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 Intensity– (+1) 2.5

• (+1.5) 4

– (+2) 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)