Quickie Questions - Astronomy - Galaxies

Date Answered Questioner (age, location) Question Answer
February 21, 2011George(New York)What is the difference between dark matter and dark energy?Matter and energy are equivalent in the sense that either can be converted into the other, such that the total matter plus energy in the universe, M, never changes. "Dark energy" is a hypothetical energy whose existence would help explain the observed accelerating expansion of the universe. Dark energy is about 73% of M, but only 1 gram in a cube 50,000 kilometers wide. "Dark matter" is also inferred to exist to explain cosmological observations, but is about 23% of M, and more variable in density than is dark energy. Both things are called "dark" because only gravity can "see" them, not light or any other forces. [Sources: Wikipedia and recalled lectures.]
April 1, 2010gianelli (philippines)why do galaxies' shapes differ?Just very recently, astronomers have explained the diversity of galaxy shapes seen in the universe. The scientists, Dr Andrew Benson of the California Institute of Technology (Caltech) and Dr Nick Devereux of Embry-Riddle University in Arizona, tracked the evolution of galaxies over thirteen billion years from the early Universe to the present day. This article describes in more details their research, but in short, their model suggests that the number of mergers between very large haloes of dark matter and the galaxies they surround, drives the final outcome—elliptical galaxies result from multiple galaxy mergers whereas disc galaxies have seen none at all.
March 23, 2010bushra (pakistan)1 is there any other galaxy in our solar systemOur solar system is just a tiny element of the Milky Way galaxy. Our galaxy belongs to the Local Group, which comprises about 30 galaxies (including dwarf galaxies), with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy.
February 3, 2010melissa (georgia)what is a drawf galaxy?A dwarf galaxy is a small galaxy composed of up to several billion stars (for comparison purposes, our own Milky Way has 200-400 billion stars).
December 22, 2009douglas (united states/CA)are we the only people or living thing in the galaxy? couse i think the galaxy is to big for us to knowAs far as we know, yes. But scientists keep looking everywhere for extraterrestrial life!
December 22, 2009douglas francel (united states/CA)are we the only people or living thing in the galaxy? couse i think the galaxy is to big for us to knowAs far as we know, yes. But scientists keep looking everywhere for extraterrestrial life!
December 17, 2009Roger (UK)Is a spiral galaxy like a whirlpool drawing stars in or like a catherine wheel throwing stars out?Spiral galaxies look like a whirlpool, althoug mainly in two dimensions. The most widely acceptable theory for the spiral structure was devised by C. C. Lin and Frank Shu in 1964. From their work it is thought that the arms are manifestations of spiral density waves and the stars do not remain forever in the position that we now see them in, but pass through the arms as they travel in their orbits.
August 7, 2009Chris ( USA)Electrons and protons orbit a nucleus, moons orbit planets, planets orbit stars, system orbit in their galaxy, so wouldn't it be logical to say galaxies orbit a central mass?Some scientists believe that many if not most galaxies harbor suppermassive black holes in their cores. These black holes have gobbled so much matter that they have the mass of billions of suns. Visit our web page Black Holes for more information.
July 27, 2009Rishiraj (West Bengal/India)what will happen to milky way and after it along with andromeda being separated from rest of universe by negative pressure of dark matter?I am not sure what you are asking about, but it has been predicted that there will be an Andromeda-Milky Way collision in about 3 billion years' time. Because galaxies are so diffuse (for example, the nearest star to the Sun is almost thirty million solar diameters away), there is a very low possibility that celestial objects will collide. If such galactical collision happens, the twogalaxies would merge in one.
May 18, 2009Salee (Sri Lanka)How does galaxi destroy?Galaxies can interact among them through gravitational collisions. There is even a term for when a galaxy takes parts of other galaxies: Galactic cannibalism.
May 18, 2009Ismail (Michigan)Why do stars rarely collide during galactic collisions?Because galactic collisions are not like the mechanic impact that we associate with, for example, a car collision, they are rather gravitational interactions.
March 25, 2009Katie (Tennessee)What is the name of our galaxy group?The Milky Way is part of a set of galaxies known as the Local Group, which includes several dozen different galaxies within 3 million light-years. Only one of these, the Andromeda galaxy, is close to the size of the Milky Way.
March 16, 2009john (florida)do any one know how many starsare in our galaxy aloneIt has been calculated that there are 100,000,000,000 stars in our galaxy.
February 27, 2009Vidya (Bangalore, India)How do you know wether there is more than one galaxy?Galaxies are visible through potent telescopes. For example, enjoy this Galaxy Collection from the Hubble Space Telescope.
