Telescopes

What is the main purpose of a telescope?

To gather more light than the unaided human eye.

What two things do telescopes improve compared to the human eye?

Brightness and sharpness of images.

What does a refracting telescope use to form an image?

A lens.

What is a major problem with refracting telescopes?

Chromatic aberration and heavy lenses.

What does a reflecting telescope use to form an image?

A mirror.

Why are modern telescopes reflectors instead of refractors?

Mirrors avoid chromatic aberration, are easier to support, and can be made larger.

What is chromatic aberration?

Different wavelengths of light refract by different amounts in a lens.

What device is used instead of photographic film in modern telescopes?

Charge-coupled devices (CCDs).

What are two advantages of CCDs?

High sensitivity to light and ability to measure brightness accurately.

What is spectroscopy used for in astronomy?

To analyze the composition, temperature, and motion of objects.

Why are larger telescopes better?

They gather more light and have better resolution.

How does light-gathering power depend on telescope size?

It is proportional to the square of the mirror’s radius.

What is resolving power?

A telescope’s ability to distinguish two close objects as separate.

What limits the resolution of ground-based optical telescopes?

Earth’s atmosphere.

What causes atmospheric blurring?

Air movement in the atmosphere.

Name two ways astronomers reduce atmospheric effects.

Adaptive optics and placing telescopes in space or on mountaintops.

What is adaptive optics?

A system that adjusts mirrors in real time to correct atmospheric distortion.

What type of telescope is used to detect radio waves?

Radio telescopes.

One advantage of radio astronomy?

Can observe day or night and through clouds.

Why do radio telescopes have poor resolution?

Radio waves have long wavelengths.

What is interferometry?

Combining signals from multiple telescopes to improve resolution.

The resolution of an interferometer equals what?

A telescope with a diameter equal to the distance between dishes.

Why must ultraviolet telescopes be in space?

Earth’s atmosphere absorbs ultraviolet radiation.

What kind of astronomy reveals dust-hidden objects?

Infrared astronomy.

Why are X-rays difficult to focus?

They only reflect at very shallow angles.

Can gamma rays be focused into sharp images?

No, gamma rays cannot be focused.

Why is full-spectrum astronomy important?

Different wavelengths reveal different physical information.

What is the main advantage of space-based telescopes?

No atmospheric distortion or absorption.