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Will Comet G3 ATLAS perform at perihelion?

What "may" be the best anticipated comet of 2025 is coming right up. Right now, there's only one comet with real potential to reach naked eye visibility in 2025: Comet C/2024 G3 ATLAS. This comet reaches perihelion at 0.094 Astronomical Units (AU, 8.7 million miles or 14 million kilometers, interior to the orbit of Mercury) from the sun on January 13th, and "may" top -1st magnitude or brighter.

At magnitude +4 in late December, Comet G3 ATLAS could become a fine object low in the dawn sky for southern hemisphere observers… if (a big "if") it holds together and performs as expected.

The comet actually produced an outburst over the first weekend of 2025, jumping from magnitude +4 to +1 (a sixteen-fold increase in brightness in a few short days). This could be a harbinger for good (or bad) things to come shortly.

"The comet has had an outburst in the last few days," Nicolas Lefaudeux told Universe Today. "If the outburst is linked to disintegration, there would probably be nothing to see after perihelion. If the outburst is linked to new active areas or splitting of a large nucleus, the display could be much better than in the simulations."

A recent International Astronomical Union Central Bureau for Astronomical Telegrams message suggests an optimistic peak of -3rd magnitude near perihelion post outburst, if the comet holds together.

The discovery

The comet was discovered by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) survey as a +19th magnitude object in the southern hemisphere constellation Apus the Bee on the night of April 5th, 2024.

The orbital period for this one is around 160,000 years. It's unclear if Comet G3 ATLAS is a first-time visitor to the inner solar system, or a new denizen coming from the distant Oort Cloud. The last time the comet swung by the inner solar system (assuming it has done so in the past), wearing clothing was the hot new thing among our homo sapiens ancestors.

Comet G3 at perihelion: Perish or prosper?

Prospects for seeing this comet will be tricky. Unlike last year's Comet C/2023 A3 Tsuchinshan-ATLAS which unfurled a magnificent tail for its evening apparition, G3 ATLAS will be a timid one both before and after perihelion, as it departs our solar neighborhood hugging the southern horizon in the dusk sky.

A daytime comet could be in the offing if G3 ATLAS over-performs at perihelion… but it will be a challenging view, very near the sun. Be sure to block the dangerous glare of the sun fully out of view behind a building or structure if you attempt to spot the comet in daylight. Like A3 T-ATLAS, the joint NASA/ESA SOHO observatory will see the comet near perihelion crossing through its LASCO C3 viewer.

Best bets for Comet G3 ATLAS

Perihelion on Monday, January 13, 2025, will see the comet just four degrees from the sun. The comet also makes its closest approach to Earth at 0.938 AU distant on the same date. The comet could reach -4th magnitude (about as bright as Venus) around the same time… if it manages to hold together at perihelion.

Here's a recent remote telescope image of the comet taken from late December by Nick James:

Comet G3 ATLAS has been elusive thus far. The comet has been bashful, skimming just five degrees above the dawn horizon leading up to perihelion in early January for northern hemisphere observers. The comet reemerges low to the west after dusk, but again, folks up north only get a very brief view 5–10 degrees above the horizon at dusk, as the comet runs parallel with the horizon southward. As usually seems to be the case with comets, the southern hemisphere gets the better view.

Here's a blow-by-blow of what to expect in the coming months from the comet. (Note that "passes near," denotes a conjunction of a degree or less):

January

• 6-Near the Lagoon Nebula (Messier 8)
• 7-Near the globular cluster (Messier 28)
• 8-Crosses the ecliptic plane northward
• 11-Enters SOHO LASCO C3 view
• 13-At perihelion, less than 5 degrees from the sun
• 14-Crosses into the constellation Capricornus
• 15-Exits SOHO LASCO C3 view, and crosses the ecliptic plane southward
• 21-Nicks the corner of the constellation Microscopium
• 22-Crosses into the constellation Piscis Austrinus

February

• 1-May drop back down below +6th magnitude
• 6-Crosses into the constellation Grus
• 21-Nicks the corner of the constellation Sculptor
• 25-Crosses into the constellation Phoenix

March

• March 1st: May drop back down below +10th magnitude.

Observing and imaging the comet will be challenging due to two main factors: First, it will never really leave the low-contrast, twilight sky for northern hemisphere observers. Second, said quoted magnitude for a comet gets "smeared out" over its apparent surface area, knocking the comet's apparent brightness down a notch or two.

We can hope that Comet G3 ATLAS is an over-performer in this regard. My strategy is to find high ground to observe from and the lowest, flattest horizon (like, say, the ocean as seen from a beach) that you can find, and sweep the horizon at low power with binoculars for the fuzzball of a comet.

Good luck and clear skies on this, the first comet quest of 2025.