Telescopes Mr. Hibbetts Special thanks to Dr. Dan Bruton, Astronomy and Physics SFA

Telescope Optics Lenses Lenses Mirrors Mirrors

Refraction... …is the bending of light rays upon passing from one transparent medium to another. …is the bending of light rays upon passing from one transparent medium to another. Convex and concave lenses refract light. Convex and concave lenses refract light.

Reflection... …is the rebounding of light rays off a smooth surface (diffuse or specular). …is the rebounding of light rays off a smooth surface (diffuse or specular). Convex and concave mirrors reflect light. Convex and concave mirrors reflect light.

Convex – bending or curving outward Convex – bending or curving outward Concave – bending or curving inward Concave – bending or curving inward

Focal Point Focal Point the place where light rays converge to a point the place where light rays converge to a point Focal Length Focal Length the distance from a curved mirror or lens to its focus the distance from a curved mirror or lens to its focus

Types of Telescopes Refracting Telescope Refracting Telescope Reflecting Telescope Reflecting Telescope Cassegrain Telescope Cassegrain Telescope

Refracting Telescope (Galilean) Refracting Telescope (Galilean) objective lens objective lens Eyepiece lens Eyepiece lens

Typical Small Refractor

Reflecting Telescope (Newtonian) Reflecting Telescope (Newtonian) a concave primary mirror a concave primary mirror flat secondary mirror flat secondary mirror eyepiece eyepiece

6-inch Newtonian Telescopes

Earl of Rosse’s Leviathan

Cassegrain Telescope Cassegrain Telescope a concave primary mirror a concave primary mirror a convex secondary mirror a convex secondary mirror eyepiece lens eyepiece lens

SFA Observatory

Cassegrain Telescopes 41” Telescope 18” Telescope

10-inch Schmidt-Cassegrain

Multiple Mirror Telescope

Types of Telescopes What are the 3 types of Telescopes? What are the 3 types of Telescopes?

Why use a telescope? Brighten Brighten Magnify Magnify Resolve Resolve

Light Gather Power HighLow Resolution HighLow Magnification HighLow

Telescopes Brighten Light-Gathering Power - cross sectional area of the telescope tube Light-Gathering Power - cross sectional area of the telescope tube

Light Gathering Power 10.7 cm camera 15.2 cm camera

Telescopes Magnify Magnification - the number of times larger an object appears through a telescope than as seen by the naked eye Magnification - the number of times larger an object appears through a telescope than as seen by the naked eye

Telescopes Resolve Angular Resolution - measure of the clarity of images Angular Resolution - measure of the clarity of images Telescope with larger diameters are able to resolve smaller objects. Telescope with larger diameters are able to resolve smaller objects.

Resolution

What makes a telescope great? Light Gathering Power Light Gathering Power Large Diameter Large Diameter Magnification Magnification Long focal length for the primary lens or mirror Long focal length for the primary lens or mirror Resolving Power Resolving Power Large diameter Large diameter Quality Lenses / Mirrors Quality Lenses / Mirrors

Why use a telescope? Brighten Brighten Magnify Magnify Resolve Resolve

On Earth, there are two major types of telescopes used: On Earth, there are two major types of telescopes used: Common Optical Telescopes Common Optical Telescopes Radio Telescopes Radio Telescopes The Earth’s atmosphere is mostly transparent for visible light and radio waves. The Earth’s atmosphere is mostly transparent for visible light and radio waves. Earth’s Atmosphere

The Hubble Space Telescope...  …is the largest telescope in space. ...is 30 times more sensitive than ground based telescope. ...orbits the Earth every 95 minutes.  …gives high resolution images because it does not suffer from the effects of atmospheric turbulence.

M100

Cat’s Eye Nebula

Hubble Deep Field

Kepler Telescope Launched in March 2009 Launched in March 2009 Mission is to find Earth-like planets around other stars Mission is to find Earth-like planets around other stars Has the most resolute camera every constructed Has the most resolute camera every constructed Has confirmed hundreds planets and found over 2,300 candidates Has confirmed hundreds planets and found over 2,300 candidates Mission officially ended in August 2013 after two motors failed Mission officially ended in August 2013 after two motors failed

Chandra and Spitzer Other important NASA telescopes Other important NASA telescopes Focus on X-Ray / Gamma Ray images Focus on X-Ray / Gamma Ray images

Observing Problems What are some problems that prevent good telescope viewing? What are some problems that prevent good telescope viewing?

Observing Problems Bad Weather Bad Weather Light Pollution Light Pollution Dispersion Dispersion Scintillation Scintillation a.k.a. “bad seeing” a.k.a. “bad seeing” This effect can be reduced with adaptive optics. This effect can be reduced with adaptive optics.

Why do stars twinkle? Stars twinkle due to turbulence in the Earth’s atmosphere. Stars twinkle due to turbulence in the Earth’s atmosphere. Turbulence - hot air rising and cool air falling Turbulence - hot air rising and cool air falling

Seeing is the measure of the steadiness of an object in the Earth’s atmosphere during astronomical observations. Seeing is the measure of the steadiness of an object in the Earth’s atmosphere during astronomical observations. Adaptive Optics allows astronomers to correct for atmospheric distortions in images. Adaptive Optics allows astronomers to correct for atmospheric distortions in images.

Mount Wilson Observatory

The 100” Telescope

Writing Assignment Imagine you are explaining the telescopes you just demoed to a friend or family member. Explain how they enhanced your vision and any interesting things you noticed. Imagine you are explaining the telescopes you just demoed to a friend or family member. Explain how they enhanced your vision and any interesting things you noticed. Which optic device did you find to be the most useful and like the most? Explain your reasons why. Which optic device did you find to be the most useful and like the most? Explain your reasons why.