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2002-Jan-07, 01:26 AM
Hi everyone! I'm Megan, the one that started 'Megan's Guestbook'!! Well, anyway I have loads of questions so dig in:
A) One night Lisa and I were talking about the stars, as usuall, and she was trying to explain to me why the stars don't really move. But the thing is is that I still don't get it. So here's my question: Why, from the humans eye, it seems like the stars don't move? And if they do, how come we can't tell??

B) What are luxons, muouns, and tachyons, and what is the difference between them?

C) What is a dwarf star, and what different types of them exist?

D) How do stars form?

E) What is the differecne between the goecentric and heliocentric theories?

F) Where does the sun get its energy?

G) What is the inversesquare law?

H) What are Kepler's Laws?

I) What are blue and red shifts, and what is the difference between them?

J) What are cosmic rays?

K) What is a singularity?

L) What is an elliptical galaxy?

M) What is an irregular galaxy?

N) What is a spiral galaxy?

O) What is magnitude? And what is it in astonomical terms?

P) What is the difference between the photosphere and the chromosphere?

Q) What is the difference between periapsis and apoapsis?

R) What is a neutrino?

S) How are stars classified?

T) What is the ergosphere?

U) What are interstellar dust grains?

V) What is a pulsar?

W) What is the Hubble Constant?

X) What is the sun made of?

Y) What is a supernova?

Z) What is a nova?

1) What is the difference between a meteroroid, a meteor, and a meterorite?

2) What is Doppler shift?

3) What are inner and outer planents, and how do they differ?

4) What are planetary atmospheres?

5) Why do stars appear to "twinkle"?

6) What is half-life?

7) What is a coma?

/phpBB/images/smiles/icon_cool.gif What is the difference between Apparent Time, Mean Time, Sidereal Time, and Universal Time?

9) What is an aurora, and what are the names of some of the famous ones?

10) What is a binary star?

11) What is the event horizon?

12) What is a Cepheid?

13) What is a nebula?

Peter B
2002-Jan-07, 03:35 AM
Wow! That's a lot of questions.

Respectfully, Megan, how old are you? This will affect to some extent the complexity of the answers we'll give you.

Simon
2002-Jan-07, 08:08 AM
Hey Meghan! That's not loads of questions, I've been on one message board where the "questions-per-post" record currently stands at 120.

Hrm... I don't know the answers to all of those, but I should be able to give pretty straightforward answers to most of them. Very simple answers, maybe, but there's so many I don't want to go in to page-long detail with each one. /phpBB/images/smiles/icon_biggrin.gif

A) Why, from the humans eye, it seems like the stars don't move? And if they do, how come we can't tell??

Have you ever driven in a car out in the country? Ever notice how that far-away tree seems to creep across the sky, as opposed to the nearby trees which whip by? It's exactly the same with stars, except that they're so far away you can only see their movements at all with sensitive instruments over a long period of time.

C) What is a dwarf star, and what different types of them exist?

There are several different types of stars called "dwarf stars," and they can get pretty confusing because they're all very different. White dwarves are the hot, glowing cores of old dead stars. Black dwarves are the cold, not-glowing cores of old dead stars. Red dwarves are living stars, just very cool and small ones. And brown dwarves are big balls of gas, maybe about 20+ times the size of Jupiter, that are bigger than planets and are smaller than stars.

D) How do stars form?

A big cloud of dust and gas in deep space starts contracting under it's own gravity until it forms a ball dense enough to start the nuclear fusion that powers a star (more on that later).

E) What is the differecne between the geocentric and heliocentric theories?

The geocentric system says that the Earth is the center of the solar system and the sun and all the planets orbit around it (geo=earth, centric=centered). I'd actually like to hear an argument about this in terms of how it applies to extra-solar planets, heh. /phpBB/images/smiles/icon_wink.gif The heliocentric system says that the Sun is the center of the solar system and Earth and all the other planets orbit around it.

F) Where does the sun get its energy?

From the nuclear fusion I mentioned earlier. In the core of the sun, it's so hot and under so much pressure that hydrogen atoms are slammed together and stick together, forming helium. That releases a lot of light, heat, radiation, and other forms of energy.

G) What is the inversesquare law?

Grr... I know it but can't think of a way to explain it. But here's a site that gives an explination and even a couple experiments:
http://www.exploratorium.edu/snacks/inverse_square_law.html

H) What are Kepler's Laws?

1st: The orbit of each planet is an ellipse.
2nd: The orbit of a planet covers equal areas in equal times.
3rd: The cube of the distance of each planet from the sun is proportional to the square of the orbital period.

