The University of Texas at Arlington

The University of Texas at Arlington

UTA Planetarium

UTA Planetarium

Ask the Astronomer Q&A

Tag: "sun"

  • Are all stars confined to certain galaxies?
  • Yes. In fact, our Sun and the stars we see in our night sky are all confined to the Milky Way galaxy. It is very difficult for people to see the stars of other galaxies because they are so distant. The nearest galaxy is the Andromeda galaxy, which is more than 2 million light years away. This galaxy can be seen in the summer skies in the Andromeda constellation, but you need to get far away from city lights. It will appear as a faint fuzzy object in the sky. If you look at pictures of galaxies taken from the Hubble Space Telescope and others, you may be able to pick out some of the brightest stars, but they are only visible to very large telescopes that have taken very long exposures of the sky.

    (Tags:  andromeda galaxy  milkyway galaxy  star  sun)
  • Are planetary distances measured to the Sun’s surface or its center?
  • The answer is actually neither. Distances in the solar system are measured from an object's center of which can be deduced from Kepler’s laws. If an object is perfectly spherical, the center of mass would be the center of the object. However, the Sun and the planets are not perfectly spherical, so the center of mass is somewhere off center. For planets in the Solar System, either the semi-major axis is given as “distance”, or the average distance is given. Average distance is simply half of (perihelion + aphelion), with other words, half of (largest distance plus smallest distance).

    (Tags:  physics  planet  solar system  sun)
  • Can we make Jupiter, Saturn, Uranus or Neptune into mini-Suns using lasers to ignite the fusion process, like they do at the National Ignition Facility? If so, will their moons begin to rotate instead of being tidally locked?
  • Your question is an interesting one. However, I must say that there is no way to turn these planets into mini-Suns by sending laser beams. Here are several major problems with your suggestion. First, laser beams would be damped in atmospheres of these planets and the beams would never reach central parts of the planets. Second, lasers beams are highly collimated, which means that we could only trigger a fusion process very locally in the upper parts of the planetary atmospheres, where gas density and temperature are relatively low. Third, the fusion process (if ever triggered) would neither be sustained nor spread throughout the atmosphere. Fourth, neither of these planets would be able to sustain nuclear reactions in their interiors (even if we found a way to ignite them there) because the interior temperatures and densities in these planets are not high enough to initiate any fusion process. Finally, I do not think that our current lasers are strong enough to even trigger a very localized fusion process in the most upper parts of atmospheres of these planets. Now, the fact that the moons are tidally locked has to do with the planet’s gravity, which would not change whether nuclear reactions would occur or not.

    (Tags:  gravity  jupiter  laser  light  neptune  planet  saturn  sun  uranus)
  • Does the plane of revolution of planets have anything to do with the angle of which their parent star rotates?
  • The revolution of all planets are in a plane called the invariable plane, that is defined with the angular momentum of the solar system. But there is an uncertainty on the invariable plane as we don’t know every object in the solar system. For this reason, we call ecliptic, the plane Earth revolves around the Sun, the plane of the Solar System for convenience. Sun’s rotation axis is tilted by about 7 degrees to the perpendicular to the ecliptic. Stars’ rotation axis has a lot to do with the invariable plane during the formation of stars, but we can’t rule that the invariable planes will be in 90 degrees tilt with rotation axis of host stars.

    (Tags:  ecliptic  solar system  star  sun)
  • How does the Sun's gravity keep Pluto in orbit, since it is so far away?
  • The Sun’s gravitational effect extends infinitely away from an object. The size and distance of the objects does not matter. In order to stay in orbit around the Sun, an object just has to follow Kepler’s Law of Motion: a^3=p^2. Where a is the semi-major axis and p is the period of rotation. In Pluto’s case a=39.264 AU (1 AU is equal to the distance between the Earth and the Sun – so Pluto is 39 times farther from the Sun than Earth is) and it’s period, p, is just over 246 years.

