Looking into Space

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Planet Earth and Beyond Looking into Space From the night sky to telescopes

On a clear, dark night you can see planets and stars in the sky. With a telescope you can see even more.

In this lesson you will learn:

• which planets you can see without a telescope
• what a constellation is, and how different cultures named them
• how a telescope forms an image and magnifies it
• the difference between optical telescopes and radio telescopes
• how lenses, mirrors and metal dishes focus light and radio waves
• about SALT, the Hubble Space Telescope and the SKA
• what makes good conditions for looking into space

There are quick checks along the way. Try each one before you move on.

1. The Night Sky

Planets and stars in the night sky

People can see planets and stars in the night sky, with their eyes alone and no telescope at all.

This is the earliest way of viewing space: simply looking up at the night sky.

Seen without a telescope Mercury, Venus, Mars, Jupiter, Saturn Needs a telescope Neptune

Five planets can be seen without a telescope: Mercury, Venus, Mars, Jupiter and Saturn.

Neptune is too faint to see with your eyes alone. You need a telescope to see it.

Venus is the brightest planet in the night sky.

Planets and stars in the night sky Five planets without a telescope Brightest planet: Venus Neptune needs a telescope

Remember:

• People can see planets and stars in the night sky.
• Five planets can be seen without a telescope: Mercury, Venus, Mars, Jupiter and Saturn.
• Neptune needs a telescope.
• Venus is the brightest planet.

2. Constellations

Constellation a group of stars that forms a pattern in the night sky

Stars can be arranged into visible constellations.

A constellation is a group of stars that forms a pattern in the night sky. Imagine lines joining the stars, like a join-the-dots picture, and the pattern appears.

Stars in the night sky Grouped into a pattern Named by a culture some with a story

Different cultures have identified and named certain constellations.

Some constellations have stories linked to them. The next step shows two examples from ancient Greek stories.

Named in ancient Greek stories Constellation Meaning Orion The hunter Scorpius The scorpion

Two constellations named in ancient Greek stories are:

• Orion, the hunter: it is named after a hunter in ancient Greek stories.
• Scorpius, the scorpion: it is named after a scorpion in ancient Greek stories.

Crux is also called the Southern Cross. On the chart, lines join its stars to show the cross pattern.

Next to it are two bright stars called the Pointers. The brighter of the two Pointers is Alpha Centauri.

Constellation: a pattern of stars Named by different cultures Some have stories Orion, Scorpius, Crux

Remember:

• Stars can be arranged into visible constellations.
• A constellation is a group of stars that forms a pattern in the night sky.
• Different cultures have identified and named certain constellations, and some constellations have stories linked to them.
• Orion (the hunter) and Scorpius (the scorpion) are named in ancient Greek stories. Crux is the Southern Cross.

3. Telescopes

A telescope shows more detail

People can see more details in the sky when they use a telescope.

A telescope even shows objects that are too faint for your eyes alone, such as the planet Neptune.

An object in the sky The telescope forms an image of it The image is magnified it looks bigger

A telescope forms an image of the object and magnifies it, which means it makes it look bigger.

The object in the sky does not change. Only its image looks bigger.

Optical telescopes Receive light . Focus it by refraction (lenses) or reflection (mirrors). Radio telescopes Receive radio waves . Focus them by reflection, typically with a metal receiving dish.

There are different types of telescopes. Two of them are:

• Optical telescopes receive light. They focus it by refraction (using lenses) or by reflection (using mirrors).
• Radio telescopes receive radio waves. They focus them by reflection, typically using a metal receiving dish.

To focus means to bring the light (or the radio waves) together at one point, called the focus.

More detail with a telescope Forms an image and magnifies it Optical telescopes: light Radio telescopes: radio waves

Remember:

• People can see more details in the sky when they use a telescope.
• A telescope forms an image of the object and magnifies it (makes it look bigger).
• There are different types of telescopes: optical telescopes receive light, and radio telescopes receive radio waves.

4. Optical Telescopes

Refraction means that light bends as it passes through a lens.

In the diagram, light from a distant object arrives as parallel rays. Each ray bends as it passes through the lens, and all the rays meet at one point: the focus. You look at the image through the eyepiece.

Reflection means that light bounces off a mirror.

In a telescope that uses reflection, the parallel rays of light bounce off a curved mirror and all meet at one point: the focus.

Southern African Large Telescope (SALT) Type Optical telescope Where Near the small town of Sutherland, in the Northern Cape province of South Africa

SALT, the Southern African Large Telescope, is an optical telescope.

