Exam 2: 11/14

·         Know the difference between apparent magnitude (how bright a star looks to us, which is dependent upon both how bright it is and how far away it is), absolute magnitude (how bright the star would appear if placed 10 parsecs from us) and luminosity (how much energy a star is gives off each second – how bright it really is).

·         In the magnitude measurement system, low numbers indicate high brightness while higher numbers indicate low brightness (a magnitude 1 star is brighter than a magnitude 7 star, while a magnitude -3 star would be brighter than both).

·         Know the inverse square relationship (if you have two stars of equal luminosity, but one is twice as far away as the other, the farther star will appear 4 times as dim as the closer star).

·         What is interstellar extinction? (the scattering and absorption of starlight by dust).

·         What is the interstellar medium and what is it composed of? (~75% H, ~25% He, ~1% dust).

·         What is a nebula? (cloud of gas and dust).

·         What are three kinds of nebulae? (dark, emission, reflection).

·         Know that emission nebulae are heated by nearby stars and are emitting light (usually reddish due to H)

·         Know that reflection nebulae glow, usually blue, because they reflect the light of nearby stars.

·         Know that dark nebulae have high percentage of dust and absorb the light from stars behind them.

·         Know the difference between an HII region (gas ionized from UV radiation from nearby hot star) and HI region (cold neutral hydrogen).

·         Know the relationship between interstellar cloud density and temperature (the hotter the cloud, the lower the density of the particles in it).

·         What is a molecular cloud, and how is it different from the interstellar medium? (cloud of gas and dust and molecules).

·         Where are stars born and under what conditions? (cold, dark molecular clouds or giant molecular clouds).

·         What is a molecule? (2 or more atoms bound together).

·         Know about a protostar: what is it? is it fusing H to He? is it on the main sequence? Are they easy to observe visually? Why or why not? How to we best observe them?

·         Know that stars tend to form in groups rather than singly.

·         Shockwaves can cause interstellar gas clouds to collapse, eventually leading to star formation.

·         What is hydrostatic equilibrium (balance between weight and pressure) and what does it apply to?

·         Brown dwarfs (0.08 solar mass) are not large enough to get hot enough to fuse H to He and enter main sequence.

·         Red dwarfs are extremely low-mass stars, but are large enough to be on main sequence. They have the longest lifetimes of any other mass star.

·         The Sun is considered to be a low to medium-mass star.

·         Red giants and supergiants are not on the main sequence, they are nearing the end of their lives. What event triggers this change? (H in core has been fused to He and core contracts.) Where does energy for expansion of outer atmosphere come from? (fusion of H to He in shell around core.)

·         White dwarfs are not on the main sequence; they are stellar corpses, no fusion.

·         Average star spends 90% of its life on the main sequence.

·         90% of all stars are on the main sequence.

·         Know that stars on the main sequence are fusing H to He in their cores.

·         The more massive a star, the shorter its life (so an O star would have shorter life than G star like sun). Why?

·         Be VERY familiar with the HR Diagram! What is measured on each axis? Where do particular kinds of stars fall on the diagram?

·         At what point in a star's life is it when it is on the main sequence, in the upper right corner, or in the lower left corner?

·         Know the spectral classes, OBAFGKM, and know in what kind of order that is in (descending temperature).

·         Know the relationship between a star's color and its surface temperature.

·         Know the luminosity classes (Ia – Brightest supergiants; Ib – Less luminous supergiants; II – Bright giants; III – Giants; IV – Sub-giants; V – Main sequence stars).

·         Know the mass - luminosity relationship of stars on the main sequence (the more luminous they are, the more massive they are).

·         Know the relationship between mass, volume and density  (for example, white dwarfs are objects that may be as massive as the Sun but are the size of the Earth, and as such would be more dense than the Sun. How does this work with red giants/supergiants?)

·         Know the relationship between the luminosity, radius and temperature of a star (for example, red stars are cool so generally not very luminous - think about where they fall on the HR diagram; but red giants and supergiants are huge and therefore more luminous because there is more surface area to radiate from. How does this work with white dwarfs?)

·         The definition for degenerate matter: when gas is so dense that its electrons are not free to change their energy levels. What kind of star is composed of degenerate matter?

·         General path for medium-mass (Sun-like) stars: most of life on main sequence fusing H to He at core; turn into red giants (no longer on main sequence); outer atmosphere expelled creating planetary nebula; end up as white dwarfs.

