TelescopesTelescopes

Chapter 5Chapter 5

ObjectivesObjectives

Telescopes……………Chapter 5

Objectives: 1. To list the parts of a telescope. 2. To describe how mirrors aid in telescope

magnification. 3. To describe three different types of

telescopes. 4. To construct a simple telescope.

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

Some of these terms should come to mind:Some of these terms should come to mind:

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 lightbending light”” onto a particular spot. onto a particular spot.

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

What are the two most important What are the two most important properties of a telescope?properties of a telescope?

1.1. ____________________________________________________________:: Also Also called called Collecting PowerCollecting Power. Telescopes with a . Telescopes with a larger collecting area can gather a greater larger collecting area can gather a greater amount of light in a shorter time.amount of light in a shorter time.

2.2. ______________________________________________________________: : Also Also called called Resolving PowerResolving Power. Telescopes that are . Telescopes that are larger are capable of taking images with larger are capable of taking images with greater detail.greater detail.

Determining a good telescopeDetermining a good telescope ______________________________________________ – how much more – how much more

light that a telescope can gather than the light that a telescope can gather than the human eye.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)

• This is the primary reason for making telescopes This is the primary reason for making telescopes largerlarger..

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 ___________________ – Light is focused to form

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

is the bending of light when it goes through is the bending of light when it goes through different media. Occurs because the speed of light different media. Occurs because the speed of light changes when it enters the lens.changes 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 _______________ to focus lightUse _______________ 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.

Focusing LightFocusing Light

A camera focuses light like an eye and captures the image A camera focuses light like an eye and captures the image with a detector.with a detector.

Because we can control the exposure time (amount of time Because we can control the exposure time (amount of time the light collects on the detector), a camera can record the light collects on the detector), a camera can record details that are too faint to see with our eyes alone. details that are too faint to see with our eyes alone.

The CCD detectors in digital cameras are similar to those The CCD detectors in digital cameras are similar to those used in modern telescopes.used in modern telescopes.

Cameras detect light with charge-coupled devices (CCDs).

Determining a good telescopeDetermining a good telescope Besides collecting light, telescopes also allow us to Besides collecting light, telescopes also allow us to

discern objects as single large object or several discern objects as single large object or several small individuals small individuals

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

diffracted.diffracted.• DiffractionDiffraction – –

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

Reflecting telescopesReflecting telescopes

Use __________________ to collect and Use __________________ to collect and focus light.focus light.

ReflectorsReflectors are slightly curved mirrors are slightly curved mirrors Light does not go through them and Light does not go through them and

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

around, each time bending it slightly around, each time bending it slightly and thus magnifying the image. and thus 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 ________________________________________________ refraction refraction makes makes

the sun look higher in the sky than it really the sun look higher in the sky than it really is.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.

InterferometersInterferometers

A device consisting of ____________A device consisting of ____________

______________________ connected ______________________ connected together to work as a single together to work as a single instrument.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?

Light PollutionLight Pollution

___________________________ is ___________________________ is city light scattering off city light scattering off the atmosphere and into a telescope.the atmosphere and into a telescope.

Scattering of human-made light in the atmosphere Scattering of human-made light in the atmosphere is a growing problem for astronomy when using is a growing problem for astronomy when using land-based telescopes.land-based telescopes.

Why do we put telescopes into Why do we put telescopes into space?space?

Benefits of Space TelescopesBenefits of Space Telescopes

Only radio and visible light pass easily through Only radio and visible light pass easily through EarthEarth’’s atmosphere. We need telescopes in s atmosphere. We need telescopes in space to observe other forms.space to observe other forms.

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.