** Currently, there are 42 known close approaches for the month of October, including comet 103P/Hartley 2, passing at 47 LD on October 20.  Hartley 2 is already visible through binoculars, passing through the the cluster-rich region of Cassiopeia and Perseus and is expected to reach unaided-eye brightness in the coming weeks.  This comet is also the target of NASA’s EPOXI mission, currently on approach for a close flyby in early November.  (Amateur astronomers are invited to contribute their observations of Hartley 2, as well as DAWN targets, Vesta and Ceres, to the Amateur Observers Program.)

** The closest known approaches this month are 2010 TS19, a 19m – 42m Apollo object passing at 3.7 LD on October 10, just 2 days after its discovery;  2010 TK, a 23m – 52m Apollo object passing at 4.4 LD on October 16; and 2003 UV11, a 370m – 820m PHA and Apollo object passing at 5 LD on October 30.  The largest NEO this month is 1998 TU3, a 3.2km – 7.2km Aten object passing at 69 LD on October 17.  This object is visible at 12th magnitude throughout this month, passing from Cetus to Sculptor.

**UPDATE: The closest approach this month is 2010 TD54, a 4.6m – 10m Apollo object passing at a mere 24,000 miles on October 12, just 2 days after its discovery!  (For some perspective, 24,000 miles is between Earth and the Moon or about the same distance at which our geostationary satellites orbit Earth.)

** The busiest dates this month include October 1, with 6 NEO passes; October 7, with 5 NEO passes; and October 3, with 4 NEO passes.

Follow the latest and upcoming close approaches with NASA’s NEO Earth Close Approach Tables.

Follow the latest traffic, discoveries, and monitoring activity with Bill Allen’s and Sandy Beach’s Asteroid/Comet Connection.

NEOs, or near-Earth-objects, are solar system objects which pass closely to our planet as they orbit around the Sun.  While most do not pose any serious threat, the history of past impacts and the likelihood of future impacts is enough to warrant aggressive discovery and research.  All across the world,  various entities and individuals are working hard to discover and track as many of these objects as possible, as soon as possible.  Many others are also researching active mitigation so that when we do discover the next big impactor, we can respond quickly and most effectively, before it strikes our planet.

There are three main groups of near-Earth-objects; Apollos, Amors, and Atens.  The ESA-created graphic, at right, illustrates the general orbital paths of each group.  You can click on the following words to learn more about each group, as well as other commonly-used NEO terms.

Aten group … Apollo group … Amor group … AU (Astronomical Unit) … LD (Lunar Distance) … Distance Converter (AU to LD to Kilometers to Miles) … PHA (Potentially Hazardous Asteroid) … H (Absolute Magnitude) … Ephemeris … JPL’s Ephemeris Generator

This map, created by the Amagh Observatory, illustrates the positions of all known near-Earth-asteroids.

This video, created by Scott Manley, illustrates 30 years of near-Earth-asteroid discoveries (more than 500,00 objects!)  The full description beneath the video is particularly interesting.