I Solar System in Detail Need to Know: • center of our solar system • brightest object in Earth's sky • star of average size, brightness, and intensity • provides light and energy need
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: What Is Our Our solar system consists of many objects m predictable orbits around the slln These orbits are predlct<1hle
! S I S ., because the gt'avity of the sun keeps the planets, dwarf planets, asteroids, comets, and other ohJects tr<1vl'ilT1g : 0 ar ystem • 111 regular paths Most orbits 111 our solar system are 111 the shape of an ellipse, rather than a perfect clfcle
The International
Astronomical union (IAU)
develops official definitions for astronomical objects
According to the IAU, a planet
is a celestial body that is in orbit
around the sun, is massive enough for its s elf - gravity to create a nearly round shape, and has cleared th e neighborhood around its orbit
as new objects are found and more information is gathered about the objects scientists are already aware of
WHAT IELSE O RBITS THE SUN?
Objects orbiing the sun that are smaller than
dwarf p l anets are called solar system bodies
These inclu e aste1'oids and c omets
Asteroids are rocky fragments left over from the
dwarf planet - a large, nearly round object orbiting
a star that has not cleared the neighborhood of its
orbit
"" , C,",lltlri" - w h e n referring to orbits, means:
, in the shape of an oval
extra tene stri a -occurring outside of Earth and
of stars, gas, and dust
gravity -physical force of nature that causes two
bodies to attract each other
the distance that light travels in one
- the me sure of the amount of matter in an
mean distance (of a planet from the sun) - the
average of the distances during one revolution of
the
orbit -path of one object around an ther, like the
moon around Earth or Earth around the sun ( see
speed - the average speed at which one
around another
pla net -very large, early round b dy in orbit
arou d a star
-referring to a time before recorded
b dy
solar system - a group of objects-including
planets, asteroids, and comets-held by the gravity
of a star
use o devic s like
Solar System Basics
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• By this definition, our solar system has eight
• planets: Men:ury, Venus, Earth, Mars,
• Jupiter, Saturn, Uranus, and Neptune Some
• astronomers call these the major planets.
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• Planets are usually classified by composition or
• size.
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TerTeStrial p la nets have a solid sUrface made
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of rock and metal, and have a slow rotation, high
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• density, and few satellites Mercury, Venus,
• Ea rth, and M ars are terrestrial planets They are
• also classified as small p l anets, with diameters
• less than 13,000 kilometers (8,077 miles)
• as hydrogen and helium), and have a rapid
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rotation, low density, and many satellites Ju piter ,
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Satu rn, U ranus , and Neptun e are }Qyian
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planets They are also classified as giant plane t s,
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• with diameters greater than 48,000 kilometers
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• WHAT IS A DWARF PLANET?
• For many years, pluto was classified as a planet,
• but the IAU officially reclassified it as a dwarf
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planet in 2006 A dwarf planet shares all the
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• characteristics of a planet exc:~that it has
• not cleared the neighborhood around its orbit
• Currently, there are five celestial bodies classified
• as dwarf planets: Ceres, Pluto, Haumea,
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formation of our solar system billions of years
ago Most asteroids are found orbiting the sun between Mars and Jupiter in a region called the
Asteroid Bel t
of our solar system Most comets come from
t he icy region beyond Neptune's orbit called the
Ku iper Bel t About a dozen new comets are
discovered each year Some take less than 200
years to orbit the sun, while others take as long
as 30 million years!
WHAT DOES THE SUN ORBIT?
