Untitled Flashcards Set

Things to know from chapts. 10, 11 & 12:

Note that some of the numbers items can be used to make more than one question.

1. What an exoplanet or extrasolar planet is: A planet orbiting a star other than the Sun is called an extrasolar planet or exoplanet.

2. When the first exoplanet was discovered: 25 years ago.

3. Why it’s hard to detect exoplanets: The star is often a billion times as bright as the planet.

   1. The star produces its own light, but the planet doesn’t. We see the planet from the starlight it reflects to us.

The star & planet are fairly close to each other, but they’re both very far away from us.

2. Remember the scale model we talked about before. The Sun was the size of a grapefruit & located in Washington, D. C. The nearest star was about the same size as a grapefruit & in California. An Earthlike planet orbiting it would be the size of a ball point & about 50 ft. from the star. 

4. About how many exoplanets we’ve now discovered: We know of thousands of them and are discovering more everyday. 

5. How bright a star is compared to an exoplanet: Stars are often a billion times brighter than the planet. 

6. That not all stars have exoplanets, but lots of them do

7. How the different ways of detecting exoplanets work and what their names are: There are 2 basic categories of detection techniques for extrasolar planets: direct & indirect.

Direct🡪 Here you actually get an image of the planet. Direct techniques are generally very difficult to do.

Indirect🡪 Here you don’t actually see the planet. Instead you infer its existence from the effect it has on the star it orbits. Indirect techniques are easier to do.

8. That the transit method often can’t be used for exoplanet detection: If we get lucky---and we usually don’t---then extrasolar planet’s orbit may be lined up edge-on to us.

When this happens the planet blocks out some of the star’s light when it passes in front of it. The star blocks out the small amount of reflected light from the planet when the latter passes behind the former.

Detection of planets by utilizing this is called the transit method.

9. The name of the satellite largely responsible for detecting exoplanets: The transit detections largely come from the Kepler spacecraft, which began operating in 2008.

10. What properties of exoplanets we can currently determine: What properties of extrasolar planets can we measure? It depends on the method used & the quality of the data.

11. But the properties include:

    1. Orbital period

    2. Orbital distance

    3. Orbital eccentricity

    4. Planetary mass

    5. Planetary size

    6. Planetary density

    7. Atmospheric composition

    8. Atmospheric temperature

12. What hot Jupiters are and how they form: A hot Jupiter is a Jovian planet that orbits within the frost line.

13. Why planets with highly elliptical orbits are so common: If planets pass very close to each other during the formation of a solar system, then their orbits can change dramatically.

One would be put into a very elliptical orbit, while the other would be ejected from the solar system altogether.

This would mean there are lonely, wandering planets out there in space.

Recently, we’ve observed some of them…

14. What makes the sun and other stars shine: It wasn’t ‘till the 1930s that people realized that the Sun’s energy source is nuclear reactions.

    1. Other stars “run” on nuclear reactions, too.

    2. A star like a Sun has enough nuclear fuel to last about 10 billion yrs.; this means the Sun is just around halfway through its life.

15. Why the sun isn’t continuing to collapse gravitationally: Remember, the Sun did collapse due to gravitation in the early history of the solar system, and this is what provided the energy that began to heat it up.

But why isn’t it still contracting?

1. Because when it got to a critical temperature, it became hot enough for the nuclear reactions to start. They became the source of the Sun’s energy, & created enough pressure to balance the gravitational collapse.

16. Layers of the sun and their properties: The Sun comes in layers. From the outside:

    1. The solar wind---this technically isn’t part of the Sun; the solar wind is made of electrically-charged particles that flow outward into space.

    2. Corona---The temperature of this part of the Sun is about 1 million K.

    3. Chromosphere---this part has a temperature 10 to 100 times less than the Corona does

    4. Photosphere---this is the part of the Sun that we see; its temperature is just under 5800 K.

    5. Convection zone---energy is transferred upward in convection cells in this region.

    6. Radiation zone---energy moves outward by radiation here. It can take 100,000 yrs. for the radiation to get out of this zone.

    7. Core---this is where the nuclear reactions occur. The temperature here may be 10 million K.

17. Difference between fission and fusion: There are two types of nuclear reaction: fission & fusion. Both produce energy.

    1. In fission large atoms are broken down into smaller ones.

    2. In fusion small atoms are stuck together to make large ones. Fusion reactions typically release more energy than fission reactions do.

18. Conditions required for nuclear fusion: To get fusion to occur, you need to make positively-charged particles stick together.

But they don’t “like” to be stuck together; they repel each other.

The way to overcome the repulsion is to collide them at high speeds, and high speeds come from high temperatures.

This is why there’s a threshold temperature for nuclear fusion to occur.

Once the particles are stuck together, they don’t fall apart again, even though they continue to repel due to their electric charges. This is because at very short distances the attractive strong nuclear force overwhelms the electrical repulsive force.

19. Proton-proton chain: The particular type of fusion reaction currently going on in the Sun & stars like it is called the proton-proton chain.

