TelescopesTelescopes

Chapter 5Chapter 5

What do you think of when someone What do you think of when someone asks you about a telescope?asks you about a telescope?

Types of telescopesTypes of telescopes

Interferometers (Interferometers (not a type of telescope, but not a type of telescope, but

decrease light interferencedecrease light interference)) Radio telescopesRadio telescopes

TelescopesTelescopes

The most basic telescopes work by The most basic telescopes work by gathering light, then focusing and/or gathering light, then focusing and/or “bending light” onto a particular “bending light” onto a particular spot.spot.

This causes an increase in the This causes an increase in the magnification of an image.magnification of an image.

Determining a good telescopeDetermining a good telescope

– – how much more light that a how much more light that a telescope can gather than the human eye.telescope can gather than the human eye.

The larger the lens, the more collecting The larger the lens, the more collecting power. power. • This allows for a brighter image This allows for a brighter image (easier for you to see)(easier for you to see)

Telescopes are first described by the Telescopes are first described by the diameter of its light collecting device (mirror diameter of its light collecting device (mirror or lens)or lens)

Once light is collected then it must be Once light is collected then it must be focused.focused.

Determining a good telescopeDetermining a good telescope

How light is focusedHow light is focused – – Light is focused to form a Light is focused to form a

particular image using a lens.particular image using a lens.• Relies on the process of Relies on the process of which is the which is the

bending of light when it goes through different bending of light when it goes through different media. Occurs because the speed of light changes media. Occurs because the speed of light changes when it enters the lens.when it enters the lens.

• Refraction also spreads the light out. Results in the Refraction also spreads the light out. Results in the colors of the rainbow.colors of the rainbow.

• – – The spreading of light or other The spreading of light or other electromagnetic radiation into a spectrum.electromagnetic radiation into a spectrum.

The light rays are bent when they go through The light rays are bent when they go through one media (air) and then another (glass)one media (air) and then another (glass)

Refracting TelescopesRefracting Telescopes

Use lenses to focus lightUse lenses to focus light Are limited by the size and quality of Are limited by the size and quality of

the lens.the lens. Most modern telescopes are Most modern telescopes are

reflecting telescopes as opposed to reflecting telescopes as opposed to refracting telescopes.refracting telescopes.

We will make a refracting telescope We will make a refracting telescope in class this week.in class this week.

Reflecting telescopesReflecting telescopes

Use reflectors to collect and focus light.Use reflectors to collect and focus light. are slightly curved mirrorsare slightly curved mirrors Light does not go through them and as a Light does not go through them and as a

result is not dispersed.result is not dispersed. Most telescopes today are reflectingMost telescopes today are reflecting Multiple mirrors bounce the light around, Multiple mirrors bounce the light around,

each time bending it slightly and thus each time bending it slightly and thus magnifying the image. magnifying the image.

Atmospheric RefractionAtmospheric Refraction

Occurs for objects viewed in the sky.Occurs for objects viewed in the sky. The gases of the atmosphere bend light The gases of the atmosphere bend light

and change the appearance of an objectand change the appearance of an object refractionrefraction makes the sun look makes the sun look

higher in the sky than it really is.higher in the sky than it really is. Atmospheric refraction is stronger closer Atmospheric refraction is stronger closer

to the horizon. Causes the sun to look flat to the horizon. Causes the sun to look flat as it sets. as it sets.

Determining a good telescopeDetermining a good telescope Besides collecting light, telescopes also Besides collecting light, telescopes also

allow us to discern objects as single large allow us to discern objects as single large object or several small individuals object or several small individuals

– – The ability of a telescope or The ability of a telescope or instrument to discern fine details. Larger instrument to discern fine details. Larger diameter telescopes have greater resolving diameter telescopes have greater resolving power than smaller ones.power than smaller ones.• Resolving power is limited because light waves Resolving power is limited because light waves

can be diffracted.can be diffracted.• DiffractionDiffraction – –

• Diffraction limits the resolving power of a Diffraction limits the resolving power of a telescope.telescope.

InterferometersInterferometers

A device consisting of two or more A device consisting of two or more telescopes connected together to telescopes connected together to work as a single instrument.work as a single instrument.

Allow for a high resolving power, the Allow for a high resolving power, the ability to see small scale features.ability to see small scale features.

Can be used to increase the power of Can be used to increase the power of radio, infrared, and visible radio, infrared, and visible wavelengths.wavelengths.

ObservatoriesObservatories

As far as telescopes discussed by the As far as telescopes discussed by the groups, for the test, make sure to groups, for the test, make sure to look over the telescopes and look over the telescopes and observatories discussed in the book.observatories discussed in the book.

Remember that SEVERAL telescopes Remember that SEVERAL telescopes are located in Hawaii (Mauna Kea)are located in Hawaii (Mauna Kea)

Why are so many telescopes in HI?Why are so many telescopes in HI? Cleaner air, less pollution, and Cleaner air, less pollution, and

relatively high elevation.relatively high elevation.

Non optical telescopesNon optical telescopes

Most X rays and UV light is absorbed Most X rays and UV light is absorbed by the atmosphere.by the atmosphere.

Radio waves can penetrate the Radio waves can penetrate the atmosphere.atmosphere.

Gamma ray telescopes measure Gamma ray telescopes measure gamma rays that are released during gamma rays that are released during nuclear explosions.nuclear explosions.

These explosions occur during stellar These explosions occur during stellar evolution. evolution.