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Comet NEOWISE
Comet NEOWISE
Comet NEOWISE
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C/2020 F3 (NEOWISE)
(Great Comet of 2020)
Comet NEOWISE photographed from Germany on July 14, 2020
Discovery[1]
Discovered byNEOWISE
Discovery dateMarch 27, 2020
Designations
CK20F030
Orbital characteristics[2][3]
EpochJuly 6, 2020 (JD 2459036.5)
Observation arc1.2 years (438 days)
Number of
observations		1,315
Aphelion538 AU (inbound)
710 AU (outbound)
Perihelion0.295 AU
Semi-major axis270 AU (inbound)
355 AU (outbound)
Eccentricity0.99921
Orbital period~4,500 yrs (inbound)
~6,800 yrs (outbound)
Inclination128.94°
61.010°
Argument of
periapsis		37.279°
Mean anomaly0.0003°
Last perihelion3 July 2020
TJupiter−0.408
Earth MOID0.362 AU
Jupiter MOID0.813 AU
Physical characteristics[1]
Dimensions~5.0 km (3.1 mi)
7.58±0.03 hours
Comet total
magnitude (M1)		7.5–12.1
0.5–1.0
(2020 apparition)

C/2020 F3 (NEOWISE) or Comet NEOWISE is a long period comet with a near-parabolic orbit discovered on March 27, 2020, by astronomers during the NEOWISE mission of the Wide-field Infrared Survey Explorer (WISE) space telescope. At that time, it was an 18th-magnitude object, located 2.0 AU (300 million km; 190 million mi) away from the Sun and 1.7 AU (250 million km; 160 million mi) away from Earth.[4]

NEOWISE is known for being the brightest comet in the northern hemisphere since Comet Hale–Bopp in 1997.[5] It was widely photographed by professional and amateur observers and was even spotted by people living near city centers and areas with light pollution.[6] While it was too close to the Sun to be observed at perihelion, it emerged from perihelion around magnitude 0.5 to 1, making it bright enough to be visible to the naked eye.[7] Under dark skies, it could be seen with the naked eye and remained visible to the naked eye throughout July 2020.[8][9] By July 30, the comet was about magnitude 5,[10] when binoculars were required near urban areas to locate the comet.

For observers in the Northern Hemisphere, the comet could be seen on the northwestern horizon, below the Big Dipper. North of 45 degrees north, the comet was visible all night in mid-July 2020. On July 30, Comet NEOWISE entered the constellation of Coma Berenices, below the bright star Arcturus.

NEOWISE was retroactively dubbed the Great Comet of 2020.

History and observations

[edit]
Discovery image – the comet appears as three fuzzy red dots in this composite of three infrared images taken by NEOWISE on March 27, 2020

The object was discovered by a team using the WISE space telescope under the NEOWISE program on March 27, 2020.[1] It was classified as a comet on March 31 and named after NEOWISE on April 1.[4] 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 0.29 AU (43 million km; 27 million mi). This passage through the planetary region increases the comet's orbital period from about 4500 years to about 6800 years.[2] Its closest approach to Earth occurred on July 23, 2020, 01:09 UTC, at a distance of 0.69 AU (103 million km; 64 million mi) while located in the constellation of Ursa Major.[11]

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,[10] when it was 0.7 AU (100 million km; 65 million mi) away from Sun and 1.6 AU (240 million km; 150 million mi) 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 0.4 AU (60 million km; 37 million mi) away from the Sun and 1.4 AU (210 million km; 130 million mi) away from Earth.[10]

By early July, Comet NEOWISE had brightened to magnitude 1.0,[12][13] 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.[citation needed] The comet was brighter than C/2011 L4 (PanSTARRS),[14] 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.[15] 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.[16] 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 5 km (3.1 mi).[1] 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.[17] 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 5 km (3.1 mi) as well.[18]Later in July 2020, other observations were also reported, including those related to coma morphology,[19] and spectrographic emissions.[20][21][22][23] On 31 July 2020, strong detection of OH 18-cm emission was observed in radio spectroscopic studies at the Arecibo Observatory.[24]On August 14, 2020, the rotation period of the comet was reported to be "7.58±0.03 hr".[25]

After its perihelion and closest approach to Earth, a number of authors have suggested considering NEOWISE as a great comet.[26][27][28][29][30][31] Others have argued that it lacked the brightness and visible tail to qualify.[32] Retroactively, in the years that followed, NEOWISE is commonly remembered as a great comet.[33][34]

