☄ NEOWISE C/2020 F3

How to follow comet NEOWISE live

The panel above recomputes the position of NEOWISE every second in your browser: its distance from the Sun and from Earth, its position in the sky (right ascension and declination). It runs on the same kind of engine observatories use, a Kepler solver applied to the JPL osculating orbital elements, so the numbers are not a static snapshot, they keep ticking.

Just below, the top-down map of the Solar System shows exactly where NEOWISE is right now among the planets. You can fast-forward time with the day slider, zoom and pan, compare its distance to another body with a click, and press "Next event" to jump straight to perihelion. It is the most direct way to grasp the orbit of NEOWISE with no math at all.

Comet fact sheet

About NEOWISE

C/2020 F3 (NEOWISE) was the astronomical surprise of 2020. Discovered on 27 March 2020 by the WISE space telescope during an infrared sky survey, it emerged from perihelion in July with brightness that exceeded all expectations for a long-period comet, reaching magnitude 0.5 in the first weeks of the month. For northern hemisphere residents it was the first visually noteworthy comet since Hale-Bopp 23 years earlier and the brightest since comet McNaught in 2007.

The 2020 context amplified NEOWISE's cultural impact without precedent: millions of people under COVID-19 quarantine ventured out before dawn to photograph it, flooding social media with images of the comet near Ursa Major. Photographs showing the comet reflected in mountain lakes with the Milky Way as a backdrop went viral across dozens of countries. No previous comet had been documented by so many people in real time.

History and discovery

The Wide-field Infrared Survey Explorer (WISE), a NASA satellite launched in 2009 for an all-sky infrared survey, was shut down in 2011 after completing its primary mission and reactivated in 2013 as NEOWISE to track near-Earth asteroids and comets. The satellite operates in 3.4 and 4.6 micrometre bands, detecting heat emitted by objects absorbing solar radiation.

On 27 March 2020, automated NEOWISE data revealed a new object in the constellation Puppis, still 1.7 AU from the Sun. Its magnitude was about 17, invisible to the naked eye, but initial orbital calculations indicated it would approach the Sun to within 0.30 AU, a favourable geometry. The question was whether it would survive the intense perihelion heating, something dynamically new comets do not always manage.

NEOWISE survived. Perihelion occurred on 3 July 2020 at 0.29 AU from the Sun, near Mercury's orbit. In the following days it emerged from the solar glare on the pre-dawn horizon at near magnitude 1, becoming the first visually spectacular comet for the general public since Hale-Bopp.

Orbit and returns

C/2020 F3 is a long-period comet with a near-parabolic orbit. Orbital calculations indicate a period of roughly 6,700 years, meaning its previous inner-Solar-System passage was around 4700 BC, when Sumerian cuneiform writing was just being developed.

Earth closest approach was on 23 July 2020 at 0.69 AU (about 103 million km). Not an exceptionally close pass in absolute terms, but combined with nucleus brightness it produced a first-rate visual spectacle. After July 2020 the comet moved rapidly outward. Naked-eye visibility lasted until late July, with the comet reaching magnitude 5 around the 30th.

Nucleus, coma and tail

NEOWISE's nucleus was estimated at roughly 5 km in diameter based on infrared observations by the NEOWISE satellite itself, which is sensitive to heat radiated by the nucleus. That size is modest compared with Hale-Bopp, but sufficient to produce spectacular activity at close Earth range.

NEOWISE's tail showed classic dual structure: a white-to-golden dust tail, curved, produced by silicate and carbon grains pushed by solar radiation pressure, and a blue-white straight ion tail formed by ionised molecules swept by the solar wind. By mid-July, the dust tail extended 15 to 20 degrees across the sky, equivalent to 30 to 40 times the apparent diameter of the Full Moon.

A notable peculiarity was the detection of sodium in the tail by the HARPS spectrograph at ESO's La Silla Observatory in Chile. The sodium component, visible only with specialised instruments, had previously been recorded in Hale-Bopp, indicating that sufficiently active comets generate this tail type when close enough to the Sun.

The sky spectacle

Between 8 and 19 July 2020, the comet was visible on the northeast horizon before dawn and, from mid-month onward, also in the northwest after dusk. The best viewing window for mid-northern latitudes was 14 to 23 July, when the comet was high enough for direct observation below and to the right of Ursa Major (the Big Dipper), with the dust tail curving upward.

Latitudes above 45 degrees north had the advantage of circumpolar viewing in mid-July. For the southern hemisphere, visibility was very limited, with the comet barely skimming the northern horizon for a few days. Photographs taken by tourists on Scottish islands and by International Space Station crews also circulated widely.

Science and observations

Although studied less intensively than Hale-Bopp due to geometry and duration, NEOWISE generated substantial scientific results. Millimetre observations with IRAM (Institut de Radioastronomie Millimetrique) telescopes in July 2020 measured production rates of key molecules in the coma.

• Water: water production rate estimated at 2 to 4 times 10 to the power of 29 molecules per second at perihelion, confirming a moderately active nucleus.
• HCN (hydrogen cyanide): detected in typical relative abundance for long-period comets, within the reference range.
• H2S (hydrogen sulfide): relatively abundant compared with other comets of similar activity, at 1.1% relative to water.
• CO (carbon monoxide): low abundance at 3.2% relative to water, suggesting the comet may have made previous inner-Solar-System passes and depleted much of its volatile CO.
• Neutral sodium: detected in the tail by HARPS/ESO, only the second comet after Hale-Bopp in which this element was clearly identified in the tail.
• Tail scintillation: researchers at the University of Bath documented rapid oscillations in the ion tail caused by solar wind turbulence, in a phenomenon called the "scintillating tail."

Facts worth knowing

• It was the brightest comet visible in the northern hemisphere since Hale-Bopp in 1997, a 23-year gap.
• At peak brightness in early July 2020, it reached near magnitude 0.5, outshining most bright stars in the sky.
• The ongoing COVID-19 pandemic turned NEOWISE viewing into an unusual social event, producing possibly the largest number of real-time public photographs ever taken of a single comet, with viral images from dozens of countries within hours.
• The WISE satellite was launched in 2009 for an all-sky infrared survey; the NEOWISE mission is a dedicated extension reactivated in 2013 for near-Earth asteroid and comet tracking.
• An orbital period of ~6,700 years means the last time this comet passed through the inner Solar System, Sumerian cuneiform writing was just beginning to be developed.
• Unlike Hyakutake and Hale-Bopp, NEOWISE did not pass close to Earth; the spectacle was due to nucleus brightness and favourable solar geometry, not a near-Earth pass.
• The NEOWISE dust tail reached 20 degrees of angular extent in mid-July, equivalent to 40 full moons lined up across the sky.
• Astronauts aboard the International Space Station photographed the comet from orbit in July 2020, producing some of the most striking images of the event.

Other comets

See the full comet catalogue.