The first near-Earth asteroid to be discovered was 433 Eros in 1898. It made history then, in part by enabling the best determination of the astronomical unit and hence the scale of the solar system.It made history again in 2000 and 2001, when NASA’s NEAR-Shoemaker probe took up orbit around it and then descended to its dusty surface. Eros is the second-largest near-Earth asteroid, after 1036 Ganymed, measuring 21 × 7 × 7 miles (34 × 11 × 11 km).
And now you have an opportunity to view this celebrated object telescopically, as it makes a swing past the Earth this month and next. This is Eros’s closest approach since the much-observed one in January 1975, when it reached magnitude 7.0, and it'll be its last close pass until January 2056.Click here to download finder charts showing its path southward across Leo, Sextans, and Hydra as it brightens from magnitude 9.2 on January 12th to 8.8 on the 18th and then 8.6 from January 25th to February 13th. It fades back to 9.0 by February 25th. Eros passes its closest to Earth on January 31st, but even then it’s not very close as near-Earth asteroids go: 0.18 a.u., or 70 times the Moon’s distance.
On the charts, the ticks mark its position at 0:00 Universal Time on the indicated dates. This falls on the evening of the previous date in the time zones of the Americas. Interpolate to put a pencil dot on the track for when you plan to look. Stars are plotted to magnitude 9.0. In late January and early February Eros will be creeping along by almost 3? per hour, so you can see its motion during an evening.
• Amateurs and students can use position measurements of Eros to (re)compute the length of the astronomical unit. Read more and join the project .
• From Italy, Gianluca Masi at Bellatrix Observatory writes, "at the Virtual Telescope we will offer a live online observing session" of Eros's passage, in exchange for a 1-euro donation, starting at 0:00 February 2nd UT.