Trajectory

[edit]

Comet NEOWISE's retrograde orbit crossed to the north of the plane of the ecliptic, to which it is inclined at approximately 129 degrees, on June 29, 2020, 01:47 UTC.[12][2] It made its closest approach to the Sun (perihelion) on July 3, 2020, at a distance of 0.29 AU (43 million km; 27 million mi). This passage increases the comet's orbital period from about 4400 years to about 6700 years.[2] On July 18, the comet peaked at a northern declination of +48 and was circumpolar down to latitude 42N.[11] Its closest approach to Earth occurred on July 23, 2020, 01:09 UTC, at a distance of 0.69 AU (103 million km; 64 million mi) while located in the constellation of Ursa Major.[11]

The comet's orbital characteristics suggest it originated from the Oort cloud. Its high orbital eccentricity of 0.99921 confirms its path is a nearly parabolic trajectory, typical of long-period comets making one of their first passages into the inner Solar System. The orbital inclination of 129 degrees classifies it as a retrograde comet, meaning it orbits the Sun in the opposite direction to Earth and the other planets. This path is what allowed it to approach the Sun from the south of the ecliptic plane before crossing northwards just before its perihelion. The difference between the inbound orbital period of about 4,400 years and the outbound period of about 6,700 years is a result of gravitational perturbations from the planets. As the comet passed through the planetary region, the slight gravitational pull from the planets transferred energy to it, accelerating it and placing it on a higher-energy, longer-period outbound orbit. This also increased its aphelion, the farthest point in its orbit from the Sun.

  • Diagram of the comet's nearly parabolic orbit
    Diagram of the comet's nearly parabolic orbit
  • Comet's position in the sky – the retrograde loops are caused by parallax from Earth's annual motion around the Sun; the most apparent movement occurs when the comet is closest to Earth
    Comet's position in the sky – the retrograde loops are caused by parallax from Earth's annual motion around the Sun; the most apparent movement occurs when the comet is closest to Earth
  • Animation of C/2020 F3's orbit around Sun   C/2020 F3  ·   Sun ·   Mercury ·   Venus ·   Earth ·   Mars
    Animation of C/2020 F3's orbit around Sun
      C/2020 F3  ·   Sun ·   Mercury ·   Venus ·   Earth ·   Mars
[edit]

The fictional comet Dibiasky on the 2021 film Don't Look Up was "very loosely" modelled after comet NEOWISE.[35][36]

[edit]

In chronological order:

  • July 7, 2020, Golden Gate Bridge, California, United States
    July 7, 2020, Golden Gate Bridge, California, United States
  • Inverted telescope image photographed on July 9, 2020
    Inverted telescope image photographed on July 9, 2020
  • July 14, 2020 near the San Francisco Peaks in the Flagstaff dark sky preserve
    July 14, 2020 near the San Francisco Peaks in the Flagstaff dark sky preserve
  • July 17, 2020, 18:59 UTC over Asterousia, Crete, as it entered into Ursa Major
    July 17, 2020, 18:59 UTC over Asterousia, Crete, as it entered into Ursa Major
  • Comet C2020 NEOWISE 17-07-2020 20:51:57 UTC La Canada observatory
    Comet C2020 NEOWISE 17-07-2020 20:51:57 UTC La Canada observatory
  • Midnight, July 18, 2020 – in a time-lapse taken from the Shenandoah National Park, Virginia, U.S. the view was rotating because the lens was on a tracking mount
    Midnight, July 18, 2020 – in a time-lapse taken from the Shenandoah National Park, Virginia, U.S. the view was rotating because the lens was on a tracking mount
  • Above Chimney Rock on July 18, 2020
    Above Chimney Rock on July 18, 2020
  • July 19, 2020 in Villanovaforru (Sardinia, Italy)
    July 19, 2020 in Villanovaforru (Sardinia, Italy)
  • NEOWISE from the Eastern Sierra Mountains – July 20, 2020
    NEOWISE from the Eastern Sierra Mountains – July 20, 2020
  • July 21, 2020 in Quebec, Canada
    July 21, 2020 in Quebec, Canada
  • Joshua Tree National Park, a dark-sky preserve, on July 21, 2020
    Joshua Tree National Park, a dark-sky preserve, on July 21, 2020
  • Time lapse from Balikesir, Turkey on July 22, 2020
    Time lapse from Balikesir, Turkey on July 22, 2020
  • Hubble image taken on August 8, 2020
    Hubble image taken on August 8, 2020

