The University of Texas at Arlington

The University of Texas at Arlington

UTA Planetarium

UTA Planetarium

Ask the Astronomer Q&A

Tag: "earth"

  • Can the Moon be seen everywhere on Earth?
  • Yes. At the same moment, the Moon looks pretty much the same shape, wherever you are on Earth. The difference made by travelling a few thousand miles to the other side of the world is very slight because the Moon is dozens of times further away than that. So, Full Moon happens at the same moment everywhere on Earth.

    (Tags:  earth  moon)
  • Could phenomena occur where planets align in a way that impacts Earth?
  • 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.

    (Tags:  2012  apocalypse  black hole  earth  gravity  milkyway galaxy)
  • Every leap year, we add a compensatory day. In the interim, why is our official time never off by one-quarter or three quarters a day?
  • The Earth orbits the sun once every 365.25 days, so every four years we add an extra day to the year (Leap Year). In the interim years we don’t have our “official” time off by any certain amount because each day is only off by 360 min/year. So to have an accurate “official” calendar, all we have to do is add an extra minute to each day, so that every day is 24 hours and 1 min. This number is so insignificant that we don’t calculate it in to our normal calendar, but over time, it will start to add up (1 day every 4 years), so that is why we add the leap day, but do not keep track of the time in the interim.

    (Tags:  earth)
  • Explain why high tides occur along the line joining the Earth and Moon, even on the opposite side of Earth from Moon and why low tides occur at 90 degrees to the line.
  • The moon's gravitational force pulls on water in the oceans so that there are "bulges" in the ocean on both sides of the planet, which we call high tides. The Moon pulls water toward it, and this causes the bulge toward the Moon. The bulge on the side of the Earth opposite the Moon is caused by the moon "pulling the Earth away" from the water on that side. Low tides occur at 90 degrees from the Moon because the water in the ocean has been pulled away from these locations towards the bulges that create the high tides. Since the Earth is rotating, each location will experience two high tides and two low tides every day.

    (Tags:  earth  moon  tides)
  • Gliese 710, an Orange dwarf star, will be headed our way in 1.5 million years. Gliese 710 is expected to come within 1.1 light years of our Solar System, perturbing the Oort Clouds and its comets. Can it grab some of the moons of the giant gas planets (Jupiter, etc) and make them satellites for itself, re-arranging our Solar System?
  • It is not likely that Gliese 710 will have any effect on the moons of the gas giant planets because 1.1 light years is still a very long way away. For reference, the Sun is about 8 light minutes away from Earth. Pluto is about 5.6 light hours away from the Sun. At 1.1 light years away, Gliese will be over 5 trillion miles from the solar system. This may be close enough for the star’s gravity to have an effect on the edge of the Oort Cloud, as you mentioned, but this will likely mean an increase in meteor showers and comets. It would not completely rearrange our solar system.

    (Tags:  brown dwarf  earth  gravity  jupiter  meteor  planet  pluto  saturn  solar system)
  • Has NASA spotted an exoplanet orbiting Alpha Centauri a and b and proxima centauri?
  • Yes! A planet, known as Alpha Centauri Bb, was discovered orbiting around Alpha Centauri B, which is part of a three-star system just 4.3 light-years away from us. Alpha Centauri Bb zips around its star every 3.2 days, orbiting at a distance of just 3.6 million miles (6 million kilometers) and is approximately the same size as Earth. For comparison, Earth orbits about 93 million miles, or 150 million km, from the sun.

    (Tags:  earth  exoplanet  nasa  observatory  planet  star  telescope)
  • Have astronauts ever been to ___?
  • Astronauts have never been anywhere besides the Earth and Moon (but there have been no Moon trips since 1972). There are plans to return to the Moon (possibly by 2020) and then astronauts may travel to Mars. A trip to the Moon takes about three days, but a one-way trip to Mars will take close to nine months.

    (Tags:  astronaut  earth  mars  moon  nasa)
  • I am led to understand that the Earth has an atmosphere due to the fact we have a magnetic field that deflects the solar wind. It is further my understanding that Mars lost most of its atmosphere (and subsequently most of its water) because the core cooled and Mars lost its magnetic field. Why then does Venus have such a thick atmosphere given that it has no magnetic field combined with the fact that it is much closer to the sun and therefore is exposed to solar wind to a much higher degree than the Earth is?
  • Actually, Earth has an atmosphere because of the size of the planet. Since gravity is directly related to the size (mass) of an object, the larger it is, the more gravity it possesses. Earth’s gravity is able to hold on to the molecules that make up our atmosphere. Mars, being about ½ the size of Earth, has much less gravity. This allowed the atmosphere on Mars to “evaporate” away into space. Venus still has an atmosphere because it is very close in size to Earth, about 90% Earth’s mass.

