Part 1: The Earth – Moon System Astronomy Part 1: The Earth – Moon System
Earth Motions…Two Types Rotation: spinning around an axis Revolution: the motion of a planet around a point in space
Earth’s Rotation Thanks to rotation we have day & night We measure the Earth’s rotation around its axis from one noon to the next noon This is about 24 hours This is called a solar day
Earth’s Revolution The Earth revolves around the sun in an elliptical orbit Earth is about 150 million km from the sun (93 mill miles) Perihelion: Earth’s closest approach to the sun Aphelion: Earth at its greatest distance to the sun Speed: 107000 kilometers (km) per hour or 66,486.72 mph
Earth’s Seasons The Earth is tilted 23.5 degrees This tilt causes our seasons So we get… Spring equinox (March 20 or 21) Autumn equinox (Sept. 22 or 23) Summer Solstice (June 21 or 22) Winter Solstice (Dec. 21 or 22)
Vernal Equinox – 21 March arctic circle tropic of Cancer equator sunlight tropic of Cancer equator tropic of Capricorn sunlight antarctic circle
Autumnal Equinox – 21 September arctic circle sunlight tropic of Cancer equator tropic of Capricorn sunlight antarctic circle
Summer Solstice – 21 June tropic of Cancer arctic circle equator sunlight equator antarctic circle sunlight
Winter Solstice – 21 December tropic of Cancer arctic circle sunlight equator sunlight antarctic circle tropic of Capricorn
Earth-Sun Motion The Earth & the sun are revolving around the Milky Way Galaxy at 250 km/s or around 560,000 mph
Earth-Sun Motion And our Galaxy is approaching, and will collide, with the Andromeda Galaxy
The Earth - Moon We have one satellite…the moon It is about 384,000 km or 239,000 miles from Earth Perigee is the closest approach Apogee is the furthest
Phases of the Moon
Half of the Moon is always lit up by the sun Half of the Moon is always lit up by the sun. As the Moon orbits the Earth, we see different parts of the lighted area. http://www.nasm.si.edu/apollo30th/moontheater/phasepage2.html
The Moon passes through four major shapes during a cycle that repeats itself every 29.5 days. The phases always follow one another in the same order: New moon First quarter Full moon Third quarter
New Moon… The lighted side of the moon faces away from the Earth. This means that the sun, Earth, and moon are almost in a straight line, with the moon in between the sun and the Earth.
First Quarter Moon The right half of the Moon appears lighted and the left side of the Moon appears dark
Full Moon The lighted side of the moon faces the Earth and the Sun The Earth, Sun, and moon are almost in a straight line, with the Earth in the middle Photo by Robin Afinowich
Third Quarter Moon Also called a last quarter moon. Only the left side of the moon appears lighted The next main phase will be a new moon again
Other Phases There are other phases that fall between the ones we already looked at Like… Waxing cresent Waxing gibbous Waning gibbous Waning cresent