2022 UR₄

2022 UR₄ is a small near-Earth asteroid that made an extremely close approach within 0.044 lunar distances (17,000 km; 11,000 mi) from Earth's center on 20 October 2022 at 22:45 UTC.^[4] It was discovered about 14 hours before closest approach by the Asteroid Terrestrial-impact Last Alert System (ATLAS) survey telescope at Mauna Loa Observatory, Hawaii on 20 November 2022.^[2] During the close approach, the asteroid passed above the northern hemisphere of Earth and reached a peak brightness of magnitude 10,^[2] just 40 times fainter than the threshold of naked eye visibility.^[a]

Notes

^ The faintest magnitude that can be seen with the naked eye is about 6.^[6] Using the formula $Δ m = -2.5 log 10 (F 1 / F 2)$ ,^[6] where $Δ m = m 1 - m 2 = 6 - 10 = -4$ is the magnitude difference between the naked eye limit and 2022 UR₄'s peak brightness, the brightness ratio $F 1 / F 2$ of the naked eye limit to the peak brightness of 2022 UR₄ is approximately $39.81 \approx F 1 / F 2 = 10 (Δ m /-2.5)$ .

^ ^a ^b ^c "2022 UR4". Minor Planet Center. Retrieved 30 November 2022.
^ ^a ^b ^c "MPEC 2022-U145 : 2022 UR4". Minor Planet Electronic Circular. Minor Planet Center. 21 October 2022. Retrieved 30 November 2022.
^ "2022 UR4". NEO Exchange. Las Cumbres Observatory. 20 October 2022. Retrieved 30 November 2022.
^ ^a ^b ^c ^d "JPL Small-Body Database Browser: (2022 UR4)" (2022-10-20 last obs.). Jet Propulsion Laboratory. Retrieved 30 November 2022.
^ "Asteroid Size Estimator". Center for Near Earth Object Studies. NASA. Retrieved 30 November 2022.
^ ^a ^b Mihos, Chris (2005). "The Magnitude Scale". Case Western Reserve University. Retrieved 30 November 2022.