    (Tags:  earth  gravity  mars  venus)
  • I know that Mars cannot hit Earth because it is so far away, but is there another reason why this is not scientifically possible?
  • Mars can never hit Earth because the two planets are in stable orbits around the Sun. The orbits do not intersect with each other, so there is no way the two objects could collide. But it is possible that Neptune and Pluto may someday collide with each other due to their intersecting orbits. We would need a catastrophic event to happen, like a star or black hole passing through our solar system, to change the orbits of the planets enough to cause Mars and Earth to collide.

    (Tags:  earth  mars  neptune  pluto)
  • 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)
  • I received an email saying that we will see Mars as big as the moon on August 27, 2010. Is this true?
  • No, this is not true. The emails started circulating in 2003 when Mars made its closest approach to Earth. It was closer than it had been in 60,000 years! But, because the distances between Mars and Earth is so great (at and average of 46.5 million miles away) and their size so small (Mars is only half the size of Earth), Mars can never look as large as the Moon. That year, it appeared as a very bright red dot in the sky. Mars is visible this month in the Western part of the sky after sunset. It will appear as a red dot low in the sky. If you want to read more about this email hoax and others we see, check out these great articles on our website!

    (Tags:  astronomy  earth  light  mars  moon  planet  solar system)
  • If Astronauts are traveling in zero gravity, why can't we travel at the speed of light? Doesn't that mean they are weightless?
  • Actually, no. The effects of gravity are felt everywhere, even in space. When an astronaut experiences weightlessness or zero-G they aren’t actually feeling a lack of a gravitational field, but instead they are experiencing free-fall. The shuttle, in Earth’s orbit, is actually free-falling around Earth, so we don’t feel a pull directly towards the surface. That is why an astronaut - and all objects – float in space. Also, gravity is what causes us to have weight, not mass. Our weight can fluctuate depending on where we are in the universe. On Earth an adult may weigh 150 pounds, but on the moon, which has a smaller gravitational field, the same person would way only 50 pounds. But his mass, the amount of material that makes the adult, does not change wherever he is. You can determine your mass by dividing out 9.8m/s^2 (which is the pull we feel from the Earth – its gravitational effect) from your weight as measured on Earth.

    (Tags:  astronaut  earth  gravity  moon  physics)
  • 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 it possible for a satellite to maintain an orbit on the far side of the Moon (always hidden from Earth), given the complicating effects of Earth's gravity? If it is possible, what would the semi-major axis be?
  • No, it would not be possible for a satellite to orbit completely hidden from the Earth. To keep a satellite on the far side of the moon, it would have to orbit the Earth, not the Moon, every 28 days. Using Kepler’s law of planetary orbits, we can find the semi-major axis of the object with this equation (p^2/(a^3). Where a is the semi-major axis and p is the period. We know we want the period to be the same as the moon’s, 28 days. Which means that the semi-major axis would be equal to the moon’s semi-major axis. So the only way for the satellite to remain on the far side of the moon, is to place it on the moon itself. It is possible for the object to share the moon’s orbit (by trailing behind or ahead of the moon), but then we would be able to see it.

    (Tags:  earth  gravity  moon  satellite  telescope)
  • Is the Earth in danger of being hit by a meteor in 2012?
  • The Earth has always been subject to impacts by comets and asteroids, although big hits are very rare. The last big impact was 65 million years ago, and that MAY have led to the extinction of the dinosaurs. Nothing is predicted to hit in 2012.

    (Tags:  2012  apocalypse  asteroid  dinosaurs  earth  extinction  meteor)
  • Is the earth really going to end in 2012?
  • No, the Earth will not end in 2012. This is another hoax that has spread due to popular media. According to the hoax, the Earth will end on December 21st, 2012; the "last day" on the Mayan calendar. This however, is not the last day of the Mayan calendar, but the last day of the millenium, according to the Mayan calendar. On December 22nd, 2012, the Mayan Calendar will start over with a new millenium. Many of you may remember a similar hoax, Y2K, about 10 years ago, which also said that the world would end. These hoaxes have a tendency to spring up every few years, and there is never any truth to them. You can read more theories about the ending of 2012 on our articles page.

    (Tags:  2012  apocalypse  earth  mayan culture)
  • 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)
  • Is there a planet Nibiru which is reported to come close to Earth on 12 December 2012?
  • No, there is no such planet Nibiru. Nibiru is also often called Planet X. According to hoaxists, Nibiru is a planet that was discovered by the Mayans that will collide with the Earth on December 21st, 2012. This is just one of the "theories" about the world ending in 2012. The truth is, the Mayans knew of no such planet. Although they were very skilled at tracking the motions of the planets, Sun and Moon, they did not know what the planets were. They would have only been able to see the 5 naked eye planets; Mercury, Venus, Mars, Jupiter and Saturn. Telescopes had not yet been discovered. If there is a planet called Nibiru it would have to be very large or very close to Earth in order for the Mayans to see it. And if it is very large or very close, then you and I would be able to see it today. If it were on a collision course with Earth, it would get brighter and brighter until we could even see it in the daylight. But of course, we can't, because it doesn't exist. Rest easy tonight, the world will continue well past the year 2012.

