Bidding farewell to a fine comet

Fiber-optic star trails, fireflies, the ISS & NEOWISE. July 17, 2020. This photo is a 52-minute star trail made from 526 consecutive shots, each six seconds long, ISO 800, 15mm at f/2.8, Nikon D810. Photo by Alan Studt.

Comet C/2020 F3 (NEOWISE) was the finest comet to grace the skies of the Northern Hemisphere in quite some years. Amateur astronomers and photographers the world over made fascinating observations and beautiful images of the comet and its surprisingly long tail. 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. or about three miles; that’s a reasonably large size but around average for a comet. The large nucleus offered plenty of volatile materials for the Sun to stir into tail formation.

On July 23 the comet reached perigee with Earth and is now speeding toward the outer Solar System, not to revisit the inner planetary neighborhood for several thousands of years. So, though relatively near Earth the object is fading fast. Lately astronomers and astrophotographers have been grabbing the last views they will have of C/2020 F3 before it fades to obscurity.

Here are some photos made by members of the Cuyahoga Astronomical Association (CAA) as a cometary farewell of sorts:

C/2020 F3 NEOWISE as viewed from Veteran’s Memorial Park in Avon Lake just before 11 p.m., July 24, 2020. Photo by Alan Studt.

Alan Studt’s lovely portrait of the comet shows its tails remain, if faded, long and expansive. He wrote, “Beautiful night by the lake last night. Took these at Veteran’s Memorial Park in Avon Lake just before 11 p.m. Pretty large group of people hanging out. The comet was definitely much dimmer than the previous Friday.”

Technical Information: Tamron 70-200mm f/2.8 lens, on a Nikon D850.
The comet image is made from 14 shots (2.5 seconds, ISO 10,000, at 200mm, f/2.8). Stacked in Deep Sky Stacker & post processed in Lightroom and Photoshop. Seventy-five shots but got the best star field alignment using only 14 shots. Also used dark & flat frames.
C/2020 F3 NEOWISE as viewed from Letha House Park in Medina County, Ohio, at 10:36 p.m. July 24, 2020. Photo by James Guilford.

James Guilford was at Letha House Park, July 24, attempting to record detailed images of the comet nucleus and close tail. The green coloration of the comet was a surprise to him, even after reading the observations of others. “All of my comet shots Friday night show a green nucleus,” Guilford said, “and it grew brighter as I processed the images later. I’d have liked to have picked up more of the tail but, given the circumstances, I’m pretty happy with what I got.” Both he and other Letha House Park observers could see a green tint by eye through telescopes. He and others also report the comet was barely within the range of eyesight but only at its highest above the horizon and only via averted vision.

Technical Information: Canon EOS 6D Mk. 2, at prime focus of 1800mm FL Cassegrain telescope, eight light exposures plus darks, ISO 1250, 15 seconds per exposure, stacked in Starry Sky Stacker, processed in Photoshop.

C/2020 F3 NEOWISE nearly lost amongst the stars. Photo by Jon Salontay.

Jon Salontay also photographed the comet that Friday. Above we see how it is nearly lost, even to the camera, amongst the stars. Technical Info.: Time – 11:32 p.m., Canon T5i with 18-75mm zoom lens at 18 mm, exposure 30 seconds at F/5.6, ISO 800. Brightness & Contrast adjusted.

C/2020 F3 NEOWISE via telescope. Photo by Jon Salontay.

Salontay then turned his telescope on the “dirty snowball.” Technical Info.: Time – 12:13 a.m., July 25. Celestron 8-inch SCT on Advanced VX Mount, Canon T5i, 15 seconds, ISO 1600. No out-of-camera adjustment.

He wrote, “Although I’ll try to follow it telescopically over the next month, how about another comet before the year is out? It’s a lot of fun.”

Penumbral Lunar Eclipse: July 4 – 5

NASA Solar and Earth images, illustration by James Guilford.
A penumbral lunar eclipse occurs when the Moon passes through the thin outer portion of the shadow Earth casts out into space.

We’re fortunate that the night of July 4 is expected to be clear, and not just for the traditional booms and flashes of celebratory fireworks. Our Moon is getting in on the act, albeit with a much more subtle display in the form of a penumbral eclipse. The eclipse will take place from 11:07 PM to 1:52 AM EDT with maximum eclipse at 12:31 AM July 5.

We say subtle because, unlike a total lunar eclipse, Earth’s Moon will not change to reddish/coppery colors. The Moon will instead become oddly shadowed for a Full Moon, as it enters the outer fringes of Earth’s shadow in space — the penumbra. Only the “top” portion of Luna will pass through the penumbra making this eclipse especially slight. Still, it’s worth a look and it won’t be at a particularly late hour. A deeper penumbral lunar eclipse will take place the night of November 30, 2020.

Moon is eclipsed when it passes through Earth's shadow. Credit: SkySafari / J. Guilford
Earth’s shadow runs away from the Sun into space and has two parts: the deep inner shadow or umbra, and the thin outer portion called the penumbra. The Moon is eclipsed when it passes through Earth’s shadow. Credit: SkySafari / J. Guilford

While it’s possible to view this eclipse with the unaided eye, binoculars will provide an enhanced view as would a small telescope.

