Astronomy For Dummies
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Here are some favorite facts about astronomy and, in particular, Earth and its solar system. With the following information under your belt, you may be ready to handle the astronomy questions on television quiz shows and inquiries from friends and family.

You Have Tiny Meteorites in Your Hair

Micrometeorites, tiny particles from space visible only through microscopes, are constantly raining down on Earth. Some fall on you whenever you go outdoors. But without the most advanced laboratory equipment and analysis techniques, you can't detect them. They get lost in the great mass of pollen, smog particles, household dust, and dandruff that resides on the top of your head.

A Comet's Tail Often Leads the Way

A comet tail isn't like a horse tail, which always trails behind as the horse gallops ahead. A comet tail always points away from the Sun. When a comet approaches the Sun, its tail, or tails, stream behind it; when the comet heads back out into the solar system, the tail leads the way.

Earth Is Made of Rare and Unusual Matter

The great majority of all the matter in the universe is so-called dark matter, invisible stuff that astronomers haven't yet identified. And most ordinary or visible matter is in the form of plasma (hot, electrified gas that makes up normal stars such as the Sun) or degenerate matter (in which atoms or even the nuclei within the atoms are crushed together to unimaginable density, as found in white dwarfs and neutron stars). You don't find dark matter, degenerate matter, or much plasma on Earth. Compared to the great bulk of the universe, Earth and earthlings are the aliens.

High Tide Comes on Both Sides of Earth at the Same Time

Ocean tides on the side of Earth that faces the Moon aren't appreciably higher than tides on the opposite side of Earth at the same time. This may defy common sense, but not physics and mathematical analysis. (The same goes for the smaller ocean tides raised by the Sun.)

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On Venus, the Rain Never Falls on the Plain

In fact, the constant rain on Venus never falls on anything. It evaporates before it hits the ground, and the rain is pure acid. (The common name for evaporating rain is virga.)

Rocks from Mars Dot Earth

People have found about 100 meteorites on Earth that come from the crust of Mars, blasted from that planet by the impacts of much larger objects — perhaps from the asteroid belt. Statistically, many more undiscovered Mars rocks must have fallen into the ocean or landed in out-of-the-way places where they haven't been spotted.

Pluto Was Discovered from the Predictions of a False Theory

Percival Lowell predicted the existence and approximate location of the object that we now call Pluto. When Clyde Tombaugh surveyed the designated region, he discovered Pluto. But now scientists know that Lowell's theory, which inferred the existence of Pluto from its gravitational effects on the motion of Uranus, was wrong. In fact, Pluto's mass is much too small to produce the "observed" effects. Furthermore, the "gravitational effects" were just errors in measuring the motion of Uranus. (Not enough information was available about Neptune's motion to study it for clues.) The discovery of Pluto took hard work, but as it happened, it was just plain luck. And although Lowell predicted the existence of a planet, as Pluto was first termed, the International Astronomical Union has since downgraded it to dwarf planet.

Sunspots Aren't Dark

Almost everyone "knows" that sunspots are "dark" spots on the Sun. But in reality, sunspots are simply places where the hot solar gas is slightly cooler than its surroundings. The spots look dark compared to their hotter surroundings, but if all you can see is the sunspot, it looks bright.

A Star in Plain View May Have Exploded, but No One Knows

Eta Carinae is one of the most massive, fiercely shining stars in our galaxy, and astronomers expect it to produce a powerful supernova explosion at any time, if it hasn't already. But because light takes about 8,000 years to travel from Eta Carinae to Earth, an explosion that occurred less than that many years ago isn't visible to us yet.

You May Have Seen the Big Bang on an Old Television

The Big Bang Theory premiered in 2007, but the real Big Bang may have made its TV debut even before that. Some of the snow — a pattern of interference that looks like little white spots or streaks on old black-and-white television sets — was actually radio waves the TV antenna received from the cosmic microwave background, a glow from the early universe in the aftermath of the Big Bang. When this radiation was actually discovered at the Bell Telephone Laboratories, scientists studied many possible causes of the unexpected "noise" in the radio receiver. They even investigated pigeon droppings, or "white dielectric material" in science speak, as a possible cause but later dropped that suggestion.

About This Article

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Stephen P. Maran, PhD, is the retired assistant director of space sciences for information and outreach at the NASA-Goddard Space Flight Center. An investigator of stars, nebulae, and comets, he worked on the Hubble Space Telescope, Space Shuttle missions, Skylab, and other NASA projects.

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