What is Light?

Light is simply a name for a range of electromagnetic radiation that can be detected by the human eye. What is electromagnetic radiation, then? Electromagnetic radiation has a dual nature as both particles and waves. One way to look at it is as changing electric and magnetic fields which propagate through space, forming an electromagnetic wave. [illustration]...

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Origin of the Universe

The universe is big in both space and time and, for much of humankind’s history, was beyond the reach of our instruments and our minds. That changed dramatically in the 20th century. The advances were driven equally by powerful ideas—from Einstein’s general relativity to modern theories of the elementary particles—and powerful instruments—from the 100- and 200-inch reflectors that George Ellery Hale built, which took us beyond...

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Light: Particle or a Wave?

Light has intrigued humankind for centuries. The most ancient theories considered light as something emitted by the human eye. Later on, it was understood that light should come from the objects seen and that it entered the eye producing the feeling of vision. The question of whether light is composed by a beam of particles or it is a certain type of wave movement has frequently been studied in the history of science. Between...

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How Is Lightning Made?

How is lightning made? People used to make up stories to answer that question. Today, science tells us how. You have heard of Ben Franklin. Did you know he flew a kite during a thunderstorm? He wanted to prove that lightning is a form of electricity. We know now that flying a kite in a storm is not safe. But, Ben was right. Lightning is a form of electricity. How does this "electricity" form? What do You Need to Make Lightning?...

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Why is it dark at night?

The question seems almost too shallow and silly and trivial even to ask. Why is it dark at night? The answers my family gave me were typical, such as, "The sun has gone to bed and pulled down the nightshade". Thanks guys! But in reality, the question is very deep and subtle. On a moonless night, the sky is dark, apart from the light of the stars (let's ignore the planets). The starlight we see comes from the several hundred billion...

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How was the Sun formed?

From studies of other stars which astronomers can see in many different stages of their 'life cycle', it seems pretty convincing from the data that the sun must have started out as a large collapsing cloud of gas inside some ancient interstellar cloud. This cloud was 'polluted' by a supernova several million years before the collapse phase ended, because we see certain isotopes of aluminum which could not have been a part of...

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WORMHOLE

White holes perform exactly opposite of black holes. A white hole emits everything, and has no gravity. Although white holes are not believed to exist they are mathematically possible. The possibility of white holes has been proven using Einstein's Theory of Relativity (Bunn). In short, the Theory of Relativity is a mathematical formula dealing with time, energy, speed, and mass. The possibility of white hole uses the time portion...

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What Is a Black Hole?

What Is a Black Hole? A black hole is a place in space where gravity pulls so much that even light can not get out. The gravity is so strong because matter has been squeezed into a tiny space. This can happen when a star is dying. Because no light can get out, people can't see black holes. They are invisible. Space telescopes with special tools can help find black holes. The special tools can see how stars that are very...

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Does the Moon rotate? And if the Moon rotates, why do we always see the same side?

The Moon is familiar; it always looks the same. We know that the Earth rotates, that’s why the Sun, Moon and stars seem to move through the sky every day. But does the Moon rotate? And if the Moon rotates, why do we always see the same side – it never seems to change. Well, the Moon does rotate. In fact, the Moon takes 27.3 days to turn once on its axis. But the Moon also takes 27.3 days to complete one orbit around the Earth. Because...

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Does the Sun rotate? Are we seeing the same face of the Sun all the time?

The Answer Yes, the Sun does rotate. We can observe this by observing sunspots. All sunspots move across the face of the Sun. This motion is part of the general rotation of the Sun on its axis. Observations also indicate that the Sun does not rotate as a solid body, but it spins differentially. That means that it rotates faster at the equator of the Sun and slower at its poles. (The gas giants Jupiter and Saturn also have differential...

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What we see in the night sky?

Planets • Mercury is difficult to see because it is always close to the sun. • Venus is white and very bright. It is always  seen right after sunset or right before sunrise,  near the horizon in the direction of the sun. • Mars is red. • Jupiter is yellow and very bright. • Saturn is also yellow, but not as bright as Jupiter. How to tell the difference between stars and planets? • Stars stay fixed in their positions...

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Advanced burning in stars

In principle, fusion can continue beyond Carbon and Oxygen. However, such advanced burning in stars Requires higher and higher temperatures because of having to overcome larger Coulomb barriers. Produces less and less energy as the masses increase. Cannot produce energy for fusion products beyond the Iron region (A~60) because that is where the peak of the binding energy curve is located: Curve of binding energy. In...

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Distances to Stars

Distances are particularly easy to calculate if we use the parsec as our distance unit. In that case, the distance of a star in parsecs is just D = 1/p where D is the distance in pc and p is the parallax angle in seconds of arc. For example, Sirius has a parallax angle of 0.38 seconds of arc and thus its distance from the Earth is d = 1/0.38 = 2.6 pc = 8.6 LY. The nearest star (other than the Sun) is the alpha-Centauri system, which has a parallax of 0.76 seconds of arc, corresponding to a distance of 1.315pc...

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Energy Transport in Stars

The energy produced by thermonuclear reactions in stars in produced in their deep interior because only there are the pressures and temperatures high enough to sustain thermonuclear reactions. However, most of the luminous energy of stars is radiated from the thin region at the surface that we call the photosphere. Methods of Energy Transport Thus, a central issue for stars is how they transport the energy produced in the core to the surface. There are 4 important categories of such transport: Radiative transport...

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When did science begin?

Here is a philosophical answers: technically, science began the day the very first humans looked at the sky or ocean and wondered why it was blue, or understood that fire cooks food....what i mean is, science is pretty much the all inclusive study of everything everywhere in order to seek out an explanation for why things are the way they are...so in reality, it began the first time someone wondered how/why anything is the way it...

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Nuclear Reactions

In the fusion of light elements to form heavier ones the nuclei (which carry positive electrical charge) must be forced close enough together to cause them to fuse into a single heavier nucleus. The Coulomb Barrier The electrical repulsion produces a barrier to this process called a Coulomb barrier, as illustrated in the following figure, which shows the potential energy of such a system as a function of the separation r between...

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Energy Production in Stars

The stars are at enormous distances from us, yet we can see thousands in the sky without the aid of a telescope. This tells us that the stars are extremely luminous. We must then ask what the source of their enormous energy could be.  Given what we know about stars like the Sun, there are two possible sources of such energy: (1) gravitational contraction and (2) thermonuclear reactions that convert mass to energy. Both play important roles in producing energy over the lifetime of a star, but the primary energy...

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Albert Einstein and the Theory of Relativity

Albert Einstein1879-1955 Newton's theory of gravitation was soon accepted without  question, and it remained unquestioned until the beginning  of this century. Then Albert Einstein shook the foundations  of physics with the introduction of his Special Theory of  Relativity in 1905, and his General Theory of Relativity in  1915. The first showed that Newton's Three Laws of Motion  were...

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