Why did Homo sapiens outlast all other human species?

   

   From-  Sky & Telescope

   By - Bob King

   Edited by - Amal Udawatta

Comet ATLAS exhibits a bright coma and short dust tail pointing southwest on December 15th. At the time it was magnitude 8.1 and 19° from the Sun.
Nick James, BAA

Comet ATLAS (C/2024 G3) is on its way! Discovered April 5th by the automated Asteroid Terrestrial-impact Last Alert System (ATLAS) when it was magnitude 19 and 4.4 astronomical units from Earth, it's now visible at 8th magnitude in Scorpius at dawn for observers at equatorial and southern latitudes. Hang tight. The future looks bright for this latest visitor from afar.

The comet's position along its orbit — gray below the ecliptic plane and white above it — is shown for December 18th. It makes a hairpin curve around the Sun at perihelion on January 13th, during which time it will rapidly brighten and then just as quickly fade.
NASA / JPL with additions by Bob King

Arriving at perihelion on January 13th, C/2024 G3 will miss the Sun by just 13.5 million kilometers, more than three times closer than Mercury's perihelion distance. Initial orbital calculations implied that the comet was making its first visit from the Oort Cloud. Statistically, a majority of smaller comets from this vast and distant repository have a bad habit of disintegrating during close solar approaches. But additional observations refined its orbit and indicated that the visitor was instead a dynamically old comet. In other words, this isn't its first trip around the Sun — the icy emissary passed this way some 160,000 years ago, about the same time humans began to wear clothing. Its apparent durability bodes well for another run.

Of course, there are no guarantees. But if it does pull through, Comet ATLAS could soar to magnitude –4.5 (as bright as Venus) around the time of perihelion, albeit at a solar elongation of just 5°. Like Comet Tsuchinshan-ATLAS, forward-scattering from dust in the coma and tail will play a role in boosting its brilliance. Although only the most adept observers and photographers might attempt to see or photograph it at that time, most of us will be better off (and safer) following the comet in the Solar and Heliospheric Observatory LASCO C3 coronagraph images. It passes through the coronagraph's field of view January 11–14th, guaranteeing we'll all get to see it, at least remotely!

Pre-perihelion warm-up

From latitude 35° south (e.g., Buenos Aires) the comet currently stands about 7° high a little more than an hour before sunrise, at the start of nautical twilight when the Sun's center lies 12° below the horizon. By month's end, its elongation decreases slightly to 17.7°, but it should brighten to about magnitude 5. While photography will pluck the comet from dawn's grasp, you'll need a small telescope or large binoculars to spot it visually.

Tick marks show the comet's position at the start of nautical twilight from December 19–30 as viewed from Buenos Aires at latitude 35° south. The bright, moving "star" at lower left is Mercury. The morning lunar crescent joins the scene on December 27–29.
Stellarium

Come New Year's Eve, the object will hover just 5° high about an hour before sunrise. Dedicated photographers will track it into the first days of January before it passes perihelion and hightails it into the evening sky. Sadly, C/2024 G3 will be completely invisible from mid-northern latitudes during its morning apparition. While its solar elongation is the same for both hemispheres, the shallow angle the comet makes to the southeastern horizon when viewed from north of the equator keeps it buried in twilight.

Post-perihelion southern showpiece?

In the animation, the Sun is surrounded by a glow that represents the area of the sky affected by twilight. "The size of the glow is about 24°, because seeing a comet in a fully dark sky requires that the sun is located 18° below the horizon and comet located at least 4° above the horizon," writes Nicolas Lefaudeux, who created the simulation. Except for a small range of latitudes the comet will not appear vertically above the Sun. The graphic covers from January 5th through February 6th.
Nicolas Lefaudeux

If C/2024 G3 soars to an optimistic –4.5 at perihelion it could still be as bright as zero magnitude with a substantial tail when it first becomes visible low in southwestern sky at dusk around January 16th. Although its brightness drops about two magnitudes between then and January 20th, solar elongation rapidly increases from 12° to 18° and continues to widen as the comet moves from Capricornus into Piscis Austrinus. By the end of January, it may still be a naked-eye object around magnitude 5 with a faint tail visible in binoculars. For Southern Hemisphere observers, C/2024 G3's evening appearance may resemble what northerners saw during Comet Tsuchinshan-ATLAS autumnal run except that it will fade more quickly. It helps that the best part of its apparition occurs during the Moon's waning phases. Full Moon is January 13th.

Comet ATLAS will be at its best for Southern Hemisphere observers from January 19–24 during mid- to late-evening twilight.
Stellarium with additions by Bob King

The northern perspective

While the viewing geometry is fair to good for Southern Hemisphere observers, seeing the comet will pose a challenge for those on the other half of the globe. Comet C/2024 G3 heads south after perihelion, so instead of rising higher in the evening sky it quickly sinks lower. From latitude 40° north, Comet ATLAS struggles to reach 2° altitude at the end of civil twilight, when the Sun sits 6° below the horizon. Where I live at latitude 47° north, I don't expect to see it at all.

That's a far less favorable scenario compared to Comet Tsuchinshan-ATLAS, which emerged at dusk on October 11th around zero magnitude, with an altitude of 6° a half hour after sunset (end of civil twilight). I saw it in the camera viewfinder that evening, but it was barely detectable with the unaided eye. Conditions rapidly improved thereafter in part because the comet tracked north.

This animation shows the comet's movement in mid-January about 30 minutes after sunset from latitude 40° north. It sticks close to the horizon as soon as it emerges from perihelion and will make a difficult target. The tail will point to the upper left (east).
Stellarium with additions by Bob King

The viewing situation is somewhat more favorable for the far southern U.S., but barring a spectacular outburst or breakup, very few folks will see it. That said, it's likely to become the brightest comet of 2025, a year in which no naked-eye comets are predicted to grace the sky. Then again, who knows what may be headed our way.