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Comet NEOWISE

View on Grokipedia
from Grokipedia
Comet C/2020 F3 (NEOWISE), commonly known as Comet NEOWISE, is a long-period comet with a near-parabolic orbit that was discovered on March 27, 2020, by NASA's Wide-field Infrared Survey Explorer (WISE) telescope operating as the NEOWISE mission. It reached its perihelion on July 3, 2020, at a distance of 0.29 astronomical units (AU) from the Sun, just inside Mercury's orbit, and survived the intense solar heating to develop prominent dust and ion tails visible from Earth. The comet's nucleus is estimated to be about 5 kilometers (3 miles) in diameter, covered in dark, sooty material, and it passed closest to Earth on July 23, 2020, at a distance of 0.69 AU. Orbitally, Comet NEOWISE follows a retrograde path with a semimajor axis of 274.5 AU and an of approximately 4,548 years, indicating it originates from the in the distant outer Solar System. This once-in-a-lifetime apparition made it the brightest comet visible in the since in 1997, reaching a peak visual magnitude of about 0.5 to 1.0, observable with the under or enhanced by . It was initially detected in as a faint object before brightening dramatically post-perihelion, drawing widespread public and scientific interest. Scientifically, observations of Comet NEOWISE revealed a heterogeneous in its nucleus, with varying abundances of molecules such as (H₂O), (CH₃OH), and (C₂H₆) detected across different regions using ground-based telescopes like the Telescope Facility and Keck Observatory. 's captured unique images of its tails from close to the Sun, while the documented its rotation and coma structure. These findings provided insights into the comet's primordial materials, aiding understanding of early Solar System formation and the diversity of objects. The event also highlighted the NEOWISE mission's role in comet hunting, which concluded in July 2024 after cataloging thousands of solar system bodies.

Discovery and Observations

Discovery

Comet C/2020 F3 (NEOWISE) was discovered on March 27, 2020, by NASA's (NEOWISE) spacecraft during its ongoing all-sky survey for potentially hazardous asteroids and comets. The initial detection captured the object at an of approximately 17 in the constellation , appearing as a series of faint sources in multiple exposures taken over a short period. The NEOWISE mission originated as a reactivation of the Wide-field Infrared Survey Explorer (WISE), a space telescope launched in 2009 to conduct an all-sky infrared survey, which entered hibernation in 2011 after depleting its cryogen. Repurposed in 2013 without cryogen to focus on near-Earth object detection, NEOWISE utilized its remaining infrared channels (at 3.4 and 4.6 micrometers) to detect thermal emissions from sunlit surfaces, enabling the identification of objects like this comet that emit more strongly in infrared than in visible light. This capability proved essential for spotting C/2020 F3, whose heat signature stood out against the cooler background of space at a heliocentric distance of about 2.1 AU. The discovery prompted immediate follow-up observations from ground-based facilities to verify the detection and assess its cometary activity. Telescopes including those of the Catalina Sky Survey and the Mount Lemmon Observatory in captured optical images showing a small and faint tail, confirming the object's cometary nature by March 29. The International Astronomical Union's [Minor Planet Center](/page/Minor Planet Center) officially announced the find on April 1, 2020, via Circular CBET 4740 and Minor Planet Electronic Circular 2020-G05, assigning the provisional designation C/2020 F3 (NEOWISE). This follows IAU conventions for non-periodic comets, with "C/" denoting the category, "2020" the discovery year, "F" indicating the latter half of March, "3" the ordinal discovery in that interval, and "(NEOWISE)" crediting the discovering mission.

