Astronomy For Dummies book cover

Astronomy For Dummies

By: Stephen P. Maran Published: 09-05-2017

Your updated guide to exploring the night sky

Do you know the difference between a red giant and a white dwarf? From asteroids to black holes, this easy-to-understand guide takes you on a grand tour of the universe. Featuring updated star maps, charts, and an insert with gorgeous full-color photographs, Astronomy For Dummies provides an easy-to-follow introduction to exploring the night sky. Plus, this new edition also comes with chapter quizzes online to help your understanding.

For as long as people have been walking the earth, those people have looked up into the night sky and wondered about the nature of the cosmos. Without the benefit of science to provide answers, they relied on myth and superstition to help them make sense of what they saw. Lucky for us, we live at a time when regular folks, equipped with nothing more than their naked eyes, can look up into the night sky and gain admittance to infinite wonders. If you know what to look for, you can make out planets, stars, galaxies, and even galactic clusters comprising hundreds of millions of stars and spanning millions of light-years.

Whether you're an amateur astronomer, space enthusiast, or enrolled in a first year astronomy course, Astronomy For Dummies gives you a reason to look into the heavens.

  • Includes updated schedules of coming eclipses of the Sun and Moon and a revised planetary appendix
  • Covers recent discoveries in space, such as water on the Moon and Pluto's demotion from "planet" status
  • Collects new websites, lists of telescope motels, sky-watching guides, and suggestions for beginner's telescopes and suppliers
  • Provides free online access to chapter quizzes to help you understand the content

Ever wonder what's out there in the big ol' universe? This is the book for you!

Articles From Astronomy For Dummies

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28 results
Famous Women in Astronomy

Article / Updated 03-07-2022

When you're studying astronomy, don't forget the women who made an impact in the field. Check out this list of amazing achievements by women astronomers and astrophysicists: Historical: Caroline Herschel (1750–1848) Discovered eight comets. Annie Jump Cannon (1863–1941) Devised the basic method for classifying the stars. Henrietta Swan Leavitt (1868–1921) Discovered the first accurate method for measuring great distances in space. Cecilia Payne-Gaposchkin (1900–1979) Proved that hydrogen is the most abundant chemical element in the stars. Sally Ride (1951–2012) A trained astrophysicist, she is the first American woman in space. Vera C. Rubin (1928–2016) Investigated the rotation of galaxies and detected the existence of dark matter. Contemporary: Jocelyn Bell Burnell Discovered pulsars in her work as a graduate student. E. Margaret Burbidge Pioneered modern studies of galaxies and quasars. Wendy Freedman Leader in measuring the expansion rate of the universe. Gabriela González Leader in detecting gravitational waves from merging black holes. Carolyn C. Porco Leads the Cassini imaging science team in the study of Saturn and its moons and rings. Nancy G. Roman As NASA’s first chief astronomer, she led the development of telescopes in space. Carolyn Shoemaker Discovered many comets, including one that smashed into Jupiter. Jill Tarter Leader in the search for extraterrestrial intelligence. Leslie A. Young Leader in the exploration of Pluto.

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Astronomy For Dummies Cheat Sheet

Cheat Sheet / Updated 03-02-2022

Astronomy is fascinating, and people have been looking at the stars since the dawn of humanity. Start your study of astronomy by reviewing the accomplishments of the very first astronomers, and then continue looking at important historical markers of the Space Age. Women have played important roles in astronomy, so be sure to check out how their discoveries have shaped what we know about space.

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10 Strange Facts about Astronomy and Space

Article / Updated 06-18-2019

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.) 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.

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Skywatching for Artificial Satellites

