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One hundred years ago, a young physicist presented a paper to the Prussian Academy of Science--a paper that we now recognize as symbolizing the birth of general relativity. By this [...]

Figuring the distance to stars and galaxies challenged both ancient Greeks and modern cosmologists. The universe may be three dimensional, but our view of it is not. The sky looks [...]

Some of astronomy's greatest moments brought incandescent insights, among the greatest the human mind has ever produced. Hubble's realization that the universe was expanding and Copernicus's dream of the moving [...]

From the point of view of a physicist, whenever anything happens in the world, it happens because of the action of some combination of four fundamental forces. The forces of [...]

We learn about the universe by looking at the heavens, which means our knowledge depends on the kinds of signals we see and the messengers that bring them to us. [...]

Cosmologists know the universe began with the Big Bang approximately 13.7 billion years ago. Astronomers know Earth formed from material in a debris disk surrounding the fledgling Sun. And planetary [...]

Q: How do astrophysicists measure a black hole's mass?--Kirt Bhatt, Columbia, Maryland A: If the black hole is sitting by itself out in space, you probably won't be able to [...]

Earth hasn't always been a green and pleasant place. In fact, our planet's infancy was a violent, chaotic time. When you visualize the hellish conditions back then, it's hard to [...]

Q: If nothing, not even light, can escape a black hole, then why do nearly all artist renderings of black holes show an accretion disk and a jet that appears [...]

Everything and everywhere began about 14 billion years ago in the Big Bang. Since then, a massive expansion of space-time has carried galaxies far away from each other. After American [...]

Sometimes the most profound insights come from the most mundane experiences. So it is with the discovery of the cosmic microwave background (CMB), which manifested itself as an engineering nuisance. [...]

Relativity has always been the odd man out in the sciences. In the general course of affairs, scientific ideas change slowly. Data challenging the old view starts to accumulate, then […]

It was born millions of years ago in a distant galaxy, accelerated to incredible speeds by a process unknown to science. For millennia it sped through the void, twisting and [...]

Imagine you are being given an important assignment by a taskmaster with a strange sense of humor. Your job is to study a forest, but you can only work according [...]

Everyone who lived before Christopher Columbus thought Earth was flat, right? Actually, Greek scientists knew Earth was a sphere thousands of years before Columbus first sailed the Atlantic. That knowledge [...]

Auguste Comte (1798-1857) is known today as an important philosopher and the father of modern sociology, but in his own lifetime he lived a shadowy kind of existence on the [...]

Most of us have a pretty good intuitive grasp of the way time affects our lives. Yet when it comes to defining the essence of time, most of us agree […]

Why is there a universe at all? How could everything we see around us have been created out of nothing? When you begin to think about how the universe began, [...]

If you look at the sky on a clear night, you can see a few thousand stars. With a telescope you can see a lot more - distant galaxies, gas [...]

Einstein's general theory of relativity remains our best explanation of the phenomenon of gravity, but it has accumulated a remarkably small number of experimental verifications. This is because Einstein's relativity [...]

The article mentions centennials of the discovery of Theory of Relativity by physicist Albert Einstein and discusses the concept of slowdown in moving clocks based on relativity. Topics discussed include use of a device called a light clock for understanding relativity, invention of space-time by Einstein and a timeline of events related to relativity following birth of Einstein on March 14, 1879 in Germany. It also discusses the concept of special relativity. INSET: WHY DO MOVING CLOCKS SLOW DOWN?.

The article provides information on what the planet Earth was like while it was still forming. The author explains that the earth was a fiery place for several hundred million years. While geological formations were taking shape, the planet was much hotter, which then led to a cooling before it became the green place that it appears as in 2007. INSET: HOW SCIENTISTS DATE RADIOACTIVE ISOTOPES.

This article focuses on Einstein's theory of relativity and explains the three tests used to validate the theory. In the general course of affairs, scientific ideas change slowly. With relativity, though, it was different. When it appeared, scientists dispensed with their usual arguments about data and took the new ideas to heart. A big reason for that reaction comes from the fact that relativity is beautiful. The beauty stems from the central principle of Einstein's work called, appropriately enough, the principle of relativity. So how does gravity get into it? Einstein realized someone standing on a scale in an ascending elevator would see her weight increase, just as if the planet on which she was standing had suddenly grown more massive. The connection between frames of reference and mass is the crux of general relativity.

Provides information on cosmic rays. Factors that led to its discovery; How solar flares send cosmic rays; Reasons for the change in the study of cosmic rays.

Focuses on the discoveries of the scientists about the shape of Earth. Arguments of second-century Egyptian astronomer Claudius Ptolemy, compiled in the book `The Mathematical Composition'; Information on the works of Eratosthenes, an Alexandrian scientist and a fellow of Ptolemy; Discoveries of Nicolas Copernicus, a fifteenth century scientist.

Discusses the various methods and instruments used in time measurement. Overview of the Stonehenge architecture; Evolution of the calendar; Details on carbon dating; Introduction of pendulum and atomic clocks.

Offers a look on parallax, the distance between the earth and the stars. Historical background; How Erastothenes of Cyrene measured the radius of the earth; How astronomers measure the distance of a star with the use of parallax.

The article presents questions and answers related to astronomy including the age of the star HE 1523-0901, the difference between comets and asteroids, and the measurement of the mass of black holes.

The article presents questions and answers related to astronomy. One reader questions why some meteor showers, such as the Geminids, have slow moving meteors, while others, such as the Perseids, have faster moving meteors. Another asks a question about the expanding universe. Another reader asks why the Moon's orbital distance is increasing over time.

The article presents questions and answers related to astronomy. A 0.2-second pulse from a magnetar can put out as much energy as the Sun does in 250,000 years. Green stars emit radiation most intensely at wavelengths in the green part of the visible light spectrum. Artists' renditions of black holes feature an accretion disk and X-rays to show particles that are falling into the black hole.

This article presents questions and answers related to astronomy. Why doesn't Jupiter's Great Red Spot have an eye, like hurricanes on Earth? --Frank Hanou, Indianapolis. Jupiter's Great Red Spot is not analogous to a terrestrial hurricane. In fact, in many ways, it's the opposite phenomenon. Earth's hurricanes are cyclonic. Jupiter's Great Red Spot is an anticyclone -- a dome of high-pressure gas rising above the surrounding atmosphere. Instead of having a central eye, the spots are encircled by a ring of calm, stable, descending gas.