1. Chapter 24: Studying the Sun (and other stars)

2. 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 light
Behaves like a wave; has wavelength (distance from crest to crest)
Visible light can be separated into distinct wavelengths by a prism
Radio waves = a few km Gamma rays = less than a billionth of a cm
Behaves like a particle; photons – small packet of light energy
Photons from the sun push the tail of a comet away.
Light with shorter wavelengths have more energetic photons!

3. Electromagnetic Spectrum
Electromagnetic Radiation(EMR) - the flow of energy at the speed of light in the form of the electric and magnetic fields.
Radio waves, infrared, visible light, ultraviolet, x-rays, and gamma rays
Electromagnetic spectrum – arrangement of EMR according to their wavelengths and frequencies
Most wavelengths are too long or short for us to see
Continuous spectrum 
A spectrum of radiation distributed over an uninterrupted range of wavelengths.

4. Absorption vs. Emission Spectrum
Emission spectrum – a series of bright lines of particular wavelengths produced by a hot gas under low pressure
Absorption spectrum – “dark line spectrum,” produced when white light passes through a gas and certain wavelengths of light are absorbed
Most often used by astronomers to identify stars.
The specific wavelengths of absorption spectral lines of stars are like “fingerprints” used to identify the elements present in the star

5. Spectrum of the sun

7. The Doppler Effect
Doppler 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

8. Tools For Studying Space
Telescopes are used to gather and collect the radiant energy from distant galaxies and stars
Types of telescopes
Optical telescopes – contain mirrors or lenses, collect visible light
Radio telescopes – giant radar dishes that detect radio waves
Space telescopes – orbit above Earth’s atmosphere to produce clearer images

9. Optical Telescopes: Properties
Light-gathering power – ability to intercept more light from distant objects, which means brighter images
larger lens or mirror = “see” farther
Resolving power – allows for sharper images and finer detail
larger lens or mirror = sharper image
Magnifying power – ability to make an image larger, depends on focal lengths of the objective and eyepiece
change the eyepiece = change the magnifying power
Moral of the story  When it comes to telescopes, size does matter

10. Optical Telescopes: Refracting
Refracting telescope – uses a lens to bend light
The objective lens produces an image by bending light from distant objects so that light converges on a focal point
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

11. Optical Telescopes: Reflecting
Reflecting telescope – uses a concave mirror to focus light
Advantages = don’t need to be optical quality, can be supported from behind the mirror, can be made much larger
Disadvantage = secondary mirror blocks some light, solution… make it bigger!

12. Radio Telescopes
The dish of the radio telescope focuses the radio waves on an antenna, transmits it to an amplifier
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

13. Space Telescopes James Webb Gotchu?!
Hubble Space Telescope was the first of its kind
Used to study everything from birth of stars to extrasolar planets
Chandra X-ray Observatory
Studies black holes by collecting X-Rays
NASA plans to launch the James Webb Space Telescope in 2013 to study infrared radiation
James Webb Gotchu?!