Comets – Wanderers of the Solar System
Comets – (from the Greek. Kometes – “star with a tail”, “comet”, “shaggy”; literally – “long-haired”), small bodies of the solar system, rotating around the sun in elongated orbits and looking like foggy objects usually with a light clot – core in the center and tail. When approaching the Sun, the tail of the comet increases, formed by gases evaporating under the solar heat.
Comet Hale-Bopp 1996
Presumably, long-period comets fly to us from the Oort Cloud, located on the outer borders of the solar system, in which millions of cometary nuclei circulate.
Comets are shapeless lumps measuring just a few kilometers, consisting of ice mixed with dust particles. Comets move in very elongated orbits, being mostly far from the Sun, where they remain invisible, and when they approach the Sun, ice begins to melt under the influence of solar heat, evaporating and disappearing into interplanetary space along with other gases. As a result, many comets, passing near the Sun, take a very unusual form.
Most comets that periodically appear in the vicinity of the Sun are rather faint objects. The exception is Halley’s comet, which almost every time it returns to the Sun appears before us as a very bright and impressive object.
In fact, the brightest and most spectacular comets appear in the sky unexpectedly, many of them, perhaps for the first time approaching the Sun. Those few weeks during which a bright comet quickly goes around the Sun, then disappearing forever or, perhaps, for many millennia in space distances, are the hottest time for comet astronomers. In rare cases, especially if the comet comes too close to the Sun, it can collapse into parts that are later observed as separate bodies (decay of the comet’s nucleus).
Comet orbit and tail tail
Periodic comet orbit and tail formation
What are they made of?
Comets look different. Everyone has a foggy gas shell – a coma, which together with the nucleus forms the head of the comet. Even if the comet is in close proximity to the Sun, its head seems to be nothing more than a foggy speck. The most remarkable detail of most comets is the tail. It is most bright when the comet is in the vicinity of the perihelion of its orbit. Here, the heat flux from the Sun is especially significant, under the influence of which gases and dust escape from the comet into outer space. Some comets have two tails: one is curved, consisting of dust particles; the other is direct, gas, elongated in the direction exactly opposite to that on the Sun. A number of comets have been observed for several (dust) tails.
The length of the comet tails can reach tens and hundreds of millions of kilometers; comets were observed, whose tails stretched almost half the sky. It is assumed that the dust lost by comets falling into interplanetary space gives rise to meteor bodies, which later, encountering at terrestrial speed at the terrestrial atmosphere, are detected in the form of meteors. Dust from comet tails also replenish interplanetary dust clouds, which, scattering the sun’s rays, give rise to a phenomenon called the zodiacal light.
The nucleus of the comet is sometimes noticeable inside the coma in the form of a bright star-shaped object, in which it is not possible to distinguish any details even in the largest telescopes. Sometimes the nucleus can be confused with various structural formations in a coma – such as a shell or emissions of matter from the comet’s nucleus. The nuclei of comets were studied in detail by spacecraft, which came close to comets.
In 2005, NASA’s Deep Impact spacecraft rammed Comet Tempel 1 and transmitted images of its surface.
Comet orbit and tail tail
For observing comets, you can use any tools. Experience shows that the giant tails of comets can be detected when observed with the naked eye, through binoculars and telescopes with a wide field of view. But to see the complex structure of a comet near its nucleus, telescopes with a large aperture and large magnification are needed.
Sketches of comets can be done with observations in any instruments, their methodology is the same as with sketches of the planets.
Photos help not only determine the exact position of the comet’s head, but also obtain an image of its tail, as well as see subtle details that, due to their low brightness, cannot be seen in other ways.
With a tool equipped with a clockwork, you can try to get a photo of the comet. With a telephoto refractor, exposure time of 5-10 minutes is sometimes enough to get a clear image of the comet’s nucleus.
To track the comet, taking into account its own movement among the stars, the telescope (or camera) must be equipped with a guiding system. In this case, the images of stars in the pictures will be in the form of dashes.