Asteroids:

Rocks that range in size from microscopic to the size of mountains, most of which orbit the sun somewhere between Mars and Jupiter. They are thought to be the remnants of a planet that never formed. Occasionally, one will be perturbed out of its orbit, and will fall towards the sun; if it passes close enough to the earth to be pulled in, it burns in the atmosphere as a meteor; what's left falls to the ground as a meteorite.

Big Bang:

The universe is about 15-20 billion years old, and is expanding. Originally, all matter and energy in the universe was concentrated in one 'super-mass', that then exploded. This original explosion, called the 'Big Bang', is considered to be the beginning of time. We can see far enough into space (and therefore far enough back in time), to observe the way things were about 12 billion years ago...or almost to the beginning. Also, we can detect left-over energy (as radio waves) from this explosion.

Billion:

1,000,000,000. This number is too large to visualize easily, since nothing in our daily experience is that big, or that numerous. If you could count one number a second, (you can't ...try saying 'eight hundred and seventy-five million, six hundred fifty-four thousand, two hundred and ninety-eight' in one second!), and you counted 20 hours every day(!), it would take you 40 years to count to one billion. And how about this picture...if you had 1 billion sugar cubes, it would take a box almost ten metres long by ten wide by ten high to hold them all.

Black Hole:

A collapsed star that is so dense, nothing can escape its gravitational force, not even light...so it looks black. In actual fact, black holes would be hard to spot except for the radiation that is given off by matter falling into the black hole.

Bussard Ram Jet:

Named after its originator, this idea for a spacecraft that could travel at speeds approaching the speed of light is well described in Larry Niven's 'future history' novels. It uses magnetic fields to collect interstellar gas (mostly hydrogen) and funnel it to a fusion motor.

Comet:

Typically a house-sized or larger ball of ice, dust, and rock, large numbers of these orbit the sun out beyond Pluto. Every once in a while, perturbations in their orbits cause one to fall toward the sun; when it does, the heat warms it up, and gasses boil off. This is the comet 'tail' we see in the sky.

Galaxy:

A large cluster of stars, typically hundreds of billions of them. Galaxies occur in a variety of shapes; the commonest ones are spirals (like our galaxy, the Milky Way), ellipsoids, and irregular shapes.

Generation Ship:

A spacecraft designed to travel between star systems at low (non-relativistic) speeds, resulting in trips lasting tens of thousands of years. It is a self-contained ecosystem; many generations of inhabitants live out their lives during the voyage.

Globular Cluster:

A smaller cluster of stars (hundreds of thousands) that occurs inside a galaxy.

Light Sail:

A sail hundreds of kilometres wide which, when attached to a spacecraft, allows it to be pushed and accelerated by light pressure from the sun, or a powerful, stationary laser. Substantial speeds can be obtained over time; despite the fact that light pressure at large distances from a star is tiny, the force is continuous. After several years, speeds are respectable.

Neutron Star:

The remaining tiny core of a star larger than the sun, that used up all its fuel and exploded. What is left is so compact and dense that, although mountain-sized, it may outweigh our sun. The matter it's made from has been compressed so tightly that protons and electrons are forced together...which results in neutrons. A neutron star can be thought of as just one giant neutron!

Nuclear Fusion:

This is the process by which atoms of one substance are forced together by high heat and pressure, to create atoms of another substance. (Actually, it's the nuclei of these atoms which are being forced together.) When they combine, large amounts of heat and other energy are given off. Typically in most stars like our sun, the atoms being 'fused' are hydrogen atoms (nuclei), which become helium. In larger, hotter stars, other atoms may be fusing as well, such as helium (combining to form carbon), or even heavier elements. Some stars are hot enough to force combinations of nuclei to form iron! Eventually, all these heavier elements made by the star are scattered through space when the star explodes as a supernova. In fact, it was such stars that lived and died very early in the history of the universe that 'seeded' space with all the elements that eventually went into the formation of our solar system. Every element in your body heavier than hydrogen or helium (like carbon, or potassium, or sodium) was created in a supernova long ago!

Pulsar:

A rotating neutron star that gives off regular 'pulses' of energy, like a lighthouse.We see or hear these pulses in our telescopes as very regular signals. When these were first discovered, astronomers were sure the precisely periodic signals they were hearing had to be a message from another world! No such luck!