Observational Campaigns

Following its discovery, Comet C/2020 F3 (NEOWISE) became the subject of intensive observational campaigns involving both space-based and ground-based assets to track its evolution and physical properties. The primary space-based effort was led by the NEOWISE spacecraft itself, which continued imaging the comet in its two active bands at 3.4 μm (W1) and 4.6 μm (W2) from late March through early August 2020, capturing data on dust and gas emissions before and after perihelion on July 3. These observations documented the comet's increasing activity as it approached the Sun, including the development of its and tails, with post-perihelion images revealing enhanced thermal emission due to solar heating. Ground-based telescopes complemented these efforts with visual, photometric, and spectroscopic measurements. Professional observatories such as , where the Spacewatch program conducted follow-up and photometry using telescopes including the 0.9-m and 2.3-m instruments, contributed precise positional data to refine the comet's orbit. On , the Infrared Telescope Facility (IRTF) employed the iSHELL spectrograph for high-resolution (resolving power ~70,000) from July 9 to August 1, while the Keck Observatory's NIRSPEC instrument (resolving power ~25,000–37,500) provided complementary spectra from August 4 to 6, detecting emissions from species like H₂O, CO, CH₃OH, and HCN. Amateur networks, coordinated through organizations like the Association of Lunar and Planetary Observers (ALPO) and the British Astronomical Association (BAA), supplied thousands of visual magnitude estimates and images, particularly as the comet brightened to naked-eye visibility in July. Observational efforts intensified from April to July 2020, coinciding with the comet's approach to perihelion and its rapid brightening from magnitude ~16 to ~1. Pre-perihelion monitoring in and May focused on faint signatures via NEOWISE and limited ground-based photometry, while June saw increased activity tracking as outbursts were detected. Post-perihelion, from mid-July onward, spectral analysis dominated, revealing variable gas production rates and molecular mixing ratios, such as stable HCN/H₂O ratios (~0.2%) alongside fluctuating CH₃OH/H₂O (~1.5–2.5%). These campaigns spanned the comet's inbound and outbound legs, enabling studies of its heterogeneous nucleus composition. Challenges included the comet's initial faintness pre-perihelion, which necessitated long integration times (up to hours) for ground-based detections amid twilight conditions, and its unpredictable brightening post-perihelion, which saturated some detectors and required adaptive exposure strategies. The NEOWISE spacecraft's cryogenic limitations also constrained post-perihelion coverage to warmer-band imaging only. Despite these hurdles, the campaigns yielded over 1,300 astrometric observations archived in the JPL Small-Body Database Browser, alongside extensive photometric and spectroscopic datasets in NASA's Planetary Data System, facilitating detailed modeling of the comet's activity.

Physical Characteristics

Nucleus Properties

The nucleus of Comet C/2020 F3 (NEOWISE) is estimated to have an effective diameter of approximately 5 km, derived from thermal observations conducted by NASA's NEOWISE spacecraft, which modeled the emission assuming a low of 0.04 typical for dark cometary surfaces. This size places it among moderately sized comet nuclei, consistent with thermal modeling that accounts for the comet's dust contribution to the overall flux. The assumption of low albedo reflects the nucleus's dark, surface materials that absorb most incident . The nucleus is likely irregular in shape, as inferred from high-resolution imaging that reveals non-spherical dust ejection patterns influenced by its . Observations from the and Gemini North telescope captured the nucleus's over intervals spanning several hours, yielding a sidereal period of approximately 7.5 hours based on periodic variations in structure and light curves. This rate suggests a tumbling or elongated body, common for primordial solar system remnants, though direct resolution of the nucleus shape was limited by its small angular size and surrounding . Surface composition analyses indicate a heterogeneous mix dominated by water , interspersed with organic refractories and silicate grains, as evidenced by the diverse molecular emissions originating near the nucleus during its active phase. The low points to a of dark, carbon-rich materials, likely complex organics and , which mantles much of the icy core and contributes to the nucleus's overall primitive, unaltered nature. Post-perihelion observations confirmed the nucleus's structural integrity, with no signs of fragmentation or disruptive outbursts despite its close solar approach at 0.29 AU, highlighting the robustness of its framework against thermal stresses. Continuous monitoring through August 2020 showed stable activity levels, underscoring the nucleus's ability to withstand intense insolation without catastrophic disassembly.