Article / Updated 11-14-2017

Hundreds of operating satellites are orbiting Earth, along with thousands of pieces of orbiting space junk — nonfunctional satellites, upper stages from satellite launch rockets, pieces of broken and even exploded satellites, and tiny paint flakes from satellites and rockets. You may be able to glimpse the reflected light from any of the larger satellites and space junk, and powerful defense radar can track even very small pieces. The best way to begin observing artificial satellites is to look for the big ones — such as NASA's International Space Station or the Hubble Space Telescope — and the bright, flashing ones (the dozens of Iridium communication satellites). Looking for a big or bright artificial satellite can be reassuring to the beginning astronomer. Predictions of comets and meteor showers are sometimes mistaken, the comets usually seem fainter than you expect, and usually you see fewer meteors than advertised. But artificial satellite viewing forecasts are usually right on. You can amaze your friends by taking them outside on a clear early evening, glancing at your watch, and saying "Ho hum, the International Space Station should be coming over about there (point in the right direction as you say this) in just a minute or two." And it will! Want to know what to watch for? Here are some characteristics you can pinpoint for both large and bright satellites: A big satellite such as the Hubble Space Telescope or the International Space Station generally appears in the evening as a point of light, moving steadily and noticeably from west to east in the western half of the sky. It moves much too slowly for you to mistake it for a meteor, and it moves much too fast for a comet. You can see it easily with the naked eye, so it can't be an asteroid — and, anyway, it moves much faster than an asteroid. Sometimes you may confuse a high-altitude jet plane with a satellite. But take a look through your binoculars. If the object in view is an airplane, you should be able to distinguish running lights or even the silhouette of the plane against the dim illumination of the night sky. And when your location is quiet, you may be able to hear the plane. You can't hear a satellite. An Iridium satellite is a wholly different viewing situation: It usually appears as a moving streak of light that gets remarkably bright and then fades after several seconds. It moves much more slowly than a meteor. And an Iridium flare or flash is often brighter than Venus, second in brilliance only to the Moon in the night sky. The Sun, located below your horizon, reflects off one of the door-size, flat, aluminum antennas on the satellite to cause the flash of light. At star parties, people cheer when they spot an Iridium flare, just like when folks see a fireball. You can even see some Iridium flares in daylight. And consider this: More than 60 Iridium satellites are in orbit. They interfere with astronomy, and professional astronomers want them to disappear, but until now at least the satellites have had a "flare" for entertaining us. A new generation of the satellites, called Iridium NEXT, are being launched (the first ten went up into space in January 2017). The NEXT satellites may be next to useless for amateur flare watchers because the design of the antennas has changed so that bright reflections from them are unlikely. The good news is that retiring all the original Iridiums will take a while, so if you start looking soon you may be able to catch some impressive flares before they're just history.

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Making Heads and Tails of a Comet's Structure

