Physics Astrophysics for Dummies Cheat Sheet Cheat Sheet / Updated 03-14-2024 The path to understanding astrophysics is both thought-provoking and brain-stretching. How did the universe come into existence, when will it end, and what role do our familiar planets and stars play in the grand scheme of the cosmos? There are many more questions in astrophysics than there are answers. The goal of this book is to put you in a position where you’re able to better formulate those questions, and know where to go for answers. As you’re getting started on your journey, use this Cheat Sheet to answer some of the first questions that come to mind. View Cheat Sheet

Geography Human Geography For Dummies Cheat Sheet Cheat Sheet / Updated 02-22-2024 Welcome to the world of Human Geography. It is a whole world that a shockingly large number of people do not even know exists. Human geography is an academic discipline regularly taught at the high school and university level that actually encompasses quite a few subdisciplines of geographic study. The traditional divisions of human geography study the following major fields. Populations and migration Urban geography Economic geography Cultural geography Political geography Within those fields, a slew of other research areas can be included under the umbrella of human geography. Areas like medical geography study the relationship between space and medical care (like the spread of infectious diseases or the impact that location has on quality of life). Political geography is a geopolitics field that tries to understand the geographic factors that influence how different countries interact. The content in this book will give you a working overview of the terms and concepts covered within the field of human geography. The materials are comparable to the content covered in a lower-level undergraduate college course or an upper-level high school course. This book is not an in-depth dive into any particular human geography topic. In fact, every topic included in this book could have entire books written about just that one idea. Many researchers have spent untold hours building the human geography field. The purpose of this book is to give you a taste of the breadth of human geography in easily digestible tidbits. Also, this is not a textbook. Instead, it is a starting place for where human geography can take you. View Cheat Sheet

Neuroscience Neurobiology For Dummies Cheat Sheet Cheat Sheet / Updated 02-12-2024 Neurobiology has all kinds of real-world (and not so real-world) applications. From curing paralysis to the possibility of cyborgs, neurobiology has answers to many fascinating questions. View Cheat Sheet

Genetics Genetics For Dummies Cheat Sheet Cheat Sheet / Updated 11-21-2023 Genetics is a complex field with lots of details to keep straight. But when you get a handle on some key terms and concepts, including the structure of DNA and the laws of inheritance, you can start putting the pieces together for a better understanding of genetics. View Cheat Sheet

Astronomy Important Events of the Space Age Article / Updated 10-19-2023 The Space Age, generally considered started by the launch of the Russian satellite Sputnik, is defined by the events surrounding space exploration and development of space technology. This list maps out major events of the Space Age: 1957 The Soviet Union launches Sputnik 1, the first artificial satellite to orbit Earth. 1958 Using the satellite Explorer 1, James Van Allen discovers Earth’s radiation belts (magnetosphere). 1960 Frank Drake begins the Search for Extraterrestrial Intelligence (SETI) at the National Radio Astronomy Observatory in Green Bank, West Virginia. 1961 Yuri Gagarin makes the first manned space flight. 1963 Valentina Tereshkova is the first woman in space. 1967 Jocelyn Bell Burnell and Anthony Hewish discover pulsars. 1969 Neil Armstrong and Buzz Aldrin walk on the moon. 1971: The Soviet Union launches the first space station, Salyut 1. 1972: The Soviet Union's Mars 3 spacecraft makes first soft landing on another planet, Mars. 1979 Using pictures from Voyager 1, Linda Morabito discovers erupting volcanoes on Jupiter’s moon, Io. 1981: NASA's Columbia shuttle becomes first winged spaceship to orbit Earth and return to airport landing. 1987 Ian Shelton discovers the first supernova since 1604 plainly visible to the naked eye. 1990 The Hubble Space Telescope launches. 1991 Alexander Wolszczan discovers planets orbiting a pulsar — the first known planets outside the solar system. 1995 Michel Mayor and Didier Queloz discover 51 Pegasi B, the first planet of a normal star beyond the Sun. 1998 Two astronomer teams discover that the expansion of the universe is getting faster, perhaps due to a mysterious “dark energy” associated with the vacuum of space. 1999 Mars Global Surveyor finds that Mars may have had an ocean at one time. 2003 The Wilkinson Microwave Anisotropy Probe satellite finds that the universe is 13.7 billion years old. 2012 The Kepler spacecraft finds that there probably are billions of planets in orbit around stars in our galaxy, and the rover Curiosity lands on Mars. 2015 The New Horizons probe explores Pluto and its moons and then heads outward in the Kuiper Belt. View Article

Astronomy Making Heads and Tails of a Comet's Structure Article / Updated 10-19-2023 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. View Article

Astronomy Planning Your First Steps into Astronomy Article / Updated 10-19-2023 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. View Article

Astronomy Photographing Meteors and Meteor Showers Article / Updated 10-19-2023 Digital cameras are now the preferred tools for photographing meteors. But digital meteor photography requires a digital single lens reflex camera (DSLR), which is an 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 40 degrees or more. The horizon is at 0 degrees altitude, and the zenith (overhead point) is 90 degrees up, so the halfway point between them is at 45 degrees; two-thirds of the way up is 60 degrees, and so on. View Article

Astronomy Skywatching for Artificial Satellites Article / Updated 10-19-2023 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 subsequent generation of the satellites, called Iridium NEXT, started being launched 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. View Article

Astronomy Spotting Sporadic Meteors, Fireballs, and Bolides Article / Updated 10-19-2023 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 Official U.S. Time site. 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. View Article