Like watching the final chapter of a show or movie series, you’re almost trembling with excitement — but you don’t know whether you’ll have the experience of a lifetime, suffer a grand disappointment, or end up with something that’s just OK.
Right now, odds are that Comet C/2019 Y4 (ATLAS) will be wonderful. Just maybe it will be the most amazing thing you will ever see — a great comet for the history books. Here’s what we might be able to expect.
Past to present
Y4 was discovered on December 29, 2019, by the Asteroid Terrestrial-impact Last Alert System (ATLAS) search program, one of the several automated sky surveys looking for potential Earth-crossing asteroids. Discovering comets is essentially a byproduct of this endeavor. At the time, C/2019 Y4 was a feeble magnitude 19.6 and located at nearly 3 astronomical units from the Sun — almost twice as far from our star as Mars. (One astronomical unit, or AU, is the average Earth-Sun distance.)
In mid-March, Y4 ATLAS surged 4 magnitudes, fueling rumors that it will just keep getting brighter, peaking at magnitude –8. But back in 2000, C/1999 S4 (LINEAR) dropped the same amount on its approach and dissolved rapidly.
David Levy wrote that “Comets are like cats. They have tails and they do whatever they want.” Despite the best observations and understanding, these dirty snowballs can fizzle out with no notice even farther from the Sun than Mars’ orbit, a distance Y4 ATLAS reaches at April’s start.
The description here covers what we’re likely to witness: a fantastic display like
Comet C/1975 V1 West delivered in 1976. Stay hopeful for the comet of a generation and realize that, at worst, it will still be a nice binocular object.