The Planets

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The Planets
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Discussing Planets

• Measure distances to planets in Astronomical
  Units (AU).
• 1 AU distance from Earth to the Sun 93
  million miles.
• Planets orbit elliptically around sun.
• Perihelion point closest to the sun
• Aphelion point farthest from the sun.

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Discussing Planets, continued

• Orbit period the amount of time it takes the
  planet to make ONE revolution around the sun (a
  planets year).
• Rate of Rotation how long it takes the planet to
  rotate once around its own axis (a planets
  day).

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The Inner Planets Terrestrial Planets

• All are mostly solid rock with a metal core.
• Lighter elements have lower boiling points cant
  condense this close to sun only rocks and metals
  can.
• Dense elements like iron are pulled by gravity to
  center of planet during accretion (planet
  formation)
• No rings
• Surfaces have many impact craters caused by
  collisions with rocky objects (asteroids).

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Mercury

• Closest to sun
• Orbit period 88 days
• Rotates slowly on its axis one day is 59 Earth
  days.
• No moons
• Very, very thin atmosphere (planet is too small
  to have enough gravity to hold gases)
• Huge temperature range between day and night.

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This image of Mercury passing in front of the sun
was captured Nov. 8, 2006 by the Solar Optical
Telescope, one of three primary instruments on
Hinode. Image credit Hinode JAXA/NASA/PPARC
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Venus

• 2nd planet from sun.
• Orbit period 225 days.
• Also rotates slowly on axis one day is 243
  Earth days.
• Shows retrograde rotation rotates around its own
  axis opposite of other planets.
• Sun rises in west and sets in east!
• No moons.

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Venus, continued

• Called Earths sister planet
• Has almost the same size, mass, and density.
• Very hot planet because of its thick atmosphere.
• Atmosphere is 96 Carbon Dioxide clouds, which
  trap heat.
• No liquid water rains sulfuric acid instead.
• Shows evidence of volcanic activity has rocks
  and surface features (mountains, canyons, etc.)
  similar to Earth.

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Earth

• 3rd planet from Sun.
• Orbit period 365.24 days
• Rotation rate 23 hours, 56 minutes
• 5th largest planet in solar system has only one
  moon.
• Only planet in solar system with
• oceans of liquid water
• Proper combination of water, temperature, and
  oxygen to support life.

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Earth, continued

• Has moderate atmosphere of Nitrogen and Oxygen
  gas, with small amounts of water vapor, carbon
  dioxide, and other gases.
• Tilted 23.5 degrees from the perpendicular North
  Pole is always tilted toward North star.
• The tilt of Earth causes seasons changes the
  angle at which sun hits Earths surface.
• N. Hemisphere toward sun summer, because days
  are longer and we get more direct sunlight.
• N. Hem. away from sun winter, longer days and
  less direct sunlight.

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Earths Moon

• 1/80th the size of Earth, with 1/6th the surface
  gravity.
• Shines because it reflects sunlight.
• Formed when a large, Mars-sized planetary body
  collided with Earth early on in its formation.
• Collision ejected Earth-like materials into
  space orbited Earth and accreted

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Earths Moon, continued

• No atmosphere wide temperature range
• Heavy cratering on Moon due to many asteroid
  impacts.
• Evidence of volcanic activity (old lava-filled
  craters).
• Craters and rocks are well preserved, (no wind,
  weather, water, or ice to erode them).
• The moon is responsible for
• Influencing ocean tides on Earth
• Stabilizing Earths rotation
• Gradually slowing Earths rotation through
  friction.
• In 1,000 years, the day will be 0.2 seconds
  longer!

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Eclipses

• Eclipse planetary body passes through the shadow
  of another.
• Umbra shadow where sunlight is completely
  blocked.
• Penumbra part of shadow where sunlight is
  partially blocked.

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• Solar eclipse moon passes between Earth and Sun
• Moons shadow blocks out sunlight in a small part
  of the Earth.
• Totally blocked (total eclipse) in the umbra.
• Partial eclipse in the penumbra.
• Lunar eclipse Earth passes between moon and sun,
  preventing sunlight from reaching the moon.

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Mars

• 4th planet from sun
• Orbit period 687 days
• Rotation 24 hours, 37 minutes
• Similar tilt in axis like Earth has seasons
• Has 2 moons, Phobos and Deimos
• Geologically active with large volcanoes (largest
  in solar system!)
• Little water is trapped in polar ice caps
• No real atmosphere

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Olympus Mons largest volcano in solar system!
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Mars Moons Phobos and Deimos

• May be the remains of one moon that was split by
  an asteroid
• Very small and irregularly shaped, not round like
  our moon
• Dark surfaces that are heavily cratered
• Craters indicated heavy bombardment by asteroids
• Very old