KEEP YOUR EYES ON COMET ISON

Dr. P. Kumarasamy, 

Associate Professor, 

PG & Resesarch Department of Zoology, 

The American College, Madurai 625002. 

pkumarasamy@gmail.com

 The word comet is derived from the Latin word comēta or comētēs meaning “long hair”, the "long-haired star”.

What are comets? 
Comets are small celestial bodies similar to asteroids with a thick dusty, icy outer layer and an inner rocky core. Hence they are often known a ‘dirty snow balls’. The hard central core of comets are called ‘nuclei’ composed of rock with an outer layer of dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia.

Comets develop a tail only when they come near the Sun during that time the icy water and gases evaporate and are blown away by the solar radiation from the central core into a long trail of particles, forming the tail. Hence the tail always faces away from the Sun.
The length of the tail grows as comets get closer to Sun and the tail shortens and disappears when it moves far away from the Sun. Every time a comet comes closer to Sun it loses some of its mass.
Comets were formed along with planets when the solar system evolved. 
All the comets that we know and see belong to our solar system.

There are basically two types of comets namely periodic comets and non-periodic comets.

Do comets emit light? 

Comets do not emit light on their own like stars do, but reflect the Sun light. So the brightness of comets increases when they approach the Sun and they become dimmer as they move away from the Sun.

Periodic and non-periodic comets 

Periodic comets revolve in an elliptical path around Sun usually with a periodicity of less than 200 years, for example the Halley’s Comet completes one revolution in 76 years. 
Such periodic comets are known to originate from a belt of icy rocks revolving around the Sun located approximately 50 Astronomical Units (AU) from the Sun and extending between the orbits of Neptune and Pluto, this belt is called as ‘Kuiper belt’. 
Compared to the ‘asteroid belt’ that exist between Mars and Jupiter, the Kuiper belt is far larger — 20 times wider and 200 times heavier.

[AU - refers to the average distance between Earth and Sun which amounts to 149,597,870 kilometers]

Non-periodic comets have their origin in a spherical cloud of comets called as ‘Oort Cloud’, situated about 50,000 AU from the Sun.

Oort cloud is a spherical cloud of comets situated about 50,000 AU from the Sun. It forms the outer most boundary of our Solar System extending at nearly a quarter of the distance to Proxima Centauri (4.2 light years), the nearest star to the Sun. 

The Comet ISON’s Rare visit 

Comet ISON a view from Hubble Space Telescope

Comet ISON is a non-periodic comet. This comet was discovered only very recently, on September 21, 2012. This comet has escaped from the orbital path of Oort cloud and for the first time it is heading towards the Sun. Eventually it will be deflected away from the Sun as it passes around the Sun on 28th November 2013. 
It will NOT come back again to our solar system! 
So this is going to be a ‘once in a life time’ event.

Nomenclature 

Comet ISON is also designated as:

• C/2012 S1 or
• Comet Nevski–Novichonok 

The name ISON:
This comet was discovered on September 21, 2012, from the analysis of images taken with a 16-inch reflector telescope that is part of the International Scientific Optical Network (ISON). At the time of discovery, ISON was over 584 million miles from the Sun (6.29 AU) that is about 6 times the distance between Earth and Sun.

C/2012 S1:
The letter C denotes that it is a non-periodic comet discovered in 2012 “S” designates that it was discovered in the second half of September 

NEVSKI–NOVICHONOK:
Vitali Nevski and Artyom Novichonok were recording images in the constellations Gemini and Cancer. They were using the 16-inch reflector at Kislovodsk Observatory in Russia, part of the ISON network. After running the images through CoLiTec, software used to detect asteroids and comets, Nevski was the one who spotted the object now known as ISON.

Size of the ISON Comet: 
Comet ISON is less than 5 kilometers in diameter (3 miles), and weighs between 3.2 billion kg (3,20,00,00,000 kg) and 3.2 trillion kg. Shape of the Comet: ISON is an irregularly shaped comet. Analyses show that it may be composed of 3 pieces of rock put together.

Speed of ISON 
How fast it moves as it travels around the Sun?

Comet ISON’s average speed will be about 125,000 kmph when it is far away from the Sun. As it nears the Sun, the speed accelerates until 28th November 2013 when goes around the Sun at a maximum speed of 1,352,000 kmph!

Comet ISON’s Eccentricity: 
Comet ISON’s eccentricity is close to 1 (to be exact 1.000003457). The eccentricity values range between 0 and 1. Value 0 denotes a perfect circle and value 1 denotes a highly eliptical shape resembling a horizontal line.
The eccentricity of comet ISON suggests that it is visiting our Solar System for the first time and it will not visit again in future.

Inclination of Comet ISON: 
The orbital path of ISON is inclined about 62.39° to the orbital path of the Earth around the Sun (ecliptic).

Closest approach to Sun: 
ISON will come nearer to Sun “perihelion position” (closest approach to the Sun) on 28 November 2013. On that day ISON will be at a distance of 0.0124 AU that is 1,860,000 km or 1,150,000 miles from the center point of the Sun. This is about the same angular diameter of Sun. Hence ISON is known as a ‘Sungrazing Comet’

The Great Comet of 1680 was first sungrazing comet to be discovered. This comet was found to have passed just 200,000 km (0.0013 AU) above the sun's surface, equivalent to about half the distance between the Earth and the Moon! 

