The Monster of the Night Skies

Comet 17P/Holmes is now twice the diameter of the Sun

Comets, of course, are no rarity. And it seems like every couple of years or so, one becomes big and bright enough that it can easily be seen from Earth. But the behavior of 17P/Holmes has mystified both hobby astronomers and professionals around the globe. Rather than shrinking as it gets further from the sun as most comets do, this one just keeps getting bigger and brighter. At the beginning of the week, the cloud of dust and gas surrounding the comet's core -- called the coma -- had already grown larger than the sun. Now, just a few days later, the coma's diameter is twice that of the sun -- the dust cloud measures some 2.7 million kilometers across whereas the sun is just 1.39 million kilometers across. And there is no sign that it is finished.

Some scientists believe the comet has collided with an asteroid and that might be why it suddenly grew so large.