    1. This reaction occurs in several steps.

    2. Different types of stars than the Sun can have other additional fusion reactions going on inside them.

The net result of the proton-proton chain is that 4 hydrogen atoms are turned into 1 helium atom, in the process energy is released.

20. How long it takes gamma-rays to get out of the sun: Gamma rays---these eventually trickle out of the Sun, but it can take a good 100,000 yrs. to happen, & in the process the gamma rays are turned into visible light.

21. How long the Sun will live and how old it is: This “thermostat” will work as long as the Sun has an adequate supply of atomic hydrogen---4 or 5 billion more years.  After that the Sun will change tremendously and finally die… It's about 4.6 billions years old. 

22. That the Sun can regulate its temperature

23. What the solar neutrino problem was, and how it was solved: But the neutrino data didn’t work out so well:

    1. At the beginning of the experiments the numbers were small, so the statistics were bad.

    2. By any accounting at the end of the experiments there were exactly one-third as many neutrinos as there should have been.

After a few decades it was finally determined that the three types of neutrino can change into each other spontaneously, but the older detectors were sensitive to only one type. The new detectors are sensitive to all three types, & come out with the right number.

24. How we know what’s going on inside the sun: Theoretical models, Measurement of the vibrations of the Sun, Measurements of the neutrinos that reach us here on Earth.

25. What sunspots are, and how they stay cooler than the surrounding regions of the Sun: Sunspots are places on the surface of the Sun which are about 2000 K cooler than the rest of the Sun’s surface. They appear dark because of their lower temperatures.

26. How much cooler Sunspots are than surrounding regions of the Sun: 2000 K cooler. 

27. Sunspots come in pairs: The amount of sunspots can never be odd. 

28. How long the sunspot cycle is: They last about 11 years. 

29. What coronal mass ejections are and how they affect earth: When the magnetic fields break, matter spills out into space; this is called a coronal mass ejections (CME). The CMEs can eventually make it out to us here on Earth, causing communication & power grid problems. (solar flares)

30. Know what luminosity is and its range: Luminosity is the total amount of power that a star emits into space. Almost all of it comes in the form of electromagnetic waves.

Apparent brightness is how bright a star appears in the sky.

Luminosity & apparent brightness are related---but not the same things; a 10 watt light bulb will appear brighter than a 250 watt light bulb if the former is 2 feet away from you and the latter is ¼ mile away from you.

This diagram shows how it works🡪

The apparent brightness depends on the square of the distance from the star and its luminosity.

Luminosity can range from about 1/10,000^th that of the Sun to about 1 million times that of the Sun---quite a wide range.

31. Know about measuring the distance to stars: For stars up to 1,500 or so light years away, we can use the parallax method, as this picture shows🡪

For stars farther away than that, the parallax is too small to reliably measure. Then we have to use other methods that we’ll talk about later.

Up ‘till the present time, parallax has been used to measure the distances to about 100,000 stars.

The new European spacecraft GAIA should be able to expand this to about 1 billion stars, up to distances of tens of thousands of light-years.

32. What class of star the Sun and Alpha Centauri are: They are class G stars.

33. Know how stellar masses are determined and their ranges: Stellar temperatures range from less than 3000 K to more than 40,000 K. Stellar temperature refers to the temperature at the surface of a star, not in its interior (where it’s much hotter). About half the stars in the Universe are part of binary systems---systems where two stars rotate around each other.

By measuring the properties these stars’ orbits, we can determine these masses through Kepler’s 3^rd law.

The range of masses is from 0.08 the mass of the Sun to at least 150 times the mass of the Sun.

34. How common binary stars are: About half the stars in the Universe are part of binary systems---systems where two stars rotate around each other.

35. That large stars don’t live as long as small ones

36. Know how stellar temperatures are measured and their ranges: Stellar temperatures range from less than 3000 K to more than 40,000 K.

Stellar temperature refers to the temperature at the surface of a star, not in its interior (where it’s much hotter).

37. Know how to interpret a Hertsprung-Russell diagram and what it tells us about stars: When you plot the temperatures vs. the luminosities of the stars, they follow a pattern. This plot is called the Hertzprung-Russell (HR) diagram.

Most of the stars fall in the main-sequence. The key property of where a star lies on the main sequence is its mass.

1. The more mass the star has, the larger, brighter, and hotter it is.

2. Also, more massive stars have short lives. Stars with very low masses have very long lives.

38. Know about the different types of star clusters: Stars tend to form in clusters. There are two types of them: open and globular.

Open clusters

1. Tend to have a few thousand stars in them,

2. Tend to be located in the disk of the galaxy,

3. Are typically about 30 light-years across,

4. Often contain stars of various ages and masses.

Globular clusters

5. Tend to be found in the halo.

6. Contain some of the oldest stars in the Universe.

7. Typically contain more than a million closely-packed stars.

8. Are ball-shaped, and typically 60 to 150 light-years in diameter.