Penumbral Lunar Eclipse of July 4 – 5, 2020 at Maximum Eclipse: 12:31 AM EDT. Simulation via SkySafari

And just in case there’s any confusion, lunar eclipses are perfectly safe to view and photograph — it’s moonlight — so nothing to worry about there.

If you shoot any photos or have impressions to share with us, you can do so via our Twitter — @Cuyastro

Penumbral Lunar Eclipse of July 4 – 5, 2020. Credit: NASA

NASA Eclipse Page available here: Penumbral Lunar Eclipse of July 4 – 5, 2020.


March 9 Membership Meeting and a visit to Mauna Kea (by a member)

Panorama of the Mauna Kea Observatories by Frank Ravizza.
Panorama of the Mauna Kea Observatories. Photo by Frank Ravizza. Used under Creative Commons License.

The monthly general membership meeting of the Cuyahoga Astronomical Association will take place March 9, 2020 from 7:30 to 9:00 p.m. CAA Member and Vice President Tim Campbell will present his talk, “Mauna Kea: Telescopes above the Clouds!” — his visit to Hawaii’s Mauna Kea mountaintop observatories (MKO). Several major telescopes are located there at 14,000 feet above sea level. Mauna Kea is one of the most important sites in Earth-based astronomy and Campbell will take attendees on a detailed tour!

The CAA’s monthly meetings are held on the second Monday of every month except December at 7:30 p.m. in the Cleveland Metroparks’ Rocky River Nature Center; 24000 Valley Parkway; North Olmsted, Ohio. Meeting programs are open to the public. Following the presentation and a brief social break, the club will conduct its membership business meeting.

Asteroid Hygiea could be classified as a dwarf planet

Image: Asteroid/Dwarf Planet Hygiea. Credit: ESO/P. Vernazza et al./MISTRAL algorithm (ONERA/CNRS)
A new SPHERE/VLT image of Hygiea, which could be the Solar System’s smallest dwarf planet yet. As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighbourhood around its orbit. The final requirement is that it have enough mass that its own gravity pulls it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea. Credit: ESO/P. Vernazza et al./MISTRAL algorithm (ONERA/CNRS)

Astronomers using ESO’s SPHERE instrument at the Very Large Telescope (VLT) have revealed that the asteroid Hygiea could be classified as a dwarf planet. The object is the fourth largest in the asteroid belt after Ceres, Vesta and Pallas. For the first time, astronomers have observed Hygiea in sufficiently high resolution to study its surface and determine its shape and size. They found that Hygiea is spherical, potentially taking the crown from Ceres as the smallest dwarf planet in the Solar System.

As an object in the main asteroid belt, Hygiea satisfies right away three of the four requirements to be classified as a dwarf planet: it orbits around the Sun, it is not a moon and, unlike a planet, it has not cleared the neighborhood around its orbit. The final requirement is that it has enough mass for its own gravity to pull it into a roughly spherical shape. This is what VLT observations have now revealed about Hygiea.

“Thanks to the unique capability of the SPHERE instrument on the VLT, which is one of the most powerful imaging systems in the world, we could resolve Hygiea’s shape, which turns out to be nearly spherical,” says lead researcher Pierre Vernazza from the Laboratoire d’Astrophysique de Marseille in France. “Thanks to these images, Hygiea may be reclassified as a dwarf planet, so far the smallest in the Solar System.”

The team also used the SPHERE observations to constrain Hygiea’s size, putting its diameter at just over 430 km. Pluto, the most famous of dwarf planets, has a diameter close to 2,400 km, while Ceres is close to 950 km in size.

Surprisingly, the observations also revealed that Hygiea lacks the very large impact crater that scientists expected to see on its surface, the team report in the study published today in Nature Astronomy. Hygiea is the main member of one of the largest asteroid families, with close to 7,000 members that all originated from the same parent body. Astronomers expected the event that led to the formation of this numerous family to have left a large, deep mark on Hygiea.

“This result came as a real surprise as we were expecting the presence of a large impact basin, as is the case on Vesta,” says Vernazza. Although the astronomers observed Hygiea’s surface with a 95 percent coverage, they could only identify two unambiguous craters. “Neither of these two craters could have been caused by the impact that originated the Hygiea family of asteroids whose volume is comparable to that of a 100 km-sized object. They are too small,” explains study co-author Miroslav Brož of the Astronomical Institute of Charles University in Prague, Czech Republic.

The team decided to investigate further. Using numerical simulations, they deduced that Hygiea’s spherical shape and large family of asteroids are likely the result of a major head-on collision with a large projectile of diameter between 75 and 150 km. Their simulations show this violent impact, thought to have occurred about 2 billion years ago, completely shattered the parent body. Once the left-over pieces reassembled, they gave Hygiea its round shape and thousands of companion asteroids. “Such a collision between two large bodies in the asteroid belt is unique in the last 3–4 billion years,” says Pavel Ševeček, a PhD student at the Astronomical Institute of Charles University who also participated in the study.

Studying asteroids in detail has been possible thanks not only to advances in numerical computation, but also to more powerful telescopes. “Thanks to the VLT and the new generation adaptive-optics instrument SPHERE, we are now imaging main belt asteroids with unprecedented resolution, closing the gap between Earth-based and interplanetary mission observations,” Vernazza concludes.