In other words, I can't explain it right, so go to one of these sites and get a better explination:
http://www.cvc.org/science/kepler.htm
http://csep10.phys.utk.edu/astr161/lect/history/kepler.html

I) What are blue and red shifts, and what is the difference between them?

Blue and red shifts are changes in the frequency of light caused my motion of the source. In other words, if a star is moving towards us, the peaks and troughs of the wave of light it emits are sort of compressed, making it a higher frequency, which makes the light look very slightly bluer. Redshift is the exact opposite, a star moving away stretches the wave out and makes it look redder.

L) What is an elliptical galaxy?

This: /phpBB/images/smiles/icon_biggrin.gif
http://antwrp.gsfc.nasa.gov/apod/ap950913.html

M) What is an irregular galaxy?

This:
http://antwrp.gsfc.nasa.gov/apod/ap950728.html

N) What is a spiral galaxy?

This:
http://www.seds.org/messier/Jpg/m31.jpg

Q) What is the difference between periapsis and apoapsis?

Periapsis is the point in an orbit where whatever's doing the orbiting (moon, spacecraft, whatever) is closest to whatever it's orbiting (planet, star, whatever). Apoapsis is the point where they're farthest away.

R) What is a neutrino?

A tiny little particle that is produced as a side-effect of nuclear fusion. They are very small and light, even for particles, and hardly interact with anything, making them hard to detect. People have been trying to make accurate measurements of them to test theories of how quantum physics works.

V) What is a pulsar?

A type of neutron star, which is the collapsed core of a star like a white dwarf except much denser. A pulsar spins many times a second and it's magnetic field emits strong beams of radio waves, sort of like a lighthouse. So in a radio telescope they appear to blink or pulse very regularly.

X) What is the sun made of?

"Twinkle, twinkle, little star,
I don't wonder what you are,
for by spectroscopic ken,
I know you are hydrogen."
I don't remeber who said that, I have it written down somewhere. Anyway, he's right, the sun and other stars are mostly made of hydrogen, along with some helium, lithium, carbon, oxygen and other heavier stuff.

Y) What is a supernova?

Usually, a supernova is a large star that has run out of hydrogen to fuse in it's core, and burns the last of it's fuel in a big explosion, which can outshine an entire galaxy for a few weeks or months.

Z) What is a nova?

As far as I remember, a nova can be just about any stellar event which causes a sudden brightening in a star.

1) What is the difference between a meteroroid, a meteor, and a meterorite?

Meteoroids are floating out in space, meteors are plunging through the atmosphere, and meteorites are on the ground. That's it.

2) What is Doppler shift?

Redshift and blueshift.

3) What are inner and outer planents, and how do they differ?

The inner planets are defined as inside the solar system's asteroid belt, and are generally small and rocky. Mercury, Venus, Earth, Mars. The outer planets are outside the asteroid belt, and with the exception of Pluto, are gas giants. Jupiter, Saturn, Uranus, Neptune, Pluto.

4) What are planetary atmospheres?

Umm... what exactly do you mean by that? The answer "the layer of air around a planet" seem a tad obvious...

5) Why do stars appear to "twinkle"?

Light bends as it goes through the atmosphere, the same way it bends as it goes through water or glass. Small variations in the density of the atmosphere make the light from a star wiggle back and forth, making it appear to twinkle. To pre-empt your next question, planets don't twinkle because they appear as very very small disks, not points, and so the variations don't affect them as much.

6) What is half-life?

The half-life for a radioactive element is the average time it takes for half of it to decay in to something else. So if a lump of radioactive material has a half-life of ten days, after ten days half of it will have decayed in to a different material. After another ten days half of what was left would have decayed, so you would have one quarter of the original material. Another ten days you would have one eighth, and so on.

7) What is a coma?

A sort of haze of dust and gas around the head of a comet.

9) What is an aurora, and what are the names of some of the famous ones?

The earth's magnetic field tends to channel the charged particles from the sun towards the earth's poles. An aurora is when there's an especially strong spurt of particles and they hit the air at the poles, making it glow with an effect similar to a neon lightbulb. They are very unpredictible and temporary, and so I don't think anyone has gotten around to naming them.

10) What is a binary star?

Two stars that are close together and orbit around each other.

11) What is the event horizon?

Any point where, if something happens past it, there's no way you can see it. Most commonly used referring to the point of black holes where the gravity is so intense that nothing can escape, not even light. And since light can't escape it, you can't see what happens past it.