    (Tags:  gravity  pluto  sun)
  • How far apart are the stars in the Big Dipper Constellation?
  • ! The Big Dipper (or to astronomers, "Ursa Major," the big bear") is a group of stars which, when viewed from Earth, forms a striking pattern, but that by no means assures that they are all close to each other and have the same distance. It is quite possible that some are close to us, others distant, and only by chance are they found together in the same part of the sky. Anyway: the numbers. Main stars are named in order of brightness in their constellation, according to the Greek alphabet, and those forming the Big Dipper are Dubhe, Merak, Phecda, Megrez, Alioth, Mizar and Alkaid. A labeled map can be found at: Their approximate distances from the Sun in light years, according to are: Dubhe--86 Merak, Phecda, and Megrez—100 Alioth—64 Mizar—95 Alkaid—78

    (Tags:  big dipper  sun)
  • I know that the Earth goes around the Sun, the Sun goes around the Milky Way, and the Milky Way is moving somewhere too. I was wondering, if there is a totally static point in space, how fast is the Earth moving from that static point of view?
  • Earth's average distance to the Sun is 150,000,000 km (93 million miles), therefore the distance it travels as it circles the Sun in one year is that radius x 2 x pi, or 942,000,000 million kilometers in a year of 24 hours/day x 365 1/4 = 8,766 hours so you divide to get 107,000 km/h or about 67,000 mph. You could also say the Earth moves around the Sun at 30 km/s. The Sun circles the center of our Galaxy at about 250 km/s. Our Galaxy is moving relative to the 'average velocity of the Universe' at 600 km/second (

    (Tags:  earth  physics  solar system  sun  universe)
  • If Jupiter had developed into a brown dwarf star what effects would that have had on Earth's development? How visible would Jupiter be during the day and at night as a star?
  • If Jupiter was a brown dwarf star, it would not affect Earth very much. Brown dwarfs do not create much light, and since Jupiter is an average of 5 AU from the Earth (5 times the distance between the Earth and the Sun) it would appear as a pinpoint of light, a little brighter than Venus in the night sky. The farther away from the object you get, the dimmer and smaller it appears in the sky. For example, if we were to travel to Pluto, there would be no daytime. The Sun appears as a very bright star compared to the other stars in the night sky. But because it is so far away, it does not cast enough light on Pluto’s surface to have a bright daytime sky.

    (Tags:  brown dwarf  jupiter  pluto  star  sun)
  • If the Sun's gravity holds the planets in orbit, why is it that we can not duplicate this?
  • Gravity is something we can replicate. It is a force that is proportional to the mass of two (or more) objects and the distance between those objects. Gravity is what holds you to the Earth. It’s what keeps the Moon in orbit around us, and us in orbit around the Sun. If we had sufficient enough mass we would be able to create a “second sun” that would change the orbits of all the planets. The only problem is creating that much mass – the sun makes up over 90% of all the mass in our solar system. It weighs 1,980,000,000,000,000,000,000,000,000,000 kg! That’s 333,000 times more than the Earth weighs.

    (Tags:  gravity  planet  sun)
  • If the weight of our planet does not fluctuate... Does this include matter and mass ON the planet as well?
  • It depends on how the weight is calculated. If we estimate the density as a function of the radius of Earth, we can calculate the total mass up to its surface, not including the matter on the planet (air, trees, animals, etc.). If we calculate the mass from Newton’s 3rd law - using the Sun’s or the Moon’s mass (assuming that their mass are well known) – then we will figure the mass of Earth with everything on the planet. However, there will not be a significant difference as the air mass and the matter on the surface is negligible. Moreover, Earth’s weight is not constant. Every year, 100,000 pounds of dust and debris falls on Earth from the sky. Of course, this increase is negligible and will not affect the planet.

