The simplest way of watching the stars is with your own two eyes. Long before telescopes or satellites, when the skies were free of city lights, people studied the stars to help tell time, predict the weather, and understand their place in the universe.

What you see when you look at the sky depends a lot on where you’re standing on the Earth. If you’re in the southern hemisphere, for example, in Australia, then maybe you’ve seen a constellation called the Southern Cross. If you’re in a country in the northern hemisphere, such as Canada, then perhaps you’ve spotted the Big Dipper on a cold winter night.

The stars, planets and constellations that we see have special meaning in different cultures. Stories about important life lessons have been passed down for generations, and some are still told today. On a dark, clear night, you can still see the celestial objects that inspired our ancestors-the same ones that give people today a sense of wonder and meaning.

Seeing in the dark

To see the faintest stars possible you have to spend about 15 minutes in the dark. This is called dark adapting. Doing this makes your Read More
The simplest way of watching the stars is with your own two eyes. Long before telescopes or satellites, when the skies were free of city lights, people studied the stars to help tell time, predict the weather, and understand their place in the universe.

What you see when you look at the sky depends a lot on where you’re standing on the Earth. If you’re in the southern hemisphere, for example, in Australia, then maybe you’ve seen a constellation called the Southern Cross. If you’re in a country in the northern hemisphere, such as Canada, then perhaps you’ve spotted the Big Dipper on a cold winter night.

The stars, planets and constellations that we see have special meaning in different cultures. Stories about important life lessons have been passed down for generations, and some are still told today. On a dark, clear night, you can still see the celestial objects that inspired our ancestors-the same ones that give people today a sense of wonder and meaning.

Seeing in the dark

To see the faintest stars possible you have to spend about 15 minutes in the dark. This is called dark adapting. Doing this makes your eyes more sensitive to light. But if a bright light suddenly shines in your eyes, you won’t be able to see faint stars for another 15 minutes or so. In big cities, light pollution makes it hard to see any but the brightest stars.

Looking back in time

When you look at a star, you’re actually seeing it as it appeared in the past. It takes sunlight about eight minutes to reach the Earth, so we see the Sun as it was eight minutes ago. Proxima Centauri, the closest star to the Sun, is 4.3 light-years away, so we see it as it was 4.3 years ago. Galaxies are so distant that we see them as they appeared millions, or even billions of years ago.

© Canadian Heritage Information Network, 2003

As the Earth orbits the Sun, it also spins on its axis, so we spend about half a day facing the Sun and half facing away from it. The Earth's rotation makes everything in the sky appear to rise in the east and set in the west. In reality, the Sun and the stars aren't moving around the Earth. Instead, it's the Earth turning on its axis that creates that impression.

A time exposure photograph centred on Polaris, the northern pole star, or on Sigma Octantis in the south, shows circles of star trails which are dramatic proof that the Earth spins on its axis. Because these stars are located above the North and South Poles (the Earth's axes of rotation), the other celestial objects appear to revolve around them.

The angle at which you see stars rise and set actually depends on where you are on the Earth. For example, if you were standing at the North or South Pole, the stars would never rise or set, they would move in large circles parallel to the horizon. If you were at the equator, all the stars would rise and set vertically. And at in-between latitudes, the stars would rise and set at an angle to the horizon.
As the Earth orbits the Sun, it also spins on its axis, so we spend about half a day facing the Sun and half facing away from it. The Earth's rotation makes everything in the sky appear to rise in the east and set in the west. In reality, the Sun and the stars aren't moving around the Earth. Instead, it's the Earth turning on its axis that creates that impression.

A time exposure photograph centred on Polaris, the northern pole star, or on Sigma Octantis in the south, shows circles of star trails which are dramatic proof that the Earth spins on its axis. Because these stars are located above the North and South Poles (the Earth's axes of rotation), the other celestial objects appear to revolve around them.

The angle at which you see stars rise and set actually depends on where you are on the Earth. For example, if you were standing at the North or South Pole, the stars would never rise or set, they would move in large circles parallel to the horizon. If you were at the equator, all the stars would rise and set vertically. And at in-between latitudes, the stars would rise and set at an angle to the horizon.

© Canadian Heritage Information Network, 2003

Spinning Sky

A time exposure photograph centred on Polaris, the northern pole star, or on Sigma Octantis in the south, shows circles of star trails which are dramatic proof that the Earth spins on its axis. Because these stars are located above the North and South Poles (the Earth's axes of rotation), the other celestial objects appear to revolve around them.

NASA

© NASA


When bright city lights shine into the sky, it’s called light pollution. Light pollution cuts down the number of stars that you can see with the naked eye. Out in the country, far from city lights, you can see about 3 000 stars, but only about 20 or 30 stars are visible from the centre of most big cities.