February 20, 2009stephanie (california)why is the milky way galaxy important?It is the galaxy where we live!
February 6, 2009bob (northcarolina)if the center of milkyway is so brite why cant we see itNo one knows what is in the center of our galaxy! It is not possible to see the Galactic center in light our eyes are sensitive to because the thick dust in the plane of our Galaxy obscures it. Please, visit NASA webpage for aditional information.
September 30, 2008Nicole (California)How many galaxies are visible to the naked eye from the United States?As far as I know the Andromeda Galaxy (also known as NGC224, and M31) it the only visible to the naked eye. This spiral galaxy is 2.3 million light years away, and it is visible, but a dark sky and good eyesight is needed.
September 9, 2008lokeswer (chennai,india)where does the nearest galaxy located in the space?why is moon called a dead planet?The nearest galaxy to our Milky Way is called the Canis Major dwarf galaxy after the constellation in which it lies, it is about 25 000 light years away from the solar system and 42 000 light years from the centre of the Milky Way.
August 25, 2008MIchelle (New Jersey)What is the Milky Way?The Milky Way galaxy is a giant star-city. Our Sun is one star in the city, and there are many, many others, our neighbors. Our Galaxy looks like a pinwheel - it is a spiral galaxy. There are spiral arms and a bright central part. The Sun is far from the center of the Galaxy. The Sun is going around the center of the Galaxy, and it takes the Earth with it!
June 19, 20086 th graders (Romania)Is the light speed big enough for us, humans, to colonize the Galaxy?The disk of the Milky Way galaxy is about 100 000 light years in diameter. This is, it would take 100 000 years, traveling at light speed, to go from one side of the galaxy to the other.
May 22, 2008Ryan (Maryland America)I DON'T want you to do my home work, The Andremoda galaxy is m31 or m33 What are both names for other galaxiesThe classification of galaxies started with the Messier catalogue. The Messier objects are a set of astronomical objects catalogued by French astronomer Charles Messier in his catalogue of Nebulae and Star Clusters first published in 1774. The first edition of the Messier catalogue covered 45 objects numbered M1 to M45. The total list consists of 110 objects, ranging from M1 to M110.
April 15, 2008Nathaniel (Indiana)Why are the Milky Way and the Andromeda Galaxy to move toward each other at 67-87mps?The Andromeda and the Milky Way galaxies are part of the Local Group, a group of over 35 galaxies, with its gravitational center located somewhere between the Milky Way and the Andromeda Galaxy. because they are so "close" (from a galactical point of view) the gravitational force between them plays an important role, which in no way contradicts the expansion of the universe!
March 18, 2008john (nevada,usa)in the expanding universe, how can galexies collide?There is always a tour de force between the gravity trying to pull galaxies together and the expansion of the universe trying to pull them apart. When big galaxies are close enough, it is gravity the predominant force.
March 3, 2008Helmut (Germany)How many (earth) years does it take the milky way to spin around itself once?The Milky Way rotates, in the vecinity of the solar system, with a period of more than 200 million years.
March 3, 2008Helmut Domas (Germany)How many (earth) years does it take the milky way to spin around itself once?The Milky Way rotates, in the vecinity of the solar system, with a period of more than 200 million years.
February 25, 2008LucifurI'd like to know how far away andromeda is from usIt is about 2.9 million light years (1 light year = 9.4605284 × 1012 kilometers).
December 10, 2007Kacey (usa)how do galaxies form???For an extensive discussion on galaxies, please, visite NASA's web page What Are Galaxies? How Do They Form and Evolve?. From this site we extracted the next paragraph: After the Big Bang, the universe was composed of radiation and subatomic particles. What happened next is up for debate - did small particles slowly team up and gradually form stars, star clusters, and eventually galaxies? Or did the universe first organize as immense clumps of matter that later subdivided into galaxies?...
October 16, 2007LawrenceI was taught in school that our Universe was created by the Big Bang Theory. You know ...everything moving out and away from its source. Also....Things that "Collide" come from opposite directions. Question...If that is so, then how do Galaxies collide?Because galaxies and other celestial bodies are in continuous change, including the formation of new ones, no all galaxies are in the original path of expansion, and so collisions occur, and quite frequently.
July 20, 2007monica (india)how many galaxies does the universe have ?There is no a final answer to your question. Currently about 100 000 galaxies have been have surveyed, but the final number could reach into de millions.
