The Solar System Tom Burbine tburbinemtholyoke.edu

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The Solar SystemTom Burbinetburbine_at_mtholyoke
.edu
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Schedule Today

• Planets Historical to the present day
• Celestial Sphere - Constellations

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Lecture

• www.mtholyoke.edu/courses/tburbine/planets.ppt

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How many planets can be seen with the naked eye
and were known to the ancient astronomers?
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• Mercury closest to Sun
• Venus
• ?
• Mars
• Jupiter
• Saturn farthest from Sun

http//antwrp.gsfc.nasa.gov/apod/ap011124.html
http//www.solarviews.com/cap/venus/venusmar.htm
http//antwrp.gsfc.nasa.gov/apod/image/0107/mars_h
st_big.jpg
http//pds.jpl.nasa.gov/planets/images/full/saturn
/2moons.jpg
http//www.solarspace.co.uk/PlanetPics/Jupiter/jup
iter.jpg
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• Mercury closest to Sun
• Venus
• Earth
• Mars
• Jupiter
• Saturn farthest from Sun

http//antwrp.gsfc.nasa.gov/apod/ap971026.html
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Scorpius
http//skytonight.com/observing/ataglance
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How can we differentiate between planets and
stars with the naked eye?

• Three reasons

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How can we differentiate between planets and
stars with the naked eye?

• 1) Planets move across the sky. Stars stay in
  the same relative positions night to night
• 2) Planets tend to be brighter
• 3) Planets can undergo retrograde motion

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Planets

• Planets is from a Greek word meaning wanderer

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What is the brightest planet in the skyand why?
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What is the brightest planet in the sky and why?

• Venus
• Because it is so close to the Earth and its
  clouds are very reflective (high albedo)

http//www.solarviews.com/browse/venus/venusmar.jp
g
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Apparent Retrograde Motion backward motion
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Retrograde Motion
http//www.nmm.ac.uk/upload/img/retro.gif
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Greek model
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How do we know that the planets were considered
very important by the ancients?
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How do we know that the planets were considered
very important by the ancients?

• Named for Gods
• Days of the week are named after the planets
• Constellations (e.g., Pisces, Aries, Taurus) in
  the Zodiac are the ones that the planets pass
  through

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Why are there 7 days of the week instead of 5?
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Why are there 7 days of the week instead of 5?

• The ancients also included the Sun and the Moon
  as planetary bodies that they could see in the
  Sky

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Days of the Week
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Why Thor and not Jupiter?
http//en.wikipedia.org/wiki/Journey_into_Mystery
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• These names come to us originally from the Greeks
  and Romans, who named the days of the week after
  their gods.
• The Germanic languages substituted Germanic
  equivalents for the names of four of the Roman
  gods

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• Sunday Sun's Day. The Sun gave people light and
  warmth every day. They decided to name the first
  (or last) day of the week after the Sun.
• Monday Moon's Day. The Moon was thought to be
  very important in the lives of people and their
  crops.
• Tuesday Tiw's Day. Tiw, or Tyr, was a Norse god
  known for his sense of justice. He was the Norse
  god of War.
• Wednesday Woden's Day. Woden, or Odin, was a
  Norse god who was one of the most powerful of
  them all.
• Thursday Thor's Day. Thor was a Norse god who
  wielded a giant hammer.
• Friday Frigg's Day. Frigg was a Norse god equal
  in power to Odin and also his wife.
• Saturday Seater's Day or Saturn's Day. Saturn
  was a Roman god.

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How many planets are there in the Solar System
today?
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Number?

• 8?
• 9?
• 11?
• 12?
• Tens?
• Hundreds?

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Today

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus discovered in 1781 by William Herschel
• Neptune discovered in 1846 by Johann Galle and
  Heinrich Louis d'Arrest from calculations of
  Urbain Le Verrier

Terrestrial Planets
Telescope that discovered Uranus
Jovian Planets (Gaseous Giants)
http//www.nasm.si.edu/ceps/etp/discovery/disc_pla
nets.html
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http//www.ibiblio.org/ais/sol-e.gif
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How many planets were there in the Solar System
two years ago?
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Two years ago

• Mercury
• Venus
• Earth
• Mars
• Jupiter
• Saturn
• Uranus
• Neptune
• Pluto discovered in 1930 by Clyde Tombaugh

http//www.phobos.pcm.hr/grafika/clyde_pluton.jpg
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http//www.boskowan.com/www/jirka/vesmir/planets/p
luto/pluto20size.jpg
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http//www.scienzita.it/lezioni/scienze_terra/imma
gini/pluto-orbit.jpg
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Pluto relative to other planets

• Pluto is very small
• Plutos orbit is the most inclined relative to
  the ecliptic (the plane of the planets orbit)
  and the most eccentric (actually is sometimes
  closer to the Sun than Neptune)

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Why did the number of planets change?
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Discovery of 136199 Eris (2003 UB313)

• Discovered in 2003 by Michael Brown
• Has estimated size larger than pluto
• If Pluto is a planet, then Eris should be a planet

http//nmazca.com/3142857/new_planet_2003ub313_orb
it.jpg
http//en.wikipedia.org/wiki/ImageAnimation_showi
ng_movement_of_2003_UB313.gif
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• Astronomy 2006 - IAU XXVIth General Assembly
• Prague
• August 14-25, 2006
• About 2,400 astronomers attended the meeting

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Initial Proposal

• "A planet is a celestial body that
• (a) has sufficient mass for its self-gravity
  to overcome rigid body forces so that it assumes
  a hydrostatic equilibrium (nearly round) shape,
  and (b) is in orbit around a star, and is neither
  a star nor a satellite of a planet."
• What would then qualify as a planet?

