2340 Hathor

On 25 October 1976, Hathor was independently discovered by Eleanor Helin during the Palomar Planet-Crossing Asteroid Survey (PCAS), and by William Lawrence Sebok, who photographed the same field almost simultaneously using Palomars 1.22-meter Schmidt telescope. On the same day, the official discoverer Charles Kowal found that Hathor had already been imaged three days earlier by Palomars 0.46-meter telescope (the same instrument used by PCAS). A forth independent discovery was made several days later by Nikolai Chernykh at CrAO on the Crimean peninsula.

The multiple discoveries were probably due to its very close approach distance to Earth.[7]^:20 After 2062 Aten, Hathor was the second discovery of an Aten asteroid. In 1978, the third Aten, 2100 Ra-Shalom was discovered. The Aten 1954 XA was already identified at Palomar in 1954, but its discovery date was later assigned to a 2003-observation at Lincoln Laboratory ETS, and is now known as (363505) 2003 UC₂₀.[7]^:21

Hathor has an Earth Minimum orbit intersection distance 0.0069 AU (1,030,000 km), which corresponds to 2.7 lunar distances (LD).[1]

When it was discovered in 1976, Hathor had one of its closest approaches to Earth at 0.007752 AU (1,160,000 km).[8] On 21 October 2014, when it passed Earth at 0.048 AU, or 18.8 LD, it was observed 22 times by the Goldstone Deep Space Network using radar astronomy over a period of 21 days from 10 to 31 October.[9] It will pass Earth again at 0.00658 AU (984,000 km) on 21 October 2069.[8]

In the 1990s, Dutch–American astronomer Tom Gehrels estimated Hathor's diameter to measure approximately 300 meters, assuming an albedo of 0.15.[1] During its close approach to Earth in October 2014, a team of astronomer published a revised estimate of 210±30 meters for its diameter.[4] The Collaborative Asteroid Lightcurve Link adopts this diameter and derives an albedo of 0.3331 with an absolute magnitude of 20.2.[6]

In November 2014, American astronomer Brian Warner obtained a rotational lightcurve of Hathor from photometric observations taken at the Palmer Divide Station in Colorado (also see § External links). Light-curve analysis gave a well-defined rotation period of 3.350 hours with a brightness variation of 0.11 magnitude (U=3).[5]