July 3, 2007Kathy (United States of America, California)How do moons, planets, and comets move toward a constellation?The Sun, and with it all the planets, moons, comets, etc., orbits the galaxy at about 220 km/s, taking nearly 220 000 000 years to complete one full orbit (galactic year). This is due to the huge size of our galaxy, and the position of the Sun on it.
May 5, 2007nicole (US,CALIFORNIA)WHAT IS A NAME FOR AN ELIPTICAL GALAXY?Elliptical galaxies are ellipsoidal agglomerations of stars, which usually do not contain much interstellar matter. Examples of elliptical galaxies are: Messier 32 (M32), M49, M59, M60, M87, M89, M105, M110.
April 7, 2007amna (uae)did you find a new planet ?
in which arm of the galaxy is the solar system ?
do you have a picture of insaid the space shuttel ?
The sun is about 26 000 light-years from the center of the Milky Way Galaxy, which is about 80 000 to 120 000 light-years across (less than 7 000 light-years thick). The solar system is situated within a smaller spiral arm, called the Local or Orion Arm, which is a connection between the Sagittarius Arm and the Perseus Arm.
February 24, 2007shelby (florida)what is size of a galaxy's nucleusDifferent galxies have different characteristics of their nucleus. For example, the Milky Way, our own galaxy, has a central elliptical bulge with a diameter of around 12 000 light-years.
January 22, 2007Jenny (Nevada/U.S.A.)Do galaxies, move, orbit around something, or do they just stay still?The revolving movement of a galaxy round its central nucleus even as it continues its proper motion. One revolution of the Sun within our the Milky Way takes about 225 million years, or 1 cosmic year. Recent measurements of variations in the universe's background radiation indicate that the Milky Way galaxy and neighboring galaxies are moving through space at 375 miles/sec or 1.3 million mph.
December 27, 2006Daniel (HAMILTON/ UNITED STATES)THIS GALAXY WE ARE IN IS CALLED OUR OR THE MILKY WAY WHAT IS THE GALAXY CLOSEST TO US CALLEDThe Milky Way's nearest large galactic neighbor is the Andromeda Galaxy. It is wider and possibly brighter than our own Milky Way.
December 14, 2006Heidi (California, Ceres)tell me everything about galaxies PLEASEDuring the early 1900's, which is not very long ago, astronomers were unaware that there were other galaxies outside our own Milky Way Galaxy. When they saw a small fuzzy patch in the sky through their telescopes, they called it a nebula. When examined closely, some of the nebulae had a spiral shape. So astronomers at first called these "spiral nebulae". These nebulae were all believed to be part of our Galaxy, our community of stars. More information on this topic can be found at our web page Galaxies.
December 13, 2006Linden (Massachusettes, United States)How far away are the Small Magellanic Clouds from Earth?The Small Magellanic Clouds are a distance of about 200 000 light-years.
December 9, 2006Yolanda (Louisiana)Which of the following is not proven to be part of the solar system: asteroids, comets, meteors, or galaxies?A typical galaxy contains ten million to one trillion (107 to 1012) stars, all orbiting a common center of gravity. A solar system is formed by planetary bodies moving around one of these stars. In other words, a solar system is just a very small part of a galaxy.
December 9, 2006nick1_10030 (ny ny)what is the difference between the solar sytem and a glaxyA typical galaxy contains ten million to one trillion (107 to 1012) stars, all orbiting a common center of gravity. A solar system is formed by planetary bodies moving around one of these stars.
February 3, 2003Eric (Canada)How many other planets do you think are outside our solar system in the Milky Way Galaxy?So far, astronomers have discovered about 100 planets outside of our solar system. Only one so far discovered is more than 160 light years from Earth (our galaxy is 90,000 light years across!), and all are large planets like Jupiter. About 30 billion stars in our galaxy are roughly "Sun-like", and astronomers guess that between 5 and 90 percent of those have planets like Jupiter. So there might be between 1.5 and 27 billion Jupiter-like planets in our galaxy. There may be many more smaller ones!
September 12, 2002Samantha (New Zealand)Why is the Milky Way called that?It got its name from the way it makes a white path through the night sky (billions of distant stars packed close together make it look uniformly white). You might look at our Milky Way page.

September 14, 2001Robert What is at the center of the Milky Way? Is it our sun or is it another sun? How many planets are in this galaxy (known)? Just curious, these questions kind of came to me.At the very center of the Milky Way, there is generally thought to be a black hole with the mass of at least 100,000 Suns. For more information on the Milky Way galaxy and where our Sun is located in the Milky Way, see this page.

