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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

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

Recognized by many cultures› Ancient Chinese – chariot› Early Egyptians – bull leg› Aboriginal - bear

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

Geometrical

Note: the stars are still in the exact same position, but now the shape has meaning!

Graphically

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