How does the appearance of a comet change when it moves in orbit around the Sun?

Most often, a comet is a mixture of frozen gases, pieces of solids. Around the sun, comets move in an elliptical orbit, sometimes very elongated. That is, the comet is either approaching the Sun, or moving away from it. When approaching the Sun, due to its thermal energy, gases begin to evaporate and a comet forms a “tail”. With distance from the Sun, the tail disappears, because the gases freeze again.