Transcript Constellations

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Constellation: Group of stars that form a
distinctive pattern in the sky
› International Astronomical Union (IAU)
designated 88 constellations

Asterism: Smaller groups of stars that form
patterns within a constellation, from the
Greek word aster, meaning star

The larger the ‘dot’, the brighter the star

Apparent magnitude: star’s brightness as
seen from Earth
› If all were placed at same distance from
Earth
Apparent magnitude scale first
developed by Greek astronomer
(around 130 BCE)
 He assigned a magnitude of 1 to the
brightest star he could see

› Faintest star was 6
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Today, stellar magnitude extends well
beyond 6 and into the minus range
› Sun now recognized as -26

Stars in constellations appear to be close
together – same line of sight
› May be light years apart!

Light year – represents the distance light
travels in one year
› At 300 000km/s, light travels about 9.5 x 1012
km in one year
Best known group of stars (Asterism)
› Not a constellation! Part of a large
constellation, Ursa Major
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Recognized by many cultures
› Ancient Chinese – chariot
› Early Egyptians – bull leg
› Aboriginal - bear

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The Big Dipper’s two end stars are known as
pointer stars
› Help to navigate the night sky
› Point toward Polaris

Polaris (“North Star”) points toward the
North
› Does not appear to move
› Stars appear to rotate counterclockwise around
Polaris

Latitude: angular
distance north or south
of the earth's equator,
measured in degrees

Latitude determines
which constellations are
observable
› Move northward,
constellations along
southern hemisphere slip
below horizon
More Constellations – The Twins

The Twins as you see
them in the sky

Allegorical
representation
More Constellations – The Twins
Graphically

Geometrical

Note: the stars are still in the exact same position, but now
the shape has meaning!

Constellation Charts

Big Dipper

Little Dipper

Dragon (Draco)
› Large, but not
very bright
› Seen best from
late May - early
Nov
Constellation Charts

Great Bear
› Ursa Major –
very large

Lion
› 3 bright stars

Hunting dogs

Little Lion
› Looks more
like a mouse
Constellation Charts

Cassiopeia
› In the milky
way
› “W” shape –
easy to
remember
› Draw a line
from where
handle joins
bowl, through
Polestar and
beyond


Cepheus
Giraffe
› Hard to see
Learning Check:
Please answer the following questions on a
separate sheet of paper:
1.
What does the term “celestial object”
mean?
2.
What unit of time does one revolution of
Earth around the Sun correspond to?
3.
Explain how calendars were helpful to
ancient civilizations
4.
Imagine you are standing at the North
Pole and see a star directly overhead.
Where do you think the star would be if
you were standing at the equator?
5.
Compare and contrast the terms
constellation and asterism in a Venn
diagram
6.
What is a star’s apparent magnitude?
7.
Define the term light year