What's up in the sky: Comet Lulin and Venus

The currently visible planets from Earth are always changing. In fact, the term "planet" comes from the Greek term, "wandering star", since they don't move like the rest of the sky.

That being said, I thought it would be informative to have a "What's up in the sky" section every couple of months to let people know what's visible if they just step outside and look up in the evening. Even from the middle of the most light-polluted cities, bright planets are still visible. I've already received a few questions pertinent to this.

Fitz asks:

I'm in Chicago, and I keep seeing what looks like a really bright star in the west. Is that Venus? What's the best way for a non-astronomer to find out these sorts of things (other than asking you!).

That's definitely Venus you're seeing. Other than the occasional airplane or bright satellite pass, Venus is the third brightest object in our sky after the Sun and the Moon. In fact, it's the object most frequently reported as a UFO.

Venus will be visible in the early evening sky in the West for the next month or so. As a planet on an orbit interior to Earth's orbit, it's currently "rounding the track" to pass in between us and the Sun, a phenomenon known as inferior conjunction. Because of this geometry, it's currently exhibiting a nice crescent phase and getting larger each night as it approaches us. At this point, with a good pair of binoculars and some keen vision, you should be able to make out that it's not merely a point of light, but a tiny crescent.

To answer the last part of your question, Sky & Telescope's This Week's Sky at a Glance provides a good overview of what's visible at any given time. Additionally, picking up some Planetarium software is also a good idea since it can be customized to your location and any date you want...there are some really good options out there. If you're a fan of open source software, I'd highly recommend Stellarium which can be downloaded from their subversion repository (side note: props to my subversion peeps).

Ben asks:

Comet Lulin is coming closest to earth tonight. Do I have a snowball's chance ... in space ... of seeing it?

Similarly, Tami asks:

I overheard a conversation yesterday that sounded like there was a comet in view the last few days, however it has been hazy here so there wasn't much view. Was there a comet visible recently? Which one? When? Where? Do you have any pics? How close is it to the earth? Is Armageddon inevitable?

Every couple of years we get a comet which is able to break the visible brightness barrier and can be seen with just the naked-eye. Comet Lulin is an example of this. Current estimates of its magnitude (brightness) place it at just above the naked-eye limit for a dark-sky site.

This comet is a bit of an interesting one. Its closest approach to the Sun was over a month ago, at a distance a good 20% greater than the Earth-Sun distance, but the geometry works out so that its closest approach to Earth was just four days ago at a distance just 40% of the Earth-Sun distance. (No worries, though, this is not even close to hitting us.)

Its orbit carries it *very* far from the Sun - over 3 light-years, in fact. At this distance, the Sun is not the only gravitational force acting on its orbit, but the gravity of other stars may start to be significant, so it's a little unclear if this comet will actually return to our solar system. Even if it does return, it won't be for another 50 million years. Whoa.

Now, that all said, it's not terribly spectacular with just the naked-eye...don't expect something similar to Comet Hale-Bopp back in 1997. You'll need a very dark sky to see it unaided, and it won't look like much more than a smudge. On good nights I can see the Milky Way from my yard, but I was unable to spot this comet with just the naked eye. With a decent pair of binoculars, though, it should stand out.

However, you'll have to hurry if you want to see this one. It's now moving away from Earth on its way out of the solar system, and won't be visible for long. It's currently rising over the Eastern horizon around sunset in the constellation Leo, though a finder chart is almost certainly necessary. You can find one here.

As for images, I'd recommend Spaceweather's Comet Lulin gallery...over 16 pages of images submitted by amateur astronomers.