The University of Texas at Arlington

The University of Texas at Arlington

UTA Planetarium

UTA Planetarium

Ask the Astronomer Q&A

Tag: "light"

  • 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)
  • General relativity proved that light can bend based on a lot of gravity being forced onto the light. What are the two proofs of this?
  • The fact that light is bent by gravity was predicted by Einstein's General Theory of Relativity. The first observational evidence was given by Eddington and his team, who measured the effect during a solar eclipse in 1919. The measured value was very close to the one predicted by Einstein's theory.

    (Tags:  albert einstein  eclipse  gravity  light  theory of general relativity)
  • How can an astronomer test to see if gas and dust from a star are being drawn into a black hole?
  • There are two ways of knowing this: 1. When dust and gas approaches a black hole, strong gravitational forces spin the dust and gas nearly at the speed of light. Accelerating particles produce X-ray radiation which radiates perpendicular to the orbital plane of the gas and dust. We can detect this radiation if the radiation direction is just right (towards Earth). The first discovered black hole, Cygnus X-1, was detected this way. 2. Computer simulations suggest if a star is nearby a black hole, star atmosphere (dust and gas around stars) would be pulled by the gravity of the black hole.

    (Tags:  black hole  gravity  light  physics  star  universe)
  • How does astronomy work?
  • Astronomy is not an easy science to study. Unlike biologists, geologists and others, astronomers can't walk up to a star or planet to study it because they are incredibly far away. Even the Earth's nearest celestial neighbor, the moon, is nearly 240,000 miles away. The closest star to Earth, the Sun, is 93,000,000 miles away. The best way to study a distant object, like a star or planet, is to study its light. We often think of light as the Electro-Magnetic Spectrum, or EM spectrum. The EM spectrum is like a rainbow, with many different forms of radiation, or light! On the coldest end of the EM spectrum we have radio waves, in the middle of the spectrum we have visible light; the small portion of the EM spectrum that our eyes can see; and at the hottest end of the EM spectrum we have gamma rays. Astronomers can collect the light from anywhere on the EM spectrum using telescopes. The larger the telescope, the more light it can detect. By studying all parts of the EM spectrum astronomers can learn about an object's temperature, distance and age, to name a few.

    (Tags:  light  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)
  • In pictures of a galaxy, I notice a big bright star in the center, is that really a gigantic star and how come I can't see that star in the night sky of the milky way?
  • First, when you are looking at a picture of a galaxy, you are not looking at our galaxy the Milky Way. The Milky Way galaxy is about 30,000 light years across, a distance far to great for us to reach. So we have never left our Milky Way galaxy to see it from above. Second, what you did see in the galaxy image was probably not one bright star but hundreds. At the center of most galaxies we have found evidence of supermassive black holes (hundreds of times the size of our sun). Orbiting around this black hole are hundreds, even thousands of very large hot stars that would glow very brightly. This is what you are seeing when you look at images of galaxies. Third, let's imagine for a moment that the galaxy image you were looking at was our Milky Way galaxy, and you went looking for the bright object in our sky. You would still not see the bright object at the center. We know this to be true because when we look towards the center of the Milky Way (near the constellation Sagittarius) we can not see the very center because there is a lot of gas and dust, called Interstellar Material, that is blocking our view. The only way that astronomers can study the center of our Milky Way galaxy is by looking at the Infrared light (heat energy) of stars, since it is the only form of energy which does not get absorbed by clouds of gas and dust.

    (Tags:  andromeda galaxy  astronomy  black hole  light  milkyway galaxy  star  universe)
  • 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)
  • 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)
  • 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 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 a light year?
  • A light year is a unit of distance. The distances to the stars are so great, it is inconvenient to use terms like miles or kilometers. So we use "light year." A light year is the distance a beam of light travels in a year. Light goes around 186,000 miles per second (in a vacuum) and in a year travels almost six trillion miles. Now, instead of saying Alpha Centauri is 25,000,000,000,000 miles away, it is much easier to say "around 4.3 light years" away. As a consequence, things we see in space are also removed from our own time. The light reaching Earth now from Alpha Centauri left 4.3 years ago. So we are actually seeing what the star looked like 4.3 years ago, even if we use a telescope. Other visible stars are dozens to hundreds of light years away, and the galaxies are millions and billions of light years away.

    (Tags:  light  physics)
  • What is the SOFIA?
  • SOFIA is an acronym for the Stratospheric Observatory For Infrared Astronomy. It is a telescope mounted to a Boeing 747 airplane. The airplane flies high above Earth's atmosphere to study objects in the infrared part of the electro-magnetic spectrum.

    (Tags:  astronomy  electromagnetic spectrum  light  observatory  physics)
  • When will we get actual pictures of the class m planets recently discovered by Kepler? Artist conceptions are cool and optimistic, however the truth is always more amazing.
  • Unfortunately, astronomers do not have the technology to actually see, or take pictures of, exoplanets. Most exoplanets are discovered by indirect methods, like looking for a dimming in a star’s light, or for the wobble in a star’s orbit – which is caused by a planet pulling on the star. In order to directly see the planet, astronomers would need much larger telescopes than have currently been built, in order to see the incredibly small bodies at great distances. One of the closest exoplanets discovered is about 22 light years away – that’s approximately 135 trillion miles away – and is only 4 times the size of Earth (at approximately 32,000 miles in diameter)! This is way too small to be seen by our telescopes. So for now, the best we can do is imagine what the planets look like, with artist conceptions.

    (Tags:  exoplanet  gravity  light  observatory  planet  star  telescope)
  • 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 speed of light referred to as the letter "c"?
  • The letter 'c' used for speed of light stands for 'constant', which means that the speed is the same in all inertial frames of reference. It has become common to use 'c' after the formulation of the Special Theory of Relativity by Einstein in 1905.

    (Tags:  albert einstein  light  physics)
  • Will we ever be able to travel at the speed of light or faster?
  • That’s a great question, but it is difficult to answer. Theory tells us that as we increase our speed to the speed of light, we will get more massive, and if we get more massive, we will need more fuel to propel us at that speed. So as we continue to get closer to the speed of light, we will get infinitely massive. The only thing that can actually reach the speed of light today, is light, which has no mass. So in order to go the speed of light, we will either need to learn how to propel an infinite mass, or discover how to make ourselves mass-less. As far as going faster than the speed of light, that may never be possible, since light itself cannot go faster than the speed of light. But who really knows, our technology gets better every day, and perhaps sometime in the future we will discover a way to travel fast enough to leave our solar system and travel among the stars.

    (Tags:  light  physics  speed of light  theory of general relativity)
  • Will we ever have the ability to teleport ourselves from one place to another?
  • No. Teleportation involves moving an object at the speed of light (or faster). But this is not possible since General Relativity tells us our mass increases indefinitely as we approach the speed of light. The speed of light is also much faster than any speed we have ever achieved on Earth. The speed of light is 186,000 miles per second!

    (Tags:  albert einstein  light  physics  speed of light  theory of general relativity)