What Are Stars?

Q:what is stars?

-Jean Carlos Pino (age 13)
William C. McGinnis school, Perth Amboy , NJ.
A:That’s an excellent question, Jean.

Stars are gigantic balls of gas, mostly hydrogen gas. There is so much gas and other material that the gravity of this huge gas-ball holds everything together. There is so much gravity that the gas becomes very dense and hot.

Our own sun is a star. Fortunately, we are far enough away from it that the gravity of the gas can’t pull us in. It would be rather unpleasant inside of a star.

The gravity is strong enough that it squeezes the gas together so tight that nuclear fusion occurs. That means that the nuclei (centers) of the atoms get stuck together and ’fuse’. This releases a lot of energy and causes the stars to heat up. The heat works its way from the inside of the star to the surface, and then radiates into space. So what we see of stars is the energy released from the nuclear reactions inside their cores and then radiated from the surface. Since most stars are VERY far away, the light takes anywhere from a few years to millions of years to reach us. So the star light that we see is very old indeed.

There are many different kinds of stars. They come in many sizes and colors. Some stars even orbit around each other. We call these binary stars. If you have any more questions about stars, please ask us to tell you more.

Math Dan

(republished on 07/19/06)

Follow-Up #1

Q:ok but is venus a star? can we see any star in the sky at night? which stars are visible?

-neelkirloskar (age 14)
pune,mah,india
A: Venus is very definitely not a star in the scientific sense of the word. It's just an ordinary planet. The reason you can see it so well is that it's closer to the Sun than us, about our size, and fairly reflective.  So you see lots of sunlight reflected off it.

I'm not quite sure how to answer the question about which stars are visible. Whether a star is visible depends both on how much light it gives off and how far away it is.

Mike W.

The number of stars ’visible to the naked eye’ varies.  In isolated rural areas or at sea it’s several thousands.  In well lighted urban areas it might be 100 or less. 
LeeH


(published on 06/07/07)

Follow-Up #2

Q:I have a quick question about stars and galaxies. Since you say that the stars are a sun just like ours, does that mean that there is millions of galaxies with their own sun and set of planets just like ours?

-Ogi (age 23)
Canada
A: We don't have the instruments yet to directly detect smallish planets like our own around other stars. However, from what we know about the universe, the answer is almost certainly yes, at least as far as the general physical features go. In fact it's quite likely that there are more than a million million million earth-like planets, just counting the visible part of the universe. As for what fraction of the planets have life on them, we really have no idea, although some people have very strong opinions on the subject.

Mike W.

(published on 10/16/07)

Follow-Up #3

Q:im having a hard time believing that the stars are really suns. So from a stars distance, does our sun look like a tiny little star?

-Christine (age 16)
indiana
A:Yes.

Mike W.

(published on 04/05/08)

Follow-Up #4

Q:what i can answer to my 4 years old son to his question,so he can understand: "Mom, what r the stars?" and "What is the difference between star and planet?"?

-nikol (age 31)
greece
A: I guess you could tell him that the Sun is a star, and that many other stars are similar to the Sun but they are very far away and so only appear as faint dots. The earth is a planet, and some of the other planets are similar to the Earth. Planets are just clumps of stuff (like the Earth) and give off no visible light, except whatever happens to bounce off them from a nearby star. Stars are extremely hot and therefore glow, like fire or an incandescent light bulb. What keeps them hot are nuclear reactions, kind of like in a hydrogen bomb, only running steadily rather than in a short burst.

There are other types of stars, and somewhat different planets (e.g. bigger colder ones like Jupiter) but I think this description may help your son get started.

Mike W.

(published on 05/10/08)

Follow-Up #5

Q:I know that stars are really suns burning away in the distance but...if there are so many suns then shouldn't there be planets they go with? It just seems strange that why do we have our own sun when there are loads more suns in the sky then does that mean there are more planets that just havent been found yet ? Thanks Rhiannon xxxxx

-Rhiannon Jones (age 16)
wales (wrexham)
A:Nice questions. You're right- there are lots of planets around other stars. Since planets are so much smaller and dimmer than stars, they're hard to see. However, in recent years a number of big planets have been found around nearby stars. As techniques have improved, smaller planets have also been found. So there are lots of planets around.

