Solar System Phenomena — Selected Comets in 2020

Comet C/2020 F8 (SWAN)

Comet C/2020 F8 SWAN in 2020.

C/2020 F8 (SWAN) was first detected on 11 April 2020 by Australian amateur astronomer Michael Mattiazzo who was analysing the 25 March data from the Solar and Heliospheric Observatory's Solar Wind ANisotropies (SWAN) camera.

Orbital Elements Date 8 May 2020
eccentricity 1.001
inclination 110.8°
semi-major axis −450.1 au (hyperbolic)
period none (hyperbolic)
perihelion distance 0.4304 au
perihelion date 27 May 2020
distance from Earth at closest approach 0.5557 au
date of closest approach to Earth 12 May 2020

The Minor Planet Center (MPC) estimates that the comet may reach sixth magnitude around the time of closest approach to Earth but the Jet Propulsion Laboratory (JPL) is far more pessimistic with a prediction of just ninth magnitude. However, observers report that the object is around fifth magnitude in early May and it is possible that the comet will reach at least third magnitude later in the month. The comet is found in the constellation of Cetus at the beginning of May, passing the fourth-magnitude star ι Ceti on 4–5 May. Moving northward, the comet continues through Pisces, gliding past the fourth-magnitude star ε Piscium on 10 May. The comet should be at its brightest over the next few days as it passes fourth-magnitude star η Piscium (Alpherg), the spiral galaxy M74, and the brighter stars of Aries. The comet passes just south of the fourth-magnitude γ star in the constellation of Triangulum on 17 May before moving into Perseus. It approaches the fourth-magnitude star 16 Persei on 19 May, grazes the fifth-magnitude star π Persei the next day and is found near the famous variable star Algol on 20–21 May. It is in the vicinity of the first-magnitude star Capella in Auriga at the beginning of June before turning south and heading toward Gemini.

At the beginning of May, the comet is visible to southern hemisphere observers in the morning. As it moves north, it comes into view for early risers in the northern hemisphere, with it appearing both in the morning and evening skies after mid-May. However, astronomers in the northern hemisphere must contend with ever-lengthening spring twilight so optical aids will probably be necessary to see the comet in less-than-dark skies.

Comet C/2019 Y4 (ATLAS)

Comet C/2019 Y4 ATLAS in 2020.

C/2019 Y4 (ATLAS) was discovered on 28 December 2019 by the Asteroid Terrestrial-impact Last Alert System (ATLAS), an automated survey in Hawaii. Its orbit is a close match for C/1844 Y1, the Great Comet of 1844 and it's thought that both comets are fragments of an earlier larger comet which broke up 5000 years ago. Perhaps there are more pieces en route!

Orbital Elements Date 30 April 2020
eccentricity 0.9992
inclination 45.38°
semi-major axis 330.6 au
period 6011 years
perihelion distance 0.2528 au
perihelion date 31 May 2020
distance from Earth at closest approach 0.7810 au
date of closest approach to Earth 24 May 2020

Prior to April, both the MPC and JPL had calculated that the comet would become bright enough to be seen by the naked eye. The MPC was forecasting zero magnitude around the time of perihelion with JPL predicting a more optimistic magnitude −5. This is brighter than the planet Venus. Its sibling, C/1844 Y1, reached second magnitude and developed a tail 10° long during its passage through the inner solar system, so there were high hopes for this object.

Unfortunately, on 6 April, astronomers reported that the nucleus of the comet was elongated which was consistent with the comet beginning to disintegate. Both the MPC and JPL revised their estimated magnitudes at perihelion, ranging from a barely visible sixth magnitude to a still-bright zero magnitude. However, further observations have confirmed that the comet has broken up and the individual pieces are unlikely to reach anything close to naked-eye brightnesses.

It is an evening sky object at the beginning of April 2020, visible in northern skies as it descends southward through the constellation of Camelopardalis. It enters Perseus in early May, passing close by the fourth-magnitude star μ Persei on 16–17 May, the third-magnitude star ε Persei on 22 May and the fourth-magnitude star ο Persei on 26 May. It then moves into Taurus, skimming past the Pleiades open star cluster just before perihelion. It appears after sunrise from June onwards, passing the third-magnitude star λ Tauri on 5 June and the fourth-magnitude star μ Tauri on 8–9 June before leaving Taurus for Orion (the comet encounters the fourth-magnitude star π4 Orionis on 16–17 June) and fading from view for southern hemisphere observers.

Comet C/2020 F3 (NEOWISE)

Comet C/2020 F3 NEOWISE in 2020.

C/2020 F3 (NEOWISE) was first seen on 27 March 2020 by the NEOWISE project, the asteroid detection wing of the Wide-field Infrared Survery Explorer (WISE) space telescope.

Orbital Elements Date 4 June 2020
eccentricity 0.9992
inclination 128.9°
semi-major axis 359.4 au
period 6813 years
perihelion distance 0.2947 au
perihelion date 3 July 2020
distance from Earth at closest approach 0.6919 au
date of closest approach to Earth 23 July 2020

The MPC is predicting that the comet will never brighten past ninth magnitude but JPL is estimating a peak brightness of second magnitude in late June and early July. Initially visible only in the evening sky from the southern hemisphere, it moves north as it passes through perihelion and becomes a morning sky object.

Early June finds the comet moving north through the constellation Orion, passing close to first-magnitude star Betelgeuse on 14 June, fourth-magnitude star μ Orionis on 16 June and fourth-magnitude star χ¹ Orionis on 26–27 June. It continues north to Gemini, moving past fourth-magnitude star 1 Geminorum on 29 June, and arcs through Auriga (passing close by third-magnitude star θ Aurigae—Mahasim—on 7 July), Lynx and Ursa Major in July. It slips past the third-magnitude star ι Ursae Majoris (Talitha) and fourth-magnitude κ Ursae Majoris (Alkaphrah) on 19 July with fifth-magnitude ω Ursae Majoris its next target five days later. It will be fading from view in early August as it passes through the open star cluster in Coma Berenices and continues south.


Comet ephemerides and orbital elements are provided by the IAU Minor Planet Center Minor Planet & Comet Ephemeris Service, the JPL HORIZONS System and the JPL Small-Body Database Browser with additional information from Seiichi Yoshida.