Comet ISON and the planet Mars as seen from Sydney at dawn in November 2013. The position of the comet is shown for different dates, eg ISON 8 means is its position on 8 November 2013. The direction of the tail, which always points away from the Sun, is marked. The length of the tail on different dates is purely indicative. Chart Nick Lomb
Comet ISON may not become the comet of the century, but it is gradually brightening as it races towards the Sun. It is likely to be at its brightest and possibly a binocular or even a naked-eye object just before and just after its close encounter with the Sun on 29 November 2013. Sadly, the geometry of the comet’s path is unfavourable for observers in the Southern Hemisphere.
Currently, skilful amateur astronomers, who are willing to lose their early morning sleep, are able to image the comet and websites such as Spaceweather.com are building up large collections of their spectacular images. Next month the comet’s increased brightness should make it easier to observe, but, as can be seen from the chart above, it is also rapidly appearing progressively lower in the dawn sky.
One of the many reasons this is an interesting comet is that it is making its first approach to the inner solar system. That means that scientists can only guess at how bright it will become at the time it is closest to the Sun. Professional and amateur astronomers will be eagerly observing the comet from the ground, while a whole fleet of spacecraft have turned their cameras in its direction.
Another major unknown is whether the comet will survive its passage through the Sun’s atmosphere, the corona. There its central core or nucleus will be subject to both strong heating and bombardment by radiation, while the Sun’s strong gravitational pull will be trying to tear it apart through tidal forces. Still the best guess from scientists is that the nucleus or at least a large chunk of it will manage to sweep around the Sun and start making its way out of the solar system.
The Hubble Space Telescope’s view of Comet ISON on 10 April 2013. Courtesy NASA and ESA
As discussed in a previous post, once the comet has made perihelion passage (perihelion is its closest point to the Sun), from the Southern Hemisphere it will be below the horizon both in the morning and evening sky. Our best chance to observe the comet with binoculars or the unaided eye is early in the morning before dawn in late November.
A site with a good view of the eastern horizon without obscuration by trees or houses will need to be chosen as the comet will be low in the sky. Dark spots overlooking the ocean could provide suitable viewing spots for Sydneysiders while the western shore of Port Phillip Bay maybe suitable for those in Melbourne. It should be noted though that a waning gibbous Moon will be in the sky at the same time as the comet and may make viewing its faint tail difficult.
Another chance is to try to view in the daytime on the day it is closest to the Sun and the days before and after, just in case the comet becomes sufficiently bright to be seen. If you do that block the Sun with a post and please take EXTREME care. Do not even consider using binoculars or a telescope! Note that the risks are real as after each eclipse of the Sun there are ill-informed or careless people who present to eye doctors with permanent and unrepairable eye damage from looking at the Sun.
If all else fails keep an eye on the Spaceweather.com gallery as that is the safest and easiest way to enjoy the brief and rare visit of Comet ISON.