Download Earth

Earth Unique in the Solar System
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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)