Telescopes & Light: Part 1

A Telescopes 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.

Which of the following is the most important feature of a

telescope?A. Ability to gather light.

B. Ability to see fine detail.

C. Ability to magnify the image.

Three main functions of a telescope

Most important!!• Gather More Light – (bigger Is 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

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 truly interested in the entire spectrum 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

Sun as seen in visible light from Earth (right) and from space in X-rays by satellites (left)

Radio wavelength observations are possible from Earth’s surface

The Very Large Array (VLA) in New Mexico

Differences in the temperature and density of small portions of Earth’s atmosphere cause passing starlight to quickly

change direction, making stars appear to twinkle.

Earth’s atmosphere hinders astronomical research

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.

High above Earth’s

atmosphere, the Hubble

Space Telescope provides stunning

details about the universe

Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere.

Not all EM radiation can penetrate Earth’s atmosphere.

Tutorial: Telescopes and Earth’s Atmosphere pg. 49

• 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 me

or 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?

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

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

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

D. 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?

A. A gamma ray telescope in Antarctica.

B. A radio telescope in orbit above the Earth.

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

D. An ultraviolet telescope located in the Mojave desert.

McDonald Observatory (Fort Davis, TX)

A Few Astronomy Factoids (Or: So You Think You Want to be an Astronomer)

• Research quality images are monochromatic.• Astronomy research is not the safest, but is

much safer than it once was due to the use of CCDs over photographic plates.

• Astronomy research is time consuming and expensive.

• Astronomers spend more time in front of a computer than at a telescope.

• Professional astronomers rarely ever actually look through an eyepiece.