Article / Updated 11-14-2017

A comet is a stuck-together mixture of ice, frozen gases (such as the ices of carbon monoxide and carbon dioxide), and solid particles — the dust or "dirt" shown here. Historically, astronomers described comets as having a head and tail or tails, but with additional research, they've been able to clarify the nature of a comet's structure. The nucleus Astronomers initially named a bright point of light in the head of a comet the nucleus. Today we know that the nucleus is the true comet — the so-called dirty ice ball. The other features of a comet are just emanations that stem from the nucleus. A comet far from the Sun is only the nucleus; it has no head or tail. The ice ball may be dozens of miles in diameter or just a mile or two. That size is pretty small by astronomical standards, and because the nucleus shines only by the reflected light of the Sun, a distant comet is faint and hard to find. Images of Halley's nucleus from a European Space Agency probe that passed very close to it in 1986 show that the lumpy, spinning ice ball has a dark crust, like the tartufo dessert (balls of vanilla ice cream coated with chocolate) served in fancy restaurants. Comets aren't so tasty, but they are real treats to the eye. Here and there on Halley's nucleus, the probe photographed plumes of gas and dust from geyserlike vents or holes, spraying into space from areas where the Sun was warming the surface. Some crust! And in 2004, NASA's Stardust probe got close-up images of the nucleus of Comet Wild-2. This nucleus seems to bear impact craters and is marked with what may be pinnacles made of ice. Those are the cold facts. Not all comet nuclei are shaped like Halley's, though. In August 2014, the Rosetta spacecraft reached Comet 67P/Churyumov–Gerasimenko, known as 67P to its friends (like me). Rosetta orbited the comet nucleus while the comet orbited the Sun until the end of the European Space Agency mission in September 2016. Its photographs revealed a nucleus shaped roughly like a dumbbell with two unequal weights. Astronomers referred to the "weights" as two lobes of the comet connected by a thinner structure they named the neck. Some astronomers stuck their necks out by theorizing that the odd-shaped nucleus was formed by the low-speed collision of two earlier objects. The coma As a comet gets closer to the Sun, solar heat vaporizes more of the frozen gas, and it spews out into space, blowing some dust out, too. The gas and dust form a hazy, shining cloud around the nucleus called the coma (a term derived from the Latin for "hair," not the common word for an unconscious state). Almost everyone confuses the coma with the head of the comet, but the head, properly speaking, consists of both the coma and the nucleus. The glow from a comet's coma is partly the light of the Sun, reflected from millions of tiny dust particles, and partly emissions of faint light from atoms and molecules in the coma. A tale of two tails The dust and gas in a comet's coma are subject to disturbing forces that can give rise to a comet's tail(s): the dust tail and the plasma tail. (Sometimes when you view a comet, you see just one kind of tail, but when you're lucky, you see both.) The pressure of sunlight pushes the dust particles in a direction opposite the Sun, producing the comet's dust tail. The dust tail shines by the reflected light of the Sun and has these characteristics: A smooth, sometimes gently curved appearance A pale yellow color The other type of comet tail is a plasma tail (also called an ion tail or a gas tail). Some of the gas in the coma becomes ionized, or electrically charged, when struck by ultraviolet light from the Sun. In that state, the gases are subject to the pressure of the solar wind, an invisible stream of electrons and protons that pours outward into space from the Sun. The solar wind pushes the electrified cometary gas out in a direction roughly opposite of the Sun, forming the comet's plasma tail. The plasma tail is like a wind sock at an airport: It shows astronomers who view the comet from a distance which way the solar wind is blowing at the comet's point in space. In contrast to the dust tail, a comet's plasma tail has the following: A stringy, sometimes twisted, or even broken appearance A blue color Now and then, a length of plasma tail breaks from the comet and flies off into space. The comet then forms a new plasma tail, much like a lizard that grows a new tail when it loses its first one. The tails of a comet can be millions to hundreds of millions of miles long. When a comet heads inward toward the Sun, its tail or tails stream behind it. When the comet rounds the Sun and heads back toward the outer solar system, the tail still points away from the Sun, so the comet now follows its tail. The comet behaves to the Sun as an old-time courtier did to his emperor: never turning his back on his master. The comet shown could be going clockwise or counterclockwise, but either way, the tail always points away from the Sun. The coma and tails of a comet are just a vanishing act. The gas and dust shed by the nucleus to form the coma and tails are lost to the comet forever — they just blow away. By the time the comet travels far beyond the orbit of Jupiter, where most comets come from, it consists of only a bare nucleus again. And the nucleus is a little smaller, due to the gas and dust that it sheds. The dust the comet loses may someday produce a meteor shower, if it crosses Earth's orbit. Halley's comet is a good example of the wasting-away process. Halley's nucleus decreases by at least a meter (39.37 inches, or slightly more than a yard) every 75 to 77 years when it passes near the Sun. The nucleus is only about 10 kilometers (10,000 meters or 6.2 miles) in diameter right now, so Halley's comet will survive only about 1,000 more orbits, or about 75,000 years. Dust shed by the famous comet causes two of the top annual meteor showers, the Eta Aquarids and the Orionids.

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Photographing Meteors and Meteor Showers