12) What is a Cepheid?

A type of star that brightens and darkens regularly, with a regular relation between the rhythm and the brightness. So if you time how long it takes to brighten and darken, you can figure out exactly how bright it is. Because of this, astronomers use them as guideposts to measure how far away things are.

13) What is a nebula?

A big collection of dust and gas; either the outer layers of a star that exploded, or a cloud that's compacting in to new stars.



WHEW!!! /phpBB/images/smiles/icon_biggrin.gif Not all of this may be 100% accurate, but I'm sure that if I've made any stupid mistakes somebody will correct me. Yay peer-review!

<font size=-1>[ This Message was edited by: Simon on 2002-01-07 03:10 ]</font>

<font size=-1>[ This Message was edited by: Simon on 2002-01-07 03:13 ]</font>

Argos
2002-Jan-07, 10:22 AM
Greetings, Megan. I praise your courage in asking what is thought to be so simple questions (though I personally think that it would take a lifetime to explain a single one).

Well done, Simon. This is what this board is about (I guess).

GENIUS'02
2002-Jan-07, 11:53 AM
B) the things that you mentioned are all subatomic particles, smaller than atoms, the main difference between them are their charges and spins.


well at least thats what i've been led to believe

GrapesOfWrath
2002-Jan-07, 12:31 PM
On 2002-01-07 03:08, Simon wrote:
9) What is an aurora, and what are the names of some of the famous ones?

The earth's magnetic field tends to channel the charged particles from the sun towards the earth's poles. An aurora is when there's an especially strong spurt of particles and they hit the air at the poles, making it glow with an effect similar to a neon lightbulb. They are very unpredictible and temporary, and so I don't think anyone has gotten around to naming them.
Probably, the two names that the question is looking for are "aurora borealis and aurora australis".

Russ
2002-Jan-07, 09:08 PM
I am truly impressed with Simon's effort to answer Megan's questions. To answer Simon's question, Megan is either late 15 or early 16. She had just turned 14 about two years ago when she first started posting to the old BABB and kicked off the "Megan's Guest Book". She has not posted all that much since but seems to be trying to make up for lost time with this one. 40 questions, WHEEEEWWW!!!!!

To Megan:

I am impressed with your questions but I think it's only fair to warn you that there are people with Dr. in front of their name still looking into the answers of some of them. I should also warn you that, in spite of Simon's valliant effort, you asked ALOT of questions. The true answers to some are too long and complex for this forum.

It will take a long time for you to understand the answers to some of your questions. For the ones on sub atomic particles (neutrinos, etc.) you will have to take chemistry and physics classes. The question on orbits and motion you'll need geometry and triganomitry. The questions on types of galaxies, star types and black holes, Doplar (Red/Blue shift) you can get the answers in a book called "Astronomy for Dummies" (the typical yellow & black cover). It's not really for dummies it just gives you answers to astonomy questions in a page or two.

I have been impressed with your posts, few as they have been. You ask good questions and have good ideas (eg your guest book). Keep asking questions and don't quit until your curriosity is satisfied. Keep talking to Lisa, she seems to be a fine lady too.

Lisa
2002-Jan-08, 04:19 AM
One of Megan's questions was definitly answered this evening. It is beautiful and clear out, not a cloud. The milky way is quite a sight. (sorry ljbrs)
Anyway, we found the Orion nebula. My scope isn't that strong, but it was enough to get a "wow" from us both. Also, Saturn's rings were cool, as were the moons of Jupiter.
Megan and I live where there's almost too many trees, but we have high hopes for summer viewing when we go camping.
Lisa

Peter B
2002-Jan-09, 05:00 AM
Some more answers (hopefully they're right...):

K) What is a singularity?

A singularity is a dimensionless point with infinite density.

O) What is magnitude? And what is it in astonomical terms?

Magnitude literally means size. The concept of orders of magnitude is often used to represent increases in size by a factor of 10. So if one object is two orders of magnitude larger than something else, itís 100 times larger. One place itís used is the Richter scale, which measures the effect of earthquakes: increasing the size of an earthquake by 1 factor on the Richter scale means it was 10 times as powerful.

In the case of stars, the magnitude system is somewhat different, and Iím not familiar with it except to the extent that the lower the number, the brighter the object.

U) What are interstellar dust grains?

It's exactly what itís name says; material which hasnít been incorporated into stars or planets. What itís made of is probably every element in the periodic table, and quite a few compounds. I seem to remember reading somewhere that even some sugars have been found in interstellar space (someone correct me?).

