The Mysterious Star

No one has admitted to breaking the curtains in your room (maybe the dog did it), but for the last few nights, you've been lying awake at night bathed in the light of the street light, and the distant full moon. Maybe it's the lack of sleep, or maybe it's your imagination but you're convinced that one of the stars in the sky is growing bigger, and isn't moving across the night sky the way stars normally do. Needing to sleep, but wanting to have an answer to this mystery, you take a Sharpie and draw a circle around the star on your window pane... you saw your dad do something similar around an insect bite once to see if the red area was getting bigger or smaller... then you slowly fall asleep. You wake up a few hours later to the sound of a noisy motorbike going past on the street outside. You look at the mark you made on the window and the star, and notice that the star has grown bigger and is no longer symetrical, it's grown a slight tail and is now 3 times the size of the small circle you drew round it on the window... you knew it wasn't normal.
You know your dad will be annoyed if you wake him up for something not important, to wake him up, click here.
To go back to sleep and leave it till the morning click here.