Learn about the Moon in a great new book New book chronicles the space program. Dave's Universe Year of Pluto. Groups Why Join? Astronomy Day. The Complete Star Atlas. Mass, m, is measured in kilograms, or kg. Energy, E, is in joules, or J. Joules are a derived SI unit, from base units kg, m, and s. In more familiar terms, a joule is the work done to produce 1 watt for 1 second. This equation shows that energy can be converted into mass and vice versa.
Keep in mind c 2 is a big number. The speed of light is roughly 3 with 8 zeros following it, which makes c 2 nine with 16 zeros following it. This will give you 90 million million joules of energy, which is equivalent to 25 million kilowatt hours. That's enough electricity for the average U. Snapshot : ALMA spots moon-forming disk around distant exoplanet.
Ask Astro : Does dark energy create the voids between galaxy clusters? Looking for galaxies in all the wrong places.
Capturing the cosmos: How to be an astrophotographer. Sky This Month : November Chiricahua Astronomy Complex: An observing mecca for amateurs. Neutron stars: A cosmic gold mine. Suddenly, you decide to slam on the brakes. Instead of zooming by you, though, the truck continues to creep up - now it's in line with your front door. You hit the accelerator, and the truck doesn't fall behind - it continues to creep up past your front tire.
Finally, you stop your car entirely and get out - still the truck creeps by. It looks like the truck has been shadowing your every move, but then you compare notes with a friend who was driving in the third lane, on the other side of the truck.
She thinks that the truck has been shadowing her , even though she was driving completely differently than you were - zooming along at the same time you were stopped, slowing down at the same time you were accelerating!
Seems impossible? It might, but the Michelson-Morley experiment proved that if trucks behaved like light beams, this is exactly what they would do. Many physicists looked for complicated ways to dismiss the results of Michelson and Morley, but Einstein did something different - he simply accepted them at face value and asked what the consequences would be if light really did behave in such a bizarre way. Einstein realized that in order for the speed of light to remain constant as seen by all observers, other things which everyone had always assumed to be constant would have to change.
The faster that two people move with respect to each other, the more they disagree about the light or the truck, in the above example , and the more they think that something with the other person must be out of whack. Einstein showed that the things which seemed out of whack would have to be length and time - each person would observe the other to be shrinking along the direction of motion and their clocks to be ticking more slowly.
As bizarre as these results seem, they do not produce any contradictions with other laws of physics, and in fact enhance our understanding of them. If we accept special relativity, it turns out, electromagnetism no longer needs any kind of "preferred reference frame" in which to operate. Rather, it works correctly from any reference frame you choose - none is more preferred than any other, and the speeds at which different reference frames move with respect to each other are truly relative , as opposed to absolute.
These ideas and others are confirmed daily in particle accelerators all around the world , as well as in many other experiments. Yet perhaps the most important insight that came from special relativity was the idea that space and time are not a sacred, immutable backdrop for the universe, but rather things that can change , from point to point and person to person.
It was this insight that paved the way for the theory of general relativity and its radical interpretation of gravity, whose ramifications are still being felt today. If you have a question about another area of astronomy, find the topic you're interested in from the archive on the side bar or search using the below search form.
If you still can't find what you are looking for, submit your question here. Applications of Relativity The theory of relativity is required whenever we study objects that are either a moving in a strong gravitational field , or b moving near the speed of light. Moving in a Strong Gravitational Field One of the most amazing aspects of the theory of relativity is that it completely changes the way we understand gravity.
Curved space: a simple analogy If the above paragraph doesn't make sense and it is unlikely to! You might think the best way to get there is to start off heading east and keep going straight until you reach Rome, as shown in the red path on this map: Original map credit: WorldAtlas.
Moving Near the Speed of Light Some of the most interesting aspects of the theory of relativity are discussed above, but the first part of the theory special relativity was developed without taking the complicated effects of gravity into account. Constancy of the speed of light In the 19th century, physicists interpreted the laws of electromagnetism to require a "preferred reference frame" for the universe, one in which light traveled. These results have truly bizarre implications.
Einstein's simple solution Many physicists looked for complicated ways to dismiss the results of Michelson and Morley, but Einstein did something different - he simply accepted them at face value and asked what the consequences would be if light really did behave in such a bizarre way.