W) What is the Hubble Constant?

It is the ratio between the distance a galaxy is from us and the speed its receding from us. (The further a galaxy is from us, the faster its moving away.)

DStahl
2002-Jan-09, 06:52 AM
I don't see that anyone answered your question about cosmic rays. Here's the tiny bit I think I remember on the subject:

Cosmic rays is a really cruddy name, because it makes you think of rays of light. But what we're really talking about are little bits of matter--one single proton, which is the same as the nucleus of a hydrogen atom; or perhaps two protons and two neutrons, which is the nucleus of an atom of helium--which are travelling along at absolutely stunning speed through space. They probably get started in the magnetic field around a black hole or a neutron star. The magnetic field whips them around and shoots them off through space, and some of these particles come zinging into Earth's atmosphere where they almost immediately crash into a molecule of nitrogen or oxygen in the air. The result is like a cannonball hitting a gallon jug of milk: stuff sprays everywhere!

That messy spray of subatomic debris was one of the first places physicists got a look at some of the oddball particles like muons...see below.

Genius answered your question B--What are muons, tachyons, and luxons--but in my usual wordy way I'll give a little more detail... /phpBB/images/smiles/icon_wink.gif

These are all subatomic particles or classes of particles...or perhaps, in the case of tachyons, hypothetical particles.

You know that atoms are made up of protons and neutrons, which live in the nucleus of the atom, and electrons, which vibrate around about the nucleus in odd-shaped patterns called orbits, right? Those are the subatomic particles most people think of first.

A muon is much like an electron except that it's something like 2010 times heavier and it's not stable, like an electron. Electrons last forever, or almost forever, but muons decay in about .000002 seconds--most often they turn into one electron and two neutrinos. They're created sometimes when cosmic rays--very fast-moving protons or the nuclei of helium atoms--slam into another atom.

Tachyons are a class of hypothetical particles that have never been observed. Now no particle we have observed can travel faster than light, and only particles with zero rest mass can travel at the speed of light. (Rest mass is the mass that a particle would have if it was not moving.) Well, a tachyon--if it exists--would be a particle that can only travel faster than the speed of light. In some ways tachyons would invert the behavior of the particles we know and love. For instance, if a proton is zooming through space and something causes it to lose energy, it slows down, same as a car or a butterfly. But if a tachyon is zooming through space and it loses energy, it speeds up. (Huh? How can that be? I don't know!)

Luxon is one name given to the class of particles that move at the speed of light. Photons are the most familiar luxons, for they're the wave-particle bits that compose light. Gravitons are another example of luxons...and another particle that is allowed by theory but which has never been directly detected. All luxons have zero rest mass.

So, we have names for the class of particles that travel at the speed of light--luxons, or "lightlike ones"--and for the class of hypothetical particles that only travel faster than the speed of light--tachyons, or "fast ones." What about heavy, normal particles like the ones that make up the atoms in cars and butterflies? We can call this class of particles tardyons or bradyons, names that both mean "slow ones."

Megan, there are lots of subatomic particles--a whole "particle zoo"--but almost all of them are unstable. At the end of the day all the weirdo particles like muons, pions, and kaons decay into only a handful of stable ones: protons and anti-protons, electrons and positrons (anti-electrons), neutrinos, and photons. (A neutron all by itself is unstable, although it takes about 15 minutes to decay--that's very long by particle standards--but if it's inside an atomic nucleus it lasts virtually forever. I guess the protons in the nucleus calm it down!)

Here are some online references:

Eduweb's Particles and Relativity FAQ (http://atschool.eduweb.co.uk/rmext04/92andwed/pf_quant.html)

Science Prof's animations (http://www.scienceprof.com/physics_3.html) includes one of subatomic particles

A nice explanation (http://www.xmission.com/~dparker/electron.html) of the discovery of the electron and other particles.

Enjoy!

--Don

<font size=-1>[ This Message was edited by: DStahl on 2002-01-09 02:06 ]</font>

<font size=-1>[ This Message was edited by: DStahl on 2002-01-09 02:38 ]</font>

GrapesOfWrath
2002-Jan-09, 12:21 PM
On 2002-01-09 00:00, Peter B wrote:
O) What is magnitude? And what is it in astonomical terms?

Magnitude literally means size. The concept of orders of magnitude is often used to represent increases in size by a factor of 10. So if one object is two orders of magnitude larger than something else, itís 100 times larger. One place itís used is the Richter scale, which measures the effect of earthquakes: increasing the size of an earthquake by 1 factor on the Richter scale means it was 10 times as powerful.

