Where and when to see it with “Earthshine”

What time will comet A3 be visible tomorrow? Comet A3, also known as Comet Tsuchinshan-ATLAS (C/2023 A3), is now putting on a show for those in the northern hemisphere.

It is bright and visible in the east before sunrise. At the end of October. it will become bright in the west after sunset.

Will you see the comet on Sunday? With good planning, clear weather and early observation, Comet A3 and its bright tail could make for a spectacular sight – if you know when and where to look – with the bonus sight of “Earthshine” in the nearby crescent.

Why Comet A3 is getting brighter — And when to see it

Comet A3 moves to a position between the Earth and the Sun. On September 27, Comet A3 arrived perihelion — the closest it is to the sun — at about 36 million miles (59 million kilometers). Comet A3 will make its closest approach to Earth on October 12, when it will pass about 44 million miles (71 million kilometers) from Earth.

These two dates are key times to see the comet, which will have two separate viewing periods for those in the northern hemisphere.

Where to see Comet A3: Sunday, September 29

Position: east-southeast, 22.3 degrees from the sun in Leo

Time: one hour before sunrise where you are (around 07:00 in the US)

Expected magnitude: +4.5

Comet distance from the sun: 58.9 million kilometers

Comet distance from Earth: 124.9 million kilometers

This morning, Comet A3 will be visible near the east-southeast an hour before sunrise. It will be placed below a 9% waning crescent moon and Regulus, the brightest star in the constellation Leo.

It should be visible just above the east-southeast about 75 minutes before sunrise and will be best seen during astronomical darkness, which will last until about 60 minutes before sunrise.

Once you look at the comet, look at the dark side of the moon “Earthshine”—the sunlight reflected from our planet’s oceans and ice caps on the lunar surface. It’s just bright enough to subtly illuminate the limb of the moon.

When to see the comet

• September 27: Comet A3 will reach its own perihelion — the closest it is to the sun — at about 36 million miles (58 million km). It will be visible in the east one hour before sunrise from September 27 to October 3.
• October 12: Comet A3 will make its closest approach to Earth at about 44 million miles (71 million kilometers) from Earth. It will be visible in the west one hour after sunset from October 12 onwards, but will fade each evening.

In both of these periods, its dusty tail will reflect sunlight precisely because of its favorable position between the sun and Earth. It’s known as “forward scattering” to astronomers because it scatters sunlight in the direction of Earth — and into the eyes of observers.

Check out my feed every day this week and next for a daily “comet tracker” with sky maps and tips for viewing Comet A3.

I wish you clear skies and open eyes.