The orbit of Comet ISON (C/2013 S1) is quite precisely known from observations. It is inclined to the plane of the ecliptic at an angle of 62°. Almost the entire orbit is on northern side of the ecliptic. The only time it travels towards the southern side of the ecliptic is inside the orbit of Earth, on November 9th, 2013, till its perihelion on November 28th, 2013.
The perihelion of sungrazer ISON is the quick turning point. The speed of the comet will increase near the sun, and at the perihelion it will travel at 680,000 kmph, around the Sun.
As seen from the Earth, before perihelion, the comet travels in the zodiacal constellations of Cancer, Leo, Virgo and Libra. The turning point of perihelion occurs in Scorpio. Thereafter the comet moves northwards through the constellations Serpens, Hercules, Corona Borealis, Draco, Ursa Minor and Ursa Major. Here are some of the dates ISON will be close to bright celestial objects.
September 2nd, 2013, ISON will be 5° from Mars and 11° from crescent Moon. The trio will be seen near the naked eye star cluster – Beehive in Cancer.
September 23rd, 2013, Mars will be just 2° away from Comet ISON in Cancer Constellation.
In its orbit Comet ISON physically passes close by Mars, just 11 million kilometres from its North Pole. Observed from Earth, Comet ISON will remain close to Mars entire September and almost the entire month of October.
October 1st, 2013, ISON and Mars are joined by the crescent Moon forming a beautiful trio of different types of objects in the Solar System, a Comet, a Planet and the Moon.
During the months of September and October, it may possibly be difficult to locate the comet because it may not have brightened much. The presence of nearby bright star or bright Mars would be an important indicator or a sign post to locate the comet.
The best instrument to locate and view the comet is a pair of binoculars. A binocular mounted on a stand would be even better than a handheld one as the vibrations would be eliminated and the view would become steady. A binocular has a wide field of view as compared to a telescope, uses two eyes to peer at the sky, so it is a comfortable astronomical instrument for a layman as well as experienced sky observer. Binocular of any size would be an asset to watch the comet. Bigger sizes like 15x70 would be better, but would require a mount, on the other hand a smaller size like 7x50 could be used hand held.
October 15th, 2013, Comet ISON is close to Regulus, the brightest star of constellation Leo, just 2° away. Interestingly Mars lies in between the comet and Regulus. This would really be a close and interesting conjunction to watch.
Before perihelion, in the months of September and October comet ISON can be seen in the morning sky towards the east. The best time to observe it would be 1 hour before sunrise. At this time your observing instrument should be ready to scan the skies. The observing location should be preferably on terra firma i.e. solid ground rather than a vibrating terrace. The view towards the eastern horizon should be clear of buildings, trees or any other obstructions. Ideally you should be on a hill station where the horizon is clearer than plains.
October 30th, 2013, Comet ISON is joined by crescent Moon, 6° away. Mars, also 6° away, but in the direction of ISON’s tail. The daily motion of the comet is increasing day by day. It leaves the vicinity of Mars and starts moving towards the Sun at an increasing speed each day.
Comet ISON has become famous because:
a) It is intrinsically bright and probably this is the reason it was discovered so early when it was still outside the orbit of Jupiter.
b) Immediately after discovery, it was located on a few pre-discovery images too and its orbit was calculated. The orbit was found to be a sungrazing one.
c) This is the first visit of the comet to the inner Solar System.
November 18th, 2013, Comet ISON, lies less than a degree away from Spica, the brightest star of Virgo constellation. The comet is just 10 days away from perihelion. Locating it in the dawn sky could be difficult, unless it has brightened considerably.
November 28th, 2013, is the comet ISON’s date with Sun, the perihelion. Astronomers as well as amateurs all over the world would be anxiously waiting on 29th November morning to see the sungrazer’s ultimate fate. Will it evaporate in a blaze of glory, or will it become a string of pearls travelling in the same orbit or something else?
The first half of December 2013 would really be an interesting one with news coming in from all around the world about the comet.
Comet ISON is being followed by many different spacecrafts at different location in the Solar System, viz. Hubble Space Telescope, Deep Impact, Spitzer Space Telescope, Curiosity – Mars Science Laboratory, International Space Station, Messenger – Mercury Orbiter, Solar Dynamics Observatory (SDO), Solar Terrestrial Relations Observatory (STEREO), Solar and Heliospheric Observatory (SOHO), Swift, Balloon Rapid Response for ISON (BRRISON), Chandra X-Ray Observatory.
December 22nd, 2013, Comet ISON travels close to the Great Hercules Cluster (globular cluster of stars).
December 29th, 2013, Comet ISON will become circumpolar for northern India, visible all night and never setting below the horizon. Over the next few days the comet will progressively become circumpolar for southern latitudes.
January 8th, 2014, Comet ISON is seen close to the Dhruv Tara or the Pole Star.