Welcome to the website for the (66391) 1999 KW4 Observing Campaign. Our intention is to provide a central clearinghouse for basic information about the near Earth asteroid (66391) 1999 KW4 and about the observations that will be obtained during its upcoming apparition.

This site will contain background information about (66391) 1999 KW4, a list of observations that are planned/scheduled/obtained, and status reports on the events leading up to the close approach. We will also produce an email list where updates can be broadcast to subscribers.

Summary of the 2019 Apparition

NEA (66391) 1999 KW4 is a near-Earth asteroid

  • Closest approach to the Earth occurs on 2019-May-25 23:04 UT
    • Speed with respect to Earth is 21.17 km/sec
  • Geocentric Distance (current best value - JPL#265)
    • 0.03464 AU
    • 13.5 Lunar distances
    • 5.1800×106 km


Current estimates suggest it should peak around mag 12.5 shortly after closest approach

Observing conditions (for observations at visible wavelengths)

Conditions are poor during the asteroid's approach to the Earth, so it may not be highly observable until shortly before the close approach. Conditions improve after close approach, so that is likely when much of the characterization will occur. (See the Observing Geometry link for more details.)

  • Before Close Approach
    • In southern skies (Dec ~-40°)
    • Within 40° of the Sun until late April
  • After Close Approach
    • Close to the equator
    • Large solar elongations and moderate phase angles

(66391) 1999 KW4 is a binary object

  • Radar observations from 2006 showed that it is a binary asteroid
    • The secondary has dimensions approximately 1/3 of the primary
    • Secondary orbits with a period ~17.4 hrs
    • Secondary's rotation is synchronous with its orbit



1999 KW4 was discovered May 20, 1999 by the Lincoln Near-Earth Asteroid Research (LINEAR) project located near Socorro, New Mexico.