Light pollution is excess or obtrusive light created by humans. Among other effects, it causes adverse health effects, obscures stars to city dwellers, interferes with astronomical observatories, wastes energy and disrupts ecosystems.
Lighting up the Darkness
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Elusive "dark matter" shows itself through its gravitational influence on a large cluster of galaxies in this composite image from NASA.
Light Year
The light year is a unit of distance that comes from the knowledge that light (or electromagnetic radiation in general) takes a finite length of time to travel through space.
Light often means the portion of the electromagnetic spectrum visible to the human eye, but can also refer to other forms of electromagnetic radiation.
Light-year
Related Category: Astronomy: General
in astronomy, unit of length equal to the distance light travels in one sidereal year. It is 9.461 × 1012 km (about 6 million million mi).
Light gathering power is one measure of the performance of a telescope.
It is roughly proportional to the square of the aperture size. A telescope with an aperture twice the diameter collects approximately 4 times as much light.
Light is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye (about 400-700 nm), or perhaps 380-750 nm.
light-year
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SUNLIGHT
By Jim Kaler
Open to Sunlight
Our own star makes daylight that removes the other stars from view. Rather than look at Sun's physical nature, examine here its marvelous effects as it plays with and off the air.
How sunlight is created
The Sun has no sharply defined surface like that of the Earth, because it is too hot to be anything but gas.
Light:
Light, a basic aspect of the human environment, cannot be defined in terms of anything simpler or more directly appreciated by the senses than itself. Light, certainly, is responsible for the sensation of sight.
Light Curves, Spectra, and Images
Tools for All Astronomers
Because most of the objects that astronomers observe are so far away, we cannot touch them - observing the light that they emit is often the only means we have of understanding them.
Light echoes can be seen from novae and supernovae. The light echoes from 1987A, observed with the Hubble Space Telescope, were especially detailed.
speed of light - Space and Astronomy Definition - Online Dictionary and Glo...
light pollution - Space and Astronomy Definition - Online Dictionary and Gl...
ice-volcanic melt - Space and Astronomy Definition - Online Dictionary and ...
The Small Magellanic Cloud (SMC) is located 210,000 light years away towards the constellation Tucana, and the open cluster of stars that make up NGC 346 spans around 200 light years.
Light Pollution and the U.S. National Science Education Standards
The only good thing about light pollution is that it makes an excellent topic for teaching and learning about science and technology and their relationships to society.
Moonlight Madness
The revolution of the Moon around the Earth causes the Moon to appear to change shape in the sky. These apparently different shapes are called "phases" of the Moon.
Arc Light is the debut novel by Eric L. Harry, a techno-thriller
Techno-thriller ...
ashen light
A faint glow occasionally observed on the dark side of Venus.
Fourth Light at Paranal!
The four telescopes of the Very Large Telescope (VLT) at Paranal, in Chile.
Light is very important to astronomy, and for obvious reasons. Astronomers are not able to go out and sample the objects of their study, namely stars and galaxies (an exception can be made for the study the solar system).
Light with the shortest wavelengths and the highest energies and frequencies in the electromagnetic spectrum; also called gamma radiation.
Gravitational Redshift ...
A light echo around the star V838 Mon.
Click on image for full size
NASA, ESA, and The Hubble Heritage Team (STScI/AURA)
What's in a Name: ...
twilight on every clear morning, unless blotted out by moonlight. It then presents a nearly vertical wedge-shaped form, the base of which extends 15° or 20° on each side of the point at which the ecliptic intersects the horizon.
The light we see today, as the cosmic microwave background, has traveled over 13 billion years to reach us.
Since light does stuff like a wave, it has a certain size. You know that not all waves are alike, and therefore not all types of light are alike.
[6.1] LIGHTSAIL CONCEPTS
[6.2] LIGHTSAIL MISSIONS
[6.3] ADVANCED LIGHTSAIL TECHNOLOGIES / MAGSAILS ...
A Planetary Delight
Throughout the history of mankind, the human race has always been fascinated by the planets. These objects seem to move in relation to the so called "fixed" background stars.
Commercial spaceflight in science fiction novels helped spark the interest, and money, of the famous men who are researching it.
Stars within 20 light-years
Larger map (some newer
objects have been omitted.
Today, 129 stars and white
and brown dwarfs are
known to be located within
20 light-years of Sol.
Modelling Binary Light Curves
Exercise 1: Binary Stars - investigate a spectroscopic binary system
Exercise 2: Eclipsing Binary Stars - simulate light curves for different eclipsing binary systems ...
The human eye can't see ultraviolet light. Thus, NASA changed the colors of these images so we can see them. To sort the images visually, NASA scientists assigned colors to EIT images recorded at particular extreme ultraviolet (EUV) wavelengths.
