Chapter 6: Sky & Motions

Question 1

The Ecliptic

Answer 1

• Sun, Moon, Planets wander through the sky, changing coordinates constantly. They all stay on an imaginary line known as the ecliptic
• The Earth’s equator is tilted from the ecliptic by 23.5 degrees
• Earth orbits the Sun along the plane of the solar system, the earth is tilted so the Sun appears to follow the ecliptic in the sky

Question 2

The Seasons

Answer 2

• Seasons are a result of Earth’s tilt
• Winter Solstice: equator tilted 23.5 degrees upward, Sun is very low in the Northern Hemisphere
• Summer Solstice: Sun crosses the highest point in the sky

Question 3

The Equinox

Answer 3

• The Sun appears right along the equator on equinox days, the Sun is “equal” to the equator
• The Sun crosses the equator in our sky, the Sun rises directly in the west and sets directly the east

Question 4

The Orbital Periods of the Moon

Answer 4

• Sidereal period: “starting” period, using the stars to measure the position of the moon. Moon orbits Earth every 27.3 days to return to the exact same spot on the sky with respect to the “starry” background. Stars are “fixed”
• Synodic period: using the sun as a measure, but the sun is not “fixed”. It takes 29.5 days to reach the exact same spot in respect to the Sun

Question 5

Apparent Moon size (close and far)

Question 6

Lunar Rotation

Question 7

Precession

Answer 7

• The moon passes through apparent phases as seen from Eart

Question 8

Solar System, common characteristics

Answer 8

• All planets orbit in nearly perfect circles (ellipticity almost always 0)
• Planets orbits are all in the same flat sheet (called a plane)
• Only the rocky planets are near the Sun
• The gaseous planets are more distant

Question 9

Introducing the Planets, common characteristics: