SIGNS IN THE HEAVENS: Green comet to fly by Earth on April 1st 2017
APRIL 1ST COMET FLYBY: Green
comet 41P/Tuttle-Giacobini-Kresak is flying over Earth's North Pole
this week where sky watchers can find it all night long not far from the
bowl of the Big Dipper. At closest approach on April 1st it will be
just 21 million km from Earth--an easy target for backyard telescopes
and almost visible to the naked eye. Amateur astronomer Yasushi Aoshima
sends this picture of the approaching comet from Fukushima, Japan:
"On March 22nd I caught 41P 'eating' M108,
the Surfboard Galaxy," says Aoshima. "The comet's green atmosphere
appeared to swallow the distant spiral galaxy as it exited Ursa Major."
Why
green? Like many comets, 41P has a verdant hue because its atmosphere
contains diatomic carbon (C2)--a substance that glows green in the near
vacuum of space.
Comet
41P is not only approaching Earth, but also the sun. April 12th is the
date of perihelion (minimum distance from the sun). This means we are
catching the comet just as solar heating is furiously searing its icy
core. The green atmosphere should be well puffed up by streamers of
vaporizing gas. Optimistic estimates of the comet's brightness place it at magnitude +6, near the lower limit of naked-eye visibility.
This
is not a Great Comet, but it should be a good one. The best time to
observe is during the dark hours before sunrise when the green fuzzball
is high in the northern sky. If you have a GOTO telescope, you can
point it using an ephemeris from the Minor Planet Center. These sky maps show approximately where to look: March 31, April 1, 2.