This page was last updated January 28, Intermediate What is a graviton? Intermediate Special Relativity Could someone travel the universe in his or her own lifetime? Beginner Traveling at light speed, how long would it take to get to the nearest galaxy? Beginner What is time dilation? Intermediate Why can't relative velocities add up to more than the speed of light? Intermediate Does a photon observe other photons moving past it at the speed of light?
Intermediate General Relativity What makes quantum mechanics and general relativity incompatible? Advanced Why are astronomers interested in gravitational waves? Intermediate If gravity isn't a force, how does it accelerate objects? Advanced Have gravitational waves been proven to exist? Intermediate Is light of different colors affected differently by gravity?
Intermediate Is light blueshifted when it is gravitationally lensed? Intermediate What is the speed of gravity? Intermediate If gravity is a "curvature of space" rather than a force, why do a ball and bullet follow different paths? Intermediate If clocks run slow in a gravitational field, how can we know the true age of the Solar System and Universe? Intermediate If photons have zero mass, why do they feel the effects of gravity? Advanced Is there such a thing as hyperspace?
Intermediate Cosmology If the Universe was infinitely dense at the Big Bang, why didn't time stand still? Beginner Can the acceleration of the Universe be analogous to apparent acceleration in a airplane?
Intermediate Did time go slower just after the Big Bang? Advanced How can the Universe expand faster than the speed of light during inflation? Advanced Can gravitational lensing from intervening galaxies cause the observed ripples in the Cosmic Microwave Background? Advanced What is the difference between the "Doppler" redshift and the "gravitational" or "cosmological" redshift? Advanced The Speed of Light Why doesn't gravity change the speed of light? Beginner Wait, I'm still confused why information can't travel faster than the speed of light.
Beginner Who first measured the speed of light? Intermediate How do scientists slow light down? Intermediate Why doesn't light from distant galaxies reach us instantaneously?
Intermediate Is the universe expanding faster than the speed of light? Intermediate What happens to a substance if its speed is more than the speed of light?
Intermediate Don't tachyons travel faster than light? Intermediate Does Cerenkov radiation travel faster than light? Intermediate Does quantum entanglement imply faster than light communication?
Intermediate Can I communicate faster than light? Advanced Has there been an experiment that measured speed faster than the speed of light in vacuum? Advanced Time Travel Is time travel possible? Beginner What would happen if you went back in time and killed your grandmother? Beginner Are time machines possible?
Intermediate Black Holes What are black holes made of? Intermediate If light has no mass, then what draws it into a black hole? Intermediate What happens to spacetime inside a black hole? Intermediate How do gravitons escape black holes to tell the universe about their gravity?
Planetary exploration spacecraft have also shown Einstein to be right about general relativity. Researchers measured the time it took for radio signals to travel from the DSN dish in Goldstone, California, to the spacecraft and back. In , the Viking landers performed an even more accurate experiment along these lines. The theory goes that Earth, a rotating body, should be pulling the fabric of space-time around it as it spins, in addition to distorting light with its gravity.
The spacecraft had four gyroscopes and pointed at the star IM Pegasi while orbiting Earth over the poles. In this experiment, if Einstein had been wrong, these gyroscopes would have always pointed in the same direction.
In order to know where you are, you need a receiver — like your phone, a ground station and a network of satellites orbiting Earth to send and receive signals. At the same time, special relativity would say time moves slower for objects that move much faster than others. While the difference per day is a matter of millionths of a second, that change really adds up.
For comparison, the energy of visible light falls between about 2 and 3 electron volts. A formation of galaxies appear to form a smiling face. Two yellow-hued blobs hang atop a sweeping arc of light. The lower, arc-shaped galaxy has the characteristic shape of a galaxy that has been gravitationally lensed — its light has passed near a massive object en route to us, causing it to become distorted and stretched out of shape. Map of dark matter made from gravitational lensing measurements of 26 million galaxies in the Dark Energy Survey.
As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases, results in a brief brightening of the background star as seen by a telescope. The artistic animation illustrates this effect. This phenomenon of gravitational microlensing enables scientists to search for exoplanets that are too distant and dark to detect any other way. This is the first picture of a black hole.
Using the Event Horizon Telescope, scientists obtained an image of the black hole at the center of the galaxy M Credit: Event Horizon Telescope Collaboration. The galaxy M87, imaged here by NASA's Spitzer Space Telescope, is home to a supermassive black hole that spews two jets of material out into space at nearly the speed of light.
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