Sun
diameter: 1,390,000 km.
mass: 1.989e30 kg
temperature: 5800 K (surface)
15,600,000 K (core)
The Sun is by far the largest object
in the solar system.
It contains more than 99.8% of the total mass of the Solar System
(Jupiter contains most of the rest).
It is often said that the Sun is an "ordinary" star. That's true in the
sense that there are many others similar to it. But there are many
more smaller stars than larger ones; the Sun is in the top 10% by
mass. The median size of stars in our galaxy is probably less than half
the mass of the Sun.
The Sun is personified in many mythologies:
the Greeks called it
Helios and the Romans
called it Sol.
Mercury
Mercury is the closest planet to the Sun and the eighth largest.
Mercury is slightly smaller in diameter than the moons Ganymede
and Titan but more than twice as massive.
orbit: 57,910,000 km (0.38 AU) from Sun
diameter: 4,880 km
mass: 3.30e23 kg
In Roman mythology
Mercury
is the god of commerce, travel and thievery, the
Roman counterpart of the Greek god
Hermes,
the messenger of the Gods. The planet
probably received this name because it moves so quickly across the sky.
Mercury has been known since at least the time of the Sumerians (3rd millennium
BC). It was sometimes given separate names for its apparitions as a
morning star and as an evening star. Greek astronomers knew, however,
that the two names referred to the same body.
Heraclitus even believed that Mercury and Venus orbit the Sun, not the Earth.
Venus
Venus is the second planet from the Sun and the sixth largest.
Venus' orbit is the most nearly circular of that of any planet, with
an eccentricity of less than 1%.
orbit: 108,200,000 km (0.72 AU) from Sun
diameter: 12,103.6 km
mass: 4.869e24 kg
Venus (Greek:Aphrodite
Babylonian: Ishtar) is the goddess of love and beauty.
The planet is so
named probably because it is the brightest
of the planets known to the ancients.
(With a few exceptions, the surface features on Venus are named for female
figures.)
Venus has been known since prehistoric times.
It is the brightest object in the sky except for the Sun and the Moon.
Like Mercury, it was popularly thought
to be two separate bodies: Eosphorus as the
morning star and Hesperus as the
evening star, but the Greek
astronomers knew better. (Venus's apparition as the morning star is also sometimes
called Lucifer.)
Earth
Earth is the third planet from the Sun and the fifth largest:
orbit: 149,600,000 km (1.00 AU) from Sun
diameter: 12,756.3 km
mass: 5.972e24 kg
Earth is the only planet whose English name does not derive
from Greek/Roman mythology.
The name derives from Old English and Germanic. There are, of course, hundreds
of other names for the planet in other languages.
In
Roman Mythology, the goddess of the Earth was Tellus -
the fertile soil (Greek:
Gaia,
terra mater - Mother Earth).
It was not until the time of Copernicus (the
sixteenth century) that it
was understood that the Earth is just another planet.
Earth, of course, can be studied without the aid of spacecraft. Nevertheless
it was not
until the twentieth century that we had maps
of the entire planet.
Pictures of the planet taken from space are of considerable importance; for
example, they
are an enormous help in weather prediction and especially in tracking and
predicting hurricanes.
And they are extraordinarily beautiful.
The Earth is divided into several layers which have distinct chemical
and seismic properties (depths in km):
0- 40 Crust
40- 400 Upper mantle
400- 650 Transition region
650-2700 Lower mantle
2700-2890 D'' layer
2890-5150 Outer core
5150-6378 Inner core
Mars
Mars is the fourth planet from the Sun and the seventh largest:
orbit: 227,940,000 km (1.52 AU) from Sun
diameter: 6,794 km
mass: 6.4219e23 kg
Mars (Greek:
Ares) is
the god of War. The planet probably got this name due to its red color;
Mars is sometimes referred to as the Red Planet. (An interesting side
note: the Roman god Mars was a god of agriculture before becoming
associated with the Greek Ares; those in favor of colonizing and
terraforming Mars may prefer this symbolism.) The name of the
month March derives from Mars.
Mars has been known since prehistoric times. Of course, it has been extensively
studied with ground-based
observatories.
But even very large telescopes find Mars a difficult target, it's just too small.
It is still a favorite of
science fiction
writers as the most favorable place in the Solar System (other than
Earth!) for human habitation. But the famous "canals" "seen" by
Lowell and others were, unfortunately, just as imaginary as
Barsoomian princesse.
Jupiter
Jupiter is the fifth planet from the Sun and by far the largest.
Jupiter is more than twice as
massive as all
the other planets combined (the mass of Jupiter is 318 times that of Earth).
orbit: 778,330,000 km (5.20 AU) from Sun
diameter: 142,984 km (equatorial)
mass: 1.900e27 kg
Jupiter (a.k.a. Jove; Greek
Zeus)
was the King of the Gods, the ruler
of Olympus and the patron of the Roman state.
