Is it possible to see a flashlight beam from earth on the moon

So the answer to your question is, "It depends on both the flashlight and on the size of your 'eye'". If the flashlight in question is a little penlight flashlight powered by a couple of AA batteries , and if the eye in question is your naked eye, then the answer is, "no -- you cannot see the flashlight from the moon". The cone of a typical flashlight is gigantic by the time it reaches the moon, and the photons are spread too thinly for your eye to detect.

If you were to use a much bigger flashlight for example, an aircraft search light , or if you were to increase the size of your eye by using a telescope, then it is possible for you to detect the flashlight from the moon. The other alternative would be to replace the flashlight with a small laser. The cone of divergence of a laser is extremely small compared to a flashlight. For example, this article discusses a laser whose beam is so tightly focused that, by the time the light reaches the moon, it has only diverged into a circle about half a mile 1 km in diameter!

You could easily see tightly focused laser light like that from the moon. Notify me of new comments via email. Notify me of new posts via email.

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Email required Address never made public. Name required. It has a resolving power of 0. I am open to correction on this, but as best I can tell, the Hubble telescope would have something like centimeter resolving power if it were pointed at something on the Earth, like the Statue of Liberty if you are a telescope expert, please write in and correct me if I am wrong. Fifteen centimeters is about half a foot.

The moon is about 1, times farther away from the Hubble Space Telescope than the Earth is. That means that if you pointed the Hubble at the moon, it would have meter resolution. At that resolution, a football stadium occupies just one or two pixels of the image. That means that there would be no way to discern the Lunar Excursion Module or any of the other equipment left on the moon. It is just too small to pick up, even with the world's best telescope. He achieved this theoretical breakthrough by thinking about…yes, light.

Einstein did "thought experiments," and in one he asked what would happen if you could ride a beam of light and look at an adjacent beam. Wouldn't the adjacent beam of light appear motionless? Maxwell's equations didn't seem to allow light to slow down or stop when moving through space. Einstein's answer—that light's speed is constant for all observers regardless of their own velocity—obliterated the classical conception of space and time. The groundwork was laid for Einstein by a famous experiment in by American scientists Albert Michelson and Edward Morley.

The Earth, according to the orthodoxy of the time, moved through a fixed ether that filled space. No one had ever detected this ether, but common sense required its existence. Michelson and Morley set out to detect it by measuring the speed of light when light beams traveled with, and perpendicular to, the motion of the Earth.

They expected light to show the effects of the "current" of this ether as Earth hurtled along. It didn't. The speed of light was the same no matter its direction. Scientists, including Michelson and Morley, were aghast and hoped that the results were simply wrong. Einstein accepted them. There is no ether, he said.

There's no absolute location in space. There isn't even any absolute time. I will confess that relativity makes my head spin. A beam of light from the headlamp of a speeding locomotive ought to move faster—says common sense—than the beam from a stationary flashlight.

It doesn't. And there's nothing anyone can do about it. Einstein's relativity presents all manner of head-scratching implications. It reveals that as objects approach the speed of light, time slows down. At the speed of light itself, time stops. This fact can help us think about the journeys made by starlight and galaxylight and quasarlight across cosmic distances.

We use the term light-year to express a unit of distance about six trillion miles [9. But if you were the light itself—if you could be the photon—you'd experience no time.

That long journey would be instantaneous. What we call light is really the same thing—in a different set of wavelengths—as the radiation that we call radio waves or gamma rays or x-rays. But in practice scientists often use the term "light" to mean the portion of the electromagnetic spectrum in the vicinity of visible light.

Visible light is unlike any other fundamental element of the universe: It directly, regularly, and dramatically interacts with our senses.

Our eyes each have about million rods and cones—specialized cells so sensitive that some can detect a mere handful of photons. The position of the eyes, semiprotected in the case of the skull close to the brain, is testament to the importance of visual data.

Light offers high-resolution information across great distances you can't hear or smell the moons of Jupiter or the Crab Nebula. So much information is carried by visible light that almost everything from a fly to an octopus has a way to capture it—an eye, eyes, or something similar. It's worth noting that our eyes are designed to detect the kind of light that is radiated in abundance by the particular star—the sun—that gives life to our planet.

Visible light is powerful stuff, moving at relatively short wavelengths, which makes it biologically convenient. To see long, stretched-out radio waves, we'd have to have huge eyes, like satellite dishes.

Not worth the trouble! Nor would it make sense for our eyes to detect light in the near infrared though some deep-sea shrimp near hot vents do see this way.

We'd be constantly distracted, because any heat-emitting object glows in those wavelengths. The eye itself is infrared—it's warm. We don't want to detect all of that stuff. There is also darkness in the daytime—shadows.

There are many kinds of shadows, more than you probably realize—certainly more than I realized until I consulted the shadow expert. I found him at the end of a long and winding drive through Topanga Canyon, just up the coast from Santa Monica, California. David Lynch is an astronomer. He's also the co-author of a book called Color and Light in Nature, in which I discovered something about shadows that I'd never thought of before.

Lynch points out that a shadow is filled with light reflected from the sky—otherwise it would be completely black. Black is the way shadows on the moon looked to the Apollo astronauts, because the moon has no atmosphere and thus no sky to bounce light into the unlit crannies of the lunar surface.

Only the faint glow of earthshine filled the shadowy recesses. Lynch is a man who, when he looks at a rainbow, sees details that elude most people. He knows, for example, that all rainbows come in pairs, and he always looks for the second rainbow—a faint, parallel rainbow, with the colors in reverse order. The intervening region is darker.

That area has a name, wouldn't you know: Alexander's dark band. We sat on Lynch's deck and drank orange juice squeezed from fruit freshly yanked from trees in his backyard. The view was spectacular, the canyon opening like a great basin, a mountain ridge obscuring the Pacific and running for half a dozen miles 9. It's called airlight. The sky is blue because the molecules in the air scatter blue light more readily than they scatter red, orange, yellow, and green.

We see distant mountains through a mass of blue sky—hence the Blue Ridge and thanks to poetic license " purple mountain majesties. Las Vegas is a multitude of colors—a place that takes light seriously and can't seem to emit enough of it. The Strip is more dazzling by the year. The casinos no longer advertise themselves with mere neon-lit roadside marquees but rather have turned their entire structures into eyeball-popping orgies of illumination.

The entirety of the MGM Grand glows emerald. Fiber optics pulse light to the tower of the Stratosphere. The vertical neon stripes adorning the Rio are visible from distant mountains. The Luxor Resort and Casino is a pyramid and, perversely, remains almost entirely dark at night, a massive black presence dramatically highlighted by the golden glass of the Mandalay Bay Resort next door.

Instead of dressing itself in countless little bulbs or immersing itself in floodlights, the Luxor aims its Sky Beam—said to be the brightest light on the planet—straight into space. I followed John Lichtsteiner, technical manager of rides and attractions at the Luxor, up three metal ladders onto the catwalk at the pyramid's peak to see the 39 xenon lamps, 7, watts each that create the Sky Beam. A sign warns that the lights, each about the size of a washing machine, are "extremely volatile" and can explode if jarred or bumped.

Lichtsteiner explained that before a computer turns on the Sky Beam each night, strobe lights flash for 30 seconds. He pressed a button on a digital console to illuminate one of the lamps.