    (Tags:  2012  apocalypse  earth  mayan culture  nibiru  planet)
  • 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)
  • The Seasons, I know why they happen but does the distance from the sun matter?
  • No, the distance from the Sun has no effect on Earth's seasons. In fact, in winter for the Northern Hemisphere, the Earth is at it's closest approach to the Sun. When the Northern Hemipshere is in summer, the Earth is at its farthest point from the Sun. The seasons are caused by Earth's tilted axis.

    (Tags:  earth  seasons)
  • There is an apocalypse that the world is going to end in 2012 which has been supported by astrophysical theories. Is that so? Or do the scientists believe the world will end based on Biblical beliefs?
  • No scientist has predicted an apocalypse for 2012. This is an internet hoax that has been going on for years. It is based on the belief that the Mayans "predicted" the world ending on December 21st, 2012, the end of the calendar. But just as the world doesn't end on December 31st each year when our calendar ends, the world will not end when the Mayan calendar ends - it will simply start a new cycle. There are many more articles about the apocalpyse, 2012, Nibiru and other related topics on this page and many NASA sites. We encourage everyone to read up on it.

    (Tags:  2012  apocalypse  earth  mayan culture  nibiru)
  • What equation would you use to determine the brightness of sunlight on a satellite when the distance from the sun is measured in AU?
  • There are two ways to calculate this: 1. Use Pogson’s equation to find brightness at desired AU (there is a special form of Pogson’s equation for this) 2. Imagine a great sphere with (R= satellite’s distance). Calculate the surface area of that sphere. Then divide the (total energy coming out of Sun’s surface) by the (area of the sphere). Now you have the amount of energy reaching up to the satellite’s unit surface. To obtain the flux (function of brightness), just multiply that (energy per unit area) by the area of detector (for human eye: 8mm wide circular lens). – note that brightness has no meaning by itself. Brightness is usually given on a scale based on a reference source. For example, stars’ magnitudes are often determined by comparing them with Star Vega (m = 0.0)

    (Tags:  earth  light  satellite)
  • What is the best place and time to see a meteor shower?
  • Meteors, sometimes called falling or shooting stars, are very common in the night sky. As Earth orbits around the Sun, it goes through debris fields, left behind by comets and other celestial objects and events. This debris falls towards the Earth, and burns up as it falls. That's what we see as a meteor. When the Earth goes through a large debris field, we can expect to see more meteors. Sometimes as many as 100 per hour. The Perseid meteor shower, which occurs every year in August, is one of the best meteor showers. To see the most meteors, go outside after midnight, when the sky is its darkest, and watch the show. Meteors will fall from all directions, but often they appear to start at one central point. In the case of the Perseid meteor showers, the meteors all appear to come from the constellation Perseus. If you can, get far away from the city to see the best possible show.

    (Tags:  earth  meteor)
  • 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 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)
  • 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 stars twinkle?
  • Stars twinkle because the light from the stars is passing through Earth’s atmosphere. As it does, it gets bent back and forth due to the turbulence in the air. At really high altitudes (like on a mountain or in a plane) or on very calm nights, the stars will not twinkle as much because there is less turbulence in the air. This is why many observatories are placed high on the mountains or in space, instead of at ground level. The less atmosphere star light has to travel through, the less it will twinkle. In space, stars do not twinkle at all.

    (Tags:  earth  light  observatory  star  telescope)
  • 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 an asteroid hit the Earth in ___?
  • Asteroids have hit the Earth in the past and will hit the Earth again someday, but not for a long time. Astronomers are keeping an eye on a couple objects. One, which will pass near the Earth in the year 2029, has a small (1:45,000) chance of an impact in 2036. The other object, depending on its spin, has either a 0 or a 1:300 chance of impact in the year 2880.

    (Tags:  asteroid  earth)
  • Will NASA ever get to Mars knowing that it's so far away?
  • I think what you mean to ask is not whether NASA will get to Mars, but will NASA send astronauts to Mars, and I think the answer is yes. We have been sending robotic probes to Mars for decades. Several are on the surface testing the soil and sending beautiful panoramic images back to us on Earth. Others are in orbit, taking high resolution images of the surface from above. The problem with sending astronauts to Mars is that it would be a 1-3 year trip. It all depends on the technology we use and how close Mars and Earth are to each other in our orbits. NASA’s Constellation Program, which was started under the Bush Administration, was a project to take the best of the Apollo and space shuttle missions, and create a spacecraft that could return astronauts to the Moon, and maybe eventually to Mars or some near-Earth asteroids. But the project was over promised, and over budget, so it was removed from the NASA budget. But, the current NASA budget has money set aside for taking us to Mars or near-Earth asteroids, it is just hoping for some help from the commercial market. It may take 10-20 years for the new system to be developed, but we will get to Mars within our lifetime.

    (Tags:  asteroid  astronaut  earth  mars  moon  nasa)
  • 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)