Basic Astronomy

Ch. 27-3 The Sun-Earth-Moon System

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Objectives: Identify the relative positions and

motions of the Sun, Earth, and Moon Describe the phases of the Moon. Distinguish between solstices and

equinoxes. Explain eclipses of the Sun and Moon.

4 Types of Earth Motion

1. Galactic/ Cosmic Year: The length of time it takes solar system to circle around the Milky Way approximately 225,000,000 years

Milky Way GalaxyWe are located in a spur off the minor Sagittarius Arm. Our local region of the galaxy is typically known as the Orion Arm

4 Types of Earth Motion

2. Precession of Axis or "Wobble" effect: approx. 26,000 years

Polaris is our current North Celestial Pole Star.

13,000 = Pole Star will be bright star of Vega , in Lyra constellation

26,000 years = Polar Star will be Polaris again

4 Types of Earth Motion

3. Revolution: Earth takes 365 days 5 hours 43 minutes or 365 1/4 days to revolve around the sun. This gives us our "year".

 

4 Types of Earth Motion

4. Rotation: Gives us our "day".

Sidereal Day:Earth’s rotation in relationship to a star. Sidereal day is23 hrs 56 min 4.1 sec. long

Solar Day:Earth’s rotation in relationship to the sun. Solar day is 24 hours long.

Seasons

Seasons

Summer Solstice:Longest day of the year in Northern Hemisphere is June 21.Sun tracks as far north as Tropic of Cancer 23 1/2° N of equator

Fall Equinox: Equal day/night. Sun tracking over celestial equator, Sept. 21.

Seasons

Winter Solstice: Shortest day of the year in Northern Hemisphere, Dec. 21.

Sun tracks as far South as Tropic of Capricorn, 23 1/2° S of equator.

Spring Equinox: Equal day/night.Sun tracking over celestial equator, March 21. 

Phases of the Moon

NEW MOON

WAXING CRESCENT

FIRST QUARTER

Moon is directly between the Sun and Earth. Far side is lighted. Near side is dark. We see the dark side.

A sliver of moon's near side is lighted.

Lighted semi-circle. 1/2 of moon is lighted. We see only a 1/4 of it.

Phases of the Moon

Lunar month vs. lunar day

Describe a lunar month vs. a lunar

day.

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Lunar month = New Moon to New Moon. Also called a synodic month = 29.5 days

A lunar day is 27.3 days long. This is the time it takes for the moon to return to the same spot in the sky relative to the stars. Also called a sidereal month.

Moon’s orbit

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under the tab. Describe the Moon’s orbit around Earth.The Moon’s orbit forms an

ellipse, an elongated circle.

Apogee: Moon is farthest away from Earth

Perigee: Moon is closest to Earth.

Eclipses

Solar Eclipse

Annular Eclipse

Lunar Eclipse

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