Speedy Comet Honda to pass near Earth next week

Speedy Comet Honda to pass near Earth next week




Posted on August 8, 2011 by astrobob




Comet Honda-Mrkos-Pajdusakova photographed by Australian amateur astronomer Terry Lovejoy on August 5.


It wasn’t but a week ago I was observing Comet Honda-Mrkos-Pajdusakova,
which for simplicity we’ll call Comet Honda-M-P. It was very low in the
southern sky in the early morning hours and a tough catch in the
constellation Pisces Austrinus the Southern Fish.
Using the “lure” of time, I made two observations – one around midnight
and the other at 2 a.m. This way I was able to track and positively
identify a faint, round hazy glow that slowly inched across the
starfield over the span of two hours. Terry’s photo above captures its
appearance well.

Sure wasn’t much to look at, but finding an old friend is always a
pleasure. I last saw the comet back in 2001 and before that in 1995.
Honda-M-P is what astronomers call a returning or periodic comet,
similar to Halley’s Comet but with a much smaller orbit and hence a
shorter times between returns. It was discovered by Japanese amateur
astronomer Minoru Honda in 1948 and seen at nearly the same time by
astronomers Antonin Mrkos and Ludmila Pajdusakova.

Honda belongs to the short-period Jupiter family of comets or those
with orbits less than 20 years under the control of the gravitational
powerhouse Jupiter. As it orbits the sun with a period of 5.3 years, it
occasionally makes close passes to the planets Venus, Earth and
Jupiter. When near Jupiter, the planet’s powerful gravity can alter the
comet’s orbit and change its period slightly. This last occurred in 1983
and will again in 2030.

Comet
Honda-M-P covers a lot of ground in the next week, plunging through the
southern constellations Grus, Tucana, Hydrus and Dorado as seen from
Australia. Credit: Chris Marriott's SkyMap


Next Monday August 15, Honda will pass very close to the Earth –
relatively speaking – at a distance of just 5.6 million miles. To put
this in perspective, that’s 23 times farther than the moon or still a
long ways off. I’ve been asked if the comet will affect the Earth in any
way, and the answer is ‘no’. Honda is only 0.6 miles across and far too
tiny to produce any measurable effects on our much more massive planet.
If anything, it’s the other way around. Earth may very slightly alter
the comet’s orbit.

When I saw the Comet Honda-M-P, it was very faint in a large amateur telescope (15-inch). Today it’s brighter at magnitude 8.5 with a coma or cometary atmosphere measuring about half the size of the full moon.

If you’re worried that Earth might pass through the coma, don’t be.
At Honda’s present distance of 9.3 million miles, the hazy glow around
the tiny cometary nucleus is about 43,000 miles across, much too small
to reach out and brush our planet. Even if we did pass through a comet’s
outer coma, its effects would likely amount to a nice show of meteors
at best. Comas are highly rarefied – any ice, dust or small rocks would
quickly vaporize on striking the upper atmosphere.

Comet Honda-M-P animation compiled using photos taken on July 21. Click for more comet photos. Credit: Michael Mattiazzo


The closer a celestial object is to Earth, the faster it appears to
move across the sky. Because the comet is closing in on minimum distance
from Earth, it’s quickly picking up speed, covering more and more
ground as we approach the 15th. Tonight for instance, it travels some
two degrees or four times the full moon’s diameter in the southern
constellation of Grus the Crane.
Tomorrow that increases to three degrees, and by the 14-15th, Honda-M-P
flys across some 10 degrees of sky- your clenched fist held at arm’s
length – in just one night!

The next night or two, the comet will still be visible from the far
southern states low in the south around 1 a.m., but by the 14th, only
southern hemisphere observers will see it. To spot the comet, you’ll
need at least a small telescope, since it’s very diffuse and will get no
brighter than 8th magnitude. The moon will also be near or at full
phase, lighting up the sky and making it even harder to find.

Two side-by-side binocular comets at dawn in Leo on October 7. Created with Chris Marriott's SkyMap


After closest approach, Honda-M-P swings back north and slowly
continues to brighten, reaching 6th magnitude (naked eye limit) in late
September, and finally appearing in the morning sky before dawn for
northern hemisphere sky watchers in early October. It’s expected to be
an easy binocular comet then, shining around 7th magnitude.

On the morning of the Oct. 7, it will be joined by Comet Elenin four
degrees (eight full moons) to its north. Although both comets will be at
different distances from Earth – 90 million miles for Honda-M-P and 22
million for Elenin - they’ll lie in approximately the same line of
sight. With wide-field binoculars you’ll be able to catch them both in
the same field of view. What a wonderful and rare sight this will be!

Speaking of Comet Elenin, southern observers continue to observe and
photograph it. It’s now magnitude 9 with a 3-4 arc minute coma and
visible in 4-inch and larger telescopes. Click HERE for the latest views of the comet with the STEREO-B (behind) solar telescope.