Age of the planets

Whistling and moaning, a 50-mile-an-hour (80-kilometer-an-hour) wind whipped amidst the telescope domes atop Kitt top. Just a couple of feet below, rotating gray in the dusk, skidded a stream of clouds that had been rising and dropping all day. And high above, comet Hale-Bopp dangled hovering like a feathery fishing lure, its follow arching off a bit, as if blown to the side by the penalizing wind.

One by one, stars winked on in a blackening atmosphere. In each of the telescope domes, teams of astronomers pleaded that the breeze would drop underneath 40 miles per hour (64 kilometers an hour), the issue at which they'd be adept to open the sliding doors and get back to work.

The sky turned indigo. Then very dark. Viewed from the summit, 6,873 feet (2,095 meters) above Arizona's Sonoran wasteland, Hale-Bopp's brilliant dirt tail, along with a dimmer, all but clear blue one, appeared to grow by qualifications. amidst the brightest comets ever glimpsed, Hale-Bopp had been visible for months from midtown Manhattan, of all locations. But here, on a moonless evening in the hills in the wasteland, the extent of Hale-Bopp's tail became visible—a wispy, delicate veil.

Along with eclipses, comets have been the most feared and adored atmosphere scenes of all. But while astronomers have been adept to forecast eclipses for thousands of years, only in the 1700s was a comet's return rightly forecast, by Edmond Halley.

Some comets sway round the sun every few years. Others, like Hale-Bopp, may take thousands of years. Most can be seen only with a telescope. But every one time in a while—a few times a years, perhaps—an outstanding one is visible to the naked eye. And in the past two years the world has seen not one but two of them.

Hyakutake in 1996 had one of the longest follows on record, extending more than halfway across the atmosphere; Hale-Bopp in 1997 had one of the most bright heads, almost as bright as the celebrity Sirius. Add the Jupiter smash into of comet Shoemaker-Levy in 1994, Halley's most recent visit in 1986, vivid comet West in 1976, and the scientifically signifiant—if visually disappointing—Kohoutek in 1973-74, and you could state that we are indeed living in the age of comets.

Hovering in the most fragile of gravitational balances, a fleet of dirty, lumpy snowballs numbering in the trillions is barely held in orbit by the pull of the sun. They are retained in the Oort cloud, a gigantic, diffuse sphere of cometary nuclei in the far reaches of the solar scheme. Close to the sun, yet still after Neptune, around what may well be their brethren, in a large computer disk called the Kuiper belt.

Comets are leftovers, scraps of material that didn't make it to planethood in the events creating our solar scheme. one time, numerous astronomers believe, the solar scheme was full of comet nuclei, chunks of ice and dirt left over from the formation of the sun. Most clumped together to form satellites, departing a relation handful—averaging perhaps a couple of miles broad, with temperatures as low as minus 400 qualifications Fahrenheit (minus 240 qualifications Celsius)—as time capsules of the early solar scheme.

They orbit in a perpetual deep freeze until some subtle gravitational nudge upsets the dainty balance. Then the large drop starts. Imperceptibly at first, a snowball wanders in the direction of the sun and gradually accelerates. As solar emission warms up the comet, the ice within sublimates, escaping as gas from vents at the exterior. occasionally jets of sublimating ice whirl off the rotating comet nucleus like a fireworks pinwheel. Dust tricked in the ice breaks free. Pushed back by the pressure of the sun's emission, the dust streams out behind the comet in what seems as a fiery tail.

our solar system

Our Solar system:

Our Cosmic Neighborhood

From our small world we have looked upon the cosmic ocean for thousands of years. very old astronomers observed points of lightweight that emerged to move amidst the stars. They called these things "planets," significance wanderers, and named them after Roman deities—Jupiter, king of the gods; Mars, the god of war; Mercury, messenger of the gods; Venus, the goddes of love and attractiveness, and Saturn, father of Jupiter and god of agriculture. The stargazers furthermore discerned comets with sparkling tails, and meteors or shooting stars apparently dropping from the atmosphere.

Since the invention of the telescope, three more planets have been found out in our solar system: Uranus (1781), Neptune (1846), and, now downgraded to a dwarf planet, Pluto (1930). In supplement, there are thousands of small bodies such as asteroids and comets. Most of the asteroids orbit in a district between the orbits of Mars and Jupiter, while the home of comets lies far beyond the orbit of Pluto, in the Oort Cloud.

The four planets nearest to the sun—Mercury, Venus, soil, and Mars—are called the terrestrial satellites because they have solid rocky surfaces. The four large satellites beyond the orbit of Mars—Jupiter, Saturn, Uranus, and Neptune—are called gas monsters. minute, distant, Pluto has a solid but icier surface than the terrestrial satellites.

almost every planet—and some of the moons—has an air. Earth's air is mainly nitrogen and oxygen. Venus has a broad air of carbon dioxide, with traces of venomous gases such as sulfur dioxide. Mars's carbon dioxide atmosphere is exceedingly slim. Jupiter, Saturn, Uranus, and Neptune are mainly hydrogen and helium. When Pluto is beside the sun, it has a slim air, but when Pluto journeys to the outside districts of its orbit, the atmosphere freezes and collapses to the planet's exterior. In that way, Pluto acts like a comet.

Moons, Rings, and Magnetospheres

There are 140 known natural satellites, furthermore called moons, in orbit round the diverse satellites in our solar scheme, extending from bodies larger than our own moon to small parts of debris.

From 1610 to 1977, Saturn was considered to be the only planet with rings. We now know that Jupiter, Uranus, and Neptune furthermore have ring systems, although Saturn's is by far the biggest. Particles in these ring schemes range in size from dirt to boulders to house-size, and may be rocky and/or icy.

Most of the planets also have magnetic fields, which extend into space and pattern a magnetosphere round each planet. These magnetospheres rotate with the planet, clearing charged particles with them. The sun has a magnetic area, the heliosphere, which envelops our whole solar system.

very old astronomers accepted that the soil was the center of the cosmos, and that the sun and all the other stars rotated round the soil. Copernicus proved that soil and the other satellites in our solar scheme orbit our sun. Little by little, we are charting the cosmos, and an obvious question arises: Are there other satellites where life might exist? Only lately have astronomers had the tools to obscurely notice large satellites around other stars in close by solar systems.