·         White dwarfs eventually radiate all their heat away, turning into black dwarfs.

·         Massive stars (about 4 times mass of Sun or larger) do not turn into white dwarfs. They can undergo a  supernova explosion, in which much of their outer atmosphere can be expelled into space (supernova remnant), leaving behind a neutron star (very dense) or pulsar. If the star is massive enough, it would turn into a black hole instead of a neutron star or pulsar.

·         Neutron stars and pulsars are very dense, rotate rapidly.

·         Understand escape velocity (the speed something much reach to escape the gravitational pull of an object).

·         Know why black holes are dark (light can't reach necessary escape velocity to leave surface of object)

·         Know speed of light as 186,000 miles per second.

 From the first exam, know the following material:

 ·         What is a light year (distance light travels in a year, ~ 6 trillion miles).

·         What is an astronomical unit (average distance between the Earth and Sun, ~ 93 million miles).

·         Know about the electromagnetic spectrum (gamma, x-ray, ultraviolet, visible light, infrared, microwave, radio).

·         Know the relative wavelengths and energy levels of the different forms of electromagnetic radiation.

·         Know the dual nature of light (wave/particle).

·         What do atoms consists of (nucleus [protons and neutrons] orbited by electrons).

·         Most of the atoms in the universe are what (H).

·         Know the charge of the primary particles in an atom (protons – positive; neutrons – neutral; electrons – negative).

·         Know the difference between a regular atom and an ionized atom (ionized atom has lost or gained one or more electrons, and therefore is not neutral).

·         Know the two ways an atom can be excited (collision; absorbing photon).

·         Know that the process going on in the Sun’s core (and all stars on main sequence) providing energy is nuclear fusion (not fission).

Exam 1: 10/09

1. What is a light year?

2. What is an astronomical unit?

3. Under what circumstances are the different measurement systems used?

4. How far away from the Sun is the nearest star?

5. What is the name of the star closest to the north celestial pole?

6. What is a circumpolar constellation?

7. Where is the observer’s zenith?

8. Where is the observer’s meridian?

9. What is the celestial sphere, and why does it appear to rotate?

10. Know the celestial coordinate system (celestial equator, RA, dec, poles)

11. In the northern hemisphere, the altitude of the north star is equal to the observer’s what?

12. Know that the sky looks different for observers on different parts of the Earth.

13. What is the ecliptic?

14. The sky is divided into 88 sections called what?

15. What causes solar and lunar eclipses, and what is the phase of the moon during each type?

16. Know latitude and longitude (Earth’s coordinate system).

17. What/when are the vernal and autumnal equinoxes?

18. What/when are the summer and winter solstices?

19. Where is the vernal equinox on the celestial sphere?

20. Why do we have seasons on Earth?

21. Know the phases of the moon (and when the new and full moon rises).

22. Know about the electromagnetic spectrum (different types of radiation in order).

23. Know the relative wavelengths and energy levels of the different forms of electromagnetic radiation.

24. What is a photon?

25. Know light is refracted when it passes from one transparent medium into another of different density.

26. For astronomical purposes, the Earth’s atmosphere is transparent to what wavelengths?

27. What is the primary function of a telescope?

28. What is the difference between a reflecting and refracting telescope?

29. What is the most common instrument astronomers use to take images?

30. Know that resolution of telescope refers to the measure of fineness of detail in image.

31. What do atoms consists of?

32. Most of the atoms in the universe are what?

33. What kind of particles orbit around the nuclei of atoms?

34. Know the charge of the particles in an atom.

35. What is the difference between a regular atom and an ionized atom?

36. Know the two ways an atom can be excited.

37. Know the three kind of spectra.

38. Know the general conditions needed to create the three kinds of spectra.

39. What is a spectroscope?

40. A nanometer is what part of a meter?

41. What is the speed of light? What is the speed of ALL electromagnetic radiation?

42. What are the two most abundant elements in the Sun?

43. Differential rotation of the Sun means what about the rotation rate of different latitudes?

44. The light we see coming from the Sun originates in what part of its atmosphere?

45. What causes granulation?

46. How do we know what the Sun is made of?

47. What process going on in the Sun’s core provides the Sun’s energy?

48. What are sunspots?

49. How long is the sunspot cycle?

50. Does the Sun have a magnetic field?

51. About how old is the Sun?

52. What is hydrostatic equilibrium?

Page created by C. Gino on 09/11/2003

Page last updated 11/08/2003