In astronomy, we often use angular measurements to describe the apparent size of an object in space and the apparent distances between objects. Often these angles are very small. Angles are also used to describe an object's location in space. The angular measure of an object is usually expressed in degrees, arcminutes or arcseconds. Just as an hour is divided into 60 minutes and a minute into 60 seconds, a degree is divided into 60 arcminutes and an arcminute is divided into 60 arcseconds. To give you an idea of how small an arcsecond is, imagine the width of a dime as seen from 2 kilometers or 1 1/4 miles away.
1 degree = 1° = 1/360 of a circle1 arcminute = 1' = 1/60 of a degree
1 arcsecond = 1" = 1/60 of an arcminute = 1/3600 of a degree To get a rough estimate of the angular size of objects in space, you can go out on clear night when the moon is up. Extend your arm towards the sky. Your fist, at arms length, covers about 10 degrees of the sky, your thumb covers about 2 degrees, and your little finger covers about 1 degree. If you look at the Moon, it should take up about 1/2 a degree in the sky. The Big Dipper should be about 20 degrees (two fists at arms length) from one end to the other.
Comets are more commonly named by the discoverers and are considered to be members of our Solar SystemSolar System. It is a small Solar System body that orbits the Sun and when it is close enough to the Sun and originates from either the Kuiper Belt or Oort Cloud. Exhibiting a visible atmosphere or a tail-both primarily from the effects of solar radiation upon the comet’s nucleus. They can have highly elliptical orbits that bring them very close to the Sun and swing them deeply into space-often beyond the orbit of Pluto.Comets have a variety of different orbital periods ranging from a few years, to hundreds of thousands of years, while some are believed to pass through the inner Solar System only once before being thrown out into interstellar space. Comets can be described as "dirty snowballs" containing a mixture of dust and frozen gases and can leave a trail of debris behind them. A comet consists of a Nucleus, Coma, and an Ion Tail or a Dust Tail.
The Kuiper Belt is pronounced to be rhymed with “viper” and is sometimes called the Edgeworth-Kuiper Belt. Its existence was predicted in 1951 by Gerald Kuiper, for whom the belt was named after. This belt is a region of the Solar System beyond the planets extending from the orbit of Neptune to approximately 55 AU from the Sun . It is the home to atleast three dwarf planets –Pluto, Haumea, and Makemake. At its fullest extent, including its outlying regions, the Kuiper Belt stretches from roughly 30 to 55 AU. It is quite thick with the main concentration extending as much as ten degrees outside the ecliptic plane and a more diffuse distribution of objects extending several times farther. It is considered to be the source of where the short-period comets come from. No spacecraft has ever traveled to the Kuiper Belt, but NASA’s New Horizon mission, plan to arrive at Pluto in 2015.
The Oort Cloud was proposed in 1950 by Dutch astronomer Jan Oort. The Oort Cloud is a giant, hypothetical spherical cloud of comets believed to lie roughly 50,000 AU, or even nearby a light-year, from the Sun and is filled with about 1 million comets. Objects in the Oort Cloud are largle composed of ices, such as water, ammonia, and methane. The vast distance of the Oort Cloud is considered to be the outer edge of the Solar System. The Oort Cloud is the source of long-period comets and possibly higher-inclination intermediate comets that were pulled into shorter period orbits by the planets. The total mass of comets in the Oort Cloud is estimated to be 40 times that of Earth and are typically tens of millions of kilometers apart. Passing stars can disturb the orbit of one of the icy bodies, causing it to come streaking into the inner Solar System as a long-period comet.
On July 16-22, 1994, over 20 fragments of Shoemaker-Levy 9 traveled at the speed of approximately 60 km./sec. collided into Jupiter providing the first direct observation of an extraterrestrial collision of Solar System objects. The pieces were later observed as a series of fragments ranging up to 2 km. in diameters. It was the first comet observed to be orbiting a planet and also the first collision of two Solar System bodies ever to be observed and the effect of the comet impact on Jupiter's atmosphere have been simply spectacular and beyond expectations. The collision was a distance of 400 million miles from Earth, so far away it didn’t affect Earth, but could at one time have been a severe danger to Earth. The scars from the impacts were more easily visible than the Great Red Spot. A collision of a large comet with an extraordinary, millennial event.
Pictures & Table of shoemaker-Levy.
Comet Shoemaker-Levy 9