Why comets are bright

I've been eager to observe it myself so I can get a sense of the very thing you want to know, but we've had more than a week of overcast skies here.

It should clear by the weekend, and I'll add my observation to the post. On December 3rd it will pass only about 6' from the center of the globular cluster, practically the comet's nucleus will be in the edge of the cluster. I've had to wait a long time to try for it, as it has been sitting in the worst of the KC light dome for weeks, and the moon has been in the way.

It was only 42 degrees above the horizon at azimuth 75 degrees - right in the top of the light dome - and as I have seen a bit of variance in its reported magnitude on COBS, I had no idea what to expect. Picked it up with averted vision; it looked about mag This Week's Sky At a Glance. By: Alan MacRobert November 12, Save Dark Skies. By: Diana Hannikainen November 11, By: Bob King November 10, By: Camille M. Carlisle November 9, By: Jennifer Willis November 8, By: Alan MacRobert November 5, Astronomy in Space with David Dickinson.

By: David Dickinson November 4, Stellar Science. By: Jure Japelj November 3, By: Monica Young November 3, Constant Contact Use. Emails are serviced by Constant Contact. Now at magnitude 12 and moderately condensed, the comet is bright enough for amateurs to seek before dawn.

Michael Mattiazzo. Comet Leonard moves rapidly southeast across the morning sky in early December, disappearing in the solar glow by the 12th. Positions are shown every three days with stars to magnitude 6. Stellarium with additions by Bob King. It turned out that the comet was "new," never having passed near the Sun before.

Only its volatile surface ices sublimated, which led to a temporary surge that fanned unrealistic expectations. This map plots Comet Leonard during its slow trek across southern Ursa Major near the 5th-magnitude star 61 Ursae Majoris 61 UMa in the finder map here nightly through October 29th. Brighter stars are labeled with magnitudes with decimals omitted.

Chart details appear at upper left. Megastar, used with permission. In another image taken on October 10, , Comet Leonard glowed at magnitude As a comet gets closer to the sun, the ice on the surface of the nucleus begins turning into gas, forming a cloud around the comet known as the coma. According to science website howstuffworks. Surrounding the coma is a hydrogen envelope that can be up to 6. As the comet gets closer to the sun, the hydrogen envelope gets bigger.

There are two main types of comet tails, dust and gas. Comet tails are shaped by sunlight and the solar wind and always point away from the sun according to Swinburne University of Technology. According to NASA, comet tails get longer as a comet approaches the sun and can end up millions of miles long.

The dust tail is formed when solar wind pushes small particles in the coma into an elongated curved path. Whereas the ion tail is formed from electrically charged molecules of gas. Comet tails may spray planets, as was the case in with Comet Siding Spring's close encounter with Mars. We can see a number of comets with the naked eye when they pass close to the sun because their comas and tails reflect sunlight or even glow because of energy they absorb from the sun.

However, most comets are too small or too faint to be seen without a telescope. Comets leave a trail of debris behind them that can lead to meteor showers on Earth. For instance, the Perseid meteor shower occurs every year between August 9 and 13 when Earth passes through the orbit of Comet Swift-Tuttle.

Astronomers classify comets based on the durations of their orbits around the sun. Short-period comets need roughly years or less to complete one orbit, long-period comets take more than years, and single-apparition comets are not bound to the sun , on orbits that take them out of the solar system, according to NASA.

Recently, scientists have also discovered comets in the main asteroid belt — these main-belt comets might be a key source of water for the inner terrestrial planets.

Scientists think short-period comets, also known as periodic comets , originate from a disk-shaped band of icy objects known as the Kuiper Belt beyond Neptune's orbit, with gravitational interactions with the outer planets dragging these bodies inward, where they become active comets.

Long-period comets are thought to come from the nearly spherical Oort Cloud even further out, which get slung inward by the gravitational pull of passing stars.

In , scientists found there may be seven times more big long-period comets than previously thought. Some comets, called sun-grazers, smash right into the sun or get so close that they break up and evaporate. Some researchers are also concerned that comets may pose a threat to Earth as well.

Comets are generally named after their discoverer. For his Ph. He faced a tall order. Each image was so massive, displaying just one at full resolution would require a grid of HD televisions. Bernardinelli scoured tens of thousands of these images for dots of light a few pixels wide. As a final step, Bernardinelli and Bernstein checked this list by hand to make sure the code did its job correctly. On June 19, the center confirmed that the object was a new discovery. In a matter of days, astronomers all over the world began turning their telescopes toward the incoming object and scouring their archives for any other images of it that had gone unnoticed.

Researchers soon found the comet hiding in archival data as far back as , improving the accuracy of its known orbit. And within 24 hours of the announcement, multiple teams of astronomers had confirmed that the comet was releasing enough dust and gas to make a visible coma, or tail, even though it was still more than two billion miles from the sun. More clues about its tail came from images taken in and by TESS, an exoplanet-hunting space telescope operated by NASA that also captured images of the incoming comet.

Eventually, they found an extremely faint signal hiding in their data—and learned that the comet had started giving off gas as far as 2. Given how feeble sunlight is at this extreme distance, the comet must either be giving off carbon dioxide or nitrogen gas, they found.

Scientists are already brainstorming what it would take to visit Bernardinelli-Bernstein with a spacecraft. Peering any deeper into the past, however, is extremely difficult. Oort cloud comets are so far away, their orbits can be nudged by passing stars, which means that modeling their orbits requires charting the motion of stars through the Milky Way.

For several years, researchers have known that about 2. But no one knows exactly where it flew by. Observations as the comet gets closer might also change its expected size. The mile estimate is based on its current brightness, as well as models of the dust and gas the comet gives off. But calculating comet size using this method is a tricky business. The Vera C. Rubin Observatory in Chile, set to come online in , will be able to track the object for at least the next decade, if not longer.

Along the way, the state-of-the-art telescope will transform our view of the solar system—and likely uncover many more comets like Bernardinelli-Bernstein.