Warming up for Valentine’s Day, Eros flies by Earth

A video compiled of still images taken by the NEAR spacecraft in 2000-2001. The asteroid rotates end over end once every 5 hours and 16 minutes. Credit: NASA

With Valentine’s Day approaching, get into the spirit early by consulting with Eros, Greek god of love, now touring the constellation Sextans in the evening sky.

Asteroid 433 Eros was the first near-Earth asteroid (NEO) ever discovered back in 1898. Some NEOs zip just thousands of miles from our planet, but Eros will only come as close as 16.6 million miles or about 70 times the distance of the moon on January 31. That still makes this approach the closest since 1975 and the best until January 2056.

While it can shine as brightly as magnitude 7.0, this time around Eros will range between magnitude 8.6-9.0. That’s a little fainter than Neptune, so you’ll need good binoculars or a small telescope to see it. My 8×40 binoculars can reach down to 9th magnitude under dark skies. The key to seeing faint objects is keeping the instrument steady. You can mount your binoculars on a tripod, hold them atop a fence post or car roof or simply brace yourself against a wall.

A reconstruction of Eros using images from NEAR-Shoemaker. Stony meteorites called L4 chondrites might be derived from the rocks on the asteroid. Click image to see many more photos and animations. Credit: NASA

Eros is a rocky asteroid measuring 21 x 7 x 7 miles and shaped a bit like a slipper. The Near-Earth Asteroid Rendezvous-Shoemaker (NEAR) probe visited the asteroid and settled into orbit around it on – get this – Valentine’s Day 2000. The following January it passed within 1.5 miles of Eros’ surface snapping many closeup pictures of the cratered landscape. Then in mid-February NASA mission controllers gently brought it to the surface where it rests to this day. The last signals from NEAR were received on February 28, 2001 before it was shut down.

There is no air on Eros and temperatures range from a daytime high of 212 degrees (water’s boiling point) to a nighttime low of 238 below. Because of its small size and mass, a 200 lb person would weigh just two ounces there. Pick up and throw one of its many rocks at just 22 mph and it would escape into space never to return.

Wide field map showing Leo, Mars and your key star Rho Leonis around 10:30 p.m. local time facing east. Maps created with Stellarium

To spot the cruising space island, you’ll need to be out around 10:30 p.m. local time when the constellation Leo along with the planet Mars are up in the eastern sky. Locate the bright star Regulus at the bottom of the sickle-shaped head of Leo. About four degrees to the lower left of Regulus you’ll see a fainter 4th magnitude star named Rho Leonis. Once you find Rho, you can use the detailed map below to star hop to Eros.

The faintest stars shown on the map are about 9th magnitude or a little fainter than the asteroid, which shines at about magnitude 8.7 from now through mid-February.

Eros is moving fast enough that you can easily its motion to the south night after night. With a telescope magnifying around 100x, its movement is detectable in just an hour or so. In both instruments, Eros will look exactly like a star, since it’s too small and too far away to show a shape. I wish you luck in love in the coming weeks!

This detailed map shows Eros in relation to Rho Leonis as it tracks south in the next couple weeks. The positions shown are around 10:30 p.m. CST and won't vary much over a few time zones on a particular night. North is to the upper left, the way you'd see it facing Leo around 10-11 p.m. your local time.

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