You Just Love the Drake Equation

Drake Equation

With a few hundred billion stars in the Galaxy, the likelihood of life somewhere in the Milky Way other than on the earth seems great. But is there any way to get a handle on just how great Not every star has a fair shake, however. Some are so massive that they don't last long enough, and others are not hot enough to warm any planets that might be there. Perhaps 15 percent of the stars in the Galaxy have the proper mass to be luminous enough (but not too luminous) to support habitable planets....

The Supernova as Creator

As you might expect, an explosion as tremendous as that of a supernova creates a great deal of debris. The Crab Nebula, in the constellation Taurus, is the remnant of a supernova that appeared in c.e. 1054. Chinese astronomers left records of that event, reporting a star so brilliant that it was visible for a month in broad daylight. The bright radio source Cassiopeia A is also a supernova remnant. But supernovae create far more than glowing remnants. Hydrogen and helium, the two most basic...

Hubbles Law and Hubbles Constant

It has been known since the early twentieth century that every spiral galaxy observed (sufficiently distant) exhibits a redshifted spectrum they are all moving away from us. Recall from Chapter 17 the Doppler effect Wavelengths grow longer (redshift) as an object recedes from the viewer. The conclusion is inescapable All galaxies partake in a universal recession. This is the apparent general movement of all galaxies away from us. This observation does not mean that we are at the center of the...

Flat Earth Big Bowl

As the sun's glow fades and your eyes become accustomed to the night, the sky gradually fills with stars. Thousands of them shimmer blue, silvery white, some gold, some reddish, seemingly set into a great dark bowl, the celestial sphere, overarching the flat earth on which you stand. Thousands of stars in the night sky Maybe that number has brought you back through a starlit ten thousand years and into the incandescent lamp light of your living room or kitchen or bedroom or wherever you are...

You Can Do This

Building a huge radio telescope like Arecibo or the Green Bank Telescope (GBT) takes a great deal of money, and so does operating one. Even if you had the cash, your neighbors (not to mention the local zoning board), might frown on your building even a modest 30-foot-diameter dish antenna in your backyard. However, remember that radio astronomy originated with nonastronomers, and there is still plenty of room in the field for amateurs, including amateurs of modest means. A small but committed...

Measuring Very Great Distances

In Chapter 17, Of Giants and Dwarfs Stepping Out into the Stars, we saw that the distance from us to the planets can be measured accurately by radar ranging, but that measuring the distance to farther objects, namely the nearer stars, requires measuring stellar parallax. But beyond about 100 parsecs parallax doesn't work well, because the apparent angular displacement becomes smaller than the angular resolution of our best telescopes. Gas velocities and a model of the rotation of the Milky Way...

Star Words Glossary

Accretion The gradual accumulation of mass usually refers to the build-up of larger masses from smaller ones through mutual gravitational attraction. active galaxy A galaxy that has a more luminous nucleus than most galaxies. altazimuth coordinates Altitude (angular distance above the horizon) and azimuth (compass direction expressed in angular measure from due north). altitude See altazimuth coordinates. angular momentum The rotating version of linear momentum. Depends on the mass distribution...

Jupiters Four Galilean Moons

The four large moons of Jupiter are very large, ranging in size from Europa, only a bit smaller than the earth's moon, to Ganymede, which is larger than the planet Mercury. Certainly, they are large enough to have been discovered even through the crude telescope of Galileo Galilei, after whom they have been given their group name. In his notebooks, Galileo called the moons simply I, II, III, and IV. Fortunately, they were eventually given more poetic names, Io, Europa, Ganymede, and Callisto,...

Types of Supernovae

Two types of supernovae are recognized. Type I supernovae contain little hydrogen, whereas Type II are rich in hydrogen. Only Type II supernovae are associated with the core collapse of high-mass stars. Type I supernovae are associated with our friends the white dwarfs. No supernova has appeared in our Galaxy, the Milky Way, since 1604. Since supernovae are among the most energetic processes known, it is not surprising that the light of a supernova can outshine the combined light of the entire...

Telephone Man Tunes In

The first true radio astronomer was not trained as an astronomer at all. Even to this day, many astronomers who work in the radio regime were trained as physicists and electrical engineers, and later learned to apply their knowledge to astronomy. Karl Jansky, the son of a Czech immigrant who settled in Oklahoma (where Karl was born in 1905), took a degree in physics at the University of Wisconsin. After graduating, Karl went to work in 1928 not as an astronomer, but as a telephone engineer with...