In the case of stars, the magnitude system is somewhat different, and Iím not familiar with it except to the extent that the lower the number, the brighter the object.
An order of magnitude has different meanings, in different contexts. Usually, it means an additional multiplication factor. "An order of magnitude larger" could mean "twice as large" in some contexts. Commonly, though, it means a multiple of ten.

Astronomical star magnitudes are based upon relative brightness, and were assigned subjectively thousands of years ago. The system was quantified, and now an order of magnitude represents an increase in brightness of 2.512 times. That number was chosen so that five magnitudes is 100 times the brightness. In other words, 2.512^5 = 100, so a first magnitude star would be 100 times brighter than a sixth magnitude star.

David Hall
2002-Jan-09, 02:13 PM
Can I chime in here? I'd like to address the questions that haven't been answered yet, and add to a couple of other answers.


K) What is a singularity?

As mentioned above, a singularity is a point where a quantity of mass has been compressed down to a single infinitely small point. It's most commonly used in reference to black holes, where gravity has squeezed matter down into a singluarity.

O) What is magnitude? And what is it in astonomical terms?

The use of magnitude in astronomy, as mentioned above, is to classify objects by their brightness. The lower the number, the brighter the object. The numbers jump in multiples of 2.5. A star with a magnitude of 1 is 2.5 times brighter than a star with a magnitude of 2. There are actually 2 kinds of magnitude, apparent magnitude--how bright the object appears when we look at it directly, and absolute magnitude--how bright the object really is, as if it were seen from a standard distance of 10 parsecs (32.6 light years) away.

The brightest star, Sirius, has an apparent magnitude of -1.5, Venus at it's brightest is -4, the full Moon is -13, and the Sun is at about -26. The dimmest stars you can see with your naked eyes are at about 6.5.

Q) What is the difference between periapsis and apoapsis?

These were defined very well above. It's interesting to note that there are other names as well. When objects are orbiting the Earth these two points are called perigee and apogee. When they are orbiting the Sun they are called perihelion and aphelion.

S) How are stars classified?

There are several ways to classify stars. The most common one compares the star's size (mass) to its temperature. If you lay them out on a chart, you get something called the Hertzsprung-Russell (http://casswww.ucsd.edu/public/tutorial/HR.html) (HR) diagram. We find that most stars fall on a simple diagonal line, and are easily separated into types by temperature/color. The largest and hottest blue stars are at the top left and the smallest and dimmest red dwarfs are at the bottom right. Each type of star is referred to by a letter. Starting with the hot blue stars and going down to red dwarfs, the letters are O, B, A, F, G, K, M.. and each letter has 10 grades 0-9. Our sun is ranked as a G2. You can remember the order easily by saying "Oh, Be A Fine Girl (Guy), Kiss Me."

Here's a very nice page which will tell you all about stars:
http://www.astro.uiuc.edu/~kaler/sow/star_intro.html (from a great star site: http://www.astro.uiuc.edu/~kaler/sow/sowlist.html

T) What is the ergosphere?

I don't know. Let's look it up. Ok... here's a definition: http://www.harcourt.com/dictionary/def/3/6/3/7/3637800.html

"ergosphere: Physics. that region around a rotating black hole, bounded on the inside by the event horizon and on the outside by the static limit. Also, ergoregion."

So it's an area surrounding a black hole, if the black hole is rotating. Other than that, I don't know any details. /phpBB/images/smiles/icon_smile.gif

Z) What is a nova?

As simon says /phpBB/images/smiles/icon_razz.gif, a nova is an exploding star. But more specifically, they usually happen when you have a binary pair of stars. One star pulls hydrogen gas off of the other and it keeps building until it reaches a critical point, when the surface explodes in a big burst of energy. Usually these stars can go through the process repeatedly. But occasionally the thieving star steals too much gas and ends up destroying itself completely in a type of supernova (different from the type mentioned above).

/phpBB/images/smiles/icon_cool.gif What is the difference between Apparent Time, Mean Time, Sidereal Time, and Universal Time?

Apparent Time is the time based on the Earth's rotation, the time-of-day you get when you measure the position of the sun. Since the Earth is not very smooth in it's rotation, Mean Time smooths them out to create an constant time-flow measurement. Sidereal Time measures the Earth's rotation, not from the sun, but from the background stars. The orbit of the Earth alters the position of the Sun in the sky, but the stars are not affected by this, so the length of the sidereal day is a little different from the Mean day. Universal Time is simply the local time of day at the Prime Meridian, the zero degree point on the Earth. It's used as the overall standard time, which is added to or subtracted from to calculate the time of day in other locations. Most astronomical events are given in UT format.