    (Tags:  earth  moon  physics  sun)
  • If we suppose Jupiter has moved from the place that it was originally created to the spot it is now in our solar system, what affect would it's gravitational movement have on Earth?
  • The current model that astronomers use to explain how the solar system formed, does not include any changes in orbit after the planet forms. There may be slight adjustments to a planet’s orbit due to mass changes over time, but nothing that will explain back and forth movements of the planets, because that would require an external force. For Jupiter to move closer or farther away from the Sun, there would have to be an external force tugging it - allowing the orbital period to change. But there is no known source in the solar system that would have the power to change the orbits by that much. Even though the planets have a small gravitational effect on each other, a change in planet configuration wouldn’t cause a dramatic change to the orbits of the other planets. Most of the gravity in the solar system comes from the Sun, so as long as the Sun remains in the system, the orbits won’t change much (if at all). That’s why Earth and Mars don’t orbit around Jupiter when they get in conjunction with Jupiter.

    (Tags:  earth  gravity  jupiter  mars  solar system  sun)
  • Is everything we see in the universe on fire or able to be seen because it is reflecting light from something on fire?
  • The answer kind of depends on what you are referring to. Take the planets of our solar system for example. They do not create their own light, they are just reflecting the Sun’s light back to us, the same is true for our Moon. On the other hand, the Sun, stars, galaxies and nebulae are all creating their own light. But I wouldn't say that they are on fire. It is true that astronomers talk about stars “burning” but we aren't referring to a fire like you may create in your fireplace or grill. What’s actually happening is Hydrogen atoms in the center of the star (like our Sun) are fusing to form Helium atoms. This creates an incredible amount of heat and light. The Sun is more than 10,000 degrees Fahrenheit!

    (Tags:  hydrogen  light  milkyway galaxy  moon  planet  star  sun)
  • Is it safe to look at Jupiter through a big telescope this month, September 2010?
  • Absolutely! Jupiter is currently near opposition. It is the best time to see Jupiter and the Galilean moons Io, Europa, Ganymede, and Callisto. Unlike the Sun, it is always safe to look at planets with telescopes. To look at the Sun, specially designed filters that take 99.9% of light away must be used. Otherwise permanent damage to the eye will occur. It is even harmful to look at the Sun directly (with unaided eye).

    (Tags:  jupiter  light  planet  solar system  sun  telescope)
  • Is there a danger from giant Solar storms predicted for 2012?
  • Solar activity has a regular cycle, with peaks approximately every 11 years. Near these activity peaks, Solar flares can cause some interruption of satellite communications, although engineers are learning how to build electronics that are protected against most Solar storms. But there is no special risk associated with 2012. The next Solar maximum will occur in the 2012-2014 time-frame and is predicted to be an average Solar cycle, no different than previous cycles throughout history.

    (Tags:  2012  apocalypse  earth  sun)
  • Isn't it possible that other planets rotate in and out of our solar system on longer cycles in elliptical orbits. E.G. Nibiru at 3,600 year cycles that our current civilization has not observed?
  • Although it is theoretically possible that more planets exist in our solar system that we have not detected, it is very unlikely. Everything in the universe has gravity, and this gravity effects everything in the universe. The closer 2 objects are to each other, the more their gravity effects surrounding objects. The same is true for large objects. The larger the object, the more gravity will effect surround objects. These effects are measurable by astronomers, even outside our own solar system. Astronomers have used this technique to find hundreds of planets in orbit around other stars. Since we have never seen any gravitational interaction on our Sun or the planets in our solar system, astronomers believe there are not any very large planets beyond the orbit of Pluto.

    (Tags:  2012  gravity  nibiru  physics  planet  pluto  solar system  sun)
  • Since it takes the moon about 28 days to orbit the earth, does that mean a solar eclipse happens somewhere every 28 days?
  • If the moon orbited in the same plane as the ecliptic – Earth’s orbital plane – we would have two eclipses every month. There’d be an eclipse of the moon at every full moon. And, two weeks later, there’d be an eclipse of the sun at new moon for a total of at least 24 eclipses every year. But the moon’s orbit is not the same as the ecliptic. It is inclined to Earth’s orbit by about 5 degrees. Twice a month the moon intersects the ecliptic at points called nodes. If the full moon or new moon is appreciably close to one of these nodes, then an eclipse is not only possible – but inevitable. Even though the moon’s orbit is inclined to that of Earth – and even though there’s not an eclipse with every full and new moon – there are more eclipses than you might think. There are from four to seven eclipses every year. Some are lunar, some are solar, some are total, and some are partial.

