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C O U R S E 
Imagining Other Earths
David Spergel, Princeton University
C O U R S E   L E C T U R E 
Dwarf Planets and Beyond, Getting a Feel for Cosmic Distances
Notes taken on June 2, 2014 by Edward Tanguay
solar system
dwarf planets besides Pluto
most massive of the dwarf planets
1% of earth's mass
discovered in 2005
has one moon Dysnomia
the largest object in the asteroid belt, which lies between the orbits of Mars and Jupiter
a ball of rock and ice 950 km in diameter, containing a third of the mass of the asteroid belt
the largest asteroid, and the only dwarf planet in the inner Solar System
it was the first asteroid to be discovered, on 1 January 1801 by Giuseppe Piazzi in Palermo, at first considered to be a planet
the unmanned Dawn spacecraft is scheduled to arrive at Ceres in early 2015
named after the Roman Goddess of Agriculture
located beyond Neptune's orbit
discovered in 2004
named after Haumea, the Hawaiian goddess of childbirth
its extreme elongation makes it unique among known dwarf planets, nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, making it a dwarf planet
perhaps the largest Kuiper belt object (KBO)
has no known satellites, which makes it unique among the largest KBOs and means that its mass can only be estimated
discovered on March 31, 2005
the name derives from Makemake in the mythology of the Rapanui people of Easter Island
many others
nearest star is Alpha Centauri
4.37 light years from the Sun
277,600 AU
actually a binary star system
this pair of stars have an 80 year orbit around a common center, and are about as close to each other as Saturn and the Sun
how long would it take to travel from Earth to Mars at 20,000 km/hr (Voyager 1 is traveling about 61,000 km/hr)
if the planets didn't move it would take about 100 days
since both are orbiting the sun, you would have to travel in a transfer orbit, so it would take about 200 days
Voyager 1
as of September 2013, Voyager 1 was at a distance of 18.7 billion kilometers (125.3 AU) from the Sun, and escaping the solar system at a speed of about 3.6 AU per year
this year Voyager 1 space craft crossed into interstellar space
the earth
distance from sun
150 million kilometers
1 AU, or astronomical unit
some planets are 10 or 20 AU from their sun
Saturn: 9 AU - 10.1 AU from Sun
the Kepler telescope has been exploring planets of other stars and has found planets even a 0.3 AU from their sun
stars twinkle and planets don't
brightest start is Sirius
Greek for "glowing"
actually two stars, Sirius A and Sirius B, distance between them varies between 8.2 and 31.5 AU
Venus always close to the Sun
will always see it soon after sunset or right after sunrise
Jupiter is always very bright
often seen directly overhead
with binoculars, you may be able to see four moons
first discovered by Galileo
Sumerians referred to the "stars" that moved "wanderers", these were planets
because planets are so much closer
cratered structure
fascinated Galileo
craters reflect the history of the moon
old view of solar system
Pluto was seen as a planet but had an odd orbit, actually crossing in closer than Neptune at times
the current system is much more messy, Pluto is just one of 50 known dwarf planets that make up the Kuiper Belt
Pluto is not that special anymore, actually smaller than Eris and about the same size as 2003 EL61
Eris: 67.69 AU
Pluto: 39.54 AU
dwarf planets are discovered through a concept called parallax
displacement or difference in the apparent position of an object viewed along two different lines
90377 Sedna
three times as far from Sun as Neptune
surface is largely a mixture of water, methane and nitrogen ices
surface is one of the reddest in the Solar System
Sirius (Dog Star) - bright in northern hemisphere
Alpha Centuri - bright in southern hemisphere
parallax is used to measure distances to distant stars as well
the parallax that a typical star would have is about:
one arc second
1 parsec
3.26 light years
206,000 astronomical units
most of the solar system is mostly space
Neptune is 30 AU
nearest star is 206,000 AU
our galaxy the Milky Way
center of our galaxy forms a bulge
distance to the center of our galaxy is about 8000 parsecs or 24,000 light years
our galaxy is one of many galaxies
the width of our galaxy is about 30,000 parsecs, or 90,000 light years
most of the young stars are forming in the spiral arms