Comets often pass through our sky, but not many comets can crack the brightness of the naked eye. This is why it is worth noting when a person approaches or exceeds this threshold.

Now, it's time to pay attention to Comet C/2021 A1 (Leonard), which is the closest to Earth this week. According to reports, the magnitude of Leonard's Comet is about 5.5 to 6—if you are in a dark place with little light pollution, it will be brighter than the naked eye threshold. Even if you can't reach the perfect observation point, you can easily see Leonard with binoculars or telescopes.

Even better, it is about to transform from a pre-dawn scene to an evening scene, which means you don't need to be an early riser or night owl to see the best comet of 2021.

As the name suggests, Leonard's Comet was discovered by Gregory Leonard in January of this year. He found it in an image taken by the Mount Leman Observatory in Arizona. This discovery occurred at the comet’s calculated perihelion—the closest distance to the sun—about a year before January 3 of the next month. Now, Comet Leonard is approaching the earth as it flies towards the intersection with the sun, and it will make the closest pass to our planet on December 12.

Leonard is a long-period comet from the outer solar system. Its aphelion distance (the point farthest from the sun) is about 3,700 astronomical units (AU), of which 1 AU is the average distance between the earth and the sun. Its orbital period is approximately 80,000 years. But this is about to change: current calculations indicate that the comet will be ejected from the solar system after passing the sun, destined to fly through interstellar space and never return. Maybe one day it will pass through another star system light-years away, just as the interstellar objects 1I/'Omuamua and 2I/Borisov recently passed through our own solar system. 

In the next few days, it is best to see Comet Leonard in the early morning before sunrise. To find it, look east one to two hours before sunrise. It will climb to the highest point of the sky before dawn, but the sky will also be the brightest at that time.

Below is a telescope star finder showing the path of Comet Leonard that was moving fast in the morning sky before December 12. Note that it will pass through several constellations in just a few days-if you take the time to observe the comet for an hour or so, you may notice it moving against the background stars in one observation. Before Leonard left the morning sky, it also had a nice photo with several globular star clusters: M12, M10, and M14.

If you want to get a rough idea of ​​the height of the sky, check out the chart below, which shows the approximate position of the comet about 30 minutes before sunrise in the Midwestern United States. Please note that this chart shows the approximate position of the constellations, such as December 10 The location of Mars and any bright stars; depending on the date and time, these signposts may appear slightly higher or lower in your sky. In other words, this chart is not as accurate as the telescope viewfinder chart above.

On the 12th, it was time to switch to the evening observation to get the best view of Leonard's Comet. At this time, it is best to go out at sunset to look for a comet in the southwest direction, because it passes Venus and Mercury first, and then Saturn and Jupiter.

Below is a chart of telescope discoverers showing the path of Comet Leonard on the night of December 12-17. The next chart continues to show its night movement through December 31. We split them into two graphs, because Leonard is still fast traversing the mid-month sky, and then slows down later in December. In addition, if you want to do some deep-sky photography, remember that Leonard passes near M16 in the middle of the moon—and a little further away from M23, M21, M25, and M22.

To give you an idea of ​​where you are in the sky, below is a chart showing Leonard's altitude above the horizon in the evening in late December. The positions of constellations, stars, and planets are displayed about 30 minutes after sunset on December 25; they may appear at different altitudes depending on the date and time of your observation (comets may be in different constellations). Again, this chart is not as accurate as the telescope viewfinder chart above.

Depending on the size, time, and location of the comet, you may hardly be able to spot a faint, fuzzy patch with the naked eye. If not, just use binoculars or telescopes to locate the comet. When using optical aids, the comet should highlight the background well. No matter how it looks to the naked eye, this comet is best seen in photos. So, it's time to pick up your camera-or your smartphone-to take some pictures!

In the next few days, Leonard should get brighter, reaching the brightest between December 12th and December 14th. After that, the comet is expected to weaken to about 8th magnitude at the end of this month. However, this is still a great binoculars or telescope sight, so don't stop following it, even if it starts to fade. 

Once Leonard leaves, keep your excitement about the comet-it will serve you early next year. In April, Comet C/2021 O3 (panstar) may explode bright enough to be in phase with Mercury in the sky Comparable.

Of course, as we all know, the behavior of comets is difficult to predict—do you remember the disappointing split of C/2019 Y4 (ATLAS) as it revolves around the sun, taking away the chance that we may be the brightest comet in 20 years to pass the earth? ?

So the best thing we can do is to keep our fingers crossed-enjoy our current good luck, because Comet Leonard continues to traverse the sky in December.

Learn about the latest details about Leonard's comet and other celestial landscapes by checking out our weekly observation column "Sky of the Week".

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