Astronomy For Dummies
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In daily life — reading the newspaper, watching the evening news, surfing the web, catching up with social media, or talking to friends — you run across many misconceptions about astronomy. Here are explanations for the most common of these errors.

"The Light from That Star Took 1,000 Light-Years to Reach Earth"

Many people mistake the light-year for a unit of time on par with units like a day, a month, or an ordinary year. But a light-year is a unit of distance, equal to the length that light travels in a vacuum over a period of one year.

A Freshly Fallen Meteorite Is Still Hot

Actually, freshly fallen meteorites are cold; an icy frost (from contact with moisture in the air) sometimes forms on a frigid stone that has recently landed. When an eyewitness says that he saw a meteorite fall to the ground and that he burned his fingers on the rock, the account may be a hoax. A quick trip through Earth's atmosphere isn't enough to substantially heat a rock that has spent the last several million years in the deep freeze of outer space.

Summer Always Comes When Earth Is Closest to the Sun

The belief that summer comes when Earth is closest to the Sun is about the most common error of them all, but common sense should tell you that the belief is false. After all, winter occurs in Australia when the United States is experiencing summer. But on any given day, Australia is just as far from the Sun as the United States. In fact, Earth is closest to the Sun in January and farthest from the Sun in July.

The Back of the Moon Is Dark

Some people think that the back of the Moon, which faces away from Earth (astronomers call it the "far side") is dark. They may even call it the "dark side" of the Moon. Sometimes the far side is dark, but sometimes it is bright, and much of the time, part of it is dark and the rest of it is bright. In that way, the far side of the Moon is just like the near side, which faces Earth. When you see a full Moon, the near side is all bright and the far side is all dark. At new Moon, when the side of the Moon that faces Earth is dark, the far side of the Moon is bright — if we could see the far side then, it would look like a full Moon.

The "Morning Star" Is a Star

The "morning star" isn't a star; it's always a planet. And sometimes two morning stars appear at once, such as Mercury and Venus. The same idea applies to the "evening star": You're seeing a planet, and you may see more than one. "Shooting stars" and "falling stars" are misnomers, too. These "stars" are meteors — the flashes of light caused by small meteoroids falling through Earth's atmosphere. Many of the "superstars" you see on television may be just flashes in the pan, but they at least get 15 minutes of fame.

If You Vacation in the Asteroid Belt, You'll See Asteroids All Around You

In just about any movie about space travel, you see a scene in which the intrepid pilot skillfully steers the spaceship past hundreds of asteroids that hurtle past in every direction, sometimes coming five at a time. Moviemakers just don't understand the vastness of the solar system, or they ignore it for dramatic purposes. If you stood on an asteroid smack dab in the middle of the main asteroid belt between Mars and Jupiter, you'd be lucky to see more than one or two other asteroids, if any, with the naked eye. Even in the asteroid belt, outer space is mostly empty space.

Nuking a "Killer Asteroid" on a Collision Course for Earth Will Save Us

You come across many common errors about asteroids, and various Hollywood doomsday movies and media reports on "killer asteroids" have provided ample but unfortunate opportunities to reinforce these misunderstandings among the public.

Blowing up an asteroid on a collision course with Earth with an H-bomb may only create smaller and collectively just-as-dangerous rocks, all still heading for the planet. A less risky idea is to attach a rocket motor to gently propel the asteroid just the slightest bit forward or backward in its orbit, steering it so it doesn't get to the same place in space as Earth at the same time. Even better, we might launch a so-called gravity tractor satellite to gently pull the asteroid from its original trajectory so it misses Earth.

The Sun Is an Average Star

You often hear or read statements that the Sun is an average star. In fact, the vast majority of all stars are smaller, dimmer, cooler, and less massive than our Sun. Be proud of the Sun — it's like a kid from the mythical Lake Wobegon, where the children are all "above average."

The Hubble Telescope Gets Up Close and Personal

The Hubble Space Telescope doesn't snap those beautiful pictures by cruising through space until it floats alongside nebulae, star clusters, and galaxies. The telescope stays in close orbit around Earth and just takes great photos. It does so because it has incredibly well-made optics and orbits far above the parts of Earth's atmosphere that blur our view with telescopes on the ground.

The Big Bang Is Dead

When an astronomer reports a finding that doesn't fit the current understanding of cosmology, members of the media are prone to pronouncing, "The Big Bang is dead." But astronomers are simply finding differences between the observed expansion of the universe and specific mathematical descriptions of it. The competing theories — including one that fits the newly reported data — are consistent with the Big Bang; they just differ in the details. Just like Mark Twain's falsely reported 1897 demise, news accounts of the Big Bang's death are greatly exaggerated.

About This Article

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About the book author:

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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