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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 km/s, light travels about 9.5 x 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

 The Twins as you see them in the sky  Allegorical representation

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

 Big Dipper  Little Dipper  Dragon (Draco) › Large, but not very bright › Seen best from late May - early Nov

 Great Bear › Ursa Major – very large  Lion › 3 bright stars  Hunting dogs  Little Lion › Looks more like a mouse

 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

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