General elections are just a few months away; Iran signs nuclear deal to end sanctions; Cyclone Helen passes through with minimal damage; Typhoon Haiyan wrecks havoc in the Philippines… While we are more bothered about such earthly events, there is something spectacular happening in the skies. A heavenly object’s visit to the sun could become the most spectacular event of the year. Comet Ison is about to undertake its closest approach to the sun during this weekend.
Many comets have the orbited the sun in the past few decades – Halley’s Comet in 1986, Comet Hale Bopp in 1997. So what’s the big deal this time I wondered! I do remember that during Hale Bopp’s visit in 1997, I had been to the planetarium in Bangalore where the Association of Bangalore Amateur Astronomers (ABAA) had organised a comet viewing session. In those days when the internet was virtually non-existent, such activities were the only way to understand the bigger events happening in the universe!
An asteroid passing by is a common occurrence, but a comet’s visit is a rare event. Scientists have counted 4,894 known comets till July 2013, but this number is steadily increasing every year. It is surprising to know that nearly 80% of the visible tail of a comet is all water vapour and dust. Due to their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes.
Is Comet Ison different from other comets?
ABAA’s President Jayanth Basavarajaiah clarified in this manner – “To begin with, Comet Ison is not a typical elliptical periodic comet that orbits the sun regularly. It is a hyperbolic sungrazing comet that means it would go too close to the sun and the solar tidal forces could tear it apart during its perihelion (passage around the sun). The sheer size of the comet of around 4-5 kilometres in diameter has allowed it to survive a lot longer than most other comets that travel so close to the Sun’s surface. Additionally, since the comet may be making its very first pass by the Sun in its lifetime, it is believed that the material ejected in the tail of the comet will be primordial material dating back to the formation of our Solar System!”
Further, Jayanth stated that due to the debris and material ejected from the comet as it melts near the Sun, scientists are able to get measurable information about the Sun’s magnetic fields, its solar wind, and other interesting information that otherwise would be rarely possible. Since Earth will pass near the comet’s orbit on 14–15 January 2014, tiny dust particles blown by the Sun’s radiation may cause a meteor shower.
Formally designated as “C/2012 S1”, the comet was named “ISON” after the organization that discovered it in September 2012, the Russia-based “International Scientific Optical Network”. Vitali Nevski and Artyom Novichonok discovered it using the 0.4-meter (16 in) reflector of the ISON located near Kislovodsk, Russia. The initial report given to the Central Bureau for Astronomical Telegrams identified the object as an asteroid, but follow-up observations by independent teams reported its cometary features. Therefore, as per the International Astronomical Union’s comet-naming guidelines, the comet was named after the team that discovered it, rather than the individual discoverers.
Best time to watch
Typically, whenever astronomers report about a celestial event like this, there is media hype about an event of a lifetime. So I asked Jayanth if there is a possibility that Comet Ison will become a great comet as bright as moon. Jayanth stated that from 14 November 2013, Comet Ison became visible to the naked eye for experienced observers located at dark sites. However, due to the full moon and glow of twilight, the comet has not become bright enough to be seen without an optical aid. After it reaches perihelion on 28 November, Comet Ison may become extremely bright if it remains intact.
Predicting the brightness of a comet is difficult, especially one that will pass so close to the Sun and be affected by the forward scattering of light. Originally, media sources predicted it might become brighter than the full moon, but based on recent observations, it is only expected to reach around −3 to −5 apparent magnitude, which is about the same brightness as Venus. If Comet Ison survives its sungrazing passage, then it promises to be a dazzling heavenly display with a long bright tail.
Comet Ison is now heading for its close encounter with the sun and its visibility in the morning sky is low, since the twilight haze obscures it. On its return path (if at all the comet survives) the comet will be again visible to the naked eye in the eastern sky from December 3rd until early January 2014 on both the hemispheres of Earth. Hopefully, Cyclones Helen and Lehar will dissipate by then and the sky will be clear for this spectacle!
In Bangalore, Association of Bangalore Amateur Astronomers will be organising a comet gazing session, while Khagol Vishwa – the Organization of Amateur Astronomers is organising one in Pune. Don’t miss this lifetime event!