| 词条 | 2018 AH | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| 释义 |
| minorplanet = yes | name = 2018 AH | background = #FFC2E0 | image = 2018AH-orbit.png | caption = Orbital diagram of {{mp|2018 AH}} with the planets of the inner Solar System | mpc_name = 2018 AH | discovery_ref = [1] | discoverer = ATLAS–MLO | discovery_site = Mauna Loa Obs. | discovered = 4 January 2018 {{small|(first observed only)}} | mp_category = NEO{{·}}Apollo [1] | orbit_ref = | epoch = 23 March 2018 (JD 2458200.5) | uncertainty = 6 | observation_arc = 46 days | aphelion = 4.1222 AU | perihelion = 0.9034 AU | semimajor = 2.5128 AU | eccentricity = 0.6405 | period = 3.98 yr (1,455 days) | mean_anomaly = 26.398° | mean_motion = {{Deg2DMS|0.2474|sup=ms}} / day | inclination = 12.419° | asc_node = 101.30° | arg_peri = 322.92° | moid = {{convert|0.00078|AU|LD|abbr=on}} | mean_diameter = 84–190 m {{small|(assumed)}}[5] 95 m {{small|(est. at 0.20)}}[6] 190 m {{small|(est. at 0.05)}}[6] | rotation = | albedo = 0.05–0.3 {{small|(assumed)}} | spectral_type = | magnitude = ~13 {{small|(peak 2018-01-03)}} | abs_magnitude = 22.503 ± 0.39044 }} 2018 AH is a sub-kilometer asteroid, classified as near-Earth object of the Apollo group, approximately {{convert|100|m|ft|abbr=on|sigfig=1|sp=us}} in diameter. It was first observed on 4 January 2018, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) on Mauna Loa and quickly followed-up by many other surveys, with precovery observations found from Pan-STARRS and PTF from the day previous. It is the largest known asteroid to pass so close to Earth ({{convert|0.001985|AU|km mi|abbr=on|lk=on}}) since {{mpl|2002 JE|9}} in 1971,[5] and until {{mpl-|153814|2001 WN|5}} in 2028, although it was only discovered two days after its closest approach on 2 January 2018, at 04:25 UTC. The Tunguska asteroid was likely of a similar size, if not slightly smaller. Description{{mp|2018 AH}} has a fairly eccentric orbit, and its distance to the Sun therefore varies from as close as 90% of the Sun-Earth distance to over 4 times that distance. Due to this, among other factors, the asteroid remained undiscovered until its 2018 approach. It is almost always dimmer than magnitude 23, dimmer than most asteroid surveys can detect. During August-October 2013 it approached within ~0.3 AU of Earth and became as bright as magnitude 22.37, still rather dimmer than most survey-discovered asteroids.2018 ApproachOn its approach to Earth in 2018, {{mp|2018 AH}} had recently passed perihelion and was moving outwards on its orbit. It therefore approached from roughly the direction of the Sun, where it was undetectable to ground-based optical observations. It reached its closest point to Earth at only 45 degrees from the Sun. It was discovered at a more observable elongation of 129 degrees and at a magnitude of 15.7, and was quickly followed up over the next several days due to its brightness. {{mp|2018 AH}} remained brighter than magnitude 23 until late February 2018, and will now be mostly unobservable again until its next Earth approach in December 2021. {{mp|2018 AH}} passed unusually close for such a bright asteroid, at an absolute magnitude of 22.5 (making it approximately 84–190 meters across).[5] The largest asteroid to pass so close to Earth in 2017 was only an absolute magnitude of 24.3 (or about 31–91 meters). Since 1900, the only asteroids larger than {{mp|2018 AH}} known to pass closer than it to Earth are listed below:Asteroid diameters marked in italics have had their size directly measured.
See also
References1. ^1 2 {{cite web |title = 2018 AH |work = Minor Planet Center |url = https://www.minorplanetcenter.net/db_search/show_object?object_id=2018+AH |accessdate = 22 February 2018}} [1][2][3]2. ^1 2 {{cite web |title = Asteroid Size Estimator |publisher = CNEOS NASA/JPL |url = https://cneos.jpl.nasa.gov/tools/ast_size_est.html |accessdate = 22 February 2018}} 3. ^1 2 3 {{cite news |title = Large asteroid 2018 AH flew past Earth at 0.77 LD, 2 days before discovery |date = 8 January 2018 |work = The Watchers – Daily news service {{!}} Watchers.NEWS |agency = The Watchers |url = https://watchers.news/2018/01/08/asteroid-2018-ah/ |accessdate = 22 February 2018}} }} External links
5 : Apollo asteroids|Minor planet object articles (unnumbered)|Near-Earth objects in 2018|Astronomical objects discovered in 2018|Discoveries by CSS |
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