Even those not normally interested in astronomy will find it hard to resist NEOWISE, the brightest comet to grace our skies since the 1997 appearance of Comet Hale-Bopp. The spectacular cosmic snowball of frozen gas, rock, and dust has been visible to those willing to wake up before dawn since early July. However, it has now risen high in the evening skies and can be viewed with the unaided eye by even the most casual stargazer.
The comet is named after NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE), which first detected it on March 27, 2020. NEOWISE hails from the outer reaches of the solar system known as the Oort Cloud, a graveyard of hundreds of billions of the icy bodies. While most drift in blissful isolation, every so often, something disturbs the orbit of one of these frozen worlds, and it begins a long journey toward our Sun.
Given that it takes thousands of years for them to reach the inner solar system, an opportunity to view a long-period comet like NEOWISE, which has a 6,800-year-long orbit, is rare to begin with. What makes it even more so is that most comets plunge directly into the Sun and disintegrate into dust.
Fortunately for us, Comet NEOWISE emerged relatively unscathed after its closest encounter with the Sun (perihelion) on July 3, 2020, at a distance of 27 million miles (43 million kilometers). As expected, the Sun's heat caused some of the comet's frozen gas and dust to vaporize and spread out behind its nucleus. While this usually results in one visible tail, images of Comet NEOWISE, captured by NASA's Parker Solar Probe (PSP) on July 5, 2020, clearly show twin tails.
"Comet NEOWISE actually has two distinct tails, one of gas and one of rocky dust, that point in slightly different directions because they react differently to the movement of the comet and the solar wind of charged particles that stream from the Sun," explains astrophysicist Karl Battams of the U.S. Naval Research Laboratory in Washington, DC.
Besides putting on a dazzling show, comets like NEOWISE, which are remnants from our solar system's creation, can also provide scientists with important clues about our origins.
"From its infrared signature, we can tell that it is about 5 kilometers [3 miles] across, and by combining the infrared data with visible-light images, we can tell that the comet's nucleus is covered with sooty, dark particles leftover from its formation near the birth of our solar system 4.6 billion years ago," said Joseph Masiero, NEOWISE deputy principal investigator at NASA's Jet Propulsion Laboratory in Southern California.
Though Comet NEOWISE, which is now headed back toward the outer solar system, will be visible for a few weeks, experts at Space.com believe the best time to seek out this rare visitor is from July 14, 2020, to July 19, 2020. The icy world will slowly start to fade from sight after its closest approach to Earth on July 22, 2020, when it will come to within 64 million miles of our planet.
To see the comet, look below the Big Dipper in the northwest horizon about an hour and a half after sunset. Though the Moon, which will be a waning crescent and visible only in the morning sky through July 20, will not steal Comet NEOWISE's thunder, NASA experts recommend finding an area away from city lights with an unobstructed view of the sky. While NEOWISE, which will look like a faint star with a short tail, will be visible to the unaided eye, binoculars or a small telescope will significantly enhance the display.
Comet NEOWISE is not the only celestial delight in store for stargazers this month. On Sunday, July 19, 2020, about 45 minutes before sunrise, Mercury, Venus, Mars, Jupiter, Saturn, and a beautiful crescent moon will all be visible simultaneously, without the need for a telescope! Astronomy educator Jeffrey Hunt told CNET, "Step outside early in the morning, at least an hour before sunrise. Find the four bright planets -- Venus, Mars, Saturn, and Jupiter. They look like overly bright stars. Brilliant Venus is low in the east-northeast. Mars is the lone 'star' in the southeast, and Jupiter and Saturn are the stars in the southwest. To your eyes, they won't look like the photos made by spacecraft, just overly bright stars."
Happy stargazing! Be sure to share your experience with us by writing your comments below.
Resources: Space.com, NASA.gov.