The number of planets in our galaxy is tough to answer, because we haven't been able to look closely at the vast majority of stars for planets that might be circling those stars. The number of known planets is less than a hundred, but there must be a lot more that we haven't seen yet.

March 1, 2000Mike (Washington, USA)When is the Andromeda Galaxy visible?

The Andromeda Galaxy is located in the constellation Andromeda. Andromeda is found during the fall in the northern hemisphere.

Andromeda is close to the celestial north pole, so very few living in the southern hemisphere can see the constellation. Those that can will see Andromeda in the spring.

July 16, 1999Chris (Michigan)Do all galaxies spin in the same direction and do groups of galaxies spin in the same direction?Galaxies in local groups seem to have random orientations and rotations. However, there is a large scale structure or pattern to the Universe. As many as 50% of the galaxies in the Universe are grouped together in clusters and super clusters which in turn are organized into huge strings and walls of galaxies millions of light years across (see a computer simulation representing this pattern here).
June 16, 1999Sergio (Oregon)How many galaxies are in the universe?
How many stars are in each galaxy?
There are over 100 billion galaxies in the visible universe. The number of stars in each galaxy varies widely, but each galaxy probably has a couple billion stars on average. Talk about alot of stars!
May 24, 1999Sam (New Jersey, USA)Except for Spiral, Irregular, and Elliptical Galaxies, are there any other types of galaxies? If so, what are they?No, galaxies are always classified in these three categories. Any galaxy that does not fit in the spiral or elliptical categories is put in the irregular category.
May 12, 1999Janet (Louisiana,USA)I accidentally found an article stating that a new galaxy in our Local Group was discovered in 1975. The article stated that the name of the dwarf satellite of our galaxy is 'Snickers'. Is this information valid?Actually, what you read is correct, although the name is Sagittarius, not Snickers. Scientists believe the really small dwarf galaxy (10,000 times smaller than the Milky Way ) is crashing into our galaxy right now! Do you feel any rumbling?...
May 7, 1999Paul (New York, USA)Are all the stars that can be seen with the naked eye part of the milky way galaxy? Are any stars not part of any galaxy? Are Deep Space non galaxy objects (ie. ring neb. dumbell neb. Orion Neb. double stars etc. messier and ngc objects)part of the milky way?All the stars we see with our eyes are part of the Nebula that we see in books like the Orion Nebula are all in the Milky Way galaxy as well. There are many in other galaxies too, but we can't get take such beautiful pictures of them because they are too far away!
March 13, 1999Felipe (California, USA) I have been looking for a 'map' of our galaxy. Perhaps not the pictures from NASA but a drawing that shows the arms and our solar system location. Could you tell me where to find it?You might like to look at this simulation of what we currently believe the Milky Way to look like.
February 5, 1999Ashley (Ohio, USA)How many galaxies are there?We don't really know. There appear to be over 100 billion in the part of the universe we can see. However, the total number depends on if the universe is infinite or not. If it is infinite, there are probably an infinite number of galaxies. If it is not infinite, there are probably a few trillion galaxies.
November 9, 1998Skye and Cassandra (Queensland, Australia)What process do you use to find out what our Galaxy looks like? How do we know what our glalaxy looks like if we have never been outside it?We know by the fact that the Milky Way spans the sky as a narrow band of stars that the galaxy must be a flat system. Since there is no mass of stars collected in one spot, we know that it must not have a huge nucleus. Based on our knowledge of othe r galaxies, we can conclude that the Milky Way must be a spiral-type galaxy with a virtually non-existant nucleus. More detailed studies also show a distinct spiral pattern based on the locations and speeds of interstellar gas clouds.
April 17, 1998Clay (Illinois, U.S.A.) If the Milky Way is a spiral galaxy why does Pluto have an odd orbit?The Milky Way has nothing to do with Pluto's orbit. Pluto revolves around the Sun (our local star). Pluto has an odd orbit because it is not one of the original planets in the solar system. It was 'caught' by the Sun's gravity some time later.
Pluto's orbit is very uncircular and at an odd angle to the Sun's equator. This tells us it was caught by the Sun and probably was an asteroid for some time.
April 7, 1998Bob (Kentucky, U.S.A.) How many galxys are out in the solar system? And how many plantes rotate around them?There are actually no galaxies in the Solar System. The Solar System is just one of many, which put together along with other stars make up a galaxy. These other solar systems may also have planets as a part of them.
