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Telescopes

• Astronomers depend on observations to form and test theories.
• Astronomers study objects remotely due to vast distances.
• Astronomers gather radiation from celestial objects but collecting enough is difficult due to distance and faintness.
• Obtaining information from radiation requires specialized tools for measuring brightness, spectra, and positions with high accuracy.

Telescope Types and Operation

• Large telescopes use mirrors to gather enough light for distant galaxies.
• Orbiting observatories avoid atmospheric effects, employing high-speed computers for data analysis.
• Modern telescopes differ greatly from old designs; astronomers use computer stations to operate telescopes remotely or analyze collected data.

Telescope Basics

• Telescopes enable observation of objects not visible to the naked eye.
• Telescopes collect more light than the eye, allowing more stars to be seen.
• Telescopes magnify details, and are also more powerful due to tools that collect light over long periods, revealing faint signals and details.

Light-Gathering Power

• The amount of light hitting the retina determines brightness.
• Astronomers use telescopes with larger collecting areas.
• Larger lenses or mirrors increase light collecting power and image brightness, allowing fainter stars to be seen.

Light Collection and Calculation

• Doubling the radius of a lens or mirror quadruples the light-gathering area.
• The human eye's dark-adapted pupil is about 8mm in diameter.
• Some telescopes have an 8-meter diameter aperture.
• Light-gathering power is proportional to the area of the telescope's objective lens or mirror.

Refractor Telescopes

• Refractor telescopes use lenses to focus light.
• Galileo used a refractor telescope to discover Jupiter's moons and observe features on the Moon.
• The largest refractor telescope is at the Yerkes Observatory in Wisconsin; it has a 102 cm lens and an 18-meter tube.

Refractor Telescope Imperfections

• Lens manufacturing requires high-purity glass.
• Lenses absorb some light, especially ultraviolet, and are heavy which causes image distortion.
• Transparent materials focus different colors at different points, causing colored edges in images (chromatic aberration).
• Chromatic aberration is reduced using lenses with long focal lengths.

Reflector Telescopes

• Modern telescopes often use mirrors (reflectors) instead of lenses (refractors) to avoid chromatic aberration and other lens issues.
• Reflector telescopes collect light with mirrors.
• The mirror is coated with a thin layer of aluminum, is easier to support, needs only one surface polished, and doesn't cause chromatic aberration.
• All large telescopes use concave mirrors.

Reflecting Telescopes Types

• With reflecting telescopes, the observer or camera must be placed in front of the mirror, blocking some light.
• Secondary mirrors are used to direct the light.
• Segmented mirrors are used in telescopes as well, composing many smaller mirrors to focus light that are known as segmented mirrors.
• The largest segmented mirror telescope has a 10.4 meter diameter consisting of 36 individual mirrors.

Resolving Power

• Resolving power depends on the ability differentiate closely spaced objects
• Resolving power is limited by light's wave nature.
• Light also undergoes diffraction while passing through openings, affecting resolution.

Angular Resolution

• The angular resolution of a telescope is limited by the wavelength divided by the telescope diameter.
• The formula is: α = 0.025λ / D, where α is in arcseconds, λ is the wavelength in nanometers, and D is the telescope diameter in centimeters.
• A telescope with a diameter of 125 cm observing at a wavelength of 500 nm has an angular resolution of 0.1 arcseconds.

Interferometers

• Interferometers expand the light-collecting area beyond a single telescope's size and achieve a higher resolution.
• Interferometers combine observations from multiple widely spaced telescopes.
• Incoming light waves from different telescopes interfere.
• Measurements depend of peaks lining up or canceling.
• Multi telescopes can create a much higher data output.
• Interferometers achieve high resolution, but their accuracy depends on the distance between mirrors, not the size.
• Interferometers enable the study of an object.