Chapter 24: Studying the Stars

AstronomyMr. SteinkenPgs. 673 - 683

Hubble Gotchu!

How do Astronomers know what they know?

Almost everything we know about Astronomy was learned by gathering and studying light from distant sources

Properties of light1. Behaves like a wave; has wavelength (distance from crest

to crest) Visible light can be separated by a prism Radio waves = a few km Gamma rays = less than a billionth of a cm

2. Behaves like a particle; photons – small packet of light energy

Photons from the sun push on vaporized gas from a comet and form the tail Light with shorter wavelengths have more energetic photons!

Electromagnetic SpectrumElectromagnetic Radiation(EMR) - radio waves, infrared,

visible light, ultraviolet, x-rays, and gamma raysElectromagnetic spectrum – arrangement of EMR

according to their wavelengths and frequenciesMost wavelengths of the EMR are to long or short for us to

see

Continuous spectrum –uninterrupted band of color emitted by an incandescent solid, liquid or gas

Absorption vs. Emission SpectrumAbsorption spectrum – “dark line spectrum,”

white light is passed through a gas and certain wavelengths of light are absorbed

Emission spectrum – a series of bright lines of particular wavelengths produced by a hot gas under low pressure

Absorption spectral lines of stars are like “fingerprints” used to identify the elements present in the star

The Doppler EffectDoppler effect – the perceived change in wavelength of a

wave that is emitted from a source that is moving away or toward an object

If the source of light is moving away from you the wavelength will stretch and cause a Red Shift

If the source of light is moving toward you the wavelength is compressed and causes a Blue Shift

Tools For Studying SpaceTelescopes are used to gather and collect the

radiant energy from distant galaxies and stars

Types of telescopes1) Optical telescopes – contain mirrors or lenses,

collect visible light2) Radio telescopes – giant radar dishes that

detect radio waves3) Space telescopes – orbit above Earth’s

atmosphere to produce clearer images

Optical Telescopes: Properties1. Light-gathering power – ability to intercept more light from

distant objects, which means brighter imageslarger lens or mirror = “see” farther

2. Resolving power – allows for sharper images and finer detaillarger lens or mirror = sharper image

3. Magnifying power – ability to make an image larger, depends on focal lengths of the objective and eyepiece

Moral of the story When it comes to telescopes, size does matter

Optical Telescopes: RefractingI. Refracting telescope – uses a lens to bend light

II. The objective lens produces an image by bending light from distant objects so that light converges on a focal point

III. Chromatic aberration – light of different colors are focused at different locations; when red light is focused there is a blue halo, when blue light is focused there is a red halo

Optical Telescopes: ReflectingI. Reflecting telescope – uses a concave

mirror to focus lightII. Advantages = don’t need to be optical

quality, can be supported from behind the mirror, can be made much larger

III. Disadvantage = secondary mirror blocks some light, solution = make it bigger!

Radio TelescopesI. The dish of the radio telescope focuses the

radio waves on an antenna, transmits it to an amplifier

II. Interferometer - several radio telescopes linked together Advantages = can run all

day every day, cheaper to build, can detect clouds of gas to cool to emit visible light

Disadvantages = take up a lot of space, hindered by human-made radio interference

Space TelescopesHubble Space Telescope was the first

of its kindUsed to study everything from birth of

stars to extrasolar planets

Chandra X-ray ObservatoryStudies black holes by collecting X-Rays

NASA plans to launch the James Webb Space Telescope in 2013 to study infrared radiation

JAMES WEBB GOTCHU?!