Communication Skills

The Communcation Skills course is very important for future career. We learn how to write a good piece of work (e.g. scientific report, short essay), how to present material oraly and how to communicate with others freely and concisely.

Comet Halley

Comets are one of the most exciting objects for astronomical observations. The word “comet” has its origin in Greek and means “long-haired”. Their dynamics, behaviour and attraction encourage professional and amateur astronomers to hunt for these celestial objects. It is also a motivation for scientists that a new comet found in the Universe receives the name of its discoverer.            

Halley’s Comet is the most famous object, which can be easily seen with a naked eye. It orbits the Sun every 76 years, coming near the Earth within a human lifetime. The first observation of the Comet Halley, which has been recorded, dates back to 240 BC. Many astronomers at different times from all over the world observed this phenomenon without realising that they actually see the same object periodically approaching the Earth. The comet was called after Edmond Halley, who had calculated its orbit and predicted the next appearance very precisely.

The orbit of the Halley’s Comet is elliptical with a high eccentricity, which is equal to 0.97, compared to 0.0167 for the Earth, or in other words, the major axis of the ellipse is about four times greater than the minor axis. Having our Sun in the focus of its path, the comet approaches the perihelion distance of 0.59 a.u. (1 a.u. is equal to 149.60×106 km) and flies away in space to the point of aphelion at the distance of 35 a.u. To visualise this distance, imagine that of Pluto’s orbit.            

The nucleus of the comet is very small; its dimensions are roughly 15x8x8 km. It is made of solids of extremely low densities of about 0.5 grams per cubic centimetre on average, due to its porous structure. The nucleus is mainly composed of ice, dust and frozen methane. Coming closer to the Sun, the comet heats up to a temperature of 340 K and the gases inside the core start to evaporate, creating a wonderful coma and a long tail, made of dust and ice. This makes the comet bright and observable. The tail is always directed away from the Sun, being affected by the solar wind – the photon pressure.           

The period of the rotation of the Comet Halley changes from one oscillation to another. This is caused mainly by the gravitational effects of the Solar System’s bodies and the evaporation processes occurring inside the nucleus of the comet. Since the Jupiter has the biggest mass after the Sun, it has the greatest effect on the comet’s motion. That is why such comets, orbiting the Sun in less than 200 years are sometimes called “Jupiter’s comets”. Also, heating up while coming close to the Sun, the comet body ejects bursts of gases in random directions, therefore slightly changing its trajectory due to reactive motion. This effect becomes noticeable because the distances, which the comet covers per one revolution, are extremely vast.            

The Halley’s Comet is believed to “predict” big changes, catastrophes and wars on the Earth. For example, the appearance of the comet in 1066 was just before the Battle of Hastings, where the English army, led by Harold II of England was defeated by William the Conqueror and a new historical epoch has started.            

The last perihelion of the Halley’s Comet was in 1986. This was the time of active space exploration and several apparatus were sent to it for a research. These missions were successful: good images of the comet’s nucleus were obtained and the composition of its body, tail and coma was investigated. The next coming of the comet is calculated to be in summer of 2061 when it will pass near the Earth at a distance of 70 million km.

Although it is quite a long time to go, the space researches are preparing for a more advanced exploration of the Halley’s Comet, because of the expected advanced level of technologies achieved by the time of the next perihelion.


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Dmitry Tugarinov © 2009