67P/Churyumov-Gerasimenko

Coma forming. Increasing distance from core.

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This is the comet that entered to news when Rosetta landed its probe, Philae, on it, at 6 billion km from Earth. 

When a comet approaches the Sun, the ice that makes up a large part of the volume of the comet, starts to vaporize. This accumulates around the comet, forming an 'atmosphere', called the coma. This completely envelops the nucleus, or core, which is the leftover comet. The main characteristic of the comet, the tail, is the coma being stretched by the solar wind.

A comet usually has two tails. One is the gas tail, the vaporized water, which is affected by the solar wind and thus always faces directly away from the Sun. The second in the dust tail. This is made of the dust loosened by the water vaporization. The dust is too heavy to be affected by the solar wind and thus follows the comet's orbit. On 13th of August this one will be on closest approach to the Sun. Still wider than the Earth's orbit, so no real visible tail. 

Picture by Rosetta.