The sun-in fact, our entire solar system -orbis the center of the Milky Way galaxy This galactc
center is about 2 6,000 light years from th e sun ,
so the trip around it takes a very long time Traveling in
an elliptical orbit at about 140
miles per
second,
the sun (and thus our solar system)
takes about
22smillion years to complete one orbit This orbital period
is known as a cosmic year
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Solar System in Detail
Need to Know:
• center of our solar system
• brightest object in Earth's sky
• star of average size, brightness, and intensity
• provides light and energy needed for life on Earth
• affects seasons, ocean currents, weather, and climate
on Earth
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I Fun Facts: contains more than 99.8% of the total mass
Need to Know:
I Fun Facts: only major planet with a name not derive d
the Anglo-Saxon word erda, meaning" ground, soil, or earth "); core can reach temperatures higher than the
surface of the sun; light from the sun takes about eight minutes to reach Earth; rotation changes slowly over
time (scientists think that, 900 million years ago, ther e
Need to Know:
• second-brightest object in Earth's sky
• Earth's only satellite
• gravitational forces between Earth and the moon cre ate high and low ocean tides
• revolution of the moon around Earth, and its location with respect to the sun, create the phases of the moon seen in the Earth's sky
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r Fun Facts: only extraterrestrial body to have been
moon; Neil Armstrong was the first person to walk on
lions ofy ars because the moon has no air); we a lwa y s
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• closest planet to the sun
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• smallest major planet
• has greatest daily temperature variations of all planets •
• has a highly eccentric orbit, causing its distance from •
the sun to vary greatly during each revolution •
Fun Facts: named after the Roman god of travel; often
visible with binoculars, but is always very close to the sun, and so is only visible at dawn and dusk; humans have seen less than half of Mercury's surface
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• Need to Know:
• second planet from the sun
• has most circular orbit of any planet
• third-brightest object in Earth's sky
• nearly the same size as Earth (95% of Earth's diameter and 80% of Earth's mass)
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• I Fun Facts: named for Roman goddess of love and
telescopes from seeing the surface; surface tem
perature is hot enough to melt lead; one Venus day is
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Trang 3Solar System in Detail (continued)
Need to know: • • known since prehistoric times
• Pioneer 10 In 1973
• has some of the most varied terrain of any terrestrial planet •
, reddish color (most likely from iron oxide in soil) • • fifth planet from the sun
• • largest planet (more than twice as massive as all other
times called the Red Planet; several spacecraft have I • • visible to the unaided eye
landed on Mars and explored its surface; has our I • • Great Red Spot (a hurricane-like storm) has been ob
solar system's largest volcano-Olympus Mons served since the 17th century and measures approxi
mately three Earths across
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a faint and thin ring system; has solar system's largest I
• ~?~'l moon-Ganymede; Galileo Galilei discovered four I
~ ea i B ~ ~~e ~ o t d · a • ~'e;~fprnil • of Jupiter's moons in 1610; Jupiter is large enough to I
l!eW!te'e\'lto:b~Pfea:s'pfrnEIS ""idll •
II contain approximately 1,300 Earths
• 167 to 418 million miles
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• first asteroid discovered by Giuseppe Piazzi in Iti01
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• Mission spacecraft launched in 2007 and is scheduled Pioneer lOfirst traversed the belt in 1972; Dawn •
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to reach Vesta in the Asteroid Belt in 2011
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Need to know:
• located between the orbits of Mars and Jupiter
• composed of rocky material remaining from the forma
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• more than 20 large (diameter greater than 125 miles) •
asteroids have been identified, but there are millions of •
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~un ~act8: total mass of all asteroids equals less than
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that of Earth's moon; Vesta, the largest known asteroid,
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is visible to the unaided eye; scientists believe asteroids
have hit Earth in the past, causing major changes in the •
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planet's geology and life
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• Need to know:
• • sixth planet from the sun
• • least dense of all planets
• • has the most prominent and easily visible rings (com
• posed of billions of small chunks of ice and rock)
• • visible to the unaided eye (but need a telescope to see
• the rings)
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• ~un ~act8: named for Roman god of agriculture; the
• diameter of Saturn's rings is about 155,000 miles, but I
• they are less than a mile thick; pressure is so strong that
a metal spaceship would be crushed like a paper cup in Saturn's atmosphere
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Need to know:
• classified as an asteroid until 2006
• only known dwarf planet in the Asteroid Belt
• not visible to the unaided eye
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I ~un ~act8: named for Roman goddess of grain and I •
I agriculture; contains about 30% of the Asteroid Belt's I •
total mass; some scientists think Ceres might contain I •
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Need to know:
• seventh planet from the sun
• not visible to the unaided eye
• has 11 known, but faint, rings
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• ~un ~act8: nam; d fo; th""., (j r ;; k sky ; o ;; nd f;;ther of
• I Cronus (Greek name for Saturn); faintly bluish color is
• caused by methane gas in atmosphere; extreme tilt
• of axis (nearly 98°) causes winter to last for 42 years in total darkness l
• ' ml,11s
",,;res
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• 2.793 billion miles
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• • 16 hours, 7 mInutes (Earth time)
• • 163.7 Earth years
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• • mostly hydrogen
• • Johann Gottfried Galle, 1846
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• Voyager 2 in 1989 (only visit)
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· Need to Know:
• • eighth planet from the sun
• not visible to the unaided eye
• has four very faint and thin rings
in atmosphere makes the planet appear blue, has a
"fluctuating" giant storm, known as the Great Dark Spot, with far less intensity than its counterpart on Jupiter; has the strongest winds in our solar system, _ !:a :ured at over 1,200 mph!
