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Stars Constellations A group of stars that appears to form a pattern in the sky Virgo AQUARIUS Constellations total of 88 different constellations can be seen in the N and S hemispheres As you move north you can see more stars. Andromeda Aries Constellations Ursa Major - (Big Bear) is the most famous constellation Constellations The Big Dipper is part of Ursa Major Constellations Two Polaris stars of Ursa Major are used to find the North star- Polaris?1&2 (pole star) Constellations- Polaris is part of Ursa Minor (the little dipper) Ursa Minor Constellations As the earth rotates on its axis the constellations move. They rotate around Polaris counter clockwise. The earth’s axis points toward the N. Star Pg. 617 (fig. 28.2) Orion in Winter Constellations Some constellations can only be seen during specific seasons This is due to earth’s rotation around sun and tilt of the earth Lyra in summer ?3,4&5 Circumpolar Rotation around Polaris What happens as you travel North? The number of circumpolar stars visible, increases as the observer moves North Can you tell what constellations these are? ?6 Ursa Major ?7 Lyra ?8 Orion Aquarius Gemini Stars- How far to a star? Closest Star = Sun 93,000,000 miles = 1 astronomical unit Next closest star Proxima Centauri 25 trillion miles 2.5 x 10 13 4.2 light years Light year Distance that light travels in one year 5,900,000,000,000 miles Polaris- 680 LY Betelgeuse (red supergiant ) is 490 LY ?9 Properties of Stars Our Sun- Diameter 855600 miles 110x earth Density 1.4 x density H20 Mass 300,000x earth How does our sun compare? Diameter average Density mid to high Mass Other stars range from 1/100th to 50x our sun How do we size up? Wow! Jupiter is BIG Our sun is REALLY BIG! Guess Not! We are REALLY SMALL! I feel so insignificant! Color? Depends on surface temperature cool Hot- ~30,000 ° C Medium- our sun (5500°C) Green stars look white to us! Classification of stars ?10 & 11 Composition of Stars How can we tell? You know this! Spectroscopy! Our sun Hydrogen (70%) Helium (28%) No 2 stars have the same spectra (like a fingerprint) -Brightness Apparent Magnitude how bright a star appears to earth observer. Depends on Distance from us what is between us true brightness Brightness- Luminosity True brightness Depends on…(2 things) 1. Size -if same size, blue is more luminous 2. Temp.- if same temp., bigger is more luminous Absolute MagnitudeRigel- foot of Orion 40,000 suns “Blue Super Giant” How stars would appear if they were all the same distance from earth. All stars place 32.6 LY from the sun Our sun abs. Mag = 4.8 Negative is brighter ?12