Passage of comets

What is a comet?

Besides the planets, satellites and asteroids, the solar system contains comets (hair in Greek). Wandering comets originate in the depths of space, several light years from the Sun. The number of periodic comets is about 2000. Comets are small glass spheres that travel from the Sun, and sometimes they are captured by our star. Their orbits are very eccentric elliptical paths around the Sun. The most famous periodic comet is Halley's comet approaches the Sun every 76 years. When a comet approaches the Sun, the outer layer vaporizes and forms a gaseous envelope (coma). Solar radiation exerts a pressure on the coma and force particles and ionized gas, forming a bright tail in the opposite direction. Comets scored the memory of mankind. They have long been synonymous with misfortune and disasters.

They were also harbingers of upheaval in an era where not happy with our real evils, we build imaginary.
This is not the messenger of woe, is the guardian of the past, one that holds the key to our origin.
In the 19th century with the separation of science and religion, the image of the comet is more negative.
They may be contemplating for weeks before they disappear to return, 10, 100 or 1000 years later. These are the vagrants of the sky, the messenger of space.

Image: NASA image of Comet Wild 2 taken by the Stardust spacecraft in 2004.

Comet Holmes November 2007

As it passed in 2007, the hair ball Comet Holmes has exceeded the size of the Sun. It is 1.4 million kilometers in diameter.
His tenuous cloud of gas and dust scatters sunlight, gases and dust from the remarkably active nucleus of the comet with a diameter in October 2007 was estimated at 3.4 km. One can easily see on the photo-cons, through the outer part of the hair, stars by transparency. The core is his even more brilliant.
Every six years, comet 17P/Holmes follows the same route without incident, but recently, in November 1892 and October 2007, the comet has mysteriously exploded as it approached the asteroid belt. Astronomers still do not know the reasons for these eruptions.

Image: Comet Holmes, NASA image of November 2007. Credit & Copyright: Jean-Charles Cuillandre (CFHT), Hawaiian Starlight. In this photograph, the bright region of the coma or coma of Comet Holmes seems slightly off, which is consistent with the hypothesis that a large fragment of the comet would be separated from the main body, before disintegrating.

103P Hartley happening around us, every 6 years

Every 6.46 years, the small comet Hartley 2 (103 / P Hartley) passes near the Earth and the Sun. 103P/Hartley or comet Hartley 2, is a periodic comet discovered by Malcolm Hartley in 1986, with the Schmidt telescope at the Siding Spring Observatory, Australia. In October 2010 it passed near Earth and the Sun. Against this backdrop of night sky of October 2, 2010 you can see right image, the comet dragging her beautiful hair greenish. It shared the image with the emission nebula NGC 281 (left) and stars in the constellation Cassiopeia (center). The shape of the nebula NGC 281 earned him the nickname Pacman Nebula. The nucleus of the comet has left a small trail of light on the sensors during the time of exposure required for shooting this photo. The comet Harley 2 with its green tail, is very controlled, Deep Impact is not the only observer space, WISE and the Hubble also observed. On November 4, 2010, the spacecraft's new mission EPOXI Deep Impact, rose to 700 km from the comet nucleus. This comet nucleus active, is similar in size and mass, Tempel-1, it measures 1.5 km. For the occasion, a new mission, called EPOXI, is to fly over Hartley 2, during his visit. This is the Deep Impact probe that is party to meet Hartley 2.

Developed in December 2007, the trip took over 2 ½ years. The probe hit the comet after a trip equivalent to 18 times the Earth-Sun distance and used three times, the gravity assist from Earth. The mission was to draw maps of temperature, measure its size, albedo, modeling its nucleus, to study the distribution of dust and gas, search for volatile compounds, identify surface features, observed distribution of craters,...

Image: The discrete comet Harley 2 with its green tail, rose to 18 million kilometers, 20 October 2010 it was closer to Earth. His brilliance was not exceptional, because Hartley 2 is a tiny comet, whose nucleus does not exceed 1.5 km. Deep Impact is not the only observer space, WISE and Hubble also observe the comet Hartley 2. Its orbital period is 6.46 years.