Soiled snowballs
Earlier than you propose your composition and arrange your gear, you is perhaps questioning what options you ought to be looking out for.
Comets are small our bodies of ice, rock, dust, and frozen gases which astronomers assume originate from the distant reaches of our solar system. As these our bodies slowly draw nearer to the Solar, solar heating causes risky supplies inside to vaporize. This blows dust away from the comet’s nucleus, forming a big, tenuous ambiance round it known as a coma.
Strain from solar radiation and the solar wind then shapes this coma right into a tail of dusty materials pointing away from the Solar. This dust tail is usually seen to us on Earth as a result of it displays daylight. And sometimes, a second tail can type from the gases which might be launched by the comet. That is typically known as the gasoline tail or ion tail, which glows not as a consequence of solar illumination however ionization.
Materials from the dust tail escapes the comet’s gravitational grasp, spreading out behind the comet alongside its orbital path, typically taking up a curved form. In the meantime, the ion tail, which is extra strongly affected by the solar wind, at all times factors straight away from the Solar. An ion tail usually presents a notable bluish colour, in stark distinction to the hazy white hue of a dust tail.
If it’s a brilliant comet, there may even be a 3rd tail known as the anti-tail. This tail might be seen emanating from the nucleus and seemingly pointing towards the Solar. Nonetheless, that is an optical phantasm that may seem as Earth crosses the airplane of the comet’s orbit when the physique is near the Solar. When considered from edge-on, the skinny sheet of cometary dust lagging behind the comet seems to be like a sunward pointing spike.
Comets usually are available in two foremost flavors: short- and long-period. Quick-period comets circle the Solar in lower than roughly 200 years, whereas long-period ones can take hundreds to thousands and thousands of years to finish a single orbit.
There additionally exists a 3rd kind of comet, generally known as a sungrazer. This particular class is liable for most of the most spectacular comets seen all through historical past. Sungrazers are characterised by very small perihelion distances — that means they cross extraordinarily near the Solar — which may make them seem spectacularly brilliant for a short interval.
Many nice comets all through historical past had been sungrazers, together with C/1965 S1 (Ikeya-Seki), C/1975 V1 (West), and C/2006 P1 (McNaught). Extra just lately, in 2013, Comet C/2012 S1 (ISON) got here inside about 730,000 miles (1.2 million km) of the Solar. Earlier than its method, giddy observers dubbed it the “comet of the century.” Sadly, ISON disintegrated shortly after its perihelion cross and by no means lived as much as its dazzling expectations. However that’s the irritating factor about comets that you just must dwell with: You by no means fairly know what you’re going to see!
