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Earth Unique in the Solar System • • • • • Total Eclipse of Sun Rainbows Snowflakes Liquid surface water Life – Diversity – 50 million species Earth Unique in the Solar System • • • • • Total Eclipse of Sun Rainbows Snowflakes Liquid surface water Life – Diversity – 50 million species • • • • • • Air (79%N2, 21%O2) 1 bar 50 deg F mean Temp 3rd Rock from Sun 365 days to revolve Blue Sky Practice problem • . You measure a separation of 0.5 arcsec between two images of the same star. You took the photo images 6 months apart. How far from us is the star? Answer • Distance = 1/separation (arcsec) • Distance = 1/0.5 • Distance = 2 pc Practice #2 • . A star has an apparent magnitude of 5. It is 20 pc from us. What is its absolute magnitude? Answer - #2 • The absolute magnitude will be a smaller number than 5 because the star will “move” to 10 pc (the standard distance from Earth) from 20 pc. • Since the star will be “closer”, it will be brighter. • A brighter star has a smaller magnitude • Thus, we expect an absolute magnitude less than 5. Answer #2 – cont. • Since the star “moves” to a distance 1/2 of its original distance, the luminous intensity will be the square of ½ or ¼. • Take the 4 to the Pogson scale – Mag – (+1) Intensity 2.5 • (+1.5) – (+2) 4 6 Answer # 2 – cont. • Therefore, we subtract 1.5 magnitudes from the original apparent magnitude of 5. • 5 – 1.5 = 3.5 ( the absolute magnitude)