ASTR 110 Exam #2

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Understand the concept of the EM spectrum, and similarities & differences types of radiation
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Understand the concept of the EM spectrum, and similarities & differences types of radiation
COMPLETE SPECTURM OF LIGHT WAVELENGTHS
- Sunlight passes through prism (rainbow color appears), prism separates light into component colors (light of each color is described by wavelength)
- ROY G BIV (longer to shorter wavelengths)
- Infrared waves: longer wavelength light energy, invisible to humans (can be sensed by thermometer
- Ultraviolet: Beyond blue side of spectrum, special instruments can detect shorter wavelengths light energy
- Longest wavelength (radio waves) to shortest wavelength (gamma rays)
- Visible light: portion of EM spectrum our eyes are sensitive to (small fraction of EM spectrum)
Image: Understand the concept of the EM spectrum, and similarities & differences types of radiation
Understand the concept of a blackbody & its relation to color & temp.
HOT, OPAQUE GASSES, LIQUIDS, & SOLIDS ALL EMIT BLACKBODY SPECTRA
Will absorb all wavelengths & reflect one (the one we see)
- Peak of blackbody spectrum is temp. of object determines the wavelength where spectrum has greatest brightness
- Peak of wavelength in blackbody spectrum tells astronomers TEMP OF STAR
Also, can tell temp by looking at color that's most INTENSE
Describe the information gleaned from starlight that has been separated by color.
Bluer something is the hotter the star is. Redder something is the cooler the star is.
Recognize the difference between continuous, emission, & absorption spectra.
Continuous Spectrum:
1. Black-and-white photograph of a continuous spectrum is completely white b/c light energy at all wavelengths exposes the film
Bright line or Emission spectrum:
1. Lines have same color as corresponding position in a continuous spectrum
2. Dark areas correspond to low brightness on graph whereas lines correspond to peaks in graph (high brightness)
Absorption Spectrum
1. Shows a white background with a series of black vertical lines corresponding to wavelengths with NO LIGHT ENERGY
o Graph of the brightness vs. wavelength of an absorption spectrum shows familiar blackbody curve interrupted by series of downward spikes associated with absorption lines
o Wavelengths of absorption lines correspond exactly to wavelengths of bright lines produced by hot gasses
o Absorption spectrum results from continuous spectrum created by star having particular wavelengths removed as continuous spectrum of light passes through thin outer atmosphere of the star
o Wavelengths that are removed by gasses in outer atmosphere are exactly those that same gasses would produce if heated and observed directly
Image: Recognize the difference between continuous, emission, & absorption spectra.
Name the 3 components to measuring radiation.
1. Collect & focus light
2. Sort the radiation by wavelength
3. Detect & record data
Understand the difference between light gathering power & resolving power.
- Allows telescope to gather & focus light from distant & dim objects, LGP is determined by aperture (big diameter or aperture of telescope... the more LGP),
LGP= 9x as much, Area=pied^2/4
- Resolve closely spaced features (two stars close together looking like one star)
Discuss the ways in which the atmosphere is not helpful to astronomy, & ways around it.
Air is not helpful to astronomy
- Weather
- Atmosphere
- Light pollution
It protects us from the outside world, satellites, and large telescopes.
Compare & contrast reflecting and refracting telescopes
Reflecting: largest telescopes, use mirrors instead of lenses, image is not as good as glass lens, mirrors are lighter, easier to make, easier to hold in place, and less expensive
- Newtonian reflector used curved mirror in back of telescope to focus light onto a second, smaller mirror near the front telescope, the secondary mirror aims light to a hole in the side of the tube where the eyepiece is located
EXAMPLE: SALT 11 m (South African large telescope)

Refracting: uses only glass lens for magnification, largest lens is at end of telescope closest to object being viewed and it's called objective lens. Second lens is what astronomer looks through and it's the eyepiece lens
- Give clearest and most crisp images
Three main concerns
1. b/c different colors of light pass through glass lenses differently, stars viewed through a refractor can have circular rainbows around them
- Adding a special coating on objective lens can reduce this chromatic aberration effect
2. Weight- hard to hold and heavy
3. Expense- big glass lenses have no flaws, difficult to make and expensive
EXAMPLE: Chabot Space & Science Center in Oakland Cali (20-inch telescope)