Article / Updated 11-14-2017

Digital cameras are now the preferred tools for photographing meteors. But digital meteor photography requires a digital single lens reflex camera (DSLR), which is expensive camera (point-and-shoot cameras and cellphone cameras don't work very well, except in the rare case when you can catch a brilliant fireball) and a lot of trial-and-error experimenting until you get it right. Further, you need a DSLR that you can set for time exposures and that accepts a cable for an intervalometer or "remote switch with digital timer." You might need to spend more on a suitable camera for meteor photography than on a decent small telescope for other observations, but the camera can be used for other purposes, not just your astronomy hobby. Here are some important guidelines for digital meteor photography: Observe from as dark a location as possible, away from urban lighting. Try meteor photography only when the Moon is below the horizon. Use a sturdy tripod so the camera doesn't shake during a time exposure. Use a wide-angle lens (because you'll catch more meteors in a single shot than with a normal lens) and set it on Infinity. Don't use a telephoto lens. Use an intervalometer or "remote switch with digital timer" to operate the camera shutter without shaking the camera and to take pictures at regular intervals during the night. Point the camera about halfway up the sky from the horizon to the zenith, or a little higher, facing whichever direction has the least interfering sky glow from city or other lights. Spend some time making test exposures to determine what settings to use on that particular night. (The best settings vary depending on how bright the sky is.) Make several 10-second exposures, some 20-second exposures, and some 30-second exposures. You're trying to determine how long you can let an exposure last (the longer the better) without skylight overexposing the picture. You may need to repeat this series of time exposures for each of two or three ISO settings. (With a larger ISO setting, you can record fainter meteors, which means more meteors, but with the larger ISO setting, the sky overexposes sooner, so you can't expose for as long a time.) With experience, you should find the "sweet spot" of exposure time and ISO that works best with your lens at your location. For more info on digital meteor photography read this expert advice. You can photograph sporadic meteors by following the preceding guidelines, but there aren't many sporadic meteors to catch on any given night. A meteor shower offers you the opportunity to snap more meteors, as long as the Moon isn't in the sky. With moonlight, you'll catch far fewer meteors, if any. When photographing a meteor shower, take the photographs when the shower radiant (the constellation from which the meteor shower seems to come) is well above the horizon, preferably 40º or more. The horizon is at 0º altitude, and the zenith (overhead point) is 90º up, so the halfway point between them is at 45º; two-thirds of the way up is 60º, and so on.

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Viewing Meteor Showers

Article / Updated 11-14-2017

Normally, only a few meteors per hour are visible — more after midnight than before and (for observers in the Northern Hemisphere) more in the fall than in the spring. But on certain occasions every year, you may see 10, 20, or even 50 or more meteors per hour in a dark, moonless sky far from city lights. Such an event is a meteor shower, when Earth passes through a great ring of billions of meteoroids that runs all the way around the orbit of the comet that shed them. The following figure illustrates the occurrence of a meteor shower. The direction in space or place on the sky where a meteor shower seems to come from is called the radiant. The most popular meteor shower is the Perseids, which, at its peak, produces as many as 80 meteors per hour. (The Perseids get their name because they seem to streak across the sky from the direction of the constellation Perseus, the Hero, their radiant. Meteor showers are usually named for constellations or bright stars [such as Eta Aquarii] near their radiants.) A few other meteor showers produce as many meteors as the Perseids, but fewer people take the time to observe them. The Perseids come in August, when the balmy nights in North America and Europe often are perfect for skywatching, but the other leading meteor showers — the Geminids and Quadrantids — streak across the sky in December and January, respectively, when the weather is worse in the Northern Hemisphere and observers' ambitions