and Tails

As Comet C/2020 F3 (NEOWISE) approached its perihelion on July 3, 2020, at 0.29 AU from the Sun, solar heating intensified the sublimation of ices from its nucleus, leading to the development of a prominent coma consisting of gas and dust. The water production rate peaked shortly after perihelion at approximately 6 × 10^{29} molecules per second on July 22, 2020, while dust production contributed to the formation of a diffuse envelope spanning about 10 arcminutes in angular diameter. The coma exhibited high activity levels, with the Afρ parameter—a measure of dust production—reaching values up to 10,000 cm shortly after perihelion on July 21, 2020, indicating substantial dust ejection influenced by the nucleus's size of roughly 5 km in diameter. Water production rates were measured at around 4.5 × 10^{29} molecules per second on July 24, 2020, decreasing to 1 × 10^{29} molecules per second by early August as the comet receded from the Sun. These rates highlight the comet's vigorous outgassing, comparable to highly active long-period comets like C/1995 O1 (Hale-Bopp). Comet NEOWISE displayed two distinct tail types: a prominent dust tail extending up to 25° in length in the anti-solar direction, curved due to the combined effects of and the comet's orbital motion, and a shorter ion tail influenced by the , often appearing bluish and reaching lengths of around 20° or more. The dust tail featured highly structured elements, including syndynic bands at scattering angles β ≈ 0.42° and β ≈ 1.63°, with a dust-sparse in between, as observed post-perihelion between July 10 and 20, 2020. The ion tail showed dynamic behavior, including disconnection events triggered by solar wind interactions, where portions of the tail were detached and reformed. Post-perihelion, the tails brightened initially due to continued sublimation and dust release, with the overall activity following a heliocentric distance dependence close to r_h^{-2} for water production. Imaging in visible light captured the curved, pinkish dust tail and the straighter, blue ion tail, while hydrogen-alpha filters revealed emissions from the extended coma, highlighting neutral hydrogen envelopes around the ion structures. These observations, conducted with ground-based telescopes and space instruments like the Parker Solar Probe's WISPR, provided detailed views of the tail evolution from July 5 to 20, 2020.

Orbital Dynamics

Orbital Elements

Comet C/2020 F3 (NEOWISE) follows a near-parabolic orbit with an eccentricity e≈0.9992e \approx 0.9992, classifying it as a long-period originating from the . This high eccentricity indicates that the comet's trajectory is only slightly bound to the Solar System, with its very close to zero, distinguishing it from both short-period comets and truly hyperbolic visitors. The key orbital elements, derived from osculating solutions at a standard epoch, include a semi-major axis a=370a = 370 , an inclination i=129.2∘i = 129.2^\circ relative to the , and a perihelion q=0.29q = 0.29 , reached on July 3, 2020. These parameters describe the comet's highly elongated and retrograde path, with the inclination confirming its retrograde motion .
ParameterValue
Eccentricity ([e](/page/E!)[e](/page/E!))0.9992Measures the orbit's deviation from a circle; near 1 indicates near-parabolic .
Semi-major axis (aa)370 AUAverage from the Sun; large value reflects the comet's distant origin.
Inclination (ii)129.2°Angle of the to the ; >90° denotes retrograde orbit.
Perihelion (qq)0.29 Closest approach to the Sun, inside .
Perihelion dateJuly 3, 2020Time of closest solar approach during the 2020 apparition.
The is approximately 6,800 years, refined from initial estimates through integration of post-perihelion observations; this value corresponds to the future after accounting for planetary perturbations. Early determinations suggested shorter periods around 4,500–5,000 years based on inbound data, but extended tracking yielded the longer estimate. These elements were computed using least-squares fitting to astrometric observations from the NEOWISE spacecraft and numerous ground-based telescopes, minimizing residuals between predicted and observed positions to solve for the six classical Keplerian parameters. The JPL Horizons system provides the refined solution, incorporating thousands of measurements spanning the comet's inbound and outbound legs. The original inbound orbit had a smaller semi-major axis (around 270 AU), indicating a more bound trajectory before entering the inner Solar System, while the future outbound shows slight expansion due to gravitational perturbations from giant planets like . This marginal near zero) suggests the comet could experience further modifications in subsequent passages, potentially altering its long-term dynamical status within the reservoir.

Trajectory and Encounters

Comet C/2020 F3 (NEOWISE) reached perihelion, its closest approach to the Sun, on July 3, 2020, at a distance of 0.29 AU, passing well inside the orbit of Mercury and subjecting the nucleus to intense solar heating that drove significant outgassing and tail formation. This close solar passage altered the comet's trajectory, lengthening its orbital period from an incoming value of approximately 4,550 years to an outbound period exceeding 6,500 years due to the strong gravitational influence of the Sun. The comet's path during this apparition followed a highly eccentric, near-parabolic orbit with an eccentricity of about 0.999, originating from the distant Oort Cloud and sweeping inbound through the inner Solar System before arcing outward. On July 23, 2020, the comet achieved its closest approach to at a minimum distance of 0.692 AU (approximately 64 million miles or 103 million kilometers), a safe separation that nonetheless provided optimal conditions for ground-based observations without posing any risk. During the 2020 apparition, the comet did not make any close passes to major planets, maintaining a trajectory that avoided significant gravitational interactions with , Saturn, or other outer bodies at that time. However, as it departs on its outbound leg toward the outer Solar System, potential future encounters with massive planets like could further perturb the orbit, potentially modifying the timing and path of its next return. This 2020 passage marked only the comet's second known perihelion in the inner Solar System, with the previous one estimated around 4,500 years ago based on the inbound , during which solar gravity similarly reshaped its path from a prior configuration. Absent additional perturbations, the comet's highly eccentric trajectory will carry it back toward the , resembling a hyperbolic path visually but remaining bound to the Sun on an elongated that extends to over 700 AU at aphelion.