Similarities: both concentrate as much light as possible & allow you to see things far
Differences: Reflector- easily make w/ large radius thus making better solution
Refractor- uses a lens as an objective to form an image
Explain why the largest telescopes are reflecting and not refracting.
Glass is heavy (it sags), large pieces have flaws (messes up image), glass is expensive
Understand the axes used on a HR diagram (& be prepared to draw one!)
x-axis: goes from hot to cool (blue to red)- spectral class shows temp & color
y-axis: luminosity (compared to the Sun) (dim to bright)
Image: Understand the axes used on a HR diagram (& be prepared to draw one!)
Given 2 stars, place them on an HR diagram and compare size, luminosity, temperature, color, & age.Star Abby: G100 Star Bobby: G0.1 Star Abby is largerKnow the major types of stars & their location on an HR diagram.Sun is G2 in the main sequence White dwarf is B0.1-0.5 Red Giant Stars is K10-11Explain the difference between a star's luminosity & its apparent brightness.Luminosity is measure of how much light a star is giving off Apparent brightness is how a star appears to us. It depends on - Star's luminosity - Star's distance from our solar systemDiscuss how stars are born & live out the majority of their livesAll stars are born from Hydrogen & convert H into He by burning. They will flare up & become Red Giants when they flare up multiple times the begin to run out of fuel to burn. all stars leave the main sequence & become red giants, final death is determined by mass (size)Describe how clusters of stars allow us to better understand stellar evolution.- Hints that solar system is NOT located at the center of the Milky Way - Astronomers estimates of the age of the universe were off - Get idea of what the rate of star formation was like during different stages in our galaxy's evolution & its chemical composition at different pointsDiscuss the 3 types of star deaths & what determines the ultimate fate of a star.Small mass: White Dwarf Medium mass: Neutron Star/Pulsar Large mass: Black HoleUnderstand the difference between type I and II supernovae.Type I supernovae: if mass of white dwarf is close to Chandrasekar limit then white dwarf is too massive to support itself= no remains of white dwarf goes into neutron star Type II supernovae: if star is 8 times (no more than 40 to 50 times the mass of the Sun) to result in rapid collapse & violent explosion of a massive starWhat evidence is used to 'see' black holes?Matter near black hole is traveling close to the speed of light, when it rubs together it gives off x rays we can seeExplain the relationship between the event horizon & escape velocity.At the event horizon, the escape velocity is equal to the speed of light. Since general relativity states that nothing can travel faster than the speed of light, so if it crosses the event horizon it cannot come back.Discuss 3 pieces of evidence that support the theory of relativity.Matter tells space-time how to curve, space-time tells matter how to move. 1. Time dilation 2. Wobble of Mercury 3. Gravitational lensingDescribe the scientific definition of a theory & a hypothesis ( & what attributes a hypothesis must possess)A hypothesis is an idea or an exploration that you can test through a study 1. Must be testable 2. Must be specific 3. Must be able to prove wrongThe theory of relativity states what about space & time?The bendBe prepared to identify the 4 different galaxy types & the range of stars each contains.1. Elliptical galaxy (older stars) 2. Spiral galaxy (old & young stars) 3. Barred spiral galaxy (filled with gas & dust) 4. Irregular galaxy (young stars) (10% of known galaxies in the Universe)Describe what type of galaxy do we live in & how we know this.The Milky Way is a spiral galaxy type, so it has arms that follow & swirl around the center. We know this b/c there have been pictures taken of the milky way outside our solar system.Explain how we know where the center of our galaxy is located.The essential modern picture is that our solar system is located on the inner edge of a spiral arm, about 25,000 light-years from the center of the galaxy, which is in the direction of the constellation of Sagittarius. B/c there will be a black hole is called Sagittarius.Understand red-shift & how it is related to recessional velocity of galaxies.Astronomers observed that light from distant objects in the universe is redshifted (shift in frequency of light towards red color). This tells us that objects are receding away from us.Discuss 2 methods used to determine distances to other galaxies.Cepheid variables: identify variable stars in the Andromeda Galaxy Type I supernovae: can be used by measuring the peak brightness of a star (b/c the light output is a known fact) Hubble's law: galaxy's distance & its recessional velocity (farther away a galaxy, fast moving away from us)Provide & explain evidence that the universe is expanding.Redshift- galaxies moving away at increasing speed Big Bang- galaxies are projected out & will not hit stuffDescribe what we can learn about the universe by running Hubble's law in reverse & explain what other evidence supports the Big Band.If we run Hubble's law backwards we will see a point where all the matter & stuff was together in one. Evidence: 1. Things moving away proportional to their distance 2. If universe were hot, there should be some remnant of height 3. Light elements abundanceDraw & label a diagram showing Hubble's constant & describe how we infer the age of the universe from this diagram.