are limited. The table lists the top annual meteor showers. The dates in the table are the nights when the showers usually reach their peak. Some showers go on for days, and others for weeks, raining down meteors at lower rates than the peak values. The Quadrantids may last for just one night or only a few hours. Top Annual Meteor Showers Shower Name Approximate Date Meteor Rate (Per Hour) Quadrantids Jan. 3–4 90 Lyrids Apr. 21 15 Eta Aquarids May 4–5 30 Delta Aquarids July 28–29 25 Perseids Aug. 12 80 Orionids Oct. 21 20 Geminids Dec. 13 100 The Quadrantids' radiant is in the northeast corner of the constellation Bootes, the Herdsman. The meteors are named for a constellation found on 19th-century star charts that astronomers no longer officially recognize. In addition to losing their namesake, the Quadrantids seem to have lost the comet that spawned them — their origin was a mystery until 2003, when astronomer Petrus Jenniskens found that an object named 2003 EH1 may be their parent comet. The Geminids are a meteor shower that seems to be associated with the orbit of an asteroid rather than a comet. However, the "asteroid" is probably a dead comet, which no longer puffs out gas and dust to form a head and tail. The object 2003 EH1, the likely parent of the Quadrantids, may be a dead comet, too. The Leonids are an unusual meteor shower that occurs around November 17 every year, usually to no great effect. But every 33 years, many more meteors are present than usual, perhaps for several successive Novembers. Huge numbers of Leonids were seen in November 1966 and again in November 1999, 2000, 2001, and 2002, at least for brief times at some locations. The next great display likely will come in 2032. Don't forget to look for it. You almost never see as many meteors per hour as lsited. The official meteor rates are defined for exceptional viewing conditions, which few people experience nowadays. But meteor showers vary from year to year, just like rainfall. Sometimes people do see as many Perseids as listed. On rare occasions, they see many more than expected. Such inconsistency is why keeping accurate records of the meteors that you count can be helpful to the scientific record. For more information on upcoming meteor showers, check out the American Meteor Society website. Do you live south of the equator? If so, check out the list of meteor showers visible from the Southern Hemisphere on the website of the Royal Astronomical Society of New Zealand. To track meteors, you need an accurate time source, a way to record your observations, and a dim flashlight to see what you're doing. The best light for astronomical observations is a red flashlight, which you can purchase, or make from an ordinary flashlight by wrapping red transparent plastic around the bulb. Some astronomers paint the lamp with a thin coat of red nail polish. If you use a white light, you dazzle your eyes and make it impossible to see the fainter stars and meteors for 10 to 30 minutes, depending on the circumstances. Letting your vision adjust to the dark is called getting dark adapted and is a step you want to take every time you observe the night sky. The best way to watch and count meteors is to recline on a lounge chair. (You can do pretty well just lying on a blanket with a pillow, but you're more likely to fall asleep in that position and miss the best part of the show.) Tilt your head so you're looking slightly more than halfway up from the horizon to the zenith — the optimum direction for counting meteors. Take notes. And be sure you have a thermos of hot coffee, tea, or cocoa! You don't have to face the radiant when you observe a meteor shower, although many people do. The meteors streak all over the sky, and their visible paths may begin and end far from the radiant. But you can visually extrapolate the meteors' paths back in the direction from which they seem to come, and the paths point back to the radiant. Identifying a radiant in that way is how you can tell a shower meteor from a sporadic one. If you do face the radiant, however, you see some meteors that seem to have very short paths, even though they appear fairly bright. The paths appear short because the meteors are coming almost right at you. Fortunately, the shower meteoroids are microscopic and won't make it to the ground. For more information on meteor showers, including historical events, facts, and advice on observing, head to the Sky and Telescope site and enter "Shooting Stars" in the search window. Then you can download the free Shooting Stars e-book (you may have to register your email address).