2020 Apparition

Visibility Conditions

During its 2020 apparition, Comet NEOWISE (C/2020 F3) was best visible to the from late through mid-, particularly in the evening sky after sunset for observers in the , where it appeared low in the northwest near the . In the [Southern Hemisphere](/page/Southern Hemisphere), visibility was limited to a brief predawn window in early , with the comet rising low in the northeastern sky before fading rapidly. This optimal period followed the comet's perihelion on July 3, allowing it to climb higher in the post-sunset sky as it receded from the Sun. The comet rose into the constellation of by late July, positioned just below the bowl of the in , making it relatively easy to locate with minimal prior knowledge of the stars. It reached its maximum solar elongation of approximately 37° on July 24, providing the widest separation from the Sun and thus the darkest sky conditions for observation during twilight. At this point, the comet's was about 10h 28m and +44°, placing it at an altitude of up to 60° for mid-northern observers by mid-evening. Clear, dark skies away from were essential for optimal viewing, as urban glow could obscure the comet's faint glow even at its peak of around 1. were recommended for early detection when the comet hovered near magnitude 3 in mid-July, enhancing visibility of its tail against the twilight horizon. The comet was accessible globally from latitudes roughly 30°N to 90°N, offering all-night visibility north of 45°N during mid- before it shifted to evening hours. viewers south of 30°S had only a short opportunity in late to early August, as the comet remained low on the horizon and quickly dimmed below naked-eye limits. Although Comet NEOWISE posed no collision risk to , with its closest approach to at 0.69 on 23, 2020,

Peak Brightness and Decline

Comet C/2020 F3 (NEOWISE) reached its peak apparent visual magnitude of approximately 0.5 to 1 shortly after perihelion on July 3, 2020, rendering it visible to the naked eye from dark-sky locations in the Northern Hemisphere. This brightness level emerged as the comet transitioned from its solar proximity, with observations confirming naked-eye detectability under clear, low-light pollution conditions during late evening or predawn hours. The comet's magnitude followed a steep brightening curve, advancing from roughly magnitude 5 in early July—when it first became prominent post-discovery—to its peak within weeks, driven by intensifying near the Sun. Following the peak, brightness declined steadily, reaching about magnitude 4 by early as the comet receded, with visual estimates tracking this fade through and photometry. This curve reflected the comet's dynamic response to solar heating, with post-perihelion observations documenting the transition from high activity to quiescence. Several factors contributed to the observed brightness profile, including forward-scattering of by particles in , which amplified as the positioned nearly between and the Sun during its closest approach on July 23, 2020. Additionally, sustained release post-perihelion, linked to sublimation of icy grains from the nucleus, prolonged visibility despite increasing heliocentric distance. Sustained supported this temporary enhancement before tapering. Despite its nucleus diameter of about 5 kilometers, NEOWISE outperformed brightness expectations for a comet of its size, achieving widespread naked-eye accessibility comparable to (C/1995 O1) in 1997, which peaked at magnitude 0 but offered similar ease of observation for northern viewers. The decline in brightness stemmed primarily from diminished cometary activity as heliocentric distance grew beyond 1 AU, reducing volatile sublimation and gas/dust ejection rates. Consequently, contracted, shrinking to approximately 5 arcminutes in diameter by October 2020, as reduced failed to replenish the envelope against expansion and dispersal.

