Frequently Asked Questions

Here are some topics which grade 6 students frequenty ask about, based on my many visits to classrooms. Note that they are quite different from the topics which appear on the curriculum! - John Percy


Q. What do astronomers do?

A. Astronomers are scientists who study the universe. Professional astronomers are highly trained, and are paid for their work. Their training consists of four years of study of math, physics, and astronomy as an "undergraduate" in university, followed by four years of "graduate" study of astronomy, after which they receive a PhD (doctorate) degree. They may work in a university, or a government research laboratory. Some are "theoreticians" who develop theories, or computer simulations; others are "observers" who use telescopes on the ground, or in space. Typical salaries range from $50,000 at the beginning, to $100,000 at retirement. Graduate students are usually paid $15-20,000 a year during their training.

Q. Have Canadian astronomers ever "discovered anything"?

A. Canadian astronomers have discovered the first example of a black hole in space, and the brightest supernova in 400 years. They have discovered comets and asteroids. But much of science is developing and testing theories of how planets, stars, galaxies and the universe are born, live, and die, and Canadian astronomers have made important contributions to this work,, too. The "media" tend to emphasize specific discoveries, but science progresses in a more systematic, less spectacular way.

Q. Where do astronomers work?

A. Most astronomers work in universities, or in government research institutes like the National Research Council. They do their work at observatories with telescopes, such as the Canada-France- Hawaii telescope on Mauna Kea in Hawaii, or the Dominion Radio Astrophysical Observatory in Penticton. These observatories are owned by governments, or universities. They also use computers to help understand their measurements of the universe, or to develop theories and simulations about how planets, stars, galaxies, and the universe "work".

Q. What are "amateur astronomers"?

A. Amateur astronomers are people who do astronomy research or education as a hobby. Very few have university training in astronomy, but they are constantly learning, and many of them have training in other branches of science. They may use their own telescope, in their backyards, to help professional astronomers study planets and stars. Some amateur astronomers discover asteroids, comets, and supernovas. Most amateur astronomers just do astronomy for the fun of it. Anyone can be an amateur astronomer - even you!

Q. Why do people become professional or amateur astronomers?

A. Because astronomy is one of the most interesting and exciting sciences to do, or to teach - either as a career or as a hobby.

Q. What is astrology?

A. Astrology is the belief that the positions of the sun, moon, and planets, at your birth and at present, have some influence on your life and fate. Astrology has no scientific basis; its predictions have been tested many times, and they don't pass the test. But it's fun to read your horoscope, or read everybody else's.


Q. What is "weightlessness"?

A. "Weight" is the pull of gravity on something, your body for instance. The earth's gravity becomes weaker as you move away from it, but it is never zero. An astronaut is not "weightless" because there is no gravity in space; the gravity in near-earth space is almost as large as gravity on the surface of the earth. Astronauts are "weightless" because they are falling to earth as they orbit around it, so there is nothing pushing upward on their feet.

Q. What's it like in space?

A. Aside from feeling "weightless", you are in a hostile environment with no atmosphere, and it is not easy to get back to earth. So you had better make sure that your life-support systems work!

Q. What is a planet? What is the difference between a planet and a moon?

A. A planet is an object which orbits around a star; it does not produce its own light, but it shines by the reflected light of its star. A moon is an object which orbits around a planet; it shines by the reflected light of it's star, like Earth's moon does. Some planets (like Pluto) are smaller than some moons (like ours).

Q. Why does the moon look so large when it is near the horizon?

A. This is called "the moon illusion", and is an optical illusion. You can tell that it is an illusion by measuring the apparent size of the moon by holding an Aspirin at arm's length; it will exactly cover the moon, whether the moon is near the horizon, or high in the sky.

Q. What is a "blue moon"?

A. This expression has come to mean "the second full moon in a month". Occasionally, two full moons occur in the same month; there is no scientific importance to this.

Q. What are moon rocks like?

A. They are very similar to earth rocks. In fact, the moon's material was once part of the earth. The moon has not been geologically "active" for about 3 billion years.

Q. Is there a "face" on Mars? What is it?

A. Among the thousands of photographs taken by the Mars Viking Orbiter in the 1970's, there was one which showed a feature which looked a bit like a face. On better photographs taken in the 1990's, it turned out to be an ordinary hill which looked slightly like a face. There is a much better face of Miss Piggy on Venus!

