Asteroid Eros at its closest since 1975 on January 31

  

Asteroid Eros will pass closer to Earth on January 31/February 1 than it has since 1975

 Asteroid 433 Eros will be making closest approach to Earth since 1975 on January 31, 2012. Eros will be passing closer on Tuesday than it has in some decades, but that’s not very close. It will be about 16.6 million miles (26.7 million km) away – some 50 times the moon’s average distance. That’s over 80 times farther than the closest point of a much smaller body that passed safely within the moon’s orbit on November 8, 2011. That object was called 2005 YU55. So there is absolutely no danger at all.

Even though it’ll be closer than since 1975 – and even though it won’t come this close again until 2056 – Eros won’t be close enough to view with the eye alone. But amateur astronomers with backyard telescopes will see it.

Eros helped astronomers pin down the exact distance to the sun in the 20th century. A similar close pass of Eros in 1931 allowed professional astronomers to refine the true scale of the solar system, starting with the Earth-Sun distance (the astronomical unit). This was the last great improvement in the scale of the solar system until interplanetary radar began making direct distance measurements in the 1960s.

Eros is a near-Earth asteroid (NEA), discovered in 1898 by astronomers Carl Gustav Witt in Berlin and Auguste Charlois in Nice. It’s about 21 miles (34 km) wide.

Eros also made history in 2000, when NASA’s NEAR Shoemaker probe approached it, went into orbit around it and even made a soft landing on its surface. This was the first such orbit of an asteroid. NEAR took over 160,000 images of Eros’ surface and helped researchers conclude that this asteroid is a solid object rather than a “flying rubble pile” as some had previously thought.