Astronomy Part 3

Solstices Summer sostice June 21 or 22 First day of summer Longest day of the year Winter solstice December 21 or 22 Beginning of winter Shortest day of the year – north of artic circle have 24 of darkness, south of Antarctic circle have 24 hours of daylight

Equinox Equinox- when the Sun is directly over the equator Means “equal night” Hours of daylight =hours of darkness everywhere on earth Autumnal equinox – Sept 22 or 23 Vernal equinox – March 21 or 22

Precession Circular motion of the earth’s axis caused by forces acting on a spinning body Forces come from gravitational pull of sun, moon, and planets

Nutation Wobbling around the axis Changes the angle by ½ degree one way or the other Occurs over 18 year period Caused by moon Slight decrease or increase of seasons

Eclipse Eclipses—shadows cast by Earth or the Moon onto each other Only occur when the Sun, the Moon, and Earth are perfectly lined up Solar eclipse—The Moon blocks sunlight from reaching a portion of Earth’s surface; occurs during new moon. Lunar eclipse—Earth blocks sunlight from reaching the Moon; the full moon becomes dark; Moon appears deep red

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Moon Phases Moon phases—As the Moon orbits around Earth, different amounts of its sunlit surface are seen. New moon—The Moon is between Earth and the Sun. The lighted part faces away from Earth. (black or not visible)

Moon Phases Waxing Moon looks like the moon grows in size, as the Moon travels around Earth more lighted part is seen; called first-quarter; occurs a week after new moon. Full moon Earth is between the Sun and the Moon; the entire lighted part faces toward Earth Waning Moon decreases in size, and less of the lighted part is seen; called third-quarter phase. The complete cycle takes 29.5 days

Moon Phases Sequence New Waxing Crescent First Quarter Waxing Gibbous Full Waning Gibbous Last Quarter Waning Crescent

Tides Caused by the gravitational attraction of the Earth, Moon, and Sun. moon has a much greater effect than Sun on tides because it is much closer to the Earth.

Tides Spring Tides- The exceptionally high and low tides that occur during new moon or full moon when the sun, moon, and earth are aligned. (nothing to do with the season)

Tides Neap Tide- The tide that occurs when the difference between high and low tide is least; Neap tides come twice a month, in the first and third quarters of the moon.

Tides http://www.youtube.com/watch?v=l37ofe9haMU&feature=related http://www.youtube.com/watch?v=5W2sM1Ma7YA&feature=related

The Sun The sun is the source of all energy on Earth. The Sun transfers energy by Radiation Conduction Convection

The Sun Radiation is the is the transfer of energy through space by light and waves Conduction is the transfer of energy when molecules collide (touch) Convection is the transfer of energy by the flow of a substance (convection currents)

The Sun’s Radiation

The Sun Light absorbed by plants is turned into food. This is called photosynthesis. Plants need Water, Carbon Dioxide and light to produce food (glucose) and Oxygen 6H20 + 6CO2 light C6H12O6 + 6O2