Comet NEOWISE — the great comet of 2020
After surviving perihelion on 3 July it hung in the north-west after dusk — the first naked-eye great comet in 23 years, its twin tails visible even from cities.
The moment of Comet NEOWISE — the great comet of 2020: https://nowsky.org/e/neowise-2020 — opens at the right place and time, replayable, no login.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
C/2020 F3 NEOWISE was found on 27 March 2020 by NASA's NEOWISE infrared space telescope. The test was perihelion on 3 July, a plunge to 0.29 AU from the Sun — earlier that year comets ATLAS and SWAN had broken apart before the Sun, but NEOWISE survived and brightened to nearly magnitude 0.
It was the first great comet visible to the naked eye from the northern hemisphere since Hale–Bopp in 1997. In early July it stood in the north-east before dawn; from mid-month it hung in the north-west below the Big Dipper in the evening. The yellow dust tail and blue ion tail split visibly, and even under city lights binoculars showed it clearly.
The summer of 2020 was a pandemic summer, and the comet was an event in the sky that could be seen from close to home. Astronauts on the International Space Station photographed it rising over Earth's limb, and after closest approach to Earth on 23 July (0.69 AU) it faded slowly.
The nucleus is about 5 km across and the period about 6,800 years — the next visit is around the year 8800. Set the sky view to Seoul at 21:30 on 15 July 2020 to see the comet and its tail low in the north-west, and use the orbit view's event replay to run through perihelion. Tail length and brightness are approximate.
Why it matters
NEOWISE was the year that showed a comet's survival is an outcome, not a forecast. In spring 2020 comet ATLAS, tipped as a great comet, disintegrated in April, and SWAN fell apart before perihelion. Only NEOWISE endured the 0.29 AU approach, and the difference lay in the size and structure of its nucleus.
That an infrared space telescope found it matters too. NEOWISE is the WISE telescope repurposed for asteroid surveillance, and the discovery showed that the near-Earth-object network catches comets as well. Its successor, NEO Surveyor, is planned for launch in 2027.
The sky of July 2020 was a rare shared astronomical experience in the middle of a pandemic. Photographs posted online outnumbered Hale–Bopp's beyond comparison, and the twin tails captured from suburbs announced an era when a smartphone camera could record a comet.
How to watch
NEOWISE is now receding into the outer solar system and is beyond any telescope. Its next return is about 6,800 years away.
Choose NEOWISE in the sky view's event list to replay mid-July 2020 — the comet hanging low in the north-west below the bowl of the Big Dipper in the evening, tail pointing upward. Move the time to early July and it stands near Capella in the north-east before dawn.
The orbit view's event replay draws the comet cutting obliquely across the ecliptic and rounding the Sun at 0.29 AU; slow the playback near perihelion to appreciate how close it went.
See this for yourself — replay the moment in the orbit view
Background
At discovery NEOWISE was a faint 17th-magnitude smudge, and even in May nobody predicted a great comet. In late June it entered the field of the SOHO solar observatory and was seen brightening rapidly, and expectations rose.
For a few days after perihelion it was visible only in morning twilight and hard to observe; by around 10 July it was firmly placed in the dawn sky. As it moved into the evening sky in mid-July the number of observers surged, and after late July it faded below 4th magnitude.
The three comets of 2020 — ATLAS, SWAN and NEOWISE — remain a control group showing how differently comets can fare in a single year. Tsuchinshan–ATLAS in 2024 became the next great comet for the northern hemisphere.
NEOWISE’s two tails were its signature. The yellow dust tail curved along the comet’s orbit while the blue ion tail, carried on the solar wind, stretched straight away from the Sun. Mid-July photographs show the ion tail splitting off longer than the dust tail, and some images caught a faint third trace thought to be a sodium tail. After perihelion the nucleus shed tens of tonnes of dust per second, and the 5 km diameter is a value inferred from that activity.
FAQ
When was it best seen?
Mid-July 2020 in the north-western evening sky; in early July it was in the north-east before dawn.
How bright did it get?
Nearly magnitude 0 just after perihelion, and 1–2 in mid-July — visible to the naked eye.
Will it return?
Not until around the year 8800 — the period is about 6,800 years.
Why did the other 2020 comets fail?
ATLAS and SWAN broke apart before perihelion; NEOWISE's 5 km nucleus survived the approach to the Sun.
Related
- Comet Tsuchinshan–ATLAS (2024)
- Comet Hale–Bopp perihelion
- Comet Hyakutake sweeps past Earth
- The Sun — object index
- Ursa Major — object index
Times and figures are approximate — verify with official sources when planning travel. Simulation uses J2000 mean elements.