Astronomical Instruments

Question 1

Explain the three main components all modern systems used to observe celestial objects have

Answer 1

• Telescope - a light bucket for collecting photons (the bigger, the better)
• An instrument that somehow “processes” the light. Examples: photometric filters, spectrometer
• A detector. Example: a CCD

Question 2

What are The most important functions of a telescope

Answer 2

1. To collect the faint light from an astronomical source and
2. To focus all the light into a point or an image

Question 3

Explain telescopes

Answer 3

• Bigger telescopes can detect fainter (= more distant, usually) object
• Collect visible radiation use a lens or mirror to gather the light
• Light-gathering power is proportional to the area of the aperture
• Have mirrors or lenses, we can compare their light-gathering power by comparing
  the apertures, or diameters, of the opening through which light travels or reflects

Question 4

Explain lenses in telescoped fully

Answer 4

• Lens is a transparent piece of material that bends behind the lens is called the focal length of the lens the rays of light passing through it. If the light rays are parallel as they enter, the lens brings them together in one place to form an image
• If the curvatures of the lens surfaces are just right, all parallel rays of light are bent, or refracted, in such a way that they converge toward a point, called the focus of the lens

Question 5

Explain eyepiece

Answer 5

• To view the image formed by the lens in a telescope
• Focuses the image at a distance that is either directly viewable by a human or at a convenient place for a detector.
• Using different eyepieces, we can change the magnification (or size) of the image and also redirect the light to a more accessible location

Question 6

Explain Chromatic aberration

Answer 6

Each wavelength of light focusses at a slightly different point, resulting in a blurry image. Only refracting telescopes suffer from this effect

Question 7

Explain refracting telescopes

Answer 7

• Consists of a long tube with a convex lens at one end and an eye piece at the other.
• Galileo’s telescopes were refractors.
• Problem: light must pass through the lens.
• The lens (which can be big) must therefore be made without flaws (perfect shape)

Question 8

Explain reflecting telescopes

Answer 8

• Doesn’t use a lens, but rather a concave mirror at its base
• The light enters through the upper open end of the telescope, and is reflected by the mirror to a point near the
  top of the tube (prime focus).
• A detector can be placed at the prime focus.
• Alternatively, a secondary mirror can be used to redirect the light to a point that is more easily accessible

Question 9

Explain spherical aberration

Answer 9

• A spherical lens does not focus its light to a single point.
• Results in a blurry image.
• The problem is fixed by using a parabolic primary mirror