    (Tags:  earth  eclipse  moon  sun)
  • The center point of the Moon's rotation is Earth, the center point of the Earth;s rotation is the Sun, the center point of the Sun's rotation is the black hole at center of our galaxy; does that mean that the universe has a central point that can be pinpointed provided we had the instruments to measure this vast distance?
  • The center of the universe would be the location where the Big Bang happened. Since that time, all matter has moved uniformly away from this point in all directions. This expansion of the universe is still happening today and is actually accelerating. So instead of orbiting some central part of the universe, the universe is actually moving away from the center. Scientists are trying to discover what is causing the acceleration of the expansion of our universe.

    (Tags:  big bang  black hole  earth  milkyway galaxy  moon  sun  universe)
  • There is a bright light every evening to the West. I thought it was a satellite but I have been looking at it since last year. Do you know what it is?
  • What you have been seeing is not a satellite but the planet Venus. Venus appears as the brightest object in the night sky right after sunset, or right before sunrise. Venus is so bright, because of the thick carbon dioxide clouds that reflect a lot of sunlight back to Earth. We only see it near the Sun, because it is closer to the Sun than Earth. Did you know, that many people mistake Venus for a UFO? This is because it can appear to flicker, move and change color in the sky when it is low in the horizon. First time skywatchers also underestimate how bright celestial objects can be in the sky.

    (Tags:  astronomy  light  planet  sun  venus)
  • There's so much talk about the alignment of the earth and sun on 12-21-2012...But what about the other planets in the same alignment? Do solar flares affect other planets when they align with the sun and the blackhole?
  • We’ve answered the first half of the question before. There are no planetary alignments in the next few decades, Earth will not cross the galactic plane in 2012, and even if these alignments were to occur, their effects on the Earth would be negligible. Each December the Earth and Sun align with the approximate center of the Milky Way Galaxy but that is an annual event of no consequence. The black hole at the center of the galaxy is over 26,000 light years away (meaning it would take 26,000 years to reach it if you were travelling at 186,000 miles per second!) This is incredibly far away, so it’s effects are not noticeable to us. Solar flares are not at all related to the black hole at the center of the galaxy. Solar flares are a natural occurrence on all stars. The number of flares and sunspots seen on the Sun changes on an 11 year cycle. Currently we are nearing a solar maximum, meaning there is an increase in solar activity including flares. The effects of these flares are seen on the other planets too. NASA has many pictures of auroral displays on Jupiter and Saturn.

    (Tags:  2012  apocalypse  black hole  milkyway galaxy  planet  solar system  star  sun)
  • What causes planets to rotate?
  • Planets are formed inside giant clouds of gas and dust that begin to rotate and collapse in on itself until it forms a star and planets. The rotation of the planets, is the left over rotation from the gas cloud that formed the planet.

    (Tags:  gravity  physics  planet  solar system  star  sun)
  • What holds the planets in place?
  • The planets are held in place by the Sun's gravity. Because the Sun is by far the largest object in the solar system, it extends its gravitational force far out into the solar system. Anything that comes inside our solar system will be sent into orbit around our Sun.

    (Tags:  gravity  physics  planet  solar system  sun)
  • What is a black hole?
  • A black hole is what happens to large stars when they run out of energy. During the main part of a its life, a star exists in a balance. Gravity tries to pull the star in closer to the middle and energy pressure pushes the star out from the core. These forces cancel out for most of the star's life. When the energy production quits in large stars, gravity pulls the star in rapidly and violently, creating a shockwave which blasts apart the outer part of the star. The inner part continues to collapse from the gravity, to the point where the gravity becomes "infinite." Nothing can get out of this corpse star, not even light, which is pulled down by the gravity, as well.

