Comet C/2021 T4 Lemon streaks across the southern sky

This space view is from 20° north of the ecliptic plane and 235° longitude. Grid lines in the plane are 1 astronomical unit (AU), the distance between the Sun and the Earth. The ram’s horn symbol represents the spring (March) equinox. The size of the earth is 500 times and the sun is 5 times exaggerated. The rods connect Comet C/2021 T4 Lemmon to the ecliptic plane at the beginning of each month in 2023. Image copyright Guy Ottewell. Used with permission.

Famous British astronomer Guy Ottewell This piece on Comet C/2021 D4 Lemon was originally published on May 25, 2023.. Reprinted with permission. Earthsky’s revisions.

Comet C/2021 T4 Lemon

Comet C/2021 T4 Lemmon was discovered in images taken on October 7, 2021. Mount Lemon ObservatoryNortheast of Tucson in Arizona. T4 The 4th in the first half of October means discovery or recovery.

Mount Lemon is the highest point of the Santa Catalina Mountains, one of the four mountain ranges surrounding Tucson. This is not to be confused with Catalina, the conspirator who tried to seize power over the Roman Republic in 63 BC. I am reminded of my speculation that the Navajo may have seen Canopus, the great star of the south, from one of the four sacred peaks around their land. In fact, it is shown as a cover image Astronomical Calendar 2023.

When discovered, Comet C/2021 T4 appeared far north, at an inclination of +12° due to the geometry of its orbit.

Comet C/2021 T4 Lemmon is a long-period comet

In fact, it is a long-lived comet; If it ever fell from its distant home – at 44,000 AU – to the inner solar system, it would have been millions of years ago. So at its current passage, it will feel gravity disruptions From planets that reduce its period to mere thousands of years.

Its orbit is inclined about 20° to the plane of the ecliptic. However, it goes in a retrograde direction, or opposite to the direction the planets rotate. As a result, it makes a very long fast sweep across our southern sky.

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Constellation chart, stars and the Milky Way, with a curved line showing the path of a comet.
Chart showing the location of Comet C/2021 T4 Lemmon from July to November 2023. Illustration copyright Guy Ottewell. Used with permission.

Inventor chart

The comet is currently 60° south (in declination -13°), 1.75 AU from the Sun and 2 AU from Earth in the morning sky. However, it is still at a dim level Around 11. Then, on June 27, 2023, its distance from us will shrink to 1 AU.

On July 18, 2023, we will pass it in opposition. At this time, it will be very close to us, at 0.54 AU, and bright, perhaps 8 or 7 magnitude, but well below the unaided eye limit. Because of its proximity, the declination on July 20 appears even further south at -56°.

Then in the following months it climbs north, low and distant in the evening sky. At the same time, it will decrease by 2 or 3 sizes. It will reach Perihelion1.48 AU from the Sun on July 31, 2023. Finally, it will ascend across the ecliptic on September 10, 2023, and join behind and north of the Sun on November 9, 2023.

Of course, we must remember that predictions of the brightness of a comet and the size of their tails are unreliable. This is because they depend on the melting of ice and the release of dust in these lumpy rotating objects.

Is the Comet-Hale Pop Still Observable? Aha!

by, Alan Hale (Guy Ottewell) alerted us to this comet in a Facebook post on May 22nd. Allen was the discoverer of the large comet Hale-Pop (C/1995 O1). And, although now 47 AU away, it remains in first place Minor Planet Center A list of currently observable comets, not due to their current size (About 20) but is considered to be still visible because it is a much earlier unnumbered timeless comet.

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Bottom line: Comet C/2021 T4 Lemmon was discovered in 2021 from the Mount Lemmon Observatory. It is now spreading across the southern sky.

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