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
arthursclipart.org
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
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The Sun
The sun is the source of all energy on Earth.
The Sun transfers energy by
1. Radiation
2. Conduction
3. 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