Big Bang Overview

What we are able to discuss is what happened very soon after the Big Bang. And we do mean very soon. From about H00 of a second after the Big Bang onward, we can outline the major steps in the universe's evolution. It is basically a story of cooling and expanding. For a thorough review of modern cosmology, see Timothy Ferris's excellent and humorous The Whole Shebang (Touchstone, 1998). At the earliest times that we can track, the universe was incredibly hot (1011 K) and filled with elementary...

Gone Fission

On December 2, 1942, Enrico Fermi, an Italian physicist who had fled his fascist-oppressed native land for the United States, withdrew a control rod from an atomic pile that had been set up in a squash court beneath the stands of the University of Chicago's Stagg Field. This action initiated the world's first self-sustaining atomic chain reaction. Fermi and his team had invented the nuclear reactor, and the world hasn't been the same since. Nuclear fission is a nuclear reaction in which an...

Aristotle Lays Down the

Fortunately for the hard-pressed astronomers of yore, total eclipses of the sun are relatively rare events. More immediately, they had nightly occurrences they couldn't explain. They could watch the sky all night and see the stars glide predictably across the sky, as if affixed to a moving celestial sphere. Likewise, the moon made its traversal with perfect regularity. But there were (so far as the ancients could see) five heavenly bodies that didn't behave with this regularity. Mercury, Venus,...

Amateur Radio Astronomy NoCost and Low Cost Approaches

As you may recall from Chapter 6, You and Your Telescope, a decent optical telescope costs at least 300 to 400. For free optical astronomy, all you need are your eyes. You can also do some radio astronomy for free if you own an FM radio or a television set. We thank Tom Crowley of Atlanta Astronomy Club for many of the following ideas. Have you ever witnessed a meteor shower The streaks of light in the night sky can be quite spectacular. Meteors are the bright trails of ionized atmosphere...

Become an Astrophotographer

Once you get hooked on looking through a telescope, sooner or later you're going to want to start recording what you see. One very enjoyable activity is to make drawings, but many serious amateurs sooner or later turn to photography. Astrophotography can be done with any good single-lens reflex (SLR) camera, the right kind of adapter to mate it with your telescope, and a sturdy tripod and mount with a tracking motor to compensate for the rotation of the earth during the long exposures are...

The Cosmological Principle

Together, the homogeneity and isotropy of the universe make up what we call the cosmological principle a cornerstone assumption in modern cosmology. If we could not make this assumption (based on observation), then our cosmology might only apply to a very local part of the universe. But the cosmological principle allows us to extrapolate our conclusions drawn from our local viewpoint to the whole universe. And consider these implications A homogeneous universe can have no border or edge (since...

The Unexplained Motions of the Heavens

V How does celestial movement mark time V The discrepancy between the solar and sidereal day and what it means V The sidereal month versus the synodic month V Understanding the tropical year and the sidereal year V The solar system according to Ptolemy The next time you're outside doing yard work in the sun, put a stick in the ground, call it a gnomon, and watch the motion of its shadow. Believe it or not, you have made a simple sundial, which was one of the earliest ways that human beings kept...

Postcards from the Edge

So here's a thought experiment Suppose it were possible to send an indestructible probe to the event horizon of a black hole. Next, suppose we equipped the probe with a transmitter broadcasting electromagnetic radiation of a known frequency. As the probe neared the event horizon, we would begin to detect longer and longer wavelengths. This shifting in wavelength is known as a gravitational redshift. This shift occurs because the photons emitted by our transmitter lose some energy in their...

Letting It AH

We now join a single fragment in the collapsing cloud that will become a 1-solar mass star. Over a period of perhaps a million years, the cloud fragment contracts. In this process, most of the gravitational energy released by the contraction escapes into space, because the contracting cloud is insufficiently dense to reabsorb the radiation. At the center of the coalescing cloud (where densities are the highest), more of the radiated energy is trapped and the temperature increases. As the cloud...

Grecian Formula

We could go on with speculation about the astronomy of the Far East, Near East, and New World (and those interested should read E. C. Krupp's Echoes of the Ancient Skies The Astronomy of Lost Civilizations, New York, 1983), but it would be just that fascinating speculation. For these early astronomers left few written records, and those they did leave either note only their observations or link such observations to religion and mythology. These earliest records do not show any effort to use...

