Comet Lemmon

[Diane Tokugawa]

From Dr. Alexei Filippenko, UC Berkeley Astronomy.

"Many of you have probably seen headlines about Comet Lemmon.

A comet is a "dirty iceball" (or an "icy dirtball" -- depending on the
relative amounts of ice and dust) that comes from the deep freeze of
the outer Solar System, beyond the orbit of Neptune. It heats up as
it gets closer to the Sun, and the ices sublimate (evaporate, but
directly from solid to gas).  This releases a cloud of dust that
becomes visible by reflecting sunlight; the "coma" of dust surrounds
the nucleus, and the tail points roughly away from the Sun. The gas
can also glow, and it points directly away from the Sun.

Comet Lemmon (C/2025 A6, formally) is now conveniently placed in the
early evening sky. It will be closest to Earth tomorrow (Oct. 21), but
visible all this week (weather permitting). Unfortunately, it's not
as nowhere near as bright as last year's Comet Tsuchinshan-ATLAS, so
you're unlikely to see it unless you have a dark sky and binoculars.

I was up at Lick Observatory last night with part of my class, and we
were able to find it, but just barely (with binoculars, not naked
eye). Here's a photo I took with my Unistellar telescope (the focus
wasn't very good, so stars look double).

I attach a chart showing where the comet will be the next few
nights. Look toward the west-northwest not too long after the end of
evening twilight; about 1-1.5 hours after local sunset is best.  Try
to find the handle of the Big Dipper, then "arc to Arcturus" (Arcturus
is a very bright star). Tonight, the comet will be about 1/3 of the
way from Arcturus to the end star of the Big Dipper's handle; tomorrow
night, it will have moved a bit to the upper left. Wednesday it will
be directly above Arcturus, and Thursday it will be above Arcturus and
a bit to the left.

You can find many photos of the comet online (e.g.,
https://earthsky.org/todays-image/comet-lemmon-c-2025-a6-photos/),
but these were taken in dark skies by serious astrophotographers, so
they are not a good representation of what you'll see. Still, if
you're interested in comets, this one is brighter than any comet
most years (but much fainter than last October's Tsuchinshan-ATLAS).”