“The comet is currently gliding through the southern constellation Fornax,” says Rhemann. “If you look carefully at the image, you can see galaxy NGC 922 near the comet’s head, and another galaxy ESO 479-2 on the left.”
Rhemann says that the comet’s emerald green atmosphere is 50 arcminutes wide. In other words–almost twice as wide as a full Moon. Its apparent diameter could double in the weeks ahead as the comet comes even closer. Because Wirtanen’s brightness is spread over such a wide area, it is diluted just below the limit of naked eye visibility, with a current magnitude near +6.0. We don’t yet know if the comet will ultimately become visible to the unaided eye–but it will certainly be an easy target for binoculars and backyard telescopes in December.
The nucleus of 46P/Wirtanen is small (~1 km) compared to greater comets such as Hale-Bopp (~30 km) and Halley (~15 km). It makes up for this deficit by hyperactivity. Recent measurements show that the core of 46P/Wirtanen is spinning once every 8.9 hours and spewing almost 1028 water molecules every second. This exceeds the expected production of such a small comet. [snip]
A COMET WITH TWO TAILS: Newly-discovered Comet Machholz-Fujikawa-Iwamoto (C/2018 V1) has sprouted a tail. Actually, two tails. Michael Jaeger of Jauerling, Austria, photographed them both on Nov. 18th as the comet was gliding through the star fields of Virgo: Why does Comet Machholz-Fujikawa-Iwamoto have two tails? Almost all comets do. The sun-warmed nucleus of a comet spews a mixture of dust and gas into space. Quickly, the mixture separates into two distinct tails: The gaseous “ion tail” is pushed straight away from the sun by solar wind. The weightier dust tail resists solar wind pressure and aligns itself more or less with the comet’s orbit. In Jaeger’s short video, the long ion tail points up and left; the stubby dust tail points up and right.
Comet Machholz-Fujikawa-Iwamoto appears to be a first-time visitor to the inner solar system. It is plunging toward the sun on nearly-parabolic orbit that will take it just inside the orbit of Mercury. Closest approach to the sun (0.38 AU) is on Dec. 3-4; closest approach to Earth (0.67 AU) is Nov. 27th. Amateur astronomers can find it–and its two tails–shining like a star of 8th magnitude in the constellation Virgo in the pre-dawn sky.
November 23– Full Moon. The Moon will be located on the opposite side of the Earth as the Sun and its face will be will be fully illuminated. This phase occurs at 05:40 UTC. This full moon was known by early Native American tribes as the Full Beaver Moon because this was the time of year to set the beaver traps before the swamps and rivers froze. It has also been known as the Frosty Moon and the Hunter’s Moon.
SOMETHING WICKED-GREEN THIS WAY COMES: A green ball of gas wider than the planet Jupiter is approaching Earth. It’s name is “Comet 46P/Wirtanen.” Italian astronomer Rolando Ligustri photographed the verdant orb on Oct. 18th using a remote-controlled telescope in Australia:
Deep inside that green ball is a furiously vaporizing nugget of dirty ice. The frozen nucleus of 46P/Wirtanen is only about 1 km wide, but astronomers say it is “hyperactive.” As many as 1.7×1028 water molecules per second have been observed emerging from the comet’s core. Mixed with the water vapor is diatomic carbon (C2)–a gaseous substance common in comet atmospheres that glows green in the near-vacuum of space.
On Dec. 16th, this hyperactive comet will come within 11.5 million km of Earth–making it one of the 10 closest-approaching comets of the Space Age. Comet 46P/Wirtanen will probably become a naked eye object for several weeks during the holidays, prompting some astronomers to call it “the Comet of the Year.”
Comet Wirtanen passes through the inner solar system every 5.4 years. Right now it is near the orbit of Mars, and it is heading in our direction. Forecasters expected it to brighten more than 200-fold between now and mid-December, eventually reaching magnitude +3, similar to the stars of the Pleiades. Stay tuned.
THE ORIONID METEOR SHOWER–UPDATE: This weekend, Earth is crossing through a stream of dust from Halley’s Comet, source of the annual Orionid meteor shower.The shower is expected to peak on Sunday, Oct. 21st, with rates of ~20 meteors per hour. However, Halley’s debris stream is broad and the shower could spill into Monday, Oct. 22nd, as well. The best time to look is during the hours before local sunrise when Orion is high in the sky and the waxing-full Moon is hanging low in the west.
The sky at dusk tonight will present the Moon And Mars for your viewing.
THE MOON AND MARS–TONIGHT: When the sun goes down tonight, step outside and face south. The waxing gibbous Moon is approaching Mars for a conjunction in the constellation Capricornus. Mars is distinctly red and it shines about 6x brighter than a 1st magnitude star–easy to see even beside the glaring Moon. Try to look before the sky fades to black. The pair will look extra beautiful surrounded by twilight blue. Sky maps: Oct. 17, 18.
The nice part about this is that it doesn’t require being up late at night. Take your tea soda or adlut beverage out and sit, relax and just enjoy something delightful
Do you fly? Frequently? Nere’s some news that might be important to you.
RADS ON A PLANE–NEW RESULTS:
Many people think that only astronauts need to worry about cosmic radiation. Not so. Ordinary air travelers are exposed to cosmic rays, too. A recent study from researchers at Harvard found that flight attendants have a higher risk of cancer than members of the general population, and the International Commission on Radiological Protection has classified pilots as occupational radiation workers.
How much radiation do you absorb? Spaceweather.com and the students of Earth to Sky Calculus have been working to answer this question by taking cosmic ray detectors onboard commercial airplanes. Flying since 2015, we have collected more than 22,000 GPS-tagged radiation measurements over 27 countries, 5 continents, and 2 oceans.
Here is what we have learned so far:
Radiation always increases with altitude, with dose rates doubling every 5000 to 6000 feet. This make sense: The closer you get to space, the more cosmic rays you absorb.
At typical cruising altitudes, cosmic radiation is 40 to 60 times greater than natural sources at sea level.
Passengers on cross-country flights across the USA typically absorb a whole body dose equal to 1 or 2 dental X-rays.
On international flights, the total dose can increase ~five-fold with passengers racking up 5 to 6 dental X-rays.
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There are several charts at the site that which flights are more open to radiation. Those flying near or over the Arctic get more than those near the Equator.
If you don’t fly because you hate the TSA or for any other reason, relax. You can always visit the dentist four or five times a year to keep up w
Why does Comet Machholz-Fujikawa-Iwamoto have two tails? Almost all comets do. The sun-warmed nucleus of a comet spews a mixture of dust and gas into space. Quickly, the mixture separates into two distinct tails: The gaseous “ion tail” is pushed straight away from the sun by solar wind. The weightier dust tail resists solar wind pressure and aligns itself more or less with the comet’s orbit. In Jaeger’s short video, the long ion tail points up and left; the stubby dust tail points up and right.
Vermont Loon Watch 