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• contains icy objects and debris, including four known
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dwarf planets, and countless comets
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~un ~act8: origin of most comets in solar system; named
for astronomer Gerald Kuiper who theorized its existence
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in the 1950s; scientists estimate at least 35,000 KBOs
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have diameters greater than 100 kilometers (62 miles)
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Need to Know:
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• smaller than Earth's moon
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• classified as a planet until 2006
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• not visible to the unaided eye
• • orbit is highly eccentric, causing Pluto to sometimes be
• closer to the sun than Neptune is
• • brightest known object in the Kuiper Belt
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• ~un ~act8: named for Roman god of the underworld; is
• 39 times farther from the sun than Earth is; light from the
• sun takes about five and a half hours to reach Pluto I
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• Need to know:
- classified as a dwarf planet in 2008 • - classified as a dwarf planet in 2008 • - classified as a dwarf planet in 2006
- has an unusual football shape • - is second-brightest object in the Kuiper Belt (after • - is largest known object in the Kuiper Belt and largest
- not visible to the unaided eye • Pluto) • known dwarf planet
• - not visible to the unaided eye • - not visible to the unaided eye
and the personification of stone; has fastest rotation • Fun Facts: named for the god of Rapa Nui (Easter •
speed of any dwarf planet or planet • I Island), South Pacific creator of humanity and god of • Fun Facts: named after the Greek goddess of discord
_ _ _ _ _ ~ • I fertility (Rapa Nui was discovered just before Easter); and strife; its discovery (especially the fact that it is
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• I appears to have a faintly red color larger than Pluto) caused the IAU to demote Pluto to
• dwarf planet status
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More Solar System "acts
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Most scientists use astronomical units (AU) to measure and describe distances The sun is the most important factor for life on Earth The sun not only provides
in our soLar system An AU is defined by the mean distance of Earth from the • nearly all the Light and energy needed for survival, it also determines night and
W sun (about 93 million miles) AUs make comparing distances from the sun much • day and the change of seasons on Earth
easier For exampLe, Pluto has a mean distance from the sun of 39-44 AU This • Day & Night Seasons
~ means it is about 40 times farther from the sun than Earth is •
Spinning on its axis at about 1,000 miles per hour, Earth's seasons are
• Earth takes about 24 hours to complete one rotation caused by the way
• This daily rotation from west to east causes the Earth tilts on its axis
• distinction between day and night, and has been as it orbits the sun
• used as the basis for measuring time for thousands (Earth tilts at 23.45'
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of years [NOTE: The sun rises in the east and sets from its elliptical plane.)
• in the west precisely because the Earth rotates from Since the axis is tilted,
• west to east Otherwise, if the Earth rotated from
different parts of Earth
east to west, the sun's rising and setting would be are oriented toward the
• west and east, respectively- the exact opposite of sun at different times of
• what actually happens.J the year
• each pLanet to those of Earth For exampLe, the ratio for the diameter of Mars is 0.53
This means that the diameter of Mars is about haLf (0.5) the size of Earth's diameter
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0055 0.12 1 011 3178 I 952 14.5 171 •
ow t 1 0.3 8 I 0 95 I 1 I 0 53 I 1121 I 9 4 5 4 01 I 3 88
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o-a, I 098 I 095 I 1 1 071 024 I 0.13 023 1 0.29
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Your weight is a measure of the pull of gravity between you and the pLanet •
you are standing on PLanets have different masses, so they also have different
gravitational pulls This means that if you could stand on the surface of every
planet, your weight would be different on each one! The chart below shows how
much a 100-pound person would weigh on the surface of each planet
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M 038 091 1 0.38 254 093 08 1.2 •
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WeIght
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COMPARING PLANETS
The chart beLow gives ratios that compare the mass, diameter, and density of
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