It is near the small town of Sutherland, in the Northern Cape province of South Africa. You will see why this is a good place for a telescope at the end of this lesson.

Hubble Space Telescope Type Optical telescope Where It orbits the Earth, above the air Launched 1990

The Hubble Space Telescope is also an optical telescope, but it is not on the ground.

It orbits the Earth, above the air. It was launched in 1990.

Refraction: light bends through a lens Reflection: light bounces off a mirror SALT: near Sutherland Hubble: orbits the Earth

Remember:

• Optical telescopes receive light and focus it by refraction (using lenses) or by reflection (using mirrors).
• Refraction: light bends as it passes through a lens.
• Reflection: light bounces off a mirror.
• SALT (the Southern African Large Telescope) and the Hubble Space Telescope are optical telescopes.

5. Radio Telescopes

Radio telescopes receive radio waves, not light.

They focus the radio waves by reflection, typically using a metal receiving dish. The radio waves bounce off the curved dish and meet at the focus, where the receiver is.

Square Kilometre Array (SKA) Type Radio telescope: a collection (an array) of dishes Where Its South African part is in the Karoo region Includes MeerKAT, a radio telescope already in the Karoo

The SKA, the Square Kilometre Array, is a radio telescope.

It is not one telescope. It is a collection of telescopes: an array of dishes. Its South African part is in the Karoo region.

The MeerKAT radio telescope, which already exists in the Karoo, forms part of the SKA.

Optical or radio? Optical telescope Radio telescope Receives Light Radio waves Focuses by Refraction (lenses) or reflection (mirrors) Reflection (typically a metal receiving dish) Examples SALT, the Hubble Space Telescope The SKA (including MeerKAT)

Both types of telescope receive something from space and focus it. The difference is what they receive:

• Optical telescopes receive light, and focus it with lenses (refraction) or mirrors (reflection).
• Radio telescopes receive radio waves, and focus them typically with a metal dish (reflection).

Radio telescopes: radio waves Focus by reflection Metal receiving dish SKA: South African part in the Karoo

Remember:

• Radio telescopes receive radio waves and focus them by reflection, typically using a metal receiving dish.
• The SKA (Square Kilometre Array) is a collection of telescopes: an array of dishes.
• Its South African part is in the Karoo, and MeerKAT forms part of it.

6. Viewing Conditions

Good conditions for looking into space are:

• cloudless skies
• limited light pollution: away from city lights
• limited air pollution

Clouds, city lights and air pollution all get in the way of the view.

South Africa: many good places to look into space SALT Near Sutherland, in the Northern Cape SKA Its South African part is in the Karoo

South Africa has many locations that meet these requirements: cloudless skies with limited light pollution and limited air pollution.

That is why South Africa is a good place for telescopes: SALT is near Sutherland in the Northern Cape, and the South African part of the SKA is in the Karoo.

Above the atmosphere No clouds No air pollution No city lights

The Hubble Space Telescope orbits the Earth, above the air.

Above the atmosphere there are no clouds, no air pollution and no city lights in the way.

Cloudless skies Limited light pollution Limited air pollution South Africa has many good locations

Remember:

• Good conditions for looking into space are cloudless skies with limited light pollution (away from city lights) and limited air pollution.
• South Africa has many locations that meet these requirements.
• The Hubble Space Telescope is above the air, where no clouds, air pollution or city lights get in the way.

Planets and stars can be seen in the night sky Constellations: star patterns named by different cultures A telescope forms an image and magnifies it Optical: light. Radio: radio waves Best: cloudless, dark skies with clean air

Looking into Space: full summary

• People can see planets and stars in the night sky. Five planets can be seen without a telescope (Mercury, Venus, Mars, Jupiter and Saturn); Neptune needs a telescope. Venus is the brightest planet.
• A constellation is a group of stars that forms a pattern in the night sky. Different cultures have identified and named certain constellations, and some have stories: Orion (the hunter) and Scorpius (the scorpion) come from ancient Greek stories. Crux is the Southern Cross.
• A telescope shows more detail. It forms an image of the object and magnifies it (makes it look bigger).
• Optical telescopes receive light and focus it by refraction (lenses) or reflection (mirrors). Examples: SALT near Sutherland, and the Hubble Space Telescope.
• Radio telescopes receive radio waves and focus them by reflection, typically with a metal receiving dish. Example: the SKA, whose South African part is in the Karoo and includes MeerKAT.
• Good conditions for looking into space: cloudless skies, limited light pollution and limited air pollution. South Africa has many such locations.

You are ready for the quiz.