Chapter 24: Studying the Sun (and other stars)

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!

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.

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

Spectrum of the sun

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

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

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

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

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!

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

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?!