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Spotting Sporadic Meteors, Fireballs, and Bolides

Article / Updated 11-14-2017

When you're outdoors on a dark night and see a "shooting star" (the flash of light from a random, falling meteoroid), what you're probably seeing is a sporadic meteor. But if many meteors appear, all seeming to come from the same place among the stars, you're witnessing a meteor shower. Meteor showers are among the most enjoyable sights in the heavens. A dazzlingly bright meteor is a fireball. Although a fireball has no official definition, many astronomers consider a meteor that looks brighter than Venus to be a fireball. However, Venus may not be visible at the time you see the bright meteor. So how can you decide whether you're seeing a fireball? Here's a rule for identifying fireballs: If people facing the meteor all say "Ooh" and "Ah" (everyone tends to shout when they see a bright meteor), the meteor may be just a bright one. But if people who are facing the wrong way see a momentary bright glow in the sky or on the ground around them, it's the real thing. To paraphrase an old Dean Martin tune, when the meteor hits your eye like a big pizza pie, that's a fireball! Fireballs aren't very rare. If you watch the sky regularly on dark nights for a few hours at a time, you'll probably see a fireball about twice a year. But daylight fireballs are very rare. If the Sun is up and you see a fireball, mark it down as a lucky sighting. You've seen one tremendously bright fireball. When nonscientists see daytime fireballs, they almost always mistake them for an airplane or missile on fire and about to crash. Any very bright fireball (approaching the brightness of the half Moon or brighter) or any daylight fireball represents a possibility that the meteoroid producing the light will make it to the ground. Freshly fallen meteorites are often of considerable scientific value, and they may be worth good money, too. If you see a fireball that fits this description, write down all the following information so your account can help scientists find the meteorite and determine where it came from: Note the time, according to your watch. At the earliest opportunity, check how fast or slow your watch is running against an accurate time source, such as the Master Clock at the U.S. Naval Observatory. If you have a smartphone, it should give you the time accurate at least to the minute. Record exactly where you are. If you have a Global Positioning System receiver handy (or a smartphone with a GPS app, such as Compass on the iPhone), take a reading of your latitude and longitude. Otherwise, make a simple sketch showing where you stood when you saw the fireball — note roads, buildings, big trees, or any other landmarks. Make a sketch of the sky, showing the track of the fireball with respect to the horizon as you saw it. Even if you're not sure whether you faced southeast or north-northwest, a sketch of your location and the fireball track helps scientists determine the trajectory of the fireball and where the meteoroid may have landed. After a daylight fireball or a very bright nighttime fireball, interested scientists advertise for eyewitnesses. They collect the information, and by comparing the accounts of persons who viewed the fireball from different locations, they can close in on the area where it most likely fell to the ground. Even a brilliant fireball may be only the size of a small stone — one that would fit easily in the palm of your hand — so scientists need to narrow the search area to have a reasonable chance of finding it. If you don't see a call for information after your fireball observation, chances are good that the nearest planetarium or natural history museum will accept your report and know where to send it. Or report your fireball observation to the American Meteor Society — just look for the prominent "Report a Fireball" link on their home page. A bolide is a fireball that explodes or produces a loud noise even if it doesn't break apart. Some people use bolide interchangeably with fireball. (You won't find an official agreement on this term; you can find different definitions in even the most authoritative sources.) The noise you hear is the sonic boom from the meteoroid, which is falling through the air faster than the speed of sound. When a fireball breaks apart, you see two or more bright meteors at once, very close to each other and heading the same way. The meteoroid that produces the fireball has fragmented, probably from aerodynamic forces, just as an airplane falling out of control from high altitude sometimes breaks apart even though it hasn't exploded. Often a bright meteor leaves behind a luminous track. The meteor lasts a few seconds or less, but the shining track — or meteor train — may persist for many seconds or even minutes. If it lasts long enough, it becomes distorted by the high-altitude winds, just as the wind gradually deforms the skywriting from an airplane above a beach or stadium. You see more meteors after midnight local time than before because, from midnight to noon, you're on the forward side of Earth, where our planet's plunge through space sweeps up meteoroids. From noon to midnight, you're on the backside, and meteoroids have to catch up in order to enter the atmosphere and become visible. The meteors are like bugs that splatter on your auto windshield. You get many more on the front windshield as you drive down the highway than on the rear windshield because the front windshield is driving into bugs and the rear windshield is driving away from bugs.

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Planning Your First Steps into Astronomy

Article / Updated 11-14-2017

If you're just starting to become interested in astronomy, get into the astronomy hobby gradually, investing as little money as possible until you're sure about what you want to do. Here's a plan for acquiring both basic skills and the needed equipment: If you have a late-model computer, invest in a free or inexpensive planetarium program. Better yet, if you have a smartphone, download and use a free or cheap planetarium app. Start making naked-eye observations at dusk on clear nights and before dawn, if you're an early riser. To plan your observations of planets and constellations, you can also rely on the weekly sky scenes at the Sky & Telescope website. If you don't have a suitable computer, plan your observations based on the monthly sky highlights in Astronomy or Sky & Telescope magazine. After a month or two of familiarizing yourself with the sky and discovering how much you enjoy it, invest in a serviceable pair of 7x50 binoculars. As you continue to observe the bright stars and constellations, invest in a star atlas that shows many of the dimmer stars, as well as star clusters and nebulae. Sky & Telescope's Pocket Sky Atlas by Roger W. Sinnott (Sky Publishing, 2007) is a good choice. For maps that are equally good but larger, consult the Jumbo Pocket Sky Atlas by the same author and publisher (2016); you'll just need a bigger pocket. Compare scenes in your star atlas with the constellations that you're observing; the atlas shows their RAs and Decs. Eventually, you'll start to develop a good feel for the coordinate system. Join an astronomy club in your area, if at all possible, and get to know the folks who have experience with telescopes. If all goes well and you want to continue in astronomy invest in a well-made, high-quality telescope in the 2.5-to-4-inch size range. Study the telescope manufacturer websites earlier in this chapter or send for catalogs advertised in astronomy magazines. Better yet, talk to experienced astronomy club members if you can. They can advise you on buying a new telescope, and they may know someone who wants to sell a used telescope. You may be able to borrow a starter telescope and try it out at home. Thanks to the New Hampshire Astronomical Society (NHAS), a movement to place such telescopes in public libraries has begun. Astronomy clubs purchase the telescopes; club members modify them for use by inexperienced borrowers and then donate them to the libraries. The telescope model adopted for this project is the Orion StarBlast 4.5, which retails for about $210. It's meant for use on a tabletop but may work for you when just placed on the ground. According to Sky & Telescope, by late 2016 NHAS had placed more than 100 of these telescopes in New Hampshire libraries, and the St. Louis Astronomical Society had placed over 130 in Missouri and Illinois libraries. Astronomy clubs in other areas are beginning to sponsor library telescopes; search the web to see whether a library telescope program exists near you. Who knows; you may have a (star) blast! If you find that you enjoy astronomy, after a few years, consider moving up to a 6- or 8-inch telescope. It may be harder to use, but you'll be ready to master it after you have some experience. Equipped with a larger telescope, you can see many more stars and other objects. You can get ideas about what larger telescopes to consider by talking to other amateur astronomers and by attending a star party, where you can see many different telescopes in operation and on display.

