1. Earth Unique in the Solar System Total Eclipse of Sun Rainbows Snowflakes Liquid surface water Life –Diversity –50 million species

2. 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 3 rd Rock from Sun 365 days to revolve Blue Sky

3. 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?

4. Answer Distance = 1/separation (arcsec) Distance = 1/0.5 Distance = 2 pc

5. Practice #2. A star has an apparent magnitude of 5. It is 20 pc from us. What is its absolute magnitude?

6. 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.

7. 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 –MagIntensity –(+1) 2.5 (+1.5)4 –(+2) 6

8. Answer # 2 – cont. Therefore, we subtract 1.5 magnitudes from the original apparent magnitude of 5. 5 – 1.5 = 3.5 ( the absolute magnitude)