This was like taking my cumulative major exams all over again (without the math). I love you all.
Why are there billions of stars?
I don’t know if anyone really knows how many stars there are in the universe. In our galaxy alone there are 100 billion-ish – and there are possibly hundreds of billions of galaxies.
There are billions of stars in our galaxy because of how the universe formed. There’s still a debate about which came first the chicken or the egg … I mean the star or the galaxy. Either the stars formed out of the primordial gasses of the universe and then were attracted (by their own gravity) into groups that we now call galaxies, OR the primordial gasses swirled into galaxy-sized clumps which then condensed (in little bits) to form the stars of those galaxies. Either way we ended up with billions of stars per galaxy.
How long do they last for?
An average star, like our Sun, lives for about 10 billion years. Our Sun is currently 4.5 billion years old – you have a while to wait until you worry about the end of the world.
Supergiant and giant stars burn out after only a few million years.
Weird stars like white dwarfs, pulsars, and neutron stars pretty much last “forever” unless something happens to them. We are unable to fathom how long they might last – 100s of billions of years? More? The universe hasn’t been around long enough for any of these types of stars to die.
Remember it this way: the bigger a fire you are, the hotter and faster you burn. Big stars burn out fast, little stars burn less fuel at a time and last a long time.
Can astronomy change?
Our understanding of astronomy is constantly changing.
For example, in 1999 astronomers were estimating that there were 125 billon galaxies in the entire universe. The new Hubble camera showed us twice as many galaxies as we were expecting to be able to see. Astronomers had to revise their predictions.
Is everything about astronomy true?
This is a philosophy question (relating to critical thinking and belief), not an astronomy question :) You’ll have to answer it yourself, that’s how philosophy works.
Science is based on hypotheses and observations. The explanations that best fit the evidence become stronger. In science you’ll never reach a true “fact,” because you can always keep testing your hypothesis. When most people agree that the evidence says your hypothesis is correct it becomes a theory. Theory is the closest you can get to fact: it’s something that’s “pretty for sure,” and something that lots of people agree seems to work.
I’d say “No, everything we believe we understand about astronomy is not true.” (Soon someone will find something we’re wrong about again, they keep doing it). I would also say “Yes, in truth the universe exists, and exists according to its own true rules.” Now go think about that for the next ten years and you’ll get a Ph.D. in Astrophysics or Philosophy. :)
What is gravity?
Gravity is a force between any two masses. (A force is something that can cause motion)
Gravity is one of the four basic forces of the universe: we can explain its effects but not its existence. The other forces are:
Electromagnetic force – causes positive and negative charges or North and South poles to be attracted to each other
Strong force – keeps a proton (or a neutron) from falling apart, and what keeps an atom in one piece
Weak force – has weird things to do with nuclear particle physics. (I hope those big words scared you because I can’t explain the weak force any better than that – I don’t understand it). Factoid: it’s the only force that can easily effect neutrinos.
What’s the strongest telescope?
Gamma Rays: Compton (decommissioned – was in space), Chandra now.
X-Ray: Chandra X-Ray Observatory in space
Ultraviolet: Hubble in space, I think.
Visual: Keck and Keck II in Hawaii, or the VLT (Very Large Telescope) in Chile, or SALT (South African Large Telescope) in South Africa, or the new one coming up in Germany (LBT – Large Binocular Telescope), Hubble’s good too, being in space.
Radio: Arecibo Observatory in Puerto Rico or the VLA (Very Large Array) in New Mexico
Infrared: Spitzer (used to be called SIRTF) in space
NASA’s Four Great Observatories: Hubble (Visual), Compton (Gamma), Chandra (XRay), Spitzer (Infra-red)
Will the universe expand forever or collapse?
The person who answers this question will win the Nobel Prize in Physics. What are you waiting for? Get started! Study this:
<<IMAGE NOT INCLUDED YET!>>
More? http://rst.gsfc.nasa.gov/Sect20/A9.html 
What is the black hole at the center of the Milky Way?
It’s a black hole (or several) at least 2 million times the mass of the Sun. It may be the powerhouse that keeps pulling on all the stars in the galaxy, causing them to swing around the center of the galaxy in orbits.
How is the Doppler Effect used to find out planet sizes?
As a planet orbits a star it tugs on the star. (Gravity always goes two ways). This causes the star to wiggle back and forth a little. If the planet is lined up right, the star moves towards and away from the Earth a little. As the star moves towards the Earth (a little) the light waves coming towards us are compressed and become a little bluer. As the star moves away from the Earth (a little) the light waves coming towards us are stretched out and become a little redder: thus red-shift and blue-shift. This is the same as the Doppler Effect.
Depending on the mass of the planet, the star will wiggle more or less (more for a bigger planet, less for a smaller planet). We can measure how much the light waves are stretched and compressed, and can know how much the star is moving, and therefore how much mass the planet has.
How effective is it for Earth-size objects?
::snort:: We all wish it were. It’s not at all. We can only find Jupiter-ish sized planets this way. For Earth-sized planets we’ll have to wait until the Kepler mission gets going. It’s detecting planets using the “Transit Method.” It looks for planets to go in front of stars and block out some of their light. It’s going to stare at the same 100 stars in the same part of the sky (near the Summer Triangle) for four or five years trying to detect planets this way.
What uses does astronomy have?