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• Pluto and at least three other bodies would be
  considered planets
• 1 Ceres
• Eris slightly bigger than Pluto
• Charon Plutos moon

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2006

• The IAU now defines "planet" as a celestial body
  that
• (a) is in orbit around the Sun,
• (b) has sufficient mass for its self-gravity to
  overcome rigid body forces so that it assumes a
  hydrostatic equilibrium (nearly round) shape, and
  
• (c) has cleared the neighborhood around its
  orbit.

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400 people voted
http//www.washingtonpost.com/wp-dyn/content/artic
le/2006/08/24/AR2006082400109.html
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• A "dwarf planet" is a celestial body that
• (a) is in orbit around the Sun,
• (b) has sufficient mass for its self-gravity to
  overcome rigid body forces so that it assumes a
  hydrostatic equilibrium (nearly round) shape,
• (c) has not cleared the neighborhood around its
  orbit, and
• (d) is not a satellite.
• Ceres, Pluto and Eris are now dwarf planets.

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http//news.bbc.co.uk/2/hi/science/nature/5283956.
stm
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Does it really matter what is a planet and what
isnt?
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• up to 1500 - seven (Moon, Mercury, Venus, Sun,
  Mars, Jupiter, Saturn) - Geocentric
  model
• 1550 - six (with Earth, without Moon and Sun) -
  Heliocentric model
• 1781 - seven (with Uranus)
• 1807 - eleven (with Ceres, Pallas, Juno and
  Vesta)
• 1845 - twelve (with Astraea)
• 1846 - thirteen (with Neptune)
• 1851 - eight (without the asteroids)
• 1930 - nine (with Pluto)
• 2006 - eight (without Pluto)
• From wikipedia

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How do you remember the order of the planets?
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Originally

• My Very Eager Mother Just Served Us Nine Pizzas

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Now

• My Very Eager Mother Just Served Us Nachos

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Originally

• People thought that all objects rotated around
  the Earth (Geocentric model)
• Celestial Sphere all stars fall on a sphere
  that rotates around the Earth

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What is a constellation?
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Constellations

• People refer to constellations as a pattern of
  stars
• Astronomers refer to constellations as specific
  regions of the sky
• In 1928, the IAU (International Astronomical
  Union) decided there were 88 constellations
• Many of the constellation names go back thousands
  of years

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Stars

• A star is a celestial body of hot gases that
  radiates energy derived from thermonuclear
  reactions in the interior

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Constellations

• The constellations are totally imaginary things
  that poets, farmers and astronomers have made up
  over the past 6,000 years (and probably even
  more!).
• The real purpose for the constellations is to
  help us tell which stars are which, nothing more.

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What is this constellation?
http//joemorris.mystarband.net/images/Orion20Con
stellation.jpg
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Orion
http//www.analyticalsci.com/Astronomy/Scobee/Orio
n.jpg
Bigger the star, the brighter it is
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Orion was the son of the god of the sea,
Poseidon and a great hunter. One story is that he
made an enemy of Hera who sent a scorpion to
sting him.
http//www.symbiose.asso.nc/res_pedago/res_pc/phys
ique/images/orion.jpg
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What are the constellations named after

• 14 men and women
• 9 birds
• 2 insects
• 19 land animals
• 10 water creatures
• 2 centaurs
• one head of hair
• a serpent
• a dragon
• a flying horse
• a river
• 29 inanimate objects

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Zodiac

• The zodiac is an imaginary belt in the heavens
  extending approximately 8 degrees on either side
  of the Sun's apparent path (the ecliptic), that
  includes the apparent paths of the Moon and the
  planets Mercury, Venus, Mars, Jupiter, Saturn,
  Uranus, and Neptune.
• A person's sign is determined by the position of
  the Sun on the date they were born

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Earth moves counterclockwise around the Sun
http//cse.ssl.berkeley.edu/lessons/indiv/beth/bet
h_intro.html
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Question

• Why do all the planets seem to follow the same
  path?

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Answer

• The planets, the Earth, and the Sun all tend to
  fall in the same plane called the ecliptic

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http//cse.ssl.berkeley.edu/img/eclip.gif
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Question

• Why is the path of the constellations on the
  zodiac not on the celestial equator?

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Answer

• The rotation axis of the Earth is inclined with
  respect to the ecliptic

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Polaris North Star
Ursa Minor
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Polaris lies near the North Celestial Pole

• During the evening, all stars seem to rotate
  around the north celestial pole

http//www.glyphweb.com/esky/_images/photos/polari
s.gif
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• http//skychart.skytonight.com/observing/skychart/
  

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Any Questions?