Hang on a moment.
Are you sure you mean a comet?
You can't see a comet moving across the sky during one night. It appears as a smudge against the night sky and appears to move with the stars during the night.
It moves night after night slowly getting brighter and fading.
Meteors or shooting stars appear to fly across the sky, these are small particles hitting the Earth's atmosphere and burning up. They can happen any time but also come in showers at certain times of the year.