The object was discovered by a team using the
WISE space telescope under the NEOWISE program on March 27, 2020. It was classified as a
comet on March 31 and named after NEOWISE on April 1. It has the
systematic designation C/2020 F3, indicating a non-periodic comet which was the third discovered in the
second half of March 2020. Comet NEOWISE made its closest approach to the Sun (perihelion) on July 3, 2020, at a distance of . This passage through the planetary region increases the comet's
orbital period from about 4500 years to about 6800 years. Its closest approach to Earth occurred on July 23, 2020, 01:09 UTC, at a distance of while located in the constellation of
Ursa Major. In early July, the comet could be seen in the morning sky just above the north-eastern horizon and below
Capella. Seen from Earth, the comet was less than 20 degrees from the Sun between June 11–July 9, 2020. By June 10, 2020 as the comet was being lost to the glare of the Sun, it was
apparent magnitude 7.0, when it was away from Sun and away from Earth. When the comet entered the field of view of the
SOHO spacecraft's
LASCO C3 instrument on June 22, 2020, the comet had brightened to about magnitude 3.0, when it was away from the Sun and away from Earth. By early July, Comet NEOWISE had brightened to magnitude 1.0, far exceeding the brightness attained by previous comets that year,
C/2020 F8 (SWAN), and
C/2019 Y4 (ATLAS). By July, it also had developed a second tail. The first tail was blue and made of
gas and ions. There was also a red separation in the tail caused by high amounts of sodium. The second twin tail was a golden color and was made of
dust, like the tail of
Comet Hale–Bopp. The comet was brighter than
C/2011 L4 (PanSTARRS), but not as bright as Hale–Bopp was in 1997. After perihelion, the comet began to fade, dropping to magnitude 2.0 in mid-July. Its nucleus activity subdued after mid-July, and its green coma was clearly visible after that. On July 13, 2020, a sodium tail was confirmed by the Planetary Science Institute's Input/Output facility. Sodium tails have only been observed in very bright comets such as Hale–Bopp and
C/2012 S1 (ISON). From the
infrared signature, the diameter of the
comet nucleus is estimated to be approximately . The nucleus is similar in size to
Comet Hyakutake and many
short-period comets such as
2P/Encke,
7P/Pons–Winnecke,
8P/Tuttle,
14P/Wolf, and
19P/Borrelly. By July 5, NASA's
Parker Solar Probe had captured an image of the comet, from which astronomers also estimated the diameter of the comet nucleus at approximately as well.Later in July 2020, other observations were also reported, including those related to coma morphology, and spectrographic emissions. On 31 July 2020, strong detection of OH 18-cm emission was observed in radio spectroscopic studies at the
Arecibo Observatory.On August 14, 2020, the rotation period of the comet was reported to be "". After its perihelion and closest approach to Earth, a number of authors have suggested considering NEOWISE as a
great comet. Others have argued that it lacked the brightness and visible tail to qualify. Retroactively, in the years that followed, NEOWISE is commonly remembered as a great comet. == Trajectory ==