2Which planet is bigger, Mercury or Jupiter ? Warm Up QuestionsWhich planet is bigger, Mercury or Jupiter ?Are the gas giant planets closer to the Sun than the rocky planets (yes/no)?How many planets are in the Solar System?Is the Sun bigger, smaller, or the same size as the Moon?What is the difference between the Solar System and the Milky Way Galaxy (just one sentence) ?These are here because in theory, you’ve given the questions to the students before class to answer. Alternatively, you can hand out the questions at the start of class and go over the answers after the students are done. The idea for giving warm up questions is identify what the students know, what they don’t know, and where their misconceptions are.
3Three types of objects orbit our Sun: Why are there only 8 planets now?Three types of objects orbit our Sun:PlanetsDwarf PlanetsPlutoidsSmall solar system bodies
4What is a planet?In August of 2007 the International Astronomical Union redefined what a planet is (no official scientific definition of a "planet" existed before). A planet:Is a body that orbits the sun (this definition only applies to our Solar System)Is large enough for its own gravity to make it roundAnd has "cleared its neighborhood" of smaller objectsSo a new the category of dwarf planet was created, which currently includes Pluto, Eris*, and Ceres**.*Eris is the largest known dwarf planet in the Solar System and the ninth largest body known to orbit the Sun. Its distance from the Sun is 97 AU.**Ceres is the smallest identified dwarf planet in the Solar System and,because it’s the largest asteroid, the only dwarf planet in the asteroid belt.
5Celestial body orbiting the Sun What is a Dwarf Planet?Celestial body orbiting the SunMassive enough to be rounded by its own gravityBUT has NOT cleared its neighboring region of planetesimalsIs not a satelliteA plutoid is a dwarf planet beyond the orbit of Neptune
6Only 5 Dwarf Planets recognized so far but there may be as many as 200 Pluto, approximatetrue colorMakemake,(Artist’s conception)Ceres, seen through(Hubble telescope)Eris, seen through(Hubble telescope)Ask student to identify which dwarf planets are plutoidsHaumea, with its 2 moons,Hi‘iaka and Namaka(Artist’s conception)
7Pacific Island Names for Planetary Objects Haumea is the Hawaiian goddess of childbirth and fertility.The the moons "Hiʻiaka" and "Namaka” are named after after two of Haumea's daughters.NOTE: Although Haumea is not spherical, it is considered a dwarf planet because it is in hydrostatic equilibrium: its ellipsoidal shape is the equilibrium state resulting from the object's rapid rotation (in much the same way as a water balloon stretches out when tossed) and not due to insufficient self-gravity.
8Pacific Island Names for Planetary Objects Makemake is the creator of humanity in the mythos of the Rapanui, the native people of Easter Island. The name choice preserves the planetary object's connection with Easter.
93. What are Small Solar System Bodies? Neither a planet nor a dwarf planetAll other objects orbiting the SunAll minor planets except dwarf planetsAsteroids (except Ceres, the largest)CometsNot massive enough to be rounded by its own gravity
10Terrestrial vs. Gaseous Planets Jupiter, Saturn, Uranus, NeptuneGaseous, has more He and HLess dense (Saturn would float)LargerSpaced farther apartFarther from the SunMercury, Venus, Earth, MarsRockyMore denseSmallerMore closely spacedCloser to the SunNOTES: He = helium; H = hydrogen
11Terrestrial Planets Mars Venus Mercury FromThis page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.MarsVenusMercuryFrom Nick Strobel’s Astronomy Notes at
12Jovian Planets, or Gas Giants UranusNeptuneSaturnJupiterFromThis page was copied from Nick Strobel's Astronomy Notes. Go to his site at for the updated and corrected version.From Nick Strobel’s Astronomy Notes at
13Do you see patterns or anomalies in these data? ANSWERS: Students may notice planets in the middle of the solar system have less extreme temperatures and shorter days compared to those closest and farthest from the sun. Venus’ data is very extreme compared to its neighbors. Pluto’s long day also stands out compared to its neighbors.From
15The Milky Way Galaxy 100,000 light years across 1,000 light years thick200 billion starsThe Milky Way Galaxy may have between 200 & 400 billion starsAs a guide to the relative physical scale of the Milky Way, if it were reduced to 130 km (80 mi) in diameter, the Solar System would be a mere 2 mm (0.08 inches) in width.The Andromeda Galaxy, also a spiral galaxy, is the nearest spiral galaxy to our own, the Milky Way, at approximately 2.5 million light-years away.You are here