The disappearing Milky Way

A fifth of the world’s population-more than a billion people-can no longer see the Milky Way. In Europe, that’s half the population; in the USA, 70 per cent. And the problem is growing.

The environment

Light pollution not only stops us from seeing the wonderful universe that we live in, but it wastes energy and costs about $2 billion worldwide each year. The more energy we waste, the more we have to produce. This means damming more rivers, building more nuclear power plants and burning more fossil fuel.

Migrating birds are drawn to floodlit buildings, where they crash and die. Even brief bursts of bright light can make nocturnal frogs stay still for hours. Lighting has been blamed for the falling numbers of some moths, fireflies changing their habits, and trees hanging on to thei Read More
When bright city lights shine into the sky, it’s called light pollution. Light pollution cuts down the number of stars that you can see with the naked eye. Out in the country, far from city lights, you can see about 3 000 stars, but only about 20 or 30 stars are visible from the centre of most big cities.

The disappearing Milky Way

A fifth of the world’s population-more than a billion people-can no longer see the Milky Way. In Europe, that’s half the population; in the USA, 70 per cent. And the problem is growing.

The environment

Light pollution not only stops us from seeing the wonderful universe that we live in, but it wastes energy and costs about $2 billion worldwide each year. The more energy we waste, the more we have to produce. This means damming more rivers, building more nuclear power plants and burning more fossil fuel.

Migrating birds are drawn to floodlit buildings, where they crash and die. Even brief bursts of bright light can make nocturnal frogs stay still for hours. Lighting has been blamed for the falling numbers of some moths, fireflies changing their habits, and trees hanging on to their leaves too long in Autumn.

© Canadian Heritage Information Network, 2003

Some countries are considering laws that enforce better lighting design and technology: ’fully shielded’ lighting fixtures that send the light down, not up, and greater use of low-pressure sodium lamps, whose yellow light astronomers can filter out.

The Italian region of Lombardy has set the standard: the light pollution law it passed in January 2000 is praised as the best one around. It was the result of a public ’outcry’ by 25 000 citizens who signed petitions to demand action against intrusive outdoor lighting.
Some countries are considering laws that enforce better lighting design and technology: ’fully shielded’ lighting fixtures that send the light down, not up, and greater use of low-pressure sodium lamps, whose yellow light astronomers can filter out.

The Italian region of Lombardy has set the standard: the light pollution law it passed in January 2000 is praised as the best one around. It was the result of a public ’outcry’ by 25 000 citizens who signed petitions to demand action against intrusive outdoor lighting.

© Canadian Heritage Information Network, 2003

The Death of Night

Nick Lomb, Curator of Astronomy at Sydney Observatory, talks about light pollution.

Sydney Observatory is in the middle of a large city. That means there are lots of lights. These illuminate the sky and make it difficult to do serious astronomical research here at the Observatory. We can still show plenty of interesting objects to the general public who visit in tens of thousands at Sydney Observatory at night but serious research is difficult. However, its not absolutely necessary to have so much light in a large city. If there are good quality lights that illuminate the streets and illuminate the footpaths for pedestrians then it is possible to cut out a lot of the light that goes up into the sky.

Canadian Heritage Information Network

© Canadian Heritage Information Network, 2003


The death of night

Australian photographer David Malin discusses light pollution

I was born in the north of England and on cold winter nights there you could see the stars high above and as a child I wondered about them. I thought they were fantastic. When I visit England now and go back to where I used to live, at night you can’t see any stars. They’re still there but they’re hidden by the street lights which have appeared in this country lane where I used to live. And that’s a very sad thing because we’ve been inspired by the stars for thousands of generations. The Pyramids are aligned by the stars, stars appear on national flags, the earliest written records we have mention the stars. And we’ve lost it. Suddenly in the last hundred years or so it’s gone. It’s a tragedy really because all the energy that gets projected into the sky, that hides the stars from view, is wasted. There’s no point in trying to illuminate the Moon. We should keep the lights on the streets where they ’re needed.

Canadian Heritage Information Network

© Canadian Heritage Information Network, 2003


The Sombrero

The Sombrero, named after the broad-brimmed Mexican hat it superficially resembles, is probably the most famous galaxy in the sky. The light from this remarkable spiral system is dominated by the billions of old, faint stars that form the vast 'bulge' around its tiny hidden nucleus. Most spirals, including the Milky Way, have clouds of old, faint stars around their nuclei, but in M104 the galaxy's light is dominated by them.

David Malin

© 1990-2002, Anglo-Australian Observatory


Learning Objectives

The learner will:

  • Define light pollution and describe its effects on the environment
  • Describe how our perspective from the Earth affects what we see in the night sky

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