ThursdaySeptember 15,

2011

(Telescopes)

The Launch PadThursday, 9/15/11

How do galaxies evolve, and what holds them

together?Young galaxies are messy and random in shape. As they grow older, gravity

forms them into more organized shapes, like spirals or ellipses.

A strong gravity source holds them together, perhaps a massive black

hole at their cores.

The Launch PadThursday, 9/15/11

Which of the following would probably be the farthest from

Earth?A. the MoonB. the SunC. the Andromeda galaxyD. a large galactic cluster

Assignment Currently Open Page Date of Notes on Website Date Issued Date Due

ESS Class Information Sheet N/A N/A 8/24 8/25

Class Procedures and Expectations TBD 8/24 8/24 8/26

Lab - Stretching the Fabric of Space TBD 8/29 8/29 8/30

Quiz 1 TBD 9/6 9/6 9/6

Quiz 2 TBD 9/12 9/12 9/12

Optical (Visible Light) Telescopes

Optical telescopes are made in two basic types:

Refracting telescopes Reflecting telescopes

Refracting Optical TelescopesRefracting telescopes use a lens (called the objective) to bend

(refract) the light to produce an image.Light converges at an area called the focus.

The eyepiece is a second lens used to examine the image directly.

Refracting telescopes have an optical defect called chromatic aberration (color distortion.)

Reflecting Optical TelescopesReflecting telescopes use a concave mirror to

gather the light, and there is no color distortion.Nearly all large telescopes are of this type.

Appearance of a galaxy in the constellation Andromeda using

telescopes of different resolution.

The top picture is not “out of focus”, it’s a

resolving issue, not a focus problem.

Optical Resolution

Deployment of the Hubble Space Telescope in Earth Orbit

Figure 23.17

April 24,

1990

Other Types of TelescopesDetecting Invisible Radiation

Photographic films are used to detect ultraviolet and infrared wavelengths.

Most invisible wavelengths do not penetrate Earth’s atmosphere, so balloons, rockets, and

satellites are used to put the cameras above the atmosphere.

Ultraviolet Telescopes

Infrared Telescopes

Radio Telescopes

Radio wavelength radiation reaches Earth’s surface, so

radio telescopes can be Earth-based.

Radio TelescopesRadio telescopes are “big

dishes” used to gather radio wavelength electromagnetic

radiation.

Radio TelescopesRadio telescopes have to be very large in order to gather

radio waves, which are about 100,000 times longer than

visible radiation waves.They are often made of a wire

mesh, and have rather poor resolution.

Radio telescopes can be wired together into a network called

a “radio interferometer.”

A steerable radio telescope at Green Bank, West Virginia

Figure 23.15 A

Radio TelescopesRadio telescopes have several advantages over optical

telescopes: they are less affected by weather

they are less expensive to build and maintainthey can be used 24 hours a day

they are able to detect material that does not emit visible radiation

and, they can “see” through interstellar dust clouds

Radio Telescope Images