We have a visitor to the inner Solar system where we live – comet NEOWISE has become visible in the evening sky and it’s a great sight. It's the best naked eye comet for the northern hemisphere so far this century, and the time to see it is now and for a week, about an hour after sunset, toward the NW.
Comets are chunks of ice, dust, and stones that formed during the birth of our solar system 4.6 billion years ago, but never became part of a planet. Most lie in a big cloud far out in the solar system, beyond Pluto, and some have orbits that bring them close to the Sun. This comet body is about 3 miles across and as it came close to the Sun, the ices were heated and streamed away, along with the soot covering the surface. Sunlight scatters off the dust and ionizes the liberated gases, giving us this great spectacle.
Comet NEOWISE is speeding through the solar system, now on its way out after passing the Sun. It is really moving – 140,000 miles/hr, but space is big so it will take a few weeks to go past the Earth. Its closest approach to Earth will be a whopping 64 million miles (July 22), so we don’t have to worry about it crashing in.
Seeing a comet is always a bit tricky as one needs a dark sky, but the comet is never too far from the Sun. As the sky becomes darker, the comet gets closer to the horizon, so you need a good horizon up to the NW. The comet is found below and a bit to the right of the Big Dipper (and near the horizon). The best time to see it is 60-90 minutes after sunset, around the time known as Nautical Twilight. It is safe to view either by naked eye or with binoculars (better), but you don’t need a telescope. The head of the comet is small, but the tail is long - ten times the angular size of the Moon!
In case you’re wondering where this goofy name comes from, it was first spotted by a small NASA observatory, named the Near-Earth Object Wide-field Infrared Survey Explorer. That’s a mouthful, so we use its acronym, NEOWISE.
If you do have a telescope or binoculars, be sure to turn around and look at Jupiter before you go inside. It'll be at its closest for this year on the night of July 15th. Look for it rising in the SE about the same time the comet is setting.