Scientific Significance

Compositional Studies

Compositional studies of Comet C/2020 F3 (NEOWISE) primarily relied on high-resolution conducted from ground-based telescopes such as the Infrared Telescope Facility (IRTF) and the W. M. Keck Observatory, capturing emissions from key volatiles during its post-perihelion phase in July and August 2020. These observations revealed a diverse inventory of molecular species, including (H₂O) as the dominant volatile, alongside (CO), (HCN), and daughter products like (CN). The data indicated a heterogeneous chemical distribution within the nucleus, with mixing ratios varying over time and spatial extent, suggesting contributions from extended sources such as icy grains. Molecular abundances were quantified relative to H₂O, showing both depletions and enhancements compared to median values for Oort cloud comets (OCCs). For instance, the CO/H₂O ratio was measured at approximately 2.16%, slightly below the OCC median of 3.5% (with a 25th–75th percentile range of 1.5%–5.5%), indicating a modestly depleted volatile fraction. In contrast, HCN/H₂O was about 0.26%, above the OCC median of 0.18% (25th–75th percentile: 0.12%–0.25%), while CN production, derived as a proxy for HCN parentage, aligned with typical cometary levels when scaled to water output. Other species exhibited variability: methanol (CH₃OH/H₂O) increased from ~0.40% pre-perihelion to 2.09%–3.25% post-perihelion, and ethane (C₂H₆/H₂O) rose from ~0.28% to 1.31%–1.73%, pointing to differential release from distinct nuclear regions. Complementary millimeter-wave observations with the IRAM telescopes confirmed these trends, reporting a low CO/H₂O of 3.2% and an elevated hydrogen sulfide (H₂S/H₂O) of 1.1%, with formaldehyde (H₂CO/H₂O) varying steeply from 0.6% to 1.8% as the comet receded. Gas production rates, linked directly to sublimation processes, were derived from hydroxyl (OH) radical emissions observed in the radio regime. On July 28, 2020 (at 0.72 AU from the Sun), the OH production rate was (3.6 ± 0.6) × 10²⁸ molecules s⁻¹, corresponding to a sublimation rate consistent with the comet's activity peak and implying ~60% of H₂O originated from extended sources rather than direct nuclear . These rates declined post-perihelion, mirroring the fade in brightness, and underscored H₂O's role as the primary driver of the coma and tails. Infrared spectra also probed the dust component, revealing signatures of amorphous silicates and organic refractory materials in the coma, with low crystallinity levels indicative of minimally processed, primordial grains preserved since the solar system's formation. The overall composition, blending volatile ices with unaltered dust, aligns with expectations for an Oort cloud comet, though the observed heterogeneity highlights dynamic release mechanisms during its close solar approach. Key analyses, including those by Faggi et al. (2021) in The Astronomical Journal and Biver et al. (2022) in Astronomy & Astrophysics, integrated ground- and space-based data to establish these profiles.

Broader Implications

The discovery and study of Comet C/2020 F3 (NEOWISE) have provided key insights into the , demonstrating its origin as a dynamically new object with minimal prior perturbation. Observations revealed non-depleted volatiles, including stable detections of H₂O, CO, HCN, and NH₃, indicating that the comet's nucleus has preserved ancient ices largely untouched by significant thermal or collisional processing, thereby offering a snapshot of primordial material from the solar system's formative epochs. Contributions from the NEOWISE mission, which detected the , have substantially enhanced the catalog of solar system objects, amassing over 1.6 million confirmed detections across nearly 45,000 unique sources, including improved statistics on populations that refine estimates of long-period fluxes and sizes. Detailed analyses of NEOWISE-discovered s, such as abundance ratios and activity patterns, have bolstered understanding of the overall inventory, aiding in the characterization of potentially hazardous near-Earth objects. The comet's pristine ices, evidenced by heterogeneous mixing ratios of species like CH₃OH (varying from 0.40% to 3.25%) and C₂H₆, support the of solar system formation by illustrating how diverse conditions could yield radially varied chemical inventories preserved in reservoirs. These findings draw parallels to interstellar objects like 1I/'Oumuamua, highlighting shared traits in volatile retention that underscore the commonality of ice-rich planetesimals across extrasolar systems. A 2025 study further suggests that NEOWISE's molecular abundances correlate with those in protostellar disks, indicating inheritance of interstellar material processed in the . The NEOWISE mission's success with this has amplified public interest in infrared astronomy, as the 2020 apparition garnered widespread attention and demonstrated the value of space-based surveys in revealing hidden solar system dynamics. Its archived continue to inform future predictions, enabling refined integrations and activity forecasts for other long-period visitors. Looking ahead, the 's perturbed —lengthened from approximately 4,500 years to about 6,800 years due to its recent perihelion passage—positions it for potential re-detection in the distant future, facilitating long-term studies of stability and evolution under gravitational influences.

