A light year is a way of measuring distance. That doesn't make much sense because "light year" contains the word "year," which is normally a unit oftime. Even so, light years measure distance.
You are used to measuring distances in either inches/feet/miles or centimeters/meters/kilometers, depending on where you live. You know how long a foot or a meter is -- you are comfortable with these units because you use them every day. Same thing with miles and kilometers -- these are nice, human increments of distance.
When...
Monday, 31 December 2012
Sunday, 30 December 2012
Origin of Light (How Light Works)
Scientists today accept the existence of photons and their weird wave-particle behavior. What they still debate is the more existential side of things, such as where light came from in the first place. To answer this question, physicists turn their attention to the big bang and the few moments that followed.
You might recall that the big bang is the birthing event that gave rise to the universe. You can read more in How the Big Bang Theory Works, but it will be useful to remind you of the basics here. About 15 billion...
Saturday, 29 December 2012
Pigments and Absorption of Light (How Light Works)
Another way to make colors is to absorb some of the frequencies of light, and thus remove them from the white light combination. The absorbed colors are the ones you don't see -- you see only the colors that come bouncing back to your eye. This is known as subtractive color, and it's what happens with paints and dyes. The paint or dye molecules absorb specific frequencies and bounce back, or reflect, other frequencies to your eye....
Friday, 28 December 2012
Making Colors of light (How Light Works)
Visible light is light that the human eye can perceive. When you look at the sun's visible light, it appears to be colorless, which we call white. Although we can see this light, white isn't considered part of the visible spectrum. That's because white light isn't the light of a single color but instead many colors.
When sunlight passes through a glass of water to land on a wall, we see a rainbow on the wall. This wouldn't happen unless...
Thursday, 27 December 2012
Lasers (How Light Works)
An interesting application of the quantum nature of light is the laser. You can get the whole story on lasers in How Lasers Work, but we're going to cover some of the key concepts here. Laser is an acronym for "light amplification by stimulated emission of radiation," which is a tongue-tying way to describe light in which the photons are all at the same wavelength and have their crests and troughs in phase. Research...
Wednesday, 26 December 2012
Producing a Photon (How Light Works)
There are many different ways to produce photons, but all of them use the same mechanism inside an atom to do it. This mechanism involves the energizing of electrons orbiting each atom's nucleus. How Nuclear Radiation Worksdescribes protons, neutrons and electrons in some detail. For example, hydrogen atoms have one electron orbiting the nucleus. Helium atoms have two electrons orbiting the nucleus. Aluminum atoms have...
Tuesday, 25 December 2012
Wave-Particle Duality of Light (How Light Works)
At first, physicists were reluctant to accept the dual nature of light. After all, many of us humans like to have one right answer. But Einstein paved the way in 1905 by embracing wave-particle duality. We've already discussed the photoelectric effect, which led Einstein to describe light as a photon. Later that year, however, he added a twist to the story in a paper introducing special relativity. In this paper, Einstein treated light as a continuous field of waves -- an apparent contradiction to his description...
Monday, 24 December 2012
Light as Particles (How Light Works)
Maxwell's theoretical treatment of electromagnetic radiation, including its description of light waves, was so elegant and predictive that many physicists in the 1890s thought that there was nothing more to say about light and how it worked. Then, on Dec. 14, 1900, Max Planck came along and introduced a stunningly simple, yet strangely unsettling, concept: that light must carry energy in discrete quantities. Those quantities,...
Sunday, 23 December 2012
Light Frequencies (How Light Works)
Once Maxwell introduced the concept of electromagnetic waves, everything clicked into place. Scientists now could develop a complete working model of light using terms and concepts, such as wavelength and frequency, based on the structure and function of waves. According to that model, light waves come in many sizes. The size of a wave is measured as its wavelength, which is the distance between any two corresponding points on...
Saturday, 22 December 2012
Light as Waves (How Light Works)
Unlike water waves, light waves follow more complicated paths, and they don't need a medium to travel through.
When the 19th century dawned, no real evidence had accumulated to prove the wave theory of light. That changed in 1801 when Thomas Young, an English physician and physicist, designed and ran one of the most famous experiments in the history of science. It's known today as the double-slit experiment and requires simple...
Friday, 21 December 2012
Light as Rays (How Light Works)
Imagining light as a ray makes it easy to describe, with great accuracy, three well-known phenomena: reflection, refraction and scattering. Let's take a second to discuss each one.
In reflection, a light ray strikes a smooth surface, such as a mirror, and bounces off. A reflected ray always comes off the surface of a material at an angle equal to the angle at which the incoming ray hit the surface. In physics, you'll...
Thursday, 20 December 2012
What is Ionizing Radiation?
