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Solar System Facts

"Men might as well project a voyage to the Moon as attempt to employ steam navigation against the stormy North Atlantic Ocean." — Dr. Dionysius Lardner, 1838

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The Earth "wobbles" around its axis, a movement known as precession of the equinoxes. This precession causes the equinoxes to move over a cycle of 26,000 years relative to the fixed stars. Since the signs of the zodiac were assigned in the 7th century B.C., the equinoxes have moved more than one sign of the zodiac. So, for example, if someone nowadays is an Aries (March 21–April 19), the sun would actually have been in Pisces when they were born. The summer solstice is now in Taurus, not Cancer (hence the term "Tropic of Cancer" is out-of-date).

In 435 B.C., the Greek philosopher Anaxagoras suggested that the sun was not just a small glowing circle of light. He maintained that it was a glowing rock larger than the Peloponnesus. For maintaining such beliefs (and, to be fair, for political reasons too), he was exiled from Athens. (source)

The Greek scientist Aristarchus believed that the motions of the heavenly bodies could easily be understood if it were assumed that all of the planets, including Earth, revolved around the sun and that the stars must be infinitely far away because they seemed motionless. Copernicus knew of Aristarchus' views and mentioned them in a passage in De Revolutionibus Orbium Coelestium that he later eliminated, as though not wishing to compromise his own originality.

[picture of bust of Aristarchus of Samos]
Aristarchus of Samos.

The first Greek astronomer to suggest the sun was the centre of the solar system was Aristarchus of Samos, around 290 B.C. No one took him seriously, and most of his writings were lost. We know of him today primarily because Archimedes (whose writings do exist) referred to Aristarchus as holding this apparently nonsensical notion. (source)

The Sun is 330,330 times larger than the Earth. (source)

To the nearest ten-thousandth of a mile, light travels at 186,282.3959 miles per second. At that rate, it takes slightly more than eight minutes to get to Earth from the sun. However, it takes light hundreds of years to travel from the sun's centre to its surface. The light must take a very indirect path to the surface due to the large number of collisions with particles within the sun.

View more facts about: Physics and Physicists

Solar flares can reach more than 100,000 miles away from the sun.

Gervasius, a monk at Canterbury some 800 years ago, reported seeing a great burst of fire on the face of the moon. He wondered if this was an omen of some great event on Earth, but as time passed and nothing occurred, scholars and others assumed that he must have been mistaken. Recently, however, astronomer Jack B. Hartung of New York University claims to have vindicated the mediaeval monk by saying that what he was was the impact of a huge meteor causing an explosion and fire on the surface. The crash created the huge crater known was the Giordano Bruno.

Excluding Earth's moon, the moons of all other planets in the solar system are named after characters from Greek mythology, except for those of Uranus, which are named after characters from Shakespeare or from Alexander Pope's "Rape of the Lock", and for those of Saturn discovered after 2000, which are named after creatures from other mythologies.

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The planet Uranus lies on its "side", and there is no adequate explanation as to why. The extreme axial tip of Uranus is 98° as it revolves around the sun. The axis of Earth is tipped at 23.5°, Mars at 24°, and Jupiter at only 3°.

The moon is just large enough to cover the sun completely, at times, as seen from Earth. It is a sheer astronomical accident that makes a total eclipse possible; there is no astronomical reason why the sun and moon "fit" so well. The moon is also small enough so that during a total eclipse the sun's corona, especially the brighter parts near the body of the sun, is completely visible. However, the moon is receding from Earth by about 3.8 centimetres per year, so in 500 million years or so, the moon will always appear smaller than the sun as seen from Earth and no total solar eclipses will not be possible. (source)

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According to the laws of gravity, the moon technically does not orbit the Earth. The two bodies actually both orbit around their common centre of gravity, which is located 1,000 miles beneath the surface of the Earth and is on a straight line between the centres of the Earth and moon. The centre of the Earth makes a small circle around that centre of gravity every 27⅓ days.

View more facts about: Physics and Physicists

The first woman in space was a Soviet, Valentina Tereshkova, in 1963. No female Americans went into space until twenty years later, when Sally Ride did in 1983. (source)

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The last person on the moon was Eugene Cernan. He and fellow explorer Harrison Schmidt left the moon at 5:40 A.M. GMT, December 13th, 1972. No humans have visited the moon since then.

View more facts about: Lasts | Technology and Inventions

Venus, not Earth, is the best-mapped planet in the solar system, with 98% of its surface mapped. On the other hand, large portions of the Earth's ocean floor have not been mapped.

View more facts about: Planet Earth

A perpetual motion machine would violate the laws of thermodynamics. No-one has ever built one, and no-one ever will. (source)

View more facts about: Physics and Physicists

Unlike Earth, Saturn is made mostly of hydrogen and helium, so its density is only 0.13 that of Earth. While it has heavier materials in the core, it is the only planet in the Solar System that is less dense than water. (source)

Saturn's moon Iapetus is a very curious moon—it seems to have a split personality! One hemisphere is covered with material darker than black velvet, while the other side is covered with material brighter than snow. (source)

On January 11, 1610, Galileo Galilei discovered Jupiter's moon Ganymede. Ganymede is the largest satellite in the solar system with a diameter of 5,268 km (3270 miles). It is larger than Mercury and Pluto and 3/4 the size of Mars. (source)

Saturn's moon Mimas has an enormous crater named Herschel that is 130 kilometers (80 miles) wide, one-third the diameter of Mimas. The impact that caused the crater probably came close to shattering Mimas. (source)

Titan is the largest of Saturn's moons. It is the second largest moon in the solar system. In fact, it is larger than both Mercury and Pluto. Scientists are particularly interested in Titan because it's one of the few known moons with its own dense atmosphere. Titan's atmosphere is also thought to be very similar to what Earth's atmosphere was a long time ago. By learning about Titan, we'll learn about our own planet. (source)

The space between Mars and Jupiter is filled with a population of irregularly shaped chunks of rock and metal called asteroids. Scientists believe the asteroids are pieces of a planet that never formed. (source)

Pluto was discovered on February 18, 1930 by Clyde Tombaugh at the Lowell Observatory in Flagstaff, Arizona. (source)

The three objects in the solar system known to have nitrogen-dominated atmospheres are Earth, Saturn's moon Titan, and Neptune's moon Triton. (source)

During the Apollo missions, 842 pounds (382 kilogrammes) of rocks were brought back from the moon. (source)

Pan, one of Saturn's smallest moons, orbits within Saturn's A-Ring and helps clear out an area between the rings called the Encke Gap. Scientists believe that if Pan didn't exist, neither would the Encke Gap. (source)

The small and rocky planet Mercury is the closest planet to the Sun. Temperatures on Mercury's surface can reach a scorching 467 degrees Celsius, but because the planet has hardly any atmosphere to keep it warm, nighttime temperatures can drop to a frigid -183 degrees Celsius. (source)

Saturn's moon Hyperion is shaped somewhat like a hamburger patty, and rotates chaotically because of the gravitational influence of nearby Titan, another of Saturn's many moons. (source)

Saturn's beautiful rings are not solid. They are made up of particles of ice, dust and rock—some as tiny as grains of sand, some much larger than skyscrapers. (source)

View more facts about: The Microscopic World

It's a small world. More than 1,000 Earths would fit into Jupiter's vast sphere. (source)

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