Comet NEOWISE — the great comet of 2020
In July 2020 this comet survived a close pass by the Sun and became visible to the naked eye — the brightest comet in the northern hemisphere since Hale–Bopp in 1997.
Available views: Orbit ✓ · Sky — (not visible in the sky)
The story
Comet C/2020 F3 NEOWISE was discovered on 27 March 2020 by NEOWISE, a NASA infrared space telescope, and the comet took the telescope's name. At first it was a very faint dot, and almost nobody expected it to become bright enough to see without a telescope.
The biggest test came on 3 July. On that day the comet passed 0.29 AU from the Sun, about 43 million km, which is inside the orbit of Mercury. Earlier that spring two promising comets, ATLAS and SWAN, had broken apart as they approached the Sun, so there was worry that NEOWISE might do the same. Instead it survived and brightened to around first magnitude.
In early July it could be seen in the north-eastern sky before dawn. From mid-July it appeared in the north-western sky after sunset, below the Big Dipper. Its yellowish dust tail and bluish ion tail split into two clear branches, and even near cities binoculars showed it well.
That summer many people could not travel because of the COVID-19 pandemic, so they watched the comet from near their homes. Astronauts on the International Space Station also photographed it rising above the edge of the Earth. The comet made its closest approach to Earth on 23 July, at 0.69 AU, and then slowly faded.
When and where to see it
Comet NEOWISE is now heading into the outer solar system and can no longer be seen with any telescope. As it passed the Sun, the pull of the planets stretched its orbit a little. On the way in, one trip around took about 4,400 to 4,500 years; now it will take about 6,700 to 6,800 years to return.
Choose NEOWISE in the sky view's event list to replay the north-western sky on a mid-July evening in 2020. The comet hangs low below the bowl of the Big Dipper, with its tail pointing upward. Move the time to a morning in early July to find it in the north-eastern sky instead.
In the orbit view's event replay, the comet's path crosses the plane of the planets at a slant as it swings around the Sun. Slow the playback around 3 July to see the comet dip inside Mercury's orbit and come back out.
See this for yourself — replay the moment in the orbit view
Past returns and history
At discovery NEOWISE was 17th magnitude, tens of thousands of times fainter than the faintest stars visible to the naked eye. By the time it entered the view of the SOHO solar observatory's camera around 22 June, it had already brightened to 3rd magnitude. From then on, hopes grew that it might become a great comet.
The two tails of NEOWISE behaved differently. The dust tail curved along the path the comet had travelled, while the ion tail was pushed by the solar wind and pointed straight away from the Sun. On 13 July a faint third tail made of sodium atoms was also confirmed. Such sodium tails are seen only rarely, in very bright comets.
The three comets of 2020, ATLAS, SWAN and NEOWISE, showed how differently comets can fare in a single year. The next comet to put on a big naked-eye show for the northern hemisphere was Tsuchinshan–ATLAS in 2024.
Why it matters
NEOWISE showed that nobody can be sure in advance whether a comet will survive a close pass by the Sun. The same year, comet ATLAS was expected to become a great comet but broke apart in April, and comet SWAN also fell to pieces. Only NEOWISE went very close to the Sun and came out intact. The difference is often explained by the size and strength of each comet's nucleus, but the exact reason is still not known.
The telescope that found it is also worth noting. NEOWISE started life as WISE, a space telescope that mapped the whole sky in infrared light. After that mission ended, it was put to work searching for asteroids that come near Earth. Finding this comet showed that an asteroid-hunting survey can also discover comets.
NEOWISE was also a great comet of the smartphone and internet age. Far more people than in 1997, the year of Hale–Bopp, could share their own photographs right away. That made the comet a sky event that many people remember together.
FAQ
When was it best seen?
In mid-July 2020, in the north-western sky after sunset. In early July it was in the north-eastern sky before dawn.
How bright did it get?
It reached around first magnitude in early July and was still visible to the naked eye in mid-July.
Will it return?
Yes, but only after about 6,700 to 6,800 years.
Why did the other 2020 comets fail?
Comets ATLAS and SWAN broke apart as they neared the Sun, while NEOWISE's nucleus, about 5 km wide, held together. Exactly why is still not certain.
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.