Phys 100 Astronomy Chapter 5 Review

Visible Light

• The longest wavelength of visible light is approximately 700 nm.
• The shortest wavelength of visible light is approximately 400 nm.
• Violet light has a wavelength of approximately 400 nm.

Electromagnetic Radiation

• Infrared radiation has a longer wavelength than visible light.
• Ultraviolet radiation has a shorter wavelength than visible light.
• Gamma-rays have a shorter wavelength than X-rays.
• Radio waves have a longer wavelength than visible light.

Telescopes

• Astronomers build optical telescopes on top of mountains because there is less air to dim the light and the seeing is better.
• The light-gathering power of a telescope is directly proportional to the diameter of the primary mirror or lens.
• The resolving power of a telescope is a measure of its ability to show fine detail and depends on the diameter of the objective.
• The magnification of a telescope is determined by the focal length of the telescope objective and the eyepiece.

Optical Telescopes

• Ultraviolet radiation from a star will not penetrate Earth's atmosphere and reach the ground.
• CCD stands for Charge-Coupled Device.
• Observations of radio waves from astronomical objects suffer from poorer resolution than visible observations because the wavelength of radio waves is much longer than the wavelengths of visible light.

Radio Telescopes

• Radio telescopes have poor resolving power because radio waves have long wavelengths.
• Radio waves can penetrate the Earth's atmosphere to reach its surface.
• The main reason for positioning many radio telescopes across a large area and combining the signals is to produce higher resolution images.

Space Telescopes

• The Hubble Space Telescope objective mirror is not affected by bad seeing or chromatic aberration.
• The Spitzer Space Telescope orbits very far from Earth because the Earth thermally emits infrared radiation, which the telescope is also constructed to observe.

Refraction and Reflection

• Refraction is the change in direction of a light ray as it passes to a medium of different optical density.
• Chromatic aberration occurs in a refracting telescope when different colors of light do not focus at the same point.
• A reflecting telescope uses a mirror as its objective, while a refracting telescope uses a lens.

Telescope Design

• The main reason for building large optical telescopes on the Earth's surface is to collect as much light as possible from faint objects.
• New telescopes use segmented mirrors, thin mirrors, and active optics to control the shape of the mirror.
• Adaptive optics is a technique that uses a high-speed computer to monitor atmospheric distortion and adjust the optics of a telescope to partially compensate for the seeing.