The age-old question, I’ve been working out a good answer to this question for years. I’m not done yet, but here’s what I have so far.
First: Understanding. We cannot understand our universe until we study it.
Second: Legacy. We (21st-century humanity) are not going to build pyramids: we’re going to build a legacy of knowledge and information.
Third: Discovery. By studying the universe and gaining understanding we may discover (either “out there” or through the technology we use to study “out there”) the answers to mysteries and problems closer to home (starvation, poverty, international cooperation, disease).
Fourth: Hope. Are we alone? Many people hope we’re not. What is the meaning of life? Besides “42,” many people hope that our discoveries in astronomy may lead us closer to an answer.
Why do supernovas happen?
There are two kinds of Supernovae: Supernovae Type Ia and Type II.
Type Ia (white dwarf and giant star)
Type Ia supernovae occur when you have two stars orbiting in a binary system: a white dwarf star and a larger companion star. If they’re close enough together, gasses fall from the bigger star onto the white dwarf, and if this happens too fast, the star explodes.
Type II (one star dying):
A star stays star-sized the same way a balloon stays balloon-sized: competing forces. In the case of a Helium balloon the Helium is pushing out, trying to escape from the balloon. If it weren’t for the air around the balloon, it would explode – allowing the Helium to escape. The air (the atmosphere) is pushing back on the balloon, trying to flatten it.
In the case of a star, the energy from the fusion reaction at the core of the star is pushing out, keeping the star big, and gravity is pushing in, trying to collapse the star into a neutron star or black hole. As long as the fusion keeps going, the star stays “inflated.” A star starts by fusing Hydrogen atoms together to make Helium atoms. When it’s used up all its Hydrogen it starts fusing Helium atoms into Carbon, Nitrogen and Oxygen. When it’s done with that it keeps on going, fusing smaller atoms into bigger ones until it gets to Iron (Fe). All of these reactions release energy, allowing the star to shine and stay “inflated.”
Unfortunately Iron doesn’t give energy back when it’s fused. Since there’s no longer fusion energy pushing out inside the core of the star, gravity begins to win. The star starts to collapse: squishing all the atoms in the star closer together, fast. This creates a very, very, very dense and heavy core to the star. The core is so dense and heavy that the outer layers of the star (that are still being pulled in by gravity) “bounce” off the surface of this core. They bounce so hard they’re thrown off into space making the biggest explosion we know of: a supernova. It also leaves behind a neutron star (that super-dense core).
What are some current studies/research being conducted about space?
Spitzer. STEREO. CloudSat. Mars Reconnaissance Orbiter. Genesis. ICEsat. Stardust.
What is the difference between quasars and pulsars?
Quasars (QUAsi-StellAr Radio sourceS) are galaxies. Pulsars are stars.
Quasars are areas in galaxies of intense activity – usually thought to be super-massive black holes at the centers of the galaxies. Pulsars are rotating neutron stars.
How important is Hawking Radiation?
It’s not going to bring about the end your life. Actually it may have already saved your life.
HERE’S THE WEIRD PART: Due to conservation of matter, we can assume that matter can be created from nothing, as long as it disappears quickly enough for the universe “not to notice.” If you imagine that a particle is created from nothing, you can get away with it if its antiparticle (like a positive number and a negative number) is also created from nothing right next to it and they immediately combine – going back into nothingness ((+1) + (–1) = 0). These imaginary particles are “virtual particles.” These effects are called Vacuum Fluctuations.
Okay. I’m going to write this in steps.
1. A black hole exists.
2. Anything that ends up within the black hole’s event horizon ultimately falls into the black hole, adding its mass to that of the black hole. It can never escape.
3. A virtual particle pair springs into existence RIGHT ON the event horizon.
4. Before they can annihilate (combine and disappear) one falls into the black hole’s event horizon. OH NO!
5. The second virtual particle is stuck! It can’t disappear anymore, its pair (its soulmate if you will) is gone forever!
6. The universe notices.
7. An extra particle is now outside the black hole’s event horizon. It’s a real particle now, not a virtual one because it existed for too long and the universe noticed.
8. But wait! You’re NOT ALLOWED to create something from nothing, so this particle had to come from somewhere.
9. The universe asks its bookkeepers where this extra particle came from.
10. The bookkeepers scramble. They’re being audited. Ummm… no one will notice if we take a little of the energy from the black hole, will they?
11. So, clearly the energy for this new particle must have come from inside the black hole.
12. The black hole is now down one particle’s worth of energy. (Another way to think of this is that the virtual particle that fell in had “negative” energy).
13. So, if you weren’t following all this anthropomorphizing of the universe (If you don’t like the fact that I made the universe act like a person) – ::poof:: it looks like a particle is now beside the black hole, and the black hole is a little smaller.
In effect, the black hole has evaporated a little bit. Big black holes are sucking in so much mass that this tiny evaporation doesn’t have any effect. Tiny black holes, on the other hand, evaporate faster than they can suck in matter. So if there were a one-atom black hole created on Earth, one might be afraid that it would suck in the atoms next to it, and the molecules next to that, and get bigger and bigger until it sucked in the Earth. Luckily a one-atom black hole would evaporate before that happened. At least, so say the physicists in Geneva who are trying to created tiny black holes.
More? http://focus.aps.org/story/v16/st12