Comet is the star of the show

Experts on Point is a University Communications series focusing on CMU faculty who have special insights into interesting, important and timely topics.

One of the brightest comets in more than 20 years is now appearing in the night sky, and Central Michigan University Physics faculty member Axel Mellinger has captured it for all to see.

Mellinger, who enjoys photographing the night sky in his spare time, created a time-lapse video of Comet NEOWISE from 327 photos he took over 35 minutes from a parking lot on the west side of Mount Pleasant.

The comet takes its name from NASA's NEOWISE space telescope, which discovered it in March. It made a close approach to the Sun on July 3 — closer even than planet Mercury. Unlike many other comets, this one survived the Sun's intense heat and developed an impressive dust tail, along with a fainter blue gas/ion tail. For the next few days, the comet will visible to the naked eye at around 11 p.m. in the northwest sky.

Don't miss it, Mellinger advises, as it will not be back for another 6,800 years.

Mellinger joined CMU in 2008 after postdoctoral stays at the University of California, Berkeley, and the University of Potsdam, Germany. He studies electret materials and currently is the secretary of the IEEE Dielectrics and Electrical Insulation Society We spoke with him about the comet and his video.

Q: What is a comet, and what makes it visible as it approaches the sun?

A: Comets are "dirty snowballs" or "icy dustballs," typically a few miles in diameter and composed of dust, rocks, water ice, and various other frozen gases, such as carbon dioxide and methane. They spend most of their time in the outer parts of the solar system, but when they approach the Sun, the frozen gases sublimate, freeing the dust. This produces a giant atmosphere, called a "coma," and tails up to 100 million miles long. The gases are ionized and blown away by the "solar wind," a stream of charged particles emitted by the Sun, forming a bluish, straight ion tail. The heavier dust particles are blown outward by radiation pressure from sunlight. The dust tail often looks yellowish-orange and is slightly curved.

Q: How rare is it for a comet to be visible to the naked eye?

A: While dozens of comets are discovered each year, naked-eye comets only appear once every few years, and really bright ones are even rarer. The last "great" comets visible in the Northern Hemisphere were Hale-Bopp in 1997 and Hyakutake in 1996. You can find a list of currently observable comets at aerith.net and cometwatch.co.uk.

Q: What do we know about Comet NEOWISE specifically?

A: Comet C/2020 F3 NEOWISE was discovered in March 2020 by a repurposed NASA space probe, launched in December 2009 to survey the sky in the infrared spectrum. The comet orbits the Sun on a highly elliptical path once every 6,800 years. It presents no danger to Earth — even at its closest approach on July 23 it will still be 64 million miles away.

Q: What can we learn about our solar system from comets?

A: Since they spend most of their time in the cold, outer regions of the solar system, comets are thought to preserve the composition of the "primordial" material that the solar system was made of. This was highlighted in 2014, when the European Space Agency's Rosetta probe orbited a comet and found deuterium — a heavy hydrogen atom with an extra neutron — at concentrations three times higher than in ocean water on Earth. Therefore, the Earth's water likely was not supplied by impacting comets.

Q: What advice can you offer for viewing, photographing or video recording the comet?

A: Comet NEOWISE is now visible in the evening sky. Don't wait too long to look for it, as it is already fading. Find a spot away from city lights with an unobstructed northwest horizon, and look in the area between the Big Dipper and the horizon (see the star chart below). The best time is around 10:30-11:30 p.m. Using a pair of binoculars or a small telescope will make the tail stand out better.

To photograph the comet, mount your camera on a tripod, since you will need exposure times of several seconds. Raise the camera's ISO setting to near maximum. Generally, DSLR cameras with their large sensors produce better images than cellphones. To create a time-lapse video, you will need to shoot hundreds of images and later combine them with video editing software.