Cultural Impact

Comet NEOWISE captured the imagination of creators worldwide during its 2020 apparition, inspiring a range of artistic and entertainment works that highlighted its ethereal beauty and timely appearance amid global challenges. In film, the 2021 satirical comedy , directed by , features a fictional comet named Dibiasky that was very loosely modeled after NEOWISE, drawing on the real comet's unexpected discovery and visibility to underscore themes of cosmic threats and human response. 's coverage included educational videos such as the "NASA Science Live: How to Spot Comet NEOWISE" broadcast, which explained the comet's path and observation tips, and a stunning 4K time-lapse from the showing NEOWISE rising above Earth. In music, independent artists released tracks evoking the comet's transient glow. , the project of , composed the instrumental piece "July 22, 2020: C/2020 F3 - Comet Neowise," part of the Astronomy, Vol. 2 series, using ambient sounds to mimic the comet's distant journey and 's perspective, released on July 22, 2020, coinciding with NEOWISE's closest approach to . Composer David Joseph Wesley created the album Apparition (Music for Comet NEOWISE), a collection of atmospheric electronic pieces inspired by the comet's tail and nocturnal visibility, available in high-resolution audio formats. Literature saw NEOWISE woven into short fiction and poetry as a metaphor for wonder and ephemerality. In the October 2020 issue of Lilith Magazine, the short story "The Neowise Comet Listens In" by Carolivia Herron blends the comet's voice with a narrative of personal reflection during the pandemic, portraying it as an impartial observer of human turmoil. Poems depicted NEOWISE as a "rare wonder" eliciting awe. Visual artists produced digital and photographic works integrating NEOWISE into landscapes and surreal scenes. On , creators like Aerroscape shared digital paintings of the comet streaking over starry skies, emphasizing its vibrant tail in stylized hues beyond photographic realism. Memes proliferated on platforms like , often editing NEOWISE into humorous pop culture contexts, such as superimposing it over fictional or portraits to play on its "celebrity comet" status. One notable integration occurred in the desert, where NEOWISE appeared above Ugo Rondinone's "Seven Magic Mountains" installation, blending natural spectacle with contemporary . Amid the , NEOWISE symbolized hope and resilience in editorials and trends, emerging as a "bright spot" during lockdowns and offering a shared celestial distraction. photographers highlighted this in year-end reviews, describing the comet as a of amid global uncertainty, with images of it illuminating darkened skies evoking renewal. Its inclusion in 2020 recap lists by outlets like reinforced its role as a less ominous harbinger compared to historical comets, instead representing scientific and communal stargazing.

Public and Media Response

The appearance of Comet NEOWISE in July 2020 generated significant media attention, with major outlets providing extensive coverage on its visibility and observation tips. published multiple articles, including guides on spotting the comet with the and featuring photographs from around the world, highlighting its status as the brightest comet of the year. Similarly, the reported on sightings across the UK, such as images of the comet over , and offered instructions for public viewing in the . contributed to the frenzy through live broadcasts, including a July 14, 2020, event where experts discussed the comet's approach to perihelion and fielded public questions. Public engagement surged, with astronomy organizations hosting viewing events to capitalize on the comet's peak naked-eye visibility. The Adler Planetarium in organized a live online observing session on July 17, 2020, guiding viewers on locating NEOWISE in the evening sky. Local clubs, such as the Astronomy Club of Asheville, encouraged member participation in observations and shared community-submitted photographs of the comet's tail. Apps and tools for sky tracking, including those from astronomy societies, saw increased use as enthusiasts followed the comet's path across constellations like . Social media platforms amplified the excitement, with NEOWISE becoming a as users shared images and videos of the comet. Posts on and proliferated, turning the event into an "Instagram star" and filling feeds with global sightings from backyards to remote landscapes. promoted citizen contributions by featuring public photos in its galleries and through live streams, fostering widespread participation in informal sharing. The #CometNEOWISE trended as stargazers documented the comet's glow against twilight skies, contributing to heightened online discussions about astronomy. Educational initiatives leveraged the comet's visibility to engage broader audiences, particularly through virtual programs amid the . NASA's "Science Live" series included a July 15, 2020, webinar on spotting NEOWISE, aimed at families and students to explain cometary orbits and observation techniques. The British Astronomical Association hosted a dedicated webinar in September 2020, reviewing public observations and providing resources for schools to incorporate the event into curricula. These efforts sparked interest in celestial events, with reports noting a surge in online searches and community astronomy activities.

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