Light and Telescopes

A Telescope is a tool used to gather light from objects in the universe

There are two different types of telescopes

• A refracting telescope uses a glass lens to concentrate incoming light

• A reflecting telescope uses mirrors to concentrate incoming starlight

Three main functions of a telescope

Most important!!• Gather More Light – (bigger = better) making

objects appear brighterfollowed by• to see fine detail

(called resolution)

and least important,• magnify

magnification = (objective lens focal length / eyepiece lens focal length)

A larger objective (lens or mirror)

provides a brighter (not

bigger) image

If you pass white light through a prism, it separates into its component colors.

ROY G B I V

spectrum

long wavelengths

short wavelengths

But visible light is only one type of electromagnetic

radiation (light) emitted by stars

Astronomers are interested in the entire spectrum of Light!

Consider This Class as Seen in Different Wavelengths of Light!

Consider Orion as Seen in Different Wavelengths of Light!

Observations at other wavelengths are revealing previously invisible sights

UV

Ordinary visible

infrared

Map of Orion region

Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds

http://oposite.stsci.edu/pubinfo/pr/97/13/A.html

Sun as seen in visible light from Earth and from space in X-rays by satellites

http://solar.physics.montana.edu/tslater/real-time/

Radio telescopes

The Very Large Array (VLA) in New Mexico

‘Twinkle, twinkle, little star’

QuickTime™ and aTIFF (LZW) decompressor

are needed to see this picture.

Atmospheric seeing

How can we improve the image quality?

1. Bigger telescope mirror2. Location, location location! (mountain tops, space)3. Adaptive optics

The planet Uranus imaged in the infrared

Earth’s atmosphere refracts light: images are blurry!

Image of stars taken with a telescope on the Earth’s surface

Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere

The Hubble Space Telescope is in space for 2 reasons:

• refraction (bending of optical starlight)

• absorption (of near ultraviolet and infrared)

visible Near infrared

Some EM radiation is absorbed by Earth’s atmosphere.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Tutorial: Telescopes and Earth’s Atmosphere pg. 43

• Work with a partner!• Read the instructions and questions carefully.• Discuss the concepts and your answers with one

another. Take time to understand it now!!!!• Come to a consensus answer you both agree on.• If you get stuck or are not sure of your answer, ask

another group.

Which is the correct reasoning for why a gamma ray telescope located in Antarctica that is to be used to look for evidence of black holes in the centers of

galaxies would not get funded?

1. There is no way to detect the presence of a black hole.

2. Gamma rays are too energetic to detect with a telescope.

3. You can’t build a functioning telescope in Antarctica.

4. Gamma rays don’t penetrate Earth’s atmosphere.

Imagine you’re the head of a funding agency that can afford to build only one telescope. Which of the three proposed

telescopes below would be best to support?

1. A gamma ray telescope in Antarctica

2. A radio telescope in orbit above the Earth

3. A visible telescope located high on a mountain in Peru

4. An ultraviolet telescope located in the Mojave desert

Imagine that you throw a ball directly upward. Which of the following statements best describes how

Newton’s second law accounts for the motion of the ball when it reaches its maximum height?

1. The ball has a velocity that is zero and an acceleration that is zero.

2. The ball has a velocity that is upward and an acceleration that is downward.

3. The ball has a net force that is downward and a velocity that is downward.

4. The ball has a net force that is downward and an acceleration of zero.

5. The ball has a net force that is downward and an acceleration that is downward.