Comet C/2009 P1 Garradd discovered by Australian amateur astronomer Gordon Garradd is visible in September 2011 through all binoculars and small telescopes as high evening object glowing at magnitude 7 . It has a bright green head (coma), a sharp nucleus and a short but well defined tail . The comet’s location is in the tiny constellation Arrow (Sagitta) in the autumn Milky Way. In late September Garradd comet enters Hercules, where it will peak in brightness from October 2011 to March 2012 at around magnitude 6, so it could be visible with the naked eye. But be careful – it looks like a faint cloud – a faint object for beginners who expect spectacular view. Anyhow since Hale-Bopp none comet was visible so bright for so long time for observers at mid-northern latitudes. And lets remain optimistic – sometimes comets behave in unexpected ways exceeding all expectations.
Closest approach to Earth was 5th of March 2012 when comet Garradd was 117.7 million miles away (1.27 astronomical units). At that time, the comet was seen glowing in the Little Dipper. It never comes closer to the Sun than Mars – at its closest approach to the Sun on December 23rd it was still 1.55 astronomical units from the Sun. Garradd would be a great comet if had passed closer to the Sun!
In March 2012 Garradd remained reasonably bright, somewhere near 7th magnitude, which makes it an inviting target for binocular and small-telescope users. In to history Garrard comet come to be known for two distinctive tails. From the perspective of earthbound comet watchers the tails are visible on opposite sides of its greenish coma.
Comets are composed of rock, dust, ice, and frozen gases such as carbon monoxide, carbon dioxide, methane, and ammonia. They have been described as dirty snowballs. Comet nuclei can range from about 100 meters to more than 40 kilometers across. It contains a variety of organic compounds. It is believed that about 4 billions years ago comets bombarded the Earth bringing the vast quantities of water and “life bricks” into Earth’s oceans. An impact 65 million years ago is believed to have killed off the dinosaurs.
Because of their low mass, comets can’t become round and have irregular shapes. Cometary nuclei are among the darkest objects in the solar system (!!!). They often reflect approximately 4 % of the light. It is interesting that Comet Ikeya-Seki was visible in the daytime in 1965, being brighter than the Moon.
The streams of dust and gas form a huge comet coma. The force exerted on the coma by the Sun’s radiation pressure and solar wind cause an enormous tail to form, which points away from the Sun. The streams of dust and gas each form their own distinct tails. The coma may be larger than the Sun (1 000 000 km across) and tails extend to 150 million km or more! Meteor showers on Earth are actually caused by Earth passing through comets’ orbits. The most famous meteor shower is the Perseid meteor shower that happens every year in period between August 9 and August 13, at the time when Earth passes through the orbit of the Swift–Tuttle comet.
Comets are classified according to the length of their orbital period: short period comets have orbital periods less than 200 years (the shortest known orbital period has Comet Encke – 3,5 years), long-period comets have periods to thousands or millions of years and single-apparition comets exit the solar system after passing the Sun once.
Asteroids and comets are considered remnants from the giant cloud of gas and dust that condensed to create the sun, planets, and moons some 4.5 billion years ago. Today comets come from the Oort Cloud and the Kuiper Belt. While trillions of comets are ringing the outer fringes of the solar system, only from 5 to 20 new comets are discovered every year and the total number of comets that have been identified so far is over 3800. The most famous comet of them all, Halley’s comet can be see every 75–76 years. Most comets are named after their discoverer except Comet Halley, which was predicted to return by Edmund Halley in 18th century.