March 19, 1998Giulio ( Milan, Italy) What makes people think that in the center of our galaxy thers'a black hole?Current data indicates that there is a very dense 'point mass' at the center of our galaxy, containing mass up to 1 million times the mass of our sun. This indicates that there is probably a black hole located there.
February 27, 1998Lauren (Texas, USA) I need to ask a scientist what she thinks is a very interesting fact about galaxies for my first grade class project. I know stars like to live in cites called galaxies. Gravity is important. And galaxies come in 3 shapes. Do you know any other real important facts about galaxies. Can the scientist tell me why she wanted to study the galaxies?All the galaxies are moving through space away from each other. The Milky Way is moving in space at a speed of about 600 km/s. Our Sun, which goes around the Milky Way at about 250 km/s takes about 220 million years to go all the way around the Milky Way.
I think the most interesting thing about galaxies is that there are SO many of them, and they move SO fast. It's hard to imagine such huge numbers.
I study the galaxies and space and other science stuff because I like to know how and why things work. I like to find out how stars make light, and what makes wind blow, and why we need oxygen to live. That is what being a scientist is--finding out how things work, and then using the knowledge to do things like make medicine or travel to outer space.
February 19, 1998Lindsay (Pennsylvania, USA) How was the Milky Way formed?Galaxies begin when a large cloud of gas and dust begins to shrink as a result of its gravity. As the cloud shrinks, stars form from the gases at the center. The motion of the shrinking also started the Milky Way spinning, which flattened it into a disk shape.
January 30, 1998Lauren (Virginia, USA)Where did Andromeda get its name? Can you tell me any other interesting information about this 'spiral' gallaxy?Andromeda is the galaxy closest to Earth, although it is still 2,500,000 light years away. It contains over 300 billion stars and is located in the constellation Andromeda. The name Andromeda comes from Greek mythology, like many other constellation s. Andromeda was a young woman who was chained to a rock in the ocean to be eaten by a monster. She was rescued by a young man, Perseus. Eventually, she was put into the sky by Athene. The constellation is also designated by the number M31. This came around because the galaxy was the 31st object on a list of objects that were not comets. Charles Messier, 18th century French astronomer, made this list--all he cared about was comets!
January 29, 1998Steve (Kansas, USA)Do you think it is possible that our galaxy and even the known universe are nothing but an infinitely small piece of something much, much more grand, something like an atom is but a small piece of cell and the cell is but a small piece of a larger organism and so on etc. Couldn't our universe be nothing but a cell of something much bigger? They say that the universe is as infinitely small as it is infinitely big!I guess it is a possibility...the only thing is, the universe is everything that exists in space and time. So, unlike a three dimensional atom which is part of a three dimensional cell which is part of a three dimensional human, this "something bigger" would have to be of a completely different set of dimensions, meaning we could have no physical contact with it. So, unless we figure out how to get into other dimensions, we will just have to use our imaginations.
January 16, 1998Steve (Kansas, USA)What direction would we have to look in order to look toward the central hub of our own Milky Way galaxy?Let's see - the galactic center lies in the direction of the constellation Sagittarius. Sagittarius is a Summer constellation in the Northern hemisphere, so you have a few more months until you'll be able to look that way Steve!
December 30, 1997Brad (Kentucky, USA)What is the name of the closest galaxy to the Milky Way?The closest galaxy to the Milky Way is a recently discovered dwarf galaxy called Sagittarius which is actually crashing through the disk of the Milky Way! Sagittarius is a tiny galaxy, it is probably more than 10,000 times smaller than our Galaxy.
December 30, 1997Anne (Philippines)If we are looking at a galaxy or a star so many millions of lightyears away through the telescope, is it possible that they no longer exist right now?It is true that light from very distant objects can take a long time to reach us. For example, light from a star 100 million lightyears away takes 100 million years to reach us, so that we see the star as it looked 100 million years ago. If the star w ere the type that lived for less than 100 million years, then it could indeed be gone by the time we see it. Most stars live for billions of years, however, and the Milky Way galaxy is only about 80,000 lightyears across. So we can be sure that most of th e stars we see in our galaxy are still there. When we look at other galaxies, we are sometimes looking across billions of light years. But while some of the individual stars we see may be gone, galaxies themselves are huge and may take tens of billions of years to split apart. So we can also be sure that they are still there.
December 4, 1997Greg (Canada)What is a galaxy?A galaxy is a collection of stars, dust, planetary bodies, etc. that are held together by gravitational attraction. A galaxy may contain several billion stars!

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