Zeus was the son of Cronus (Saturn).
Jupiter is the fourth brightest
object in the sky (after the Sun, the
Moon and Venus).
It has been known since prehistoric times as a bright "wandering star".
But in 1610 when Galileo
first pointed a telescope at the sky he
discovered
Jupiter's four large moons
Io,
Europa,
Ganymede and
Callisto
(now known as the
Galilean moons) and recorded their motions
back and forth around Jupiter. This was
the first discovery
of a center of motion not apparently centered on the Earth.
It was a major point in
favor of Copernicus's
heliocentric theory of the
motions of the planets (along with other new evidence from his telescope:
the phases of Venus
and the mountains on the Moon).
Galileo's outspoken support of the Copernican theory got him in trouble with
the Inquisition.
Today anyone can repeat Galileo's observations (without fear of retribution :-)
using binoculars or an inexpensive telescope.
Saturn
Saturn is the sixth planet from the Sun and the second
largest:
orbit: 1,429,400,000 km (9.54 AU) from Sun
diameter: 120,536 km (equatorial)
mass: 5.68e26 kg
In Roman mythology, Saturn is the god of agriculture. The associated Greek god,
Cronus,
was the son of Uranus and Gaia and the father of Zeus (Jupiter).
Saturn is the root of the English word "Saturday" Saturn has been known since prehistoric times.
Galileo was the first to observe it with a
telescope in 1610;
he noted its odd appearance but was confused by it.
Early observations of Saturn were
complicated by the fact that the Earth passes through the plane of Saturn's
rings every few years
as Saturn moves in its orbit. A
low resolution image of
Saturn therefore changes drastically.
It was not until 1659
that Christiaan Huygens correctly inferred
the geometry of the rings.
Saturn's rings remained unique in the known solar system
until 1977 when very faint rings were discovered around
Uranus (and shortly
thereafter around Jupiter and
Neptune).
Uranus
Uranus is the seventh planet from the Sun
and the third largest (by diameter).
Uranus is larger in diameter but smaller in mass than
Neptune.
orbit: 2,870,990,000 km (19.218 AU) from Sun
diameter: 51,118 km (equatorial)
mass: 8.683e25 kg
Careful pronunciation may be necessary
to avoid embarrassment; say "YOOR a nus" not "your anus" or "urine us".
Uranus
is the ancient Greek deity of the Heavens, the earliest supreme god.
Uranus was the
son and mate of Gaia
the father of
Cronus (Saturn)
and of the Cyclopes and Titans (predecessors of the Olympian gods).
Uranus, the first planet discovered in modern times, was discovered by
William Herschel while systematically searching
the sky with his telescope on March 13, 1781.
It had actually been seen many times before but ignored as simply another star
(the earliest recorded sighting was in 1690 when John Flamsteed
cataloged it as 34 Tauri).
Herschel named it "the
Georgium Sidus"
(the Georgian Planet) in honor of his patron,
the infamous (to Americans) King George III
of England; others called it
"Herschel". The name "Uranus" was
first proposed by Bode in conformity with the
other planetary names from classical mythology but didn't come into
common use until 1850.
Neptune
Neptune is the eighth planet from the Sun
and the fourth largest (by diameter).
Neptune is smaller in diameter but larger in mass than
Uranus.
orbit: 4,504,000,000 km (30.06 AU) from Sun
diameter: 49,532 km (equatorial)
mass: 1.0247e26 kg
In Roman mythology
Neptune
(Greek:
Poseidon)
was the god of the Sea.
After the discovery of Uranus, it was noticed that its orbit was not as it
should be in accordance with Newton's laws.
It was therefore predicted that another more distant planet must be
perturbing Uranus' orbit. Neptune was
first observed by Galle
and d'Arrest on 1846 Sept 23
very near to the locations independently predicted by
Adams and
Le Verrier
from calculations based on the observed
positions of Jupiter,
Saturn and Uranus.
An international dispute arose between the English and French
(though not, apparently between Adams and Le Verrier personally) over priority
and the right to name the new planet;
they are now jointly credited with Neptune's discovery.
Subsequent observations have shown
that the orbits calculated by Adams and Le Verrier diverge from Neptune's
actual orbit fairly quickly. Had the search for the planet taken place a few
years earlier or later it would not have been found anywhere near the predicted
location.
More than two centuries earlier, in 1613, Galileo
observed Neptune when it happened to be
very near Jupiter,
but he thought it was just a star. On two successive nights he actually noticed that it moved
slightly with respect to another nearby star. But on the subsequent nights it was
out of his field of view. Had he seen it on the previous few nights Neptune's motion
would have been obvious to him. But, alas, cloudy
skies prevented observations on those few critical days.
(source:
http://nineplanets.org)
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