Astronomy Notes – Unit 1 – Earth
q (1) Earth’s Motion
o rotates about its axis
§ Sidereal Day = 23 h, 56 m, 4.1 s
§ Solar Day = 24 h
o revolves around the Sun
§
Length of Year
=
o Leap Year – Gregorian Calendar
§ adds a 29th day to February in all years evenly divisible by four, except for centennial years (those ending in -00), which receive the extra day only if they are evenly divisible by 400.
o Leap Seconds – Coordinated Universal Time (UTC)
q (2) Tilt of the Earth’s axis - currently = 23.27 degrees
o varies 22.1 – 24.5 degrees over a 41,000 year cycle
o Seasons
o Summer and Winter Solstice
o Spring (or Vernal) Equinox
o Fall (or Autumnal) Equinox
o Tropic of Cancer, Tropic of Capricorn
o
1) Rotate: To spin on an axis.
2) Axis: Imaginary line through the center of an object.
3) Revolve: To move around a central point.
4)
Summer
Solstice: The position of the Sun on
about June 21, when it is farthest north of the equator.
5)
Winter
Solstice: The position of the Sun on
about December 21, when it is farthest south of the equator.
6)
Spring (or
Vernal) Equinox: The position of the
Sun on about March 21, when it crosses the equator and heads north.
7)
Fall (or
Autumnal) Equinox: The position of
the Sun on about September 23, when it crosses the equator and heads south.
8)
Equator:
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9)
Tropic of
Cancer:
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10) Tropic of Capricorn:
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