Monday night: Where is the asteroid now?

Asteroid 2004 BL86 was to come closest to the Earth at 10:20 a.m. today. About one-third mile across (1,600-1,800 feet), it will come within 745,000 miles of Earth. It's the last big asteroid flyby until 2027.

• 745,000 miles equals about three times the distance between the Earth and Moon. Sounds far, but if you stack all the planets in our Solar System in a line between the Earth and Moon, they'd barely fit. Saturn would lose its rings.

• To find the asteroid tonight, look for the constellation Cancer. BL86 will be in Cancer all night long - it rises in the ENE; by 8 p.m. it was to be due east; between midnight and 1 a.m. it's to be directly overhead.

• Can I see it? Not very well. In a desert at night with a clear, black sky overhead you could see it with binoculars. Around Chicago, you'll need a telescope, and even then it'll look like a faint star - a pinprick of light.

• Then what's that bright object in Cancer? Jupiter. Jupiter is gorgeous right now. Look at that.

• Lincoln Near Earth Asteroid Research (LINEAR) is constantly looking for near-Earth objects. The term "near Earth" is slightly misleading - objects could be 20 times the distance of the moon away. SpaceWeather.com keeps track of potentially hazardous asteroids, about 1,500 at any one time. Smaller asteroids are harder to predict - the Chelyabinsk meteor that hit Russia on Feb. 15, 2013, was about 65 feet in diameter and went undetected until it entered the Earth's atmosphere.

• About 1,000 pounds of space stuff hits Earth every day, most of it falling in the oceans. The Adler has a fragment of a meteor that exploded in 2003 over Route 30 south of Chicago.

• What are chances of a big asteroid hitting Earth? About every 100 million years we get hit by a really large rock. Sleep well.

Source: Larry Ciupik, Adler Planetarium senior astronomer; NASA