5.6 - Observing the Universe

Optical telescopes

• Telescopes let us see distant objects in space more clearly.
• An optical telescope detects visible light.
• Optical telescopes use refraction and reflection to gather light from a distant object and form an image.

Improving the image

Image quality can be improved in two ways:

1. Increase the aperture - The aperture is the diameter of the objective lens (the large lens where light enters). A larger aperture collects more light, so fainter objects can be seen.
2. Use a higher quality objective lens - This produces a sharper, clearer image.

Observing from above the atmosphere

• Earth's atmosphere absorbs a lot of the electromagnetic radiation coming from space, so some wavelengths never reach telescopes on the ground, as the graph below shows.
• Placing a telescope on a satellite in space avoids the atmosphere entirely.
• Telescopes in space receive radiation that would otherwise be absorbed, giving a clearer view and more accurate measurements of distant astronomical objects.

Light pollution, air pollution and siting

Ground-based telescopes are limited by two main factors:

1. Light pollution - Artificial light from street lamps and buildings makes faint objects hard to see.
2. Air pollution - Pollutants reflect and absorb light coming from space.

Getting the best view from the ground

• Place the telescope on top of a mountain, where there's less atmosphere above it.
• Place it in a dark location far from cities to minimise light pollution.

Observing across the whole spectrum

• Visible light is only one part of the electromagnetic spectrum.
• Different astronomical objects emit and reflect radiation in different parts of the spectrum, and many can't be detected in visible light at all.
• To build a complete picture of the Universe, astronomers use a range of telescopes that cover the entire electromagnetic spectrum.

Telescopes across the spectrum

• The earliest telescopes were all optical telescopes.
• Telescopes have since been developed for every part of the electromagnetic spectrum, revealing details about the Universe that can't be seen in visible light.

Different telescopes reveal different things

• X-ray telescopes - Detect violent, high-temperature events, such as exploding stars.
• Radio telescopes - Detected cosmic microwave background radiation, which helped scientists learn about the origins of the Universe.

How telescopes keep improving

• Larger telescopes give better resolution and gather more light, so fainter and more distant objects can be detected.
• Modern telescopes work alongside computers, which process data to produce sharper images and analyse huge amounts of information continuously.