Telescopes

What is the main job of a telescope?

To collect light and focus it to a point so it can be detected.

Q: What are the two main qualities that make one telescope better than another?

• Light-collecting ability

• Image sharpness (resolution)

Why is light-collecting ability important?

Because collecting more light lets us see fainter objects.

What does image sharpness measure?

How close two objects can be and still appear separate.

What are the two ways telescopes focus light?

• Refraction (lenses)

• Reflection (mirrors)

What is a refracting telescope?

A telescope that uses lenses to bend (refract) light.

What physical process causes refraction?

Light changing direction when it passes between materials (air → glass).

Why are large refracting telescopes difficult to build?

• Glass is heavy

• Lenses must be supported only by their edges

• Glass must be optically perfect throughout.

What is a reflecting telescope?

A telescope that uses mirrors to focus light.

Why are reflectors preferred in modern astronomy?

• Mirrors can be supported from behind

• Easier to build very large telescopes.

What determines a telescope’s light-gathering power?

The diameter of the telescope aperture.

What is the aperture of a telescope?

The diameter of the main optical element.

Light-gathering power depends on what mathematical relationship?

Collecting area = πD² / 4.

If you double the diameter of a telescope, how much more light does it collect

Four times more light.

Why does doubling the diameter increase light collection by 4×?

Because light collection depends on area, which scales with D².

How much more light can a large telescope collect compared to the human eye?

About 6 million times more light.

What is resolving power?

The ability to see fine detail or separate two close objects.

In general, what improves resolution in telescopes?

Larger telescopes (larger diameter).

What physical effect limits telescope resolution?

Diffraction of light.

What happens during diffraction?

Light spreads out when passing through an opening, limiting resolution.

How do astronomers measure sizes in the sky?

Using angular measurements.

How many arcminutes are in a degree?

60 arcminutes.

How many arcseconds are in an arcminute?

60 arcseconds.

What does high resolution mean for a telescope?

A smaller angular separation can be distinguished.

Why do stars appear to twinkle?

Because Earth’s atmosphere bends light due to moving pockets of air.

What is seeing in astronomy?

The blurring of images caused by Earth’s atmosphere.

Why do space telescopes have better resolution than ground telescopes?

They avoid atmospheric distortion.

Besides visible light, what can telescopes detect?

Other wavelengths of electromagnetic radiation.

Why are radio telescopes so large?

Radio waves have long wavelengths, requiring large dishes for good resolution

Why do modern telescopes use segmented mirrors?

To build extremely large mirrors using smaller pieces.