Two rare comets fly across Vietnam's sky

On the nights of October 20 and 21, Vietnam's night sky will simultaneously see two rare comets: Lemmon (C/2025 A6) and SWAN (C/2025 R2).

Comet Lemmon - Photo: THE WIRED

This is an event that many experts are calling a "chance of a lifetime," when two comets can be seen almost parallel, something that has rarely happened in modern observational history.

Comet Lemmon was discovered in January 2025 by Mount Lemmon Observatory (USA).

According to NASA and National Geographic , Lemmon will reach its closest point to Earth on October 21, at a distance of about 89 million km.

With an estimated magnitude of 3.5 to 4.5, this could be the brightest comet of 2025 and is quite likely to be visible to the naked eye if the sky is dark and clear.

Experts predict that Lemmon will not return to the Solar System for more than 1,300 years, making this appearance extremely special.

Meanwhile, comet SWAN was discovered by Ukrainian amateur astronomer Vladimir Bezugly in September 2025, through data from the SOHO-SWAN telescope.

SWAN made its closest approach to Earth on October 20, at a distance of only about 39 million km.

Comet SWAN - Photo: LIVE SCIENCE

However, observations from the Northern Hemisphere show that the comet is quite low on the southwestern horizon, making it more difficult to see with the naked eye in Vietnam.

Space.com astronomers say SWAN could make for a spectacular sight if conditions are ideal, but it's likely only visible through binoculars or a telescope.

In Vietnam, the best time to observe these two comets is about 30 to 90 minutes after sunset, from 6:30 p.m. to 8:30 p.m.

With Lemmon, observers should look to the west or northwest, where the comet appears near the constellation Ursa Major, specifically in the area extending from the "handle" of the Big Dipper.

Meanwhile, SWAN will appear very low in the south-southwest, near the constellation Aquarius, so visibility will depend largely on weather, terrain and ambient brightness.

The best conditions for observation are in places away from urban lights, with clear views and clear skies.

It is necessary to choose an area with less light to see the comet more easily - Photo: SPACE

Observers can use apps like SkyMap or Star Walk to locate the Big Dipper and Aquarius as landmarks. Binoculars or a tripod-mounted camera will increase the chance of capturing the faint light trail of the comet.

Experts also note that comets are unpredictable celestial bodies. Their brightness and shape can change rapidly due to the effects of solar wind and sublimation - when ice in the comet's core turns directly into gas, creating a long, shimmering "tail" that reflects sunlight.

So, observers should take advantage of this opportunity between October 20 and 22, before they fade and disappear from sight.

If you're lucky, you'll see Lemmon's faint green streak stretching across the western sky, a vivid testament to the icy travelers' magical movements through the Solar System.

With a clear sky, not too many clouds, the night of October 21st may be the night we witness a "reunion" that may only happen once in a lifetime.

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HOANG THI

Source: https://tuoitre.vn/hai-sao-choi-hiem-cung-bay-qua-bau-troi-viet-nam-20251020172943002.htm