Q. What are Saturn's rings, and could you walk on them?

A. Saturn's rings are made of millions of chunks of ice and rock, which orbit the planet above its equator. Most of these chunks are small, but some are as big as you, or even bigger. But their gravity would be very weak, so you could not stand on them. If you were in the rings in a spacecraft or spacesuit, you could "float" from one chunk to another.

Q. Is Pluto a planet?

A. Pluto was the ninth large object discovered orbiting the sun. It is the smallest of the nine planets. There are thousands of even smaller objects orbiting the sun - asteroids and comets. Pluto could be called a large asteroid or comet but, for historical reasons, most astronomers prefer to call it a planet.

Q. Is Pluto always the ninth planet?

A. No. For about 30 years of its 250-year orbit around the sun, Pluto is closer to the sun than Neptune.

Q. Is there a tenth planet - "Planet X"?

A. There are thousands of asteroids and comets orbiting the sun, but they are all much smaller than Pluto, so we do not call them planets. There does not appear to be any other large planet beyond Pluto.


Q. What are asteroids and comets?

A. Asteroids are rocky objects which orbit the sun mostly between the orbits of Mars and Jupiter. The largest is 1000 km across, but most are 1-10 km across, or smaller. Comets are icy objects which orbit the sun mostly outside the orbit of Pluto. The largest is 100 km across, but most are 1-10 km across, or smaller.

Q. Are asteroids made from a planet which exploded?

A. No, asteroids appear to be the remains of a planet which never formed. When the solar system formed, 4.5 billion years ago, the other planets formed from chunks of material which stuck together. It appears that Jupiter's gravity prevented a planet from forming in the space between Mars' and Jupiter's orbit.

Q. Why do comets have tails?

A. When a comet comes near the sun, some of the ice evaporates to form a gas. The sun's light and wind pushes this gas away, forming a tail. The tail always points away from the sun, no matter which way the comet is going.

Q. Do asteroids and comets ever hit the earth?

A. Yes. Bits of dust from asteroids and comets encounter the earth all the time. When they flash through the atmosphere, we see a "meteor" or "shooting star". Larger chunks of asteroids may fall to earth, and we call them "meteorites". If they are very large, they may make a "crater" or hole in the ground. There are dozens of impact craters in Canada. Very large asteroids and comets hit the earth every 10-100 million years, and may destroy much of the life on earth. Scientists believe that an impact, 65 million years ago, caused the extinction of many species on earth, including dinosaurs.

Q. How much warning would we have, and what could we do?

A. Since astronomers are discovering and cataloguing most large asteroids and comets, we would probably have many years warning - or more. It is possible that we could then use some kind of missile or explosive to change the orbit of the object, but we would have to be very careful in doing that.


Q. Is there life on any of the other planets in the solar system?

A. Astronomers have not found life on any other planet in the solar system. Billions of years ago, Mars was habitable, and simple life may have existed there. But there is no sign of fossil life in any of the Mars rocks which have been studied. It is also possible that simple life exists beneath the icy crust of Europa - one of the moons of Jupiter. Astronomers believe that there is a deep ocean beneath the icy crust, and we know that there are simple life forms around the deep ocean "vents" on earth.

Q. Are UFO's and "flying saucers" real?

A. A UFO is an unidentified object in the sky. Many natural and man-made objects may be "unidentified" because the person who sees them does not know what they are, but there is no evidence that any UFO's are alien spacecraft or "flying saucers".

Q. Could life exist anywhere else in the universe?

A. Yes, it could. There are hundreds of billions of stars in our Milky Way galaxy, and many of them have planets. These stars and planets are made of the same stuff as our solar system. Many of the planets may be habitable, and life may have developed on some of them. Since many of the stars and planets are much older than the sun and earth, life could have become very advanced.

Q. Are there other planets in the universe? How many?

A. Astronomers have recently discovered planets around many other stars like the sun. They are about the size of Jupiter. Some have orbits which are different from Jupiter's: they orbit close to their star, or they move in orbits which come close to their star, and then move further away. There may be billions of other planets in our Milky Way galaxy. We cannot yet detect planets as small as the Earth, around other stars, but there probably are earthlike planets around other stars, and some of them would be habitable. There might even be Earth-like satellites, orbiting around some of the newly-discovered "extra-solar planets".

