Asteroid. Hubble Space Telescope image of an asteroid (blue, at upper centre) seen in the constellation Centaurus. This time-exposure image shows the asteroid path against a background of stars (white). The asteroid has a visual magnitude (brightness) of 18.7 and its trail is 19 arc seconds long. Around 2 kilometres across, the asteroid was 145 million kilometres from Earth when the image was taken. The orange and blue specks were created by energetic subatomic particles known as cosmic rays. Asteroids are small lumps of rock circling the sun which usually, as here, orbit between Mars and Jupiter.