First Astronomy Exam-Review
Terms
undefined, object
copy deck
- How did the greeks know the earth was round?
- During lunar eclipses they saw the shadow of the earth move over the moon and saw that it was round, so they decided it was a sphere. They also observed that as you went further north or south you saw different stars, so you need a round earth rather than a flat one for that to happen.
- Why did greeks reject a heliocentric model for the solar system but Copernicus did not?
- They thought we should be able to see paralax but they couldn't. However, this was just because the stars were too far away to perceive parallax with the naked eye, so Copernicus did not reject it because he knew that the further away something is, the smaller the shift in its location.
- What is the approximate limit to which sky positions can be measured with the unaided eye?
- 1 arc minute
- What were the important observations Tycho Brahe made with the naked eye? What were their results?
- He made several decades worth of scrupulous naked eye observations of the planets, hoping to be able to figure out how they really moved. Tycho himself didn't figure this out but Kepler did a little while later.
- How did Galileo's observations of Jupiter provide him with evidence that the Copernican system might be correct? How did his observations of Venus show that Ptolemy's model was definitely wrong but were in favor of a Copernican model?
- Galileo observed Jupiter and saw that it had a moon going around it so there was something in the universe other than earth around which things could orbit! Also he could see the phases of Venus, which the Ptolemeic model could not account for.
- What observations did Kepler use to derive his three laws of planetary motion?
- He used the planetary measurements of Tycho Brahe.
- What are these three laws?
-
1) the orbit of the planet is an ellipse with the sun at one focus of the ellipse.
2) If you take an artificial line connecting the planet and the sun, that line sweeps out equal areas in equal times. The net result of this is that the planet moves faster in the portion of its orbit when it is closer to the sun and more slowly when its further away.
3) P^2 = A^3 The orbital period in years equals the average distance of the planet from the sun cubed. - What are Newton's three laws of motion?
-
1) The Law of Inertia: A body at rest tends to stay at rest; a body in motion tends to stay in motion at constand velocity unless it's acted upon by an outside force.
2) Force= Mass x Acceleration. A body will accelerate in the direction that you push on it and the Mass is its resistance to acceleration, so the bigger the mass the more you have to push it.
3) For every action there's an equal and opposite reaction. - How did Newton's law of gravity lead to the orbit of a planet around the sun?
-
Force of Gravity=(constant x product of the two masses)/r^2
Example: the moon pulls on the earth and the earth pulls on the moon, but the moon does most of the pulling because it has less mass. If you imagine a planet going around the sun and you suddenly take the force of gravity away, the planet would just go flying off into space (the law of inertia). The second law states that there is a force of gravity that is pulling the planet toward the sun. It accelerates the planet in the direction of the sun, so its direction but not its inertia is changed. The third law says that, just as the sun is pulling on the planet, the planet is pulling on the sun a little too (a tiny wobble). - Be able to sketch a schematic diagram of the electromagnetic spectrum including: the correct ordering of the different types of light:
-
Longest to Shortest:
Radiowaves, infrared, visible light, ultraviolet, x-rays, gamma rays.
Remember: the longer the wavelength, the lower the frequency and the lower the energy per photon. - Understand the mathmatical relationship betwen frequency, wavelength, and speed.
- c=f x lamda
- How are energy and frequency related?
- Energy is proportional to frequency.
- What do the three types of spectra look like? What types of objects produce them?
-
Continuous: all the colors are present, produced by dense objects
Absorption: all the colors are present but there are some dark lines that represent where various electrons of various elements have jumped up to the next energy level because they were excited by photons of light they have absorbed. (produced when light from a solid, dense gas, whatnot penetrates a tenuous gas)
Emission: Dark background and only some bright lines. (exactly oposite to an absorption spectrum) Here, an electron is already up at another level and drops spontaneously, giving off bright colors. (If you look at an absorption spectrum from another angle where you wont see the continuous spectrum, this is what you get.) - What is thermal radiation?
- The same thing as the continuous spectrum, also called BlackBody radiation (!!) If you heat up a dense object not all the colors wil be equally represented. The object will have a peak wavelength. When you heat it to higher temperatures, all the colors get brighter and the peak wavelength shifts to shorter wavelengths.
- What is Doppler Shift?
- This is when a source of any type of wave (sound, light) is moving relative to the observer. The observer will perceive a change in the wavelength as the source moves closer or away from the observer. If the source and observer are moving towards each other, the observer will encounter the waves more frequently than she would if the sourse were stationary (higher frequency, shorter wavelength). if the source and the observer are moving apart, the wavelengths get longer and the frequency, less.) This measures radial velocity (e.g. velocity toward or away from you, not velocity sideways).