So far in 2020, two comets have come our way (Comet SWAN and Comet ATLAS) with the promise of putting on a nice show, but both broke apart before they reached their closest point to the Sun.
Now, a third comet is approaching the Sun, but unlike the first two, this one looks like it will remain intact when it swings closest to the Sun (called “perihelion”) on July 3rd.
Update: Comet NEOWISE has lived up to expectations with numerous sightings shared on social media!
This comet bears the name of the satellite that discovered it on March 27th: NEOWISE, an acronym for Near Earth Object Wide-field Infrared Survey Explorer, used to assist NASA’s efforts to identify and characterize the population of near-Earth objects, such as asteroids. And occasionally, as in this case, it also can discover a comet.
Fun Fact: Comet NEOWISE’s nucleus is 5 km (over 3 miles) across!
When it was first discovered, NEOWISE (Catalogued as C/2020 F3) was shining about 25,000 times fainter than the faintest star that can be glimpsed with the naked eye, and accessible only with large telescopes.
However, during the spring, observers in the Southern Hemisphere noted this object got brighter as its distances from both the Sun and Earth decreased. From May 10th to June 7th, its brightness increased 12-fold. As projected on the sky, the comet and the Sun were rapidly closing together and shortly thereafter the comet was lost in the Sun’s brilliant glare.
But the comet was moving within the range of the orbiting NASA’s Solar and Heliospheric Observatory (SOHO), a space probe which is monitoring the Sun from an orbit roughly 930,000 miles (1.5 million km) sunward of Earth. From this orbit, SOHO is able to observe the Sun 24 hours a day. Using its Large Angle and Spectrometric Coronagraph (LASCO-3) which creates an artificial solar eclipse, NEOWISE could be monitored as it passed near to the Sun.
On June 22nd, the comet appeared to significantly brighten, and on June 27th, just before it passed out of the field of the LASCO-3 camera, it had become 100 times brighter compared the last visual views of it less than three weeks before. It also appeared to have developed a rather bright, albeit short and stubby forked-shaped dust tail.
Contentious Comet Forecasts
The comet is currently out of sight due to its proximity to the solar glare. When it is closest to the Sun on July 3rd, the comet will be 27.3 million miles (44 million km) from the Sun, when it will be well-cooked and subjected to temperatures of up to 1100° F (593° C). Thereafter, rapid motion to the northeast and then east will quickly carry it away from the Sun.
According to the latest prediction from by the Harvard-Smithsonian Center for Astrophysics and the British Astronomical Association, the comet might peak near 0 magnitude, placing it at a brightness ranking it among the brightest stars in the sky.
A Word of Caution?
When a comet brightens this quickly it could be a sign that the nucleus is unstable. Comet NEOWISE might yet disintegrate.
However, Michael Mattiazzo, an amateur comet observer based in Australia, thinks that Comet NEOWISE has a better shot of surviving its closest approach to the Sun compared to the previous two comets which broke up and completely faded out of view. “I’d say there’s a 70 percent chance this comet will survive perihelion,” notes Mattiazo, adding. “Comet NEOWISE could be a case of ‘third time lucky.’”
But others are not so sure.
Comet expert, John E. Bortle, for one, is raising a red flag. “I’m getting the sinking feeling that once again folks are going to start anticipating a spectacular show. Of course, I could be dead wrong and a nice display may be in the offing, but I fear that we are crying wolf once again.”
When and Where to Look
In short, nobody knows what will emerge from out of the twilight sky. The brightness of a comet depends on several factors and is not easily predictable.
The first views of NEOWISE could come as early as July 5th or 6th in the morning sky, very low above the northeast horizon. By around July 11th, the comet will reach an altitude of nearly 10 degrees (10 degrees is roughly equal to the width of your fist held at arm’s length). Then over the next ten days it will gradually slide back down toward the north-northeast horizon, eventually disappearing from dawn visibility.
A far-better viewing opportunity will come in the evenings starting around July 12th, low in the west-northwest sky. In the evenings to follow, the comet will rapidly climb higher in the sky. On the 22nd, NEOWISE will make its closest approach to the Earth, a distance of 64 million miles (103 million km). By the 25th, the comet will appear 30 degrees (“three fists”) up from the west-northwest horizon as darkness falls.
Although on successive July evenings the comet will grow intrinsically fainter, it will be farther from Sun, setting later and visible in a darker sky.
Perhaps the best overall view will come in the evenings between July 14th and 19th, when the comet will stand 10 to 15 degrees above the west-northwest horizon. It should be shining as bright as the six brightest stars in the Big Dipper with a gently curving tail pointed upward and to the right from the comet’s star-like head.
Get The Best View Possible
But if the comet falls short of the forecasts, little or nothing may be seen. Prospective comet watchers should seek the most favorable conditions possible. Even a potentially bright comet, like this one, can be obliterated by thin horizon clouds, haze, humid air, smoke, twilight glow, city lights, or moonlight. Binoculars are recommended for locating it.
Comets: Dirty Snowballs
Comets far out in space might be thought of as gigantic “snowballs” made of frozen gases, chunks of rock, and dust. As a comet comes closer to the Sun, it is warmed and gradually, the frozen gases sublimate, going directly from a frozen state to a gaseous vapor. The vapors are then excited by the ultraviolet light from the Sun and begin to glow as does fluorescent paint.
Emissions from the Sun strike the particles of dust and glowing gas, causing some of this material to be “blown” back from the head of the comet to become its tail. The comet’s gaseous substances—methane, ammonia, water vapor and others—are so filmy that if compressed, they could be squeezed into an ordinary suitcase and carried down the street.
Though Comet NEOWISE might not seem spectacular to the average person, it is already considered unusually bright by astronomers. After it rounds the Sun, it will head out from the inner part of the solar system, increasing its distance from the Sun each day, presumably returning to the “happy hunting grounds” of comets on the outer fringes of the solar system. It is expected to return to the Sun’s vicinity again in about 6,800 years!
If you’re out looking for NEOWISE in the coming days, good luck, and here’s hoping for clear skies!