Q. Can anything travel faster than light?

A. Only light travels at light-speed - 300,000 kilometers per second. A typical spacecraft travels at 10 km/s, so light travels thousands of times faster. Nothing can travel faster than light. Because light travels at a finite speed of 300,000 km/s, we see the moon as it was a second ago; we see the sun as it was 8 minutes ago; we see the stars as they were years, or thousands of years ago; we see the nearest galaxy (M31 - the Andromeda Galaxy) as it was 2,000,000 years ago; and we see the edge of the universe as it was 10 billion years ago. Astronomers can look backward in time!

Q. What is a "light year"?

A. It is the distance which light travels in a year, at 300,000 km/s. That works out to about 10 million, million km. A light year is NOT a unit of time.

Q. Can we travel to other planets, around other stars?

A. Right now, our spacecraft travel at only 10 km/sec (36,000 km/h) so it would take tens of thousands of years to reach even the nearest star. And it would be very difficult and expensive. Perhaps in hundreds of years, we can develop faster ways to travel.

Q. What is a "wormhole"?

A. A wormhole is an imaginary passage through space and time. There is no evidence that wormholes exist, but some science fiction writers imagine that they could be used as a short-cut through space and time.

Q. Can we communicate with life on planets around other stars?

A. Yes. Using present-day radio technology, we could send and receive radio messages from civilizations, like us, on planets around other stars in our Milky Way galaxy. Our radio, TV, and radar transmissions could be detected by civilizations around nearby stars.

Q. Is science fiction a useful way to predict the future?

A. Some science fiction writers have thought very carefully about the future, and their stories are very useful for thinking about future trends. Other science fiction (often called "fantasy") has very little scientific value.


Q. What are stars made of?

A. About three-quarters hydrogen, one-quarter helium, and a very small amount of the other chemical elements.

Q. Why do astronomers study the stars?

A. It helps us to understand how our sun was born, how and why it "shines", and how and why it will die. It also helps us to understand how the universe - and everything in it - was born, lives, and dies.

Q. How was the sun born, how does it live, and how will it die?

A. The sun was born from a cloud of gas and dust called a nebula - probably with hundreds of other stars - about 4,500,000,000 years ago. It's "littermates" have long since dispersed. The sun shines by converting hydrogen into helium in its core, in a process called "thermonuclear fusion". In about 5,000,000,000 years, the sun will start to run out of energy, and will swell up into a red giant. It will engulf the orbits of Mercury, Venus, Earth, and perhaps Mars. Then the sun will run out of energy. Its outer layers will drift into space. Its core will slowly shrink to become a white dwarf - a million times denser than water. The white dwarf will slowly cool, over billions of years. The sun will not explode, and will not become a black hole. Several nearby stars have white dwarfs orbiting around them.

Q. What will happen to the earth when the sun dies?

A. Five billion years from now, the sun will engulf the earth, and the earth will "fry". Then the sun will shrink to become a white dwarf, and the earth will "freeze". But there are many other problems which the earth must solve before then - overpopulation, pollution etc.

Q. What is a constellation?

A. A constellation is a pattern of stars in the same direction in the sky. The stars in the constellations may be at vastly different distances, but they appear to be in the same direction. Different civilizations have adopted different star patterns as part of their mythology and culture; constellations have no scientific significance. In "western" astronomy, there are 88 constellations; the same as the number of keys on a piano. Other cultures have other constellations which are related to their religion, mythology, or environment.

Q. How many stars can I see?

A. Of the 400 billion stars in our Milky Way galaxy, you may be able to see a few dozen from the city, a few hundred from the suburbs, and a few thousand from the very darkest, clearest place on earth. With binoculars or a telescope, you can see more.

Q. Why do stars twinkle?

A. Because of the disturbing effect of air currents in the earth's atmosphere. Planets appear slightly larger, and light from different parts of their surface comes through different parts of the atmosphere, cancelling out most of the shimmering effect.

Q. Can I photograph the stars?

A. Yes, if you have a camera with a time exposure, fast film, and a tripod. Point your camera at the sky (avoid nearby lights, if possible), and try exposures of 8, 16, 32, and 64 seconds - longer if you have a dark site.

