ASTR 1 Lecture 3: Astr 04/11/18

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12 Jun 2018

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Chapter 1 (1.3): The Earth, Moon and Sun

1. Moon Phases

a. What determines the appearance of the moon

i. What is moonlight?

1. Reflected sunlight

ii. Why does the moon rise in the east and set in the west?

1. Because the Earth is spinning

iii. Why does the moon’s appearance change?

1. This is because it orbits the earth.

iv. When does a full moon rise?

v. When does a new moon rise?

vi. Does an astronomer on the moon see the Earth “rise” or “set”?

vii. Do they see phases of the Earth?

viii. When does a first quarter moon rise?

2. Eclipses

a. Lunar Eclipse = When the earth casts a shadow in the moon ( E between M and

b. Solar Eclipse = Moon casts shadow on earth ( M between E and S )

i. The Earth moon and sun are rarely ever perfectly aligned!

c. Partial vs full shadows… the sun is not a dot!

i. Full - Umbra

ii. Partial - Penumbra

1. Penumbral Lunar Eclipse - Moon passes through penumbra

2. Partial lunar eclipse -

d. Why does the moon appear red during a full lunar eclipse?

e. Blue light is scattered more efficiently on Earth’s atmosphere (in the daytime the

sky looks blue)

f. Red light is scattered less efficiently (setting sun looks red) and the path of light

(all colors) is being bent by mass (general relativity)

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