The Moon and The Planets

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The Moon and The Planets

• Dr Bryce

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Class Notices

• First homework due this afternoon

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The Moon

• Earths Satellite
• Takes about 27 days to
  orbit the Earth
• On average 380,000,000 m
• Or 3.8108 m from the Earth

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Things we have noticed about the Moon

• Phases
• Always see same side
• Looks bigger on the Horizon
• Moves Eastwards across the Sky, against
  background stars

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In another example

• Remember that Moonlight is reflected Sunlight.

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Phases of the Moon 29.5-day cycle
new crescent first quarter gibbous full gibbous la
st quarter crescent

• waxing
• Moon visible in afternoon/evening.
• Gets fuller and rises later each day.

• waning
• Moon visible in late night/morning.
• Gets less and sets later each day.

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There is no dark side!
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Eclipses

• This photo shows an annular Solar Eclipse.
• The Moons angular diameter is too small to cover
  the Sun
• Just the Earth the Moons orbit is an ellipse so
  the distance to the Moon varies
• If the Moon is further away its angular diameter
  is smaller.

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Time lapse photography of a Total Solar Eclipse
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Some definitions

• Solar Eclipse the Moon is between the Earth and
  the Sun.
• Lunar Eclipse the Earth is between the Moon and
  the Sun
• As the Earth is much larger it has a bigger
  shadow so Lunar Eclipses are more common and
  visible from more of the Earth

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More definitions

• Totality The time period in which the Moon
  completely covers the Sun, normally just a couple
  of minutes. The sky becomes dark and you can see
  the stars.
• Partial The Moon doesnt completely cover the
  Sun and you see a crescent or a bite taken out of
  the Sun.
• Health warning Do not look at the Sun with your
  naked eye or with binoculars, even during an
  partial eclipse you can blinded.

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The Moon isnt in the same plane as the Earth/Sun
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So we dont get eclipses every month
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Path of Totality
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Summary Two conditions must be met to have an
eclipse

• It must be full moon (for a lunar eclipse) or new
  moon (for a solar eclipse).
• AND
• The Moon must be at or near one of the two
  points in its orbit where it crosses the ecliptic
  plane (its nodes).

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Planets

• A view of the Solar System
• Notice Plutos orbit
• Notice that our part of
  the Solar System is
  so close to the
  Sun.

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Our view of the planets
Mercury difficult to see always close to Sun in
sky Venus very bright when visible morning or
evening star Mars noticeably red Jupiter very
bright Saturn moderately bright
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The two types of Planets
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Terrestrials
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Jovians plus Pluto
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Some interesting Moons
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The Planets and Our Culture