Q. How far away are the stars?

A. The nearest star is about 5 light years away (about 40 million, million kilometers). Other stars that we see are hundreds, or thousands of light years away,

Q. If the stars are so far away, we see them as they were many years ago. Is it possible that they are no longer there?

A. This is unlikely, because the stars have lifetimes of millions, or billions of years, and they do not change much - even in thousands of years.

Q. What is the brightest star?

A. The sun is the brightest star, of course, but Sirius is the brightest star in the night sky. The North Star is not the brightest star; its brightness is just average.

Q. What is a nebula?

A. A nebula is a large cloud of gas and dust in space. Stars may be born in a nebula, if there is something to start the gas and dust contracting.

Q. What is a supernova? Will the sun ever explode as a supernova?

A. Massive stars and some other rare kinds of stars explode at the end of their lives, when they run out of energy. That is because there is no longer any internal force to prevent them from collapsing under their own weight. Their cores collapse, releasing vast amounts of gravitational energy which blows the star apart in a "supernova explosion". Betelgeuse, in Orion, is a star which may explode as a supernova. There are also lesser explosions called "novae" which occur in "close binary stars" - rare stars which have a companion star in close orbit around them. The sun will not explode as a supernova or nova.

Q. What is a "black hole"?

A. Very rarely, very massive stars collapse under their own weight, and crush their cores into "black holes" - objects so dense that nothing - not even light - can escape. There are only a handful of black holes in our Milky Way galaxy, and the nearest is thousands of light years away. These black holes are "visible" because they have normal stars orbiting around them. The existence, and the mass, of the black hole can be deduced from the motion of the normal star. A small amount of material from the atmosphere of the normal star can fall into the black hole. Before it does, it gets very hot, and produces X-rays. Black holes can therefore be detected by X-ray telescopes in space. The material of the black hole, and any additional material which falls into it, becomes very dense. Astronomers do not know its exact state. The black hole can exist almost forever. It will not explode, or change into something else, or go somewhere else.


Q. What is the Milky Way Galaxy?

A. The sun is one of 400 billion stars in our galaxy - the Milky Way galaxy. We see the combined light of these stars as a faint band in the sky, called the Milky Way. Many of these stars are thought to have planets, so there may be billions of other planets in the Milky Way galaxy. The sun orbits the centre of the Milky Way galaxy, 30,000 light-years away, every 200,000,000 years.

Q. Are there other galaxies in space? How many?

A. We can see a hundred billion galaxies in space, each with hundreds of billions of stars. The nearest other large galaxy to our own Milky Way galaxy is called "M31" (because it was #31 in a catalogue which was compiled by the French astronomer Charles Messier). It is also called the Andromeda Galaxy, because it is in the direction of the constellation Andromeda.

Q. What is the universe?

A. The universe consists of hundreds of billions of galaxies - everything that exists.

Q. Is the universe expanding? How do we know?

A. Yes, the universe of galaxies is expanding - it is getting bigger. We know this because the waves of light from distant galaxies are "stretched" as the galaxies move away. Astronomers can detect and study this with special instruments called spectrographs on their telescopes. Most astronomers believe that the universe will expand forever; important new research on this topic is constantly being done.

Q. What is the "big bang"?

A. Astronomers believe that the universe began in a "big bang", about 15 billion years ago, and that this produced the expansion. The universe expanded from a state of very high density and temperature. The "big bang theory" is supported by several pieces of evidence; astronomers can observe the radiation and the chemical elements which were created in the "big bang".

Q. Does the universe have an "edge"?

A. When we look outward in the universe, we look backward in time. At the limit of our vision, we encounter a time, ten billion years ago, when the universe was opaque or cloudy. We cannot see out (or back in time) any further.

Q. How do astronomers know the age of the universe?

A. The age can be calculated from the speed of the expansion of the universe, and from its size. It can also be calculated from the age of the oldest stars, and from the age of the radioactive chemical elements. Although the calculations differ slightly, all of them suggest that the universe is about 14 billion years old.

Q. What is beyond the universe?

A. Since we cannot see beyond the edge of the universe, we cannot tell whether there are other universes beyond ours, or whether ours is all there is.

Q. What came before the big bang?

A. Since we cannot see the universe as it was before the big bang, we cannot tell what (if anything) existed then. But there are some theories which suggest that our universe came into being within a previously-existing universe.