then 3, 4, 5 are dimmer still. Naked eye limit is right
around 6th magnitude. Binoculars are good down to 9th magnitude,
and a small 6 inch telescope gets you down to 13th magnitude objects. Now there are a few stars and planets that are even brighter
than first magnitude, so we go zero, then negative magnitudes for
say, Jupiter at -2nd magnitude, Venus at -4th magnitude, and the full
moon at -13th magnitude. So that's how the system works.
Thus the two brightest stars, at 2nd magnitude, in Pegasus are
Enif (Epsilon Pegasi) and the third base star of the Great Square,
or Alpha Andromedae (Alpheratz).  The rest are all dimmer than these
stars, but still quite prominent in a moonless, non-light polluted
sky.
Oh, notice that to name the stars, we change the constellation name
to the Latin Genitive Case...Pegasus goes to Pegasi...or in English
it's the Possessive case. The reason for this is because the constellation "owns" that star, so we change the ending to the other
case. If it ends in "a" then it's feminine, so we add an 'e' and pronounce it as "i"....for instance, Cassiopeia becomes Cassiopeiae,
the ae dipthong pronounced as "I"......and if the constellation ends
in "us" then it's masculine, so we change the 'us' ending to an "i"
and pronounce it AS an "I"...so Pegasus becomes Pegasi and Scorpius
becomes Scorpii, and Aquarius becomes Aquarii, and so on.
{I didn't invent the system, I only report on the proper way to do
it). What happens when we exhaust the 24 letters of the Greek Alphabet for the brighter constellation stars? Then we go to Flamsteed numbers, thus in Pegasus are the faint stars 51 Pegasi and 82 Pegasi, and so on.  That's the way it works for ALL constellations, so now you know the rest of the story.

Hope all this helps, and if you need even more detailed information
for your report, please do not hesitate to write again.
Clear Skies,
Tom Whiting
Erie, PA USA

FOLLOW UP:
Oh, I forgot to mention that we astronomers use the Great Square as
a sky check to see how much light pollution or how transparent it is outside at night, by counting the stars inside the Square.  If you can only see the 2 stars marking the pitcher's mound (Upsilon and Tau Pegasi) then the sky is not very clear.  We typically like to see in dark country skies at least a dozen other faint stars inside the Great Square. At a really dark, moonless location, counts of up to two dozen are possible.  I personally have counted over 48 stars
inside the Square at a prime observing location at Cherry Springs
State Park, near Coudersport, Pennsylvania.....a designated astronomy dark sky (and protected) State Park. (No white light allowed at night there).  So Pegasus provides us solid evidence as
to how transparent, and how non-light polluted, our atmosphere is.
Clear Skies,
Tom