Scientists look at the Sun with special telescopes that are able to see only specific colors of light -- even the wavelengths that are invisible to your eye. The Sun looks different, depending on which wavelengths we choose.
Pieternel Levelt: Shining Light on Atmospheric Ozone
06.10.04
A scientist, an athlete, a parent, a manager, a problem solver -- Pieternel Levelt of the Netherlands is all of these things.
When it's in a dark phase, more artificial light from the night side would be visible from Earth than reflected light from the day side.
At the beginning of March, four planets -- Venus, Mars, Saturn and Jupiter -- light up the starry sky at nightfall. Make friends with them now and they'll introduce you to reclusive Mercury at this year's springtime planetary festival.
Light-Year (ly)
Most objects in space are so far away, that using a relatively small unit of distance, such as an astronomical unit, is not practical.
LIGHT AND RADIATION
Given the impossibility of traveling to such remote parts of the universe, how do astronomers know anything about objects far from Earth?
Light Cone
(a) The history, in space-time, of a light flash.
(b) A cone representing the transmission, at the speed of light, of an event's existence on a spacetime diagram.
Light Blows Away Giant Molecular Clouds
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This cloud of gas and dust is being deleted. Likely, within a few million years, the intense light from bright stars will have boiled it away completely.
light year The distance that light, moving at a constant speed of 300,000 km/s, travels in one year. One light year is about 10 trillion kilometers.
line of nodes The line of intersection of the Moon's orbit with the ecliptic plane.
Lighthouse Model
The spinning neutron star produces beams of radiation that sweep across your line of sight like a lighthouse beam does for ships at sea.
light pollution
light, typically from artificial sources, that reaches the night sky, obscuring the view of faint astronomical objects
light-gathering power ...
Light fog and rising bright Moon (4 days past full) washed out the image of that very difficult target. North is to the left.
Map created in Guide 7.0 - 7°45' x 10°. North is up.
Cassiopeia Page ...
LIGHT-EMITTING DIODE (LED) - Diode that has been constructed to optimize the emission of light as conductionelectrons and holes recombine at a p-n junction and maximize the fraction of the produced light that escapes the device and is ...
Light Bucket
An optical receiving telescope that collects photons but is not diffraction limited. Its effective field-of-view is larger than a diffraction limited telescope and cannot discriminate so well from background noise photons.
Light year The distance that light traverses in a vacuum during one year (approximately 9,460,529,700,000 km).
Lunation The period of time between two consecutive New Moons.
Light-Emitting Diode -- A semiconductor diode, made from certain materials (e.g. Gallium Arsenide), in which light is emitted in response to the forward-bias current.
Light Bucket
A common slang term for a large aperture. The cure for 'Aperture Fever'.
Maksutov-Cassegrain
See catadioptric.
Light-year: A light-year is a unit of length. The distance that light travels in one year, about six trillion miles.
Luminosity: The amount of energy a star emits in 1 second.
M ...
Light bucket Slang term for a telescope of large aperture.
Light Year The distance travelled by light in one year. 9.4607 × 1012 km or 63,240 AU or 0.3066 parsecs.
Limb The edge of the disc of a celestial body.
Light cone- a surface in space-time that marks out the possible directions for light rays passing through a given event
Limb- an edge or border, as of the sun, Moon, or any planet ...
Light year: Distance that light can travel in 1 year. Light travels at a speed of 300,000 km / sec, so this distance is equal to 9.46 x 1012 kilometers.
Light echoes: this has given an independent distance to the LMC, by using the time of illumination of a circumstellar ring (seen from IUE, Panagia et al. 1991 ApJL 380, L23) to give an absolute front-back size, ...
light
Electromagnetic radiation that is visible to the human eye.
light year
A unit of length used in astronomy which equals the distance light travels in a year.
light year
The distance traveled by light in one year, equal to approximately 9,460,536,000,000 kilometres. A parsec is another common unit of distance in astronomy, and is equal to 3.26 light years.
Light year -- A measure of distance, the distance light travels in one year, about 63,197 AU.
LMC -- Large Magellanic Cloud, the larger of two small galaxies orbiting nearby our Milky Way galaxy, which are visible from the southern hemisphere.
Light - Light is a form of radiant energy that we can see with our eyes, and record with film and CCD cameras.
Light Gathering Power
The ability of a telescope to collect light. Proportional to the are of the telescope objective lens or mirror
Light-Year ...
Light Year
the distance light travels in a year, at the rate of 300,000 kilometers per second (671 million miles per hour); 1 light-year is equivalent to 9.46053e12 km, 5,880,000,000,000 miles or 63,240 AU.
 See also: Earth, Sun, Time, Star, Solar
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