We really have no idea what fraction of these other planets have life, because we don't know how likely life is to get started even on a hospitable planet.


Mike W,

(published on 07/12/08)

Follow-Up #6

Q:I know that Stars are suns and alot of the above questions helped me win a debate with my girlfriend, so thanks for the ammunition. Another debate we are having are about twinkling stars, she seems to think they're aeroplanes or helicopters... i know they're stars but why do they twinkle? and why is it only a select few? thanks

-Conor (age 22)
Belfast, N.Ireland
A:Stars twinkle because the light from them passes through the atmosphere, which has density variations which change in time. That's like passing through a constantly shifting set of lenses. It makes the image move  around just a little. I think it happens with all stars, unless you're viewing from space. Maybe it's most noticeable with the brighter ones.

Mike W.

(published on 01/26/09)

Follow-Up #7

Q:what do stars have to do with black holes

-tom barnett (age 12)
brightlingsea colchester essex england
A:There are several connections between visible stars and black holes. Large stars collapse to form black holes when they use up their nuclear fuel.  Often one star will be in orbit around a black hole. Stars cluster in groups called galaxies, which often have very large black holes near the center. Stars sometimes get swallowed  up by black holes.

There are probably other connections, but those come to mind.

Mike W.

(published on 07/16/09)

Follow-Up #8

Q:what are the shooting stars and how does that happen? thanks

-ravi (age 13)
london, uk
A: Well, they are not really stars at all but tiny bits of micro-meteorites that enter the earth's atmosphere and are heated to incandescence by the friction of the air. They get white hot and make a streak of light through the sky.   They usually get burned up before they reach the ground but a particularly large one can make it all the way.  Several times a year the earth passes through large clouds of meteor dust and an exceptional display of shooting stars can be seen.  One good example is the Perseids shower which occurs around August 12th this year.    Take a look at http://stardate.org/nightsky/meteors/ for more details.

LeeH

(published on 07/19/09)

Follow-Up #9

Q:Are the stars we see at night all in our Solar system, or galaxy or perhaps even further / closer. ?

-Tom wells (age 16)
United kingdom
A: All of the stars you can see with the naked eye are from our own galaxy, the Milky Way. On a moonless night you can see several galaxies, such as the Andromeda, as faint smudges but you can't discern individual stars without a big telescope. 

LeeH

(published on 07/26/09)

Follow-Up #10

Q:In the first question that was presented, you stated that stars are gases mainly compressed by gravity. Where does this gravity come from and it is just a bunch of covalent/ionic or metallic bonds? Not sure if i will read your reply so could u please send it to my email

-Edwin A (age 18)
California
A: We only do Web postings, not email answers.
Anyway, gravity doesn't consist of those other types of bonds, which all come from electromagnetic forces. Gravity follows very different laws than electromagnetism does. For example, gravity is always attractive.

There are attempts to at least understand gravity in the same framework as the other forces, but so far those haven't been fully successful. At the level of ordinary experience, gravity is a completely separate force.

Mike W.

(published on 09/19/09)

Follow-Up #11

Q:I have basic knowledge about astronomy. I always wondered though. What age stage our sun is on as a star? like supernova whitedwarf etc...

-Tessa (age 20)
Australia
A: Our sun, a very ordinary star, is living comfortably in middle age as it travels along the road of the Main Sequence evolution line.  It was born about 4.5 billion years ago and will live another 4 or 5 billion years before old age sets in.  At this time much of the fuel in the sun will have been burned and the sun will turn first into a red giant and then shrink into a white dwarf and senility.  During the red giant phase, the sun's radius increases and will actually engulf the inner planets including the earth. After that it will collapse into a very small whitish star. The Sun is not massive enough to become a supernova or a black hole.
See  http://en.wikipedia.org/wiki/Stellar_evolution  for some interesting details.


LeeH

(published on 10/10/09)

 

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