    (Tags:  black hole  gravity  light  sun)
  • What is the average number of planets that orbit a star?
  • In most cases, only one planet is discovered around stars that are known to host planets. There are a few stars where second, third and fourth planets have been discovered. With numbers, there are 334 planetary systems discovered with a total of 394 planets as of today. Out of 334, only 41 systems are multi-planet systems. Discovery of a planet system like our solar system is has not been made yet; however, this does not indicate the Solar System is unique. Discovery of smaller planets is an extremely difficult task. For example, if we were looking to the Solar System from a nearby star, we probably would not discover smaller planets in the first place, and think the Sun has 2 planets; Jupiter and Saturn.

    (Tags:  jupiter  planet  saturn  solar system  star  sun)
  • What is the largest planet of the solar system?
  • The largest planet is Jupiter. It is so large, that we could fit 1000 Earth's inside of it. However, compared to the Sun, Jupiter is very small. We could fit 1000 Jupiter's inside the Sun.

    (Tags:  earth  jupiter  planet  solar system  sun)
  • What is the possibility of dropping U-238 into Jupiter, for example, to trigger the proton-proton chain reaction? Or, the CNO cycle (carbon-nitrogen-oxygen) to turn all the gas giants into mini-Suns? After all, U-238 has a half life of 4.5 Billion years, and we have a surplus of U-238!
  • Although it may allow us to get rid of our Uranium, this wouldn't work to create another Sun. Atoms bombs like those made with U-238 create fission reactions, which are the opposite of fusion reactions. In fission, you are breaking apart an atom and creating smaller ones – and a lot of energy! In fusion, like within a star, 2 small atoms are joining together to make a larger atom – and again a lot of energy. So, sending our atom bombs to Jupiter would only blow it up, not start a fusion reaction. The only way to start a fusion reaction is to add more mass. To make Jupiter into a small brown dwarf star, we would need to add about 9 more Jupiter’s worth of Hydrogen to the planet. To make a Sun-sized star out of Jupiter, we would have to add 100 more Jupiter’s worth of Hydrogen. That’s a lot of Hydrogen!

    (Tags:  brown dwarf  hydrogen  jupiter  sun)
  • What is the size and brightness of the Sun as viewed from the different planets in the Solar System?
  • We have a few simple calculations that you can use to find the size (in degrees) and the brightness of the Sun on each planet. In fact, these calculations will work for the brightness and size of the Sun from anywhere in the universe, as long as you know the distance of the object from the Sun in AU. To find the size of the Sun in degrees: a = 0.5/distance (in AU) where a is the size in degrees and 0.5 is the size of the Sun as seen from Earth. To find the brightness of the Sun as compared to its brightness as seen on Earth: M = 2.5 * log(distance)^2 – 26.74 Where M is the apparent magnitude of the Sun and 26.74 is the magnitude of the Sun as seen on Earth.

    (Tags:  earth  jupiter  mars  moon  planet  pluto  saturn  solar system  star  sun  venus)
  • When is the Sun predicted to become a black hole?
  • The Sun will never become a black hole. A black hole is what remains after a star, many times larger than the Sun, dies. The star will explode in a supernova, and then collapse in on itself, until it disappears completely, leaving only its gravity behind. The Sun, which is too small to become a black hole, will die. In about 5 billion years, the Sun will use up all its Hydrogen, and expand. Then it will shoot off the outer layers of the atmosphere, leaving just the core behind. We see many examples of stars that have died this way, just search the internet for pictures of Planetary Nebulae. One of the most famous of these planetary nebulae is the Ring Nebula, in the constellation of Lyra, the Harp.