Introduction - Waves and Particles
Energy emitted from a source is generally referred to as radiation. Examples include heat or light from the sun, microwaves from an oven, X rays from an X-ray tube, and gamma rays from radioactive elements
Ionizing Radiation
Ionizing radiation is radiation with enough energy so that during an interaction with an atom, it can remove tightly bound electrons from the orbit of an atom, causing...
Wednesday, 19 December 2012
Comet Hyakutake :The Great Comet of 1996
On January 30, 1996, Comet Hyakutake was discovered using 25×150 binoculars. The comet was designated Comet C/1996 B2 (Hyakutake). As subsequent observations of the new comet were obtained, the IAU Central Bureau was able to compute the comet’s orbital elements, and these computations indicated that the comet passed as close as 0.10 AU from the Earth on March 25, 1996! The comet became a bright unaided-eye object and remained so...
Tuesday, 18 December 2012
Galaxy Clusters and Large-Scale Structure
Groups and clusters of galaxies
Galaxies are preferentially found in groups or larger agglomerations called clusters. The Local Group consists of our own galaxy, the larger spiral galaxy Andromeda (M31) and several smaller satellites, including the Large and Small Magellenic Clouds.
Fornax is a small cluster of spiral and elliptical galaxies near our Local group.
Regular clusters have a concentrated central core and a well-defined...
Monday, 17 December 2012
Star clusters
Star cluster -Star cluster: A bunch of stars (ranging in number from a few to hundreds of thousands) which are bound to each other by their mutual gravitational attraction.
When stars are born they develop from large clouds of molecular gas. This means that they form in groups or clusters, since molecular clouds are composed of hundreds of solar masses of material. After the remnant gas is heated and blow away, the stars collect...
Sunday, 16 December 2012
The Age of the Universe
Universe - The Universe is commonly defined as the totality of existence, including planets, stars, galaxies, the contents of intergalactic space, and all matter and energy. Definitions and usage vary and similar terms include the cosmos, the world and nature.
The age of universe is 14-18 billion years.
Hubble Time -
The inverse of the Hubble constant H has the units of time because the Hubble...
Saturday, 15 December 2012
Does vacuum have friction?
A BALL spinning in a vacuum should never slow down, since no outside forces are acting on it. At least that's what Newton would have said. But what if the vacuum itself creates a type of friction that puts the brakes on spinning objects? The effect, which might soon be detectable, could act on interstellar dust grains.
In quantum mechanics, the uncertainty principle says we can never be sure that an apparent vacuum is truly empty. Instead, space is fizzing with photons that are constantly popping into and out of existence...
Friday, 14 December 2012
What is a vacuum? Is it matter?
A vacuum, to us, is a space
with no matter in it. As a practical matter though, it's really a space with
very little matter in it. You might already know that it's REALLY hard to get
all the matter out of any space. Believe it or not, vacuums are very important
and are becoming more useful every day. There is actually a whole branch of
science dedicated to creating and studying vacuums.
Many
modern devices (like the integrated circuit...
Wednesday, 12 December 2012
What is a Star?
A star is a huge ball of burning plasma that is held together by gravity.
The key to a star's existence is a phenomenon known as hydrostatic
equilibrium. The inward gravitational pressure created by the star's
mass is balanced by the outward radiation pressure created by the nuclear fusion taking place in the core.
The mechanism driving the outward radiation pressure in a star's core
is the nuclear fusion process where hydrogen is fused into helium via
the proton-proton chain. This reaction is exothermic, that is it
produces...
Tuesday, 11 December 2012
Did Galileo Invent the Telescope?
No. This is one of those things that "everyone knows," yet is absolutely incorrect. I'll talk about the reason for this mistake in a moment. First, let's give credit to the person who really invented the telescope. Who invented the telescope?
I don't know. No one does, really. However, there is some good evidence and many people believe that Leonard Digges invented both the reflecting and refracting telescopes. He was a well known mathematician and surveyor as well as a great populariser of science. His son, the famous...
Monday, 10 December 2012
What Happens To The Human Body In A Vacuum?
In the 1981 movie "Outland", starring Sean Connery, there is a scene
where a construction worker in space gets a hole in his suit. As the air
leaks out, the internal pressure drops and his body is exposed to a
vacuum, we watch in horror through his faceplate as he swells, and
explodes.
A somewhat similar scene is in the 1990 Arnold Schwarzenegger movie,
"Total Recall." In that movie, Schwarzenegger leaves the pressure of the
...
Sunday, 9 December 2012
How Long Does a Star Live?
The length of a star's life depends on how fast it uses up its
nuclear fuel. Our sun, in many ways an average sort of star, has been
around for nearly five billion years and has enough fuel to keep going
for another five billion years. Almost all stars shine as a result of
the nuclear fusion of hydrogen into helium. This takes place within
their hot, dense cores where temperatures are as high as 20 million
degrees. The rate of...
