Comet Halley (Edmund Halley)

The best known comet of all is Halley, which has returned with a 74-79 year period since 240 B.C. The following image shows a famous view of the full tail of Halley recorded from the Mount Wilson Observatory. Comet Halley from Mount Wilson Edmund Halley and His Comet The English astronomer Edmund Halley was a good friend of Isaac Newton. In 1705 he used Newton's new theory of gravitation to determine the orbits...

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The Hot Big Bang

The big bang starts off with a state of extremely high density and pressure for the Universe. Under those conditions, the Universe is dominated by radiation. This means that the majority of the energy is in the form of photons and other massless or nearly massless particles (like neutrinos) that move at near the speed of light. As the big bang evolves in time, the temperature drops rapidly as the Universe expands and the average velocity of particles decreases. Finally, one reaches a state where the energy of the...

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Dark Matter

There are many reasons to believe that the universe is full of "dark matter", matter that influences the evolution of the universe gravitationally, but is not seen directly in our present observations. FIGURE: Superposed on an optical picture of a group of galaxies is an X-ray image taken by ROSAT. The image shows hot gas (which produces X-rays) highlighted in false red color . The presence of this confined gas indicates...

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Matter in the Universe

Matter is generally considered to be anything that has mass and volume. The volume is determined by the space in three dimensions that it occupies. The mass is determined by its rest mass (or invariant mass), which is measured by the acceleration a body has when a force is applied. The greater the mass, the slower the acceleration for the same force. Matter is thus a general term for the substance of which all observable physical objects consist The matter in the universe is created by the big bang, but not in the...

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Cosmology

Cosmology is the study of the larger issues: how "big" is the Universe, does it have an "end", what is its large-scale structure, how old is the Universe, how long will it live? Cosmology is the study of the origin and the development of the Universe. As such, it is concerned with the large scale, both with respect to distance, and with respect to the past and future for the Universe. The Central Themes of Modern Cosmology The central tenet of modern cosmology is the idea that the Universe is expanding, and that...

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Motion of the Sun

The Sun is in motion, just like any other star. Motion of the Sun Relative to Local Stars First, the Sun and the other stars in its vicinity partake of the general rotation of the galaxy (the Milky Way Galaxy rotates once about every 225 million years). This corresponds to an average velocity of about 220 km/s. The space velocities that we measure for other stars then correspond to deviations from this average motion for the stars around the Sun. This happens because the Sun and the stars near it are on somewhat...

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Limitations of the Human Eye

The human eye is a remarkable biological invention, a shining triumph of the process of evolution. Although the human eye was the detector that started us on mankind's exploration of the Cosmos, it has some shortcomings that ultimately limit that exploration: The eye has limited size and therefore limited light-gathering power. The eye has limited frequency response, since it can only see electromagnetic radiation in the visible wavelengths. The eye distinguishes a new image multiple times a second, so it cannot...

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Planet found in nearest star system to Earth

This artist’s impression shows the planet orbiting the star Alpha Centauri B, a member of the triple star system that is the closest to Earth. Alpha Centauri B is the most brilliant object in the sky, and the other dazzling object is Alpha Centauri A. Our own Sun is visible to the upper right. The tiny signal of the planet was found with the HARPS spectrograph on the 3.6-meter telescope at ESO’s La Silla Observatory in Chile....

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