Here's a page explaining the various measurements of time: http://www.astroleague.org/al/astrnote/astnot10.html


9) What is an aurora, and what are the names of some of the famous ones?

As GOW said, there are two aurorae, Borealis and Austrialis, or the Northern and Southern lights.
Here's a nice page about aurorae: http://www.exploratorium.edu/learning_studio/auroras/

It's possible to classify them by color and form, but of course they are always changing. Here's a page on how to classify observations: http://www.users.zetnet.co.uk/astro_pics/aur_rec.html

Keep up the good work Megan. I'm looking forward to your next list. /phpBB/images/smiles/icon_smile.gif

_________________
David Hall
"Dave... my mind is going... I can feel it... I can feel it." (http://www.occn.zaq.ne.jp/cuaea503/whatnots/2001_feel_it.wav)

<font size=-1>(minor editing)</font>


<font size=-1>[ This Message was edited by: David Hall on 2002-01-09 09:34 ]</font>

David Hall
2002-Jan-09, 03:01 PM
Whups! Looks like I missed one.

P) What is the difference between the photosphere and the chromosphere?

These are layers of the Sun's outer atmosphere. The photosphere is the visible surface of the Sun, and the chromosphere is the layer of hot gas above that. Above the Chromosphere is the Corona, a diffuse glowing cloud of very hot gas.

Check out the definitions here:

http://www.astronomysight.com/as/info/planets/sun.html

That is all.

DStahl
2002-Jan-09, 08:09 PM
Oh, oooh, can I add something to the singularity discussion? Pretty please?

Our best and most precise theories about how the universe is put together break down when we try to use them to figure out exactly what a singularity is and what happens there. So while the definitions of a singularity given above are the best ones we know, there's a bit of wiggle-room because neither the theory of relativity nor the theory of quantum dynamics can really tell us exactly how space, time, and matter behave right at the thingamajig we call...singularity!

I just find that very, very cool.

--Don

J-Man
2002-Jan-09, 09:10 PM
I can add a little on this one... I assume an understanding of the concept of variables and equations.

G) What is the inversesquare law?

Basically the inverse square law applies to any formula that looks like f(x) = x/r^2 (Read: function of x equals x divided by r-squared.) An inverse proportion is one that goes down as the related factor goes up and vice-versa. So in our example equation, f(x) goes down (smaller number) as r goes up (larger number). Since the denomenator (bottom part of the fraction) is r-squared, this is an inverse-square proportion. The same as an inverse proportion except that f(x) gets smaller much faster as r gets bigger because the denomenator is r times r.

The first example of an inverse square law with respect to astronomy is light brightness.
(Sorry, no equation comes to mind.)
Basically, the "brightness" of a source of light decreases as the distance squared between the source and observer increases.

The second example of an inverse square law with respect to astronomy is Newton's gravitational force equation.
F = GmM/r^2
This equation says that the force of gravity will decrease as the square of the distance between two objects increases.

There are many other areas of physics that have inverse square relationships, one that comes to mind is electromagnetism.

quantumdrift
2006-Nov-15, 06:54 PM
9) What is an aurora, and what are the names of some of the famous ones?



According to the space.com page on auroras (http://www.space.com/auroras)


Auroras, also commonly referred to as the southern and northern lights, are a luminous atmospheric phenomenon that generally appear as bright colorful bands of light. Auroras are often visible in the night sky in both the northern and southern regions of the Earth.

antoniseb
2006-Nov-15, 08:53 PM
Ummm, why did you resurrect this almost five year old thread?

sarongsong
2006-Nov-16, 07:37 AM
Ah---that explains why 'Megan' has no profile or post count!

mickal555
2006-Nov-17, 05:58 AM
jkkurum?

adnanmaniar
2006-Nov-18, 05:13 AM
Megan) What are blue and red shifts, and what is the difference between them?


Here is a link, which can explain you much easier. Very good site
http://www.users.bigpond.com/telescopes/telescopes039.htm

Kaptain K
2006-Nov-18, 11:41 AM
Come on folks. Megan has not posted here since April of 2002! Why are you dredging up and answering 4 1/2 year old questions?

antoniseb
2006-Nov-18, 11:46 AM
I should have closed this thread earlier.