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	September 2010 Teachers! Look here for great resources! Canadian Astronomy starts here! Learn more about the night sky!

Frequently Asked Questions

Questions about Astronomers

Questions about the Moon and Planets

Questions about Asteroids and Comets

Questions about Extraterrestrial Life and Planets

Questions about Stars and the Sun

Questions about Galaxies and the Universe

Do you have a question we haven't answered here? Check out Cornell's Ask An Astronomer!

QUESTIONS ABOUT ASTRONOMERS

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. Typical salaries range from $40,000 at the
beginning, to $100,000 at the end. Graduate students are usually
paid $15-20,000 a year.

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. 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
departments 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. These observatories are
owned by governments, or universities. They also use computers
to help understand their measurements of the universe, or to
develop theories 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. 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, unsuccessfully. But it's fun to read
your horoscope, or read everybody else's.

QUESTIONS ABOUT THE MOONS AND PLANETS

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 great 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 a planet; it also shines by the reflected light
of the star, like Earth's moon does. Some planets (like Pluto) are
smaller than some moons.

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 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.

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
orbiting the planet 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 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.

QUESTIONS ABOUT ASTEROIDS AND COMETS

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. 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.

QUESTIONS ABOUT EXTRATERRESTRIAL LIFE AND PLANETS

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. 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. 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.

QUESTIONS ABOUT THE SUN AND STARS

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 - 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, war 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,
canceling 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. Rare, massive 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 quantities of 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 rare, 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.

QUESTIONS ABOUT GALAXIES AND THE UNIVERSE

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 faint light of these stars as a faint band in
the sky, called the Milky Way. Many of these stars are thought to have\par
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 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, billions of 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 between 10 and 15 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.

with files from J.R. Percy (2003), University of Toronto


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