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Shopping for Telescopes the Smart (and Economical) Way

Article / Updated 11-14-2017

A cheap, mass-manufactured telescope, often called a drugstore or department store telescope, is usually a waste of money. And it still costs more than a hundred or maybe several hundred dollars. A good telescope, bought new, may run you several hundred dollars to $1,000, and you certainly can pay more. But you can find alternatives: Used telescopes are often sold through ads in astronomy magazines or in the newsletters of local astronomy clubs. If you can inspect and test a used telescope and you find what you like, buy it! A well-maintained telescope can last for decades. In many areas, amateurs can observe with the larger telescopes operated by astronomy clubs, planetariums, or public observatories. The technology of amateur telescopes is advancing at a rapid pace, and a former astronomer's dream can be today's obsolete equipment. Quality and capabilities are going up, and prices are generally fair, perhaps because reliable manufacturers are in competition for your money. Generally, a good refractor gives better views than a good reflector that has the same aperture, or telescope size. Aperture refers to the diameter of the main lens, the mirror, or, in a more complicated telescope, the size of the unobstructed portion of the optics. But a good refractor is more expensive than a comparable reflector. The Maksutov-Cassegrains and Schmidt-Cassegrains are good compromises between the low cost of a reflector and the high performance but high cost of a refractor. For many astronomers, these hyphenated telescope types are the preferred models. One of the best small telescopes is the Meade ETX-90. Its aperture is 3.5 inches, almost the smallest size of any telescope that you should start with. (If you find a good instrument at a good price from a 2.5-inch aperture on up, especially in a refractor, consider it for purchase.) The ETX-90 sells for about $400 and comes with an Autostar computerized controller and a tripod. This instrument automatically points at almost any object you specify if that object is in view from your location at that time. The Autostar can even find moving objects, such as planets, based on stored information, and it's equipped to give you a "tour" of the best sights in the sky, selected with no input from you. A good competing telescope for the ETX-90 is the Celestron SkyProdigy 90. It's comparably sized and equipped and has the capability to automatically align itself on the sky, after which it points to almost any celestial object that you select. It goes for about $600. You definitely don't want to spend this much money on a telescope until you see the same model in action at an astronomy club observing meeting or a star party. But the price is no more than you pay for a fine camera and an accessory lens or two. You can find larger telescopes for less money — check the ads in current issues of astronomy magazines — but you have to invest much more effort in learning to use them effectively. Some brand-name telescopes are sold through authorized dealers that tend to have expert knowledge. But take their advice with just a wee bit of salt. Here are some key websites to browse for telescope product information: Celestron, for many years the favorite manufacturer for thousands of astronomers Meade Instruments Corporation Orion Telescopes & Binoculars On each of these websites, you can find the instruction manuals for many of the telescopes that they sell. Consider taking a look at the manual before you buy a telescope so you know whether it will be helpful when you run into problems. If you don't live in the United States, you may be able to find dealers for the telescope brands in your country. The Widescreen Centre in London carries Celestron, Meade, and Orion telescopes. In Australia, the Binocular and Telescope Shop, with locations in Sydney and Melbourne, is among the dealers that carry these telescopes.

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