The Atmospheres of Uranus and Neptune

The atmospheres of Uranus and Neptune have not been probed by unmanned space vehicles, but they have been studied spectroscopically from the earth, revealing that, like Jupiter and Saturn, they are mostly hydrogen (about 84 percent) and helium (about 14 percent). Methane makes up about 3 percent of Neptune's atmosphere, and 2 percent of Uranus's, but ammonia is far less in abundance on either planet than on Jupiter and Saturn. Because Uranus and Neptune are colder and have much lower...

Blocking Light

Why is it that dust blocks our optical view of the Milky Way It's due to the size of the dust grains. Let's think about this for a moment. A satellite dish can be made out of a wire mesh, perforated by small holes. Why doesn't this structure let the radio waves slip through, like water through a sieve Because it's catching radio waves, and radio waves are big. So big, in fact, that as long as the holes are small enough, the radio waves don't even know the holes are there. The waves reflect off...

Luminosity Versus Apparent Brightness

Ask an astronomer this question, and she will respond that the flashlight, a few feet from your eyes, is apparently brighter than the distant headlights, but that the headlights are more luminous. Luminosity is the total energy radiated by a star each second. Luminosity is a quality intrinsic to the star brightness may or may not be intrinsic. Absolute brightness is another name for luminosity, but apparent brightness is the fraction of energy emitted by a star that eventually strikes some...

Anatomy of a Wave

We can understand how electromagnetic radiation is transmitted through space if we appreciate that it involves waves. What is a wave The first image that probably jumps to mind is that of ocean waves. And ocean waves do have some aspects in common with the kind of waves that we use to describe electromagnetic radiation. One way to think of a wave is that it is a way for energy to be transmitted from one place to another without any physical matter being moved from place to place. Or you may...

Dragon Eats the Sun Ancient Chinese Astronomy

As we said, the ancient Babylonians began making systematic observations of the heavens by 3000 b.c.e., and the Chinese weren't far behind. Records exist that show they had observed a grouping of bright planets (called a conjunction) that occurred around 2500 b.c.e., and, sometime before this, had arrived at the concept of a 365-day year, based on what appeared to be the sun's annual journey across the background stars. A distinctly Western conception of the monster the ancient Chinese believed...

The Parallax Principle

First, how do we know that the nearest stars are so far away For that matter, how do we know how far away any stars are We've come a long way in this book, and, on our journey, we have spoken a good deal about distances by earthly standards, often extraordinary distances. Indeed, the distances astronomers measure are so vast that they use a set of units unique to astronomy. When measuring distances on the earth, meters and kilometers are convenient units. But in the vast spaces between stars...

Ashes to Ashes Dust to Dust

In the chapters of this book's final section, we will consider questions of time and eternity as they relate to the universe. But as to the solar system, we know that it was born about 4.6 billion years ago, and that it will die when its source of energy (the sun) dies of old age. Just as the specifics of the formation of the solar system depended on the formation of the sun, so its death will be intimately related to the future of our parent star. The evolution of the sun will presumably...

Latecomers Uranus and Neptune

Since ancient times, the inventory of the solar system was clear and seemingly complete a sun and, in addition to Earth, five planets, Mercury, Venus, Mars, Jupiter, and Saturn. Then came along one of those scientific busybodies that the eighteenth century produced in abundance. Johann Daniel Titius, or Tietz 1729-1796 , a Prussian born in what is now Poland, poked his curious nose into everything. He was a physicist, biologist, and astronomer who taught at the University of Wittenberg. It...

The Apollo Missions

The data from the unmanned probes and orbiters was overwhelming in its volume and detail. Some critics continued to argue Why send human beings The manned missions clearly captured public attention, beginning with the Soviet Vostok series 1961-1963, including Vostok 6, which carried the first woman into space, Valentina V. Tereshkova and the U.S. Mercury series 1961-1963 . The Mercury series included two suborbital flights and the first U.S. manned flight in orbit, Friendship 7, commanded by...

Rich Field Telescopes Increasing in Popularity

Worth investigating is a relatively new category of telescope. Ultra compact and reasonably priced, rich-field reflectors are typically handheld with a Newtonian focus. What they have in common is a short-tube design that offers low degrees of magnification but a bright, wide field of view typically a few degrees . They range in price from about 250 to 400 and can weigh as little as 4 or 5 pounds. Highly portable and relatively rugged, these telescopes nevertheless have the disadvantage that,...