Star Words Glossary

Accelerating expansion Recent observations of very distant supernovae suggest that the expansion of the universe is accelerating that is, the universe is expanding more quickly now than it did in the distant past. accretion The gradual accumulation of mass this 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...

Making Waves

Electromagnetic radiation sounds like dangerous stuff and, in fact, some of it is. But the word radiation need not set off air raid sirens in your head. It just describes the way energy is transmitted from one place to another without the need for a direct physical connection between them. In this book, we use it as a general term to describe any form of light. It is important that radiation can travel without any physical connection, because space is essentially a vacuum that is, much of it is...

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, and it occurs because the photons emitted by our transmitter lose some energy in their escape...

Cores Jets and Lobes A Radio Galaxy Anatomy Lesson

Another kind of active galaxy is called a radio galaxy. Although Seyferts are an active subclass of spiral galaxies, radio galaxies are an active subclass of elliptical galaxies. Radio galaxies come in many types, often classified by their shapes. Some radio sources have emissions only in their nucleus. In others, two narrow streams, or jets, of oppositely directed radio emissions emerge from the galaxy nucleus. The jets in these so-called double radio sources often end in wispy, complex puffs...

Foreword

I was going to be a marine biologist until my parents bought me a telescope when I was in the seventh grade. I took it outside and set it up in my backyard in suburban Fort Worth, Texas. The sky was clear, and the stars were out. One bright star caught my attention. I pointed the small telescope at it to figure out why it was so brilliant. Pointing that little telescope took a bit of work, but I finally centered the bright dot in the finder scope and carefully looked through the main eyepiece....

The Parallax Principle

First, how do we know which of all the stars in the night sky are the nearest to us For that matter, how do we know how far away any stars are You've come a long way in this book, and on this 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 Earth, meters and kilometers are convenient units, but in the vast...

Lets Take a Picture

While we can see Andromeda with our eyes or a modest amateur telescope as a fuzzy patch of light, we require photographic equipment or an electronic CCD camera to make out the kind of detail in a galaxy that we are used to seeing in glossy astronomy magazine pictures. To see sweeping arms and dark bands of dust in other galaxies, we need to collect more light, either by using a larger aperture (a big telescope) or waiting longer (taking a sufficiently exposed conventional or electronic...

The Chemistry of Life

According to those who study high-redshift supernovae, the universe is about 14 billion years old. Earth, like other planetary bodies in the solar system, appears to be about 4.5 billion years old, and the fossil record shows that Earth was not devoid of life for very long, perhaps for only a few hundred million years after it coalesced from the solar nebula. The oldest fossils known on Earth, Precambrian microfossils, are from western Australia and are about 3.5 billion years old. They...

Views from the Voyagers and Galileo

During the 1970s and 1980s, two Voyager space probes gave us unprecedented images of the jovian planets. Voyager 1 visited Jupiter and Saturn, and Voyager 2 added Uranus and Neptune to the list. The Voyager missions also revealed volcanic activity on Io, one of Jupiter's moons. As for Saturn, a new, previously unknown system of rings emerged several thousand ringlets. Ten additional moons were discovered orbiting Uranus, which also revealed the presence of a stronger magnetic field than had...

Ellipticals Stellar Footballs

Elliptical galaxies present a strikingly different appearance from the spirals. When viewed through a telescope, they look a bit dull compared to their flashy spiral cousins. They have no spiral arms nor any discernable bulge or disk structure. Typically, these galaxies appear as nothing more than round or football-shaped collections of stars, with the most intense light concentrated toward the center and becoming fainter and wispier toward the edges. Of course, the orientation of an elliptical...

Life on Mars

Science fiction has long portrayed Mars as home to intelligent life, and the American astronomer Percival Lowell, early in the twentieth century, created a great stir with his theory of Martian canals. Actor-director-writer Orson Welles triggered a nationwide panic with his 1938 radio dramatization of H. G. Wells's War of the Worlds, about a Martian invasion of Earth. People of Earth seemed primed to believe that life might exist on Mars. Given our fascination with the red planet and its...