Closest encounter with Earth: 
The closest distance between ISON Comet and Earth occurs on 26 December 2013 at that time the ISON Comet will pass about 0.4292 AU (64,210,000 km; 39,900,000 miles) from Earth.

Location of ISON in the night sky: 

In October:

• ISON will pass through the constellation Leo, passing near Leo's brightest star Regulus and then passing near Mars in the night sky, and these brighter objects might make ISON easier to locate. Near equator the comet will be visible fairly high during morning twilight at ~04:40am (from Oct 19-31)

In November:

• ISON will be brighter and will sweep past Spica in the constellation Virgo, and the planet, Saturn. It reaches perihelion on 28 November. 

In December:

• ISON will be growing dimmer, but, assuming that it remains intact, it will be visible from both hemispheres of Earth, possibly with a long tail. ISON will be well placed for observers in the northern hemisphere during mid to late December 2013. 
• In early December it will be between between Libra and Ophiuchus. 
• On 22 December it will be in Hercules near the globular cluster M13. 
• By 25 December it will be close to the Plough (Ursa Major), 
• On 26-27 December, ISON will be at its closest to Earth at 64 million km. 
• At the end of December the comet is in Draco and will be visible in the north west by evening, in the morning sky before before sunrise in east. 

In January 2014:
On 8 January, it will move north on the celestial sphere, passing within two degrees of Polaris .

DATE	TIME	DEGREES FROM HORIZON	CONSTELLATION/STAR
06-11-2013	3AM-5AM	04°-30° E	Between Leo & Crater, below Mars
23-11-2013	5AM	04° SE	Below Spica (Virgo)
13-12-2013	5AM	02° E	Serpens (SE of Corona Borealis)
21-12-2013	5AM	12° NE	Corona Borealis
28-12-2013	4AM  to 5AM	04°- 15°NE	Draco
04-01-2013	5AM	12° N	Ursa Minor
07-01-2013	5AM	10° N	near Pole Star
10-01-2013	5AM	05° N	Just below Pole Star- Last Day

Interesting Facts: 

• Comet ISON seems to be a new comet fresh from the Oort cloud. 
• Comet ISON is believed to be making its first trip to the sun, and so is hoped to still have most of its ancient volatile chemicals intact. Analysis of these Volatiles will throw more light on the origin of solar system and possibly the origin of life on Earth. 
• It will be one of the brightest comets in history. Hence ISON is tagged as a "comet of the century" 
• The comet ISON will be visible to the naked eye between 6-11-2013 and 23-11-2013 and between 13-12-2013 and 10-01-2014. 
• Seeing this comet ISON is a unique opportunity as this will be its first and last visit to our solar system! 
• Between 14 and 15 January 2014 Earth will pass near the orbit of ISON Comet well after the comet has passed. During this time, micron-sized dust particles from the comet blown by the Sun's radiation may likely cause a meteor shower or noctilucent clouds. 
• Comet ISON observations by NASA show that this new comet ISON is emitting about 1 million kilograms of icy carbon dioxide gas, about 54.4 million kilograms of dust and 86400 kg of water every day in the form of a long tail that always faces away from the Sun. 
• The tail of the comet may reach a maximum of about 300,000 kilometers (186,400 miles) long, more than four times the circumference of Earth! 
• Comet ISON is expected to lose 10% of its size / mass during its first-ever flyby near the Sun. 
• As ISON fly close to Sun anything can happen the comet may get fragmented or completely disintegrated or may remain intact, let us wait and see! 
• NASA is sending a Scientific Balloon Facility to study the Comet ISON called the Balloon Rapid Response for Comet ISON (BRRISON) 
• Comet ISON Observing Campaign (CIOC) of NASA is coordinating a global observation campaign that employs a variety of observation from the Earth and from space. For example, NASA's Hubble Space Telescope, Solar and Heliospheric Observatory (SOHO) a sun-watching spacecraft, Solar Dynamics Observatory, Stereo probes, and the Solar and Heliophysics Observatory, operated NASA, the European Space Agency (ESA) and Japan. 
• ISON is going to be the first comet in human history to be observed from more than one planet. On 1 October 2013, ISON passed close to Mars at a distance of about 0.072 AU (10.8 million km). At that time the cameras of the Curiosity Mars rover took snaps of ISON. The Mars Reconnaissance Orbiter also made some images with its HiRISE instrument on 29 September 2013.

Further reading & viewing: 

Comet ISON Debris Hitting Earth:

http://www.youtube.com/watch?v=DKFXcaR5UaMComet ISON NEWEST

Moving Images October 10, 2013:

http://www.youtube.com/watch?v=K4-HFtqNmR0 

For ISON path interative animations visit:

http://www.mattastro.com/ison/interactive.html
http://theskylive.com/ephemerides-computation?obj=ison
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=ison;orb=1;cov=0;log=0;cad=0#orb