    (Tags:  black hole  gravity  physics  star  sun)
  • Why are planets round?
  • Simply put, planets are round because of gravity. Gravity pulls all the matter of a planet equally towards the center, creating a ball. Objects that are smaller, like asteroids, are not round, because there isn’t enough gravity to compress the object into a sphere. Instead they look like giant potatoes floating in space. In fact, planets themselves are not perfectly round either. We call them oblate spheres. Because they rotate on their axis as they go around the sun, the motion flattens the top and bottom of the planet a little bit, making the diameter at the equator greater than the diameter measured from the poles. This same effect is seen on the Sun and stars.

    (Tags:  asteroid  earth  gravity  planet  star  sun)
  • Why do planets rotate around the sun?
  • Planets and stars are formed in immense clouds of gas and dust. This gas and dust collapses in on itself and begins to spin as it collapses. The densest parts of the cloud become stars and planets. The planets get their motion around the Sun because of the rotation of the cloud that formed them. And Newton tells us that they will continue to orbit the Sun forever (an object in motion will stay in motion unless acted upon by another force).

    (Tags:  gravity  physics  planet  solar system  sun)
  • Why doesn't Mercury have moons?
  • Most moons are captured asteroids or rocks left over from the formation of the solar system. Since Mercury is so close to the Sun, asteroids and comets that come close by are captured by the Sun’s gravity. They are either pulled in to the Sun and burned up or they go around the Sun as comets. Mercury doesn’t have as strong a pull of gravity as the Sun, so it is unlikely that it would be able to redirect the path of any incoming objects to turn them into moons.

    (Tags:  asteroid  comet  gravity  mercury  moon  sun)
  • Why is Pluto so cold?
  • Planets are warm because they trap heat from the Sun, but Pluto is so far away that it doesn't get much heat or light from the Sun. Light from the Sun takes 6 hours to reach Pluto. Compare that to the 4 minutes that it takes light from the Sun to reach Earth. In fact, Pluto is so far away that the Sun would begin to resemble all the other stars that we see at night.

    (Tags:  earth  light  pluto  solar system  star  sun)
  • Why is the earth not at 0° solar longitude on March 21 (the vernal equinox, 1st day of spring), but at 180°? Confusingly, the vernal equinox supposedly marks the 0°
  • In the diagram (, Earth is about at 90 degrees, if you consider the vernal equinox at +X-axis. On March 21, Earth would be at 180 degrees, just like you said. Now, why Earth is not at zero degrees since it is vernal equinox? Because we determine equinoxes according to the Sun’s position, not Earth’s. Put Earth on the Vernal Equinox point (180 degrees). Which direction you see the Sun?

    (Tags:  earth  physics  sun)
  • Will our magnetic field ever get destroyed by magnetic storms from the sun?
  • Although the Sun may give off a strong shock wave that may disturb our magnetic field, it cannot be destroyed by them. Geomagnetic storms are a temporary disturbance of Earth’s magnetic field by a solar wind shock wave. Earth’s magnetic field is providing adequate protection for life on Earth. However, astronauts are under a greater risk. Satellites can also be affected by a strong solar storm. Even high flying jets have a small risk of being exposed. There is a nice article in Wikipedia about the largest geomagnetic storm in history: From August 28 until September 2, 1859, numerous sunspots and solar flares were observed on the sun, the larges flare occurring on September 1. A massive CME headed directly at Earth due to the solar flare and made it within eighteen hours – a trip that normally takes three to four days. On September 1-2, the largest recorded geomagnetic storm occurred. The horizontal intensity of the geomagnetic field was reduced by 1600 nT as recorded by the Colaba observatory near Bombay, India. Telegraph wires in both the US and Europe experienced induced emf, in some cases even shocking telegraph operators and causing fires. Auroras were seen as far south as Hawaii, Mexico, Cuba, and Italy – phenomena that are usually only seen near the poles. If you would like to know more about this superstorm, you can read more on the Wikipedia site by searching for the 1859 solar superstorm.

    (Tags:  earth  electromagnetic spectrum  planet  solar system  star  sun)