OBSERVING THE SKY;
THE BIRTH OF ASTRONOMY, PART I:
INTRODUCTION TO THE SKY
January 18, 2005
Chapter 2, Pages 18─29
Thursday: Chapter 2, Pages 29─41
I. Patterns in the sky; constellations
A. Greek/Roman constellations and other myths and legends
B. Creation of Universe (Earth, Sun, Moon, stars)
C. Stories with moral/lesson
II. Motion and cycles
A. Cycles (lunar phases, day/night)
B. Importance: time (Big Dipper); seasons (Big Dipper, Scorpius); harvest/plant (Pleiades)
II. Size and shape of stars on charts
III. Asterism vs. constellation: Pleiades; Big/Little Dipper vs. Ursa Major/ Ursa Minor (Big and Little Bear);
Winter Hexagon (Auriga, Gemini, Canis Minor, Canis Major, Orion, Taurus)
IV. Orion, measuring angles
V. 3-D nature of constellations
THE WINTER/SPRING SKY
The brightest stars of the winter/early spring sky (see chart below) are found in the following constellations:
Orion (the hunter)
Auriga (the charioteer)
Taurus (the bull)
Canis Major (the big dog)
Gemini (the twins)
Canis Minor (the little dog)
These constellations can be found almost directly overhead at 9:00 p.m. There are 88 officially designated
constellations. The area of the sky surrounding and including the constellation is called by the constellation’s name.
This helps astronomers describe the locations of objects in the sky.
The brightest star in Orion is Rigel; the brightest star in Taurus is Aldebaran; and the brightest stars in Gemini are
Pollux and Castor; the brightest star in Auriga is Capella; the brightest star in Canis Major is Sirius; the brightest star
in Canis Minor is Procyon. When connected, the seven brightest stars in these six constellations form an asterism
called the Winter Hexagon. An asterism is an easily recognized shape made from the brightest stars of one or more
constellations. Sirius, Procyon and Betelgeuse (the second brightest star in Orion) form an asterism known as the
Winter Triangle.
From a dark site, the Milky Way can be seen between Sirius and Procyon. In some Native American sky lore, the
Milky Way is thought to be a trail of cornmeal spilled by a dog. Sirius, in Canis Major, represents the mischievous
dog. In ancient Arabian sky lore, the Milky Way represents a river that separates two sisters. One sister is
represented by Sirius, and the other by Procyon.
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The Pleiades, or Seven Sisters, appears within the constellation Taurus. The Pleiades is actually an open star cluster,
which is a group of stars that formed within a nebula. The Pleiades usually appears as a fuzzy patch, but most people
can distinguish 5 or more individual stars even from a moderately dark site. The Hyades is another open star cluster,
which makes up the face of Taurus. Aldebaran is a red-orange giant star within this cluster, and is often called the eye
of Taurus.
Many so-called stars are actually double stars. Double stars are actually two stars orbiting around a common center.
They appear as a single star without the aid of a telescope. Capella, Sirius, and Procyon are double stars. Castor is a
multiple star: three double stars in one. Pollux, the other twin of Gemini, is a single yellow giant star which appears
even brighter than Castor’s six stars.
Looking north at about 9:00, you will see the circumpolar constellations. These are the constellations that appear to
circle Polaris, the North Star. The W shape of Cassiopeia (the queen) is upside down now, looking more like an M.
Cepheus (the king) is below Cassiopeia. It is shaped like a house with the point of the roof approximately toward
Polaris.
Ursa Major (the great bear) is visible to the north with the handle pointing toward the horizon. From a very dark site,
Ursa Minor (the small bear) may be visible below Polaris. Within these constellations, there are two familiar
asterisms: the Big Dipper in Ursa Major and the Little Dipper in Ursa Minor. The bowl of the Big Dipper is formed
by four prominent stars which also form the rear portion of the bear’s body. The handle is formed by three prominent
stars which form the bear’s tail. From even a moderately dark site, a second star can be seen near the center handle
star. These stars are Alcor and Mizar. The best known star in the Little Dipper is at the end of its handle: Polaris, the
North Star or Pole Star. Its overall shape is similar to the Big Dipper, except that its handle curves in the opposite
direction.
By 10:00, Leo (the lion) is rising in the East. The head and neck of Leo look like a backwards question mark. If you
imagine someone poking holes in the bottom of the bowl of the Big Dipper, the water would drip onto Leo’s back.
Regulus is the brightest star in Leo.
Asterisms and Their Constellations
The Ten Brightest Stars in the Winter Sky
Star
Constellation
Asterism
Constellation(s)
Sirius
Capella
Rigel
Procyon
Betelgeuse
Aldeberan
Pollux
Adhara
Castor
Bellatrix
Canis Major
Auriga
Orion
Canis Minor
Orion
Taurus
Gemini
Canis Major
Gemini
Orion
Big Dipper
Little Dipper
Winter Hexagon
Ursa Major
Ursa Minor
Auriga, Taurus, Orion,
Canis Major, Canis
Minor, Gemini
Canis Major, Canis
Minor, Orion
Orion
Cassiopeia
Leo
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Winter Triangle
Orion’s Belt
“M,” “ W”
Question Mark
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