If you’re looking for nature’s version of a straight-edge, look no further than Comet PANSTARRS. We had the opportunity to see its millions-mile-wide dust fan edge-on this weekend. Well, not all of us did. Moonlight spoiled the visual view but astrophotographers found ways around the moonlight to produce spectacular images.
Tail lengths estimates varied, but wide-angle amateur photos show it extending up to 16 degrees long. That’s 32 full moons side by side. The physical tail length captured in the photos is about 23 million miles (37.5 million km) long, but since it’s projected at an angle to its orbit, the full extent is considerably longer, likely approaching 93 million miles or the Earth-sun distance.
The beam-like tail is called an anti-tail because it points toward the sun in the opposite direction of a normal comet tail. It’s composed of dust particles shed over the past several months.
Not only do those bits of dust and rock line its orbital track, they also migrate outward into a vast sheet or cloud extending beyond PANSTARRS’ orbit. The short, broader tail is the normal dust tail, where dust particles are being pushed away from PANSTARRS in real time by the pressure of sunlight.
While the comet is still visible in 50mm binoculars in dark, moonless skies, the tail(s) will shorten and fade in the coming weeks as the distance between it and Earth widens.
Jupiter, Mercury and Venus are still clustered together low in the northwestern sky after sunset for the next few nights. My sky was mostly cloudy and I never got more than a glimpse of the three over the weekend.
Others were more fortunate. Alex Sokolow saw them squeezed between two apartment buildings when the three were in their most compact arrangement on the 26th.
Even if you got hit with bad weather or circumstance this weekend, you can still see our planetary friends together the next few nights. Jupiter is dropping fast but passes closest to Venus tonight – the two will be just a degree apart.
Have you ever seen Mercury? If not, this is the best evening opportunity this year to do so for northern hemisphere sky watchers.