C/2019 Y4 (ATLAS)

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C/2019 Y4
Comet C/2019 Y4 (ATLAS) on March 14, 2020
Discovered byAsteroid Terrestrial-impact Last Alert System (ATLAS)
Discovery date2019-12-28
Orbital characteristics A
Observation arc82 days
Number of
Aphelion662 AU
Perihelion0.25284 AU
Semi-major axis331 AU
Orbital period6026 a
Argument of
Longitude of
Earth MOID0.63 AU (94,000,000 km)
Jupiter MOID1.397 AU
Last perihelion3rd Millennium BC

Current observed magnitude=9.0
Current Estimated magnitude=11.40
Coma Diameter=40' or 20 arcminutes or 742,000 Km
Nucleus Diameter=28 Miles or 45 Km
Distance from Earth=1.060 AU
Distance from Sun=1.5 AU

Family/Group= Nearly isotropic
Next perihelion2020-05-31, 00:21:35 UT
Barycentric period~4800 years (inbound)[1]
~5200 years (outbound)

C/2019 Y4 (ATLAS), or Comet ATLAS, is a comet with a near-parabolic orbit, which was discovered by the ATLAS survey on December 28, 2019.[2] As of April 2, 2020, the comet may be disintegrating.[3][4]

C/2019 Y4 (ATLAS) was the brightest comet of 2020 when it had an apparent magnitude of about 7. It can be found in the constellation of Camelopardalis as a diffuse object with a telescope. Due to the fragmentation event, it is unknown if the comet will continue to brighten, but it might be visible to the naked eye sometime in April or May 2020. It will reach its nearest point to Earth on May 23 and come to perihelion (closest to the Sun) on May 31.

On April 6, 2020, astronomers reported, on The Astronomer's Telegram, the possible disintegration of Comet ATLAS. [3][4]


Comet ATLAS was discovered on CCD images taken on December 28, 2019, with a 0.5 m (20 in) reflecting telescope atop Mauna Loa in Hawaii.[5] The images were taken as part of the Asteroid Terrestrial-impact Last Alert System (ATLAS). At the time of its discovery, the comet shone at magnitude 19.6 in the constellation Ursa Major as viewed from Earth.[6][7] Larry Denneau was the first to identify the object's cometary appearance,[6] placing the object on the Minor Planet Center's Possible Comet Confirmation Page, alerting other astronomers. Further observations over subsequent days identified a coma; a comet tail became increasingly apparent as observations continued.[5]

Initial observation and brightness[edit]

Between the beginning of February and near the end of March, Comet ATLAS brightened from magnitude 17 to magnitude 8, representing a 4000-fold increase in brightness.[8] In March 2020, the comet's brightness increased four magnitudes.[7] C/2019 Y4's currently green or aqua colour arises from emissions of diatomic carbon with a 1.2° or 10' or 3.3 million km multicolour tail, more than twice as wide as Sun. The outer reaches of ATLAS' tail are still faint, but the gaseous filaments can be sweeping across the stars.[9] As a diffuse object, the comet will need to reach an apparent magnitude of around 3–4 to be obvious to the casual observer. As of early April, the comet appears to be fading.[10]


At the time of its discovery Comet ATLAS was nearly 3 astronomical units (AU) from the Sun.[7] The first orbital calculations for the comet were published on the Minor Planet Electronic Circular, and were based on observations taken between December 28, 2019, and January 9, 2020, which indicating a 4,400-year orbital period and a perihelion of 0.25 AU. Similarities were noted between the orbital elements of C/2019 Y4 and the Great Comet of 1844 (C/1844 Y1), suggesting that C/2019 Y4 is a fragment of the same parent body.[5][9]

The JPL Small-Body Database using an epoch of February 18, 2020, shows ATLAS with an orbital period of approximately 6,000 years, but this solution includes misleading perturbations while inside of the planetary region. A more useful barycentric solution before the comet entered the planetary region shows an inbound orbital period of about 4,800 years.[1] The comet will reach its nearest point to the Sun on May 31, 2020.[11] After leaving the planetary region, the comet will have an outbound orbital period of about 5,200 years.


During January to March 2020, the comet was located in the constellation of Ursa Major. Throughout the month of April, the comet will be in the constellation of Camelopardalis. On May 12 it will move into Perseus. It will be at its closest point to Earth on May 23 during a New Moon when the comet will be 17 degrees from the Sun. At its periheleon on May 31, it will be in the Taurus constellation 12 degrees from the Sun.[12]

Comet's trajectory in the sky with 7-day markers
Imaged on March 28, 2020


  1. ^ a b JPL Horizons barycentric solution for epoch 1950 (before entering planetary region)
    Goto JPL Horizons
    Ephemeris Type: Orbital Elements
    Center: @0 (Solar System Barycenter)
    Time Span: 1950-01-01 to 2050-01-01 and Step Size: 100 years
    1950-Jan-01 is "PR= 1.76E+06 / 365.25 days" = 4818 years
  2. ^ Dickinson, David (February 25, 2020). "Comet Y4 Atlas in Outburst: First Good Comet for 2020?". Universe Today. Retrieved February 29, 2020.
  3. ^ a b Ye, Quanzhi; Zhang, Qicheng (April 6, 2020). "ATel #13620: Possible Disintegration of Comet C/2019 Y4 (ATLAS)". The Astronomer's Telegram. Retrieved April 6, 2020.
  4. ^ a b Steele, I.A.; Smith, R.J.; Marchantn, J. (April 6, 2020). "ATel #13622: C/2019 Y4 ATLAS - confirmation of nuclear change". The Astronomer's Telegram. Retrieved April 7, 2020.
  5. ^ a b c Green, Daniel W. E. (January 11, 2020). "COMET C/2019 Y4 (ATLAS)". Liste de distribution des circulaires de l'Union Astronomique Internationale et du Minor Planet Center (Mailing list). Retrieved March 25, 2020.
  6. ^ a b "MPEC 2020-A112 : COMET C/2019 Y4 (ATLAS)". minorplanetcenter.net. Minor Planet Electronic Circular. Cambridge, Massachusetts: Minor Planet Center. January 10, 2020. Retrieved March 24, 2020.
  7. ^ a b c Ling, Alister (March 25, 2020). "Comet ATLAS may soon be visible to the naked eye". Astronomy. Kalmbach Media. Retrieved March 27, 2020.
  8. ^ Yirka, Bob (March 23, 2020). "Comet ATLAS may put on quite a show". Phys.org. Science X Network. Retrieved March 27, 2020.
  9. ^ a b King, Bob (March 25, 2020). "Comet ATLAS: Will it Become a Naked-Eye Object?". Sky & Telescope. AAS Sky Publishing, LLC. Retrieved March 27, 2020.
  10. ^ Comet C/2019 Y4 (ATLAS): after an unexpected, a bit irregular, rising in brightness the comet is now fading
  11. ^ "C/2019 Y4 (ATLAS)". JPL Small-Body Database Browser. Jet Propulsion Laboratory. Retrieved March 24, 2020.
  12. ^ Rao, Joe (March 16, 2020). "Newfound Comet ATLAS is getting really bright, really fast". Space.com. Retrieved March 21, 2020.

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