Radio Telescope:

Ordinary telescopes collect light waves; a radio telescope collects radio waves. It is much like a satellite TV dish, except it has to be much bigger because the radio signals from space it collects can be very faint. Most objects in space...stars, galaxies, black holes, some planets... emit radio waves as well as waves of other sorts (including visible light.) You can listen to radio waves from space on your own radio telescope! Any radio, when tuned between stations, gives off a hissing noise...this contains signals from the sun and Jupiter!

Red Dwarf:

Typically, either a star which has used up all its fuel and is cooling off...or a very small star that never got very hot in the first place. (Jupiter is almost big enough to have become a dwarf star). In either case, these are the longest-lived stellar objects. Hot stars burn fast and die quickly (a few million years); our sun is an average yellow star with a lifetime of 10 billion years; red dwarves may live for hundreds of billions of years!

Red Giant

Very large stars (much larger than the sun) will be extremely hot in their cores, but their outer layers are cool by comparison, and appear red. Such large stars are either 'giants' or 'supergiants', depending on their size relative to the sun.

Relativity

This is the branch of physics dealing with objects that travel at speeds approaching the speed of light (300,000 km per second). Such objects will gain mass, while experiencing a contraction in length (in the direction of motion) and a contraction of elapsed time. As a simple example, if you left earth travelling at near the speed of light, you would, while moving, become wafer-thin, weigh 10,000 kg, ...and when you returned from your journey 1 year later, you would be only one month older! Strange as these effects seem, they have been proven true. We can actually observe, with instruments, tiny particles from the sun arriving at earth, with masses higher than normal. Their lifetimes (before they disintegrate due to nuclear decay) are longer than they should be, because time is running slower for them.

Science Fiction:

This is the branch of literature that deals with the effects of future technologies on society. In particular, 'hard' science fiction strives to make realistic assumptions about the future, and attempts to describe how people will adapt to that particular future. This genre of fiction (like most others) contains many poor examples...bad writing, improbable settings, unimaginative ideas...in fact, 90% of it is crap! (Sturgeon's Law says that 90% of everything is crap. Think about it!). For a sampling of what good science fiction is, see our Resources page.

S.E.T.I.: The search for extra-terrestrial intelligence, using radio and light telescopes. It has been underway sporadically for 2-3 decades. Visit our Links page for current project information.

Space:

Space is mostly empty, but it's not quite a perfect vacuum. Electromagnetic waves (light, radio, x-rays, gamma rays...) are passing through it from all over. There are also a few hydrogen atoms in every cubic centimetre of space...not very much, but enough to detect from earth. Our solar system of nine planets and the sun is just about all space. It's like an orange (the sun) at the 50-yard line in the center of a football stadium, with Pluto a sand grain way up in the furthest bleachers. (The nearest star would be another orange 2000 km away, with nothing in between but 'space'!)

The Electromagnetic Spectrum: Visible light is one form of radiation. It is composed of waves that travel at 300,000 km per second. Other examples are waves that are very long (radio), and waves that are very short (x-rays). Visible light has a wavelength that our eyes are sensitive to, so we can see it. So we can 'see' a star. But stars and other objects in space also radiate waves with other wavelengths. We can build receivers to detect the radio waves they give off, and other devices to detect their emitted x-rays.

Star: A star is a large ball of gas, mostly hydrogen and helium, which burns by nuclear fusion. Larger, hotter stars may also contain shells of heavier elements that they have produced by fusion.

Supernova:

This is the explosion of a star that was much more massive than the sun. When it runs out of fuel, the pressure of radiation from its center ceases, and the star collapses in on itself (due to the force of gravity). As the cooler outer layers hit the incredibly hotter inner ones, the star explodes, spewing matter out into space, and giving off stupendously large amounts of light and other radiation. Supernovas shine so brightly that a single exploding star can outshine the entire galaxy that contains it. In the process of exploding, the star wipes out any solar system of planets it might have had, and the radiation may even have effects on living things on planets of nearby stars. It is suggested that the Star of Bethlehem was a supernova...one was recorded by Chinese astronomers at about the time of Jesus' birth. Of course, the actual explosion took place about 30.000 years before that...that's how long the light took to get here. Supernovas often leave behind a remnant, which may be a pulsar, or a black hole.

White Dwarf: This is the remaining core of a sun-sized star that has exploded. It is very dense...a handful of white dwarf matter would weigh tons.

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