Winter solstice brings longest night, warm comforts

A wintry scene along the Superior Hiking Trail in northern Minnesota photographed earlier this week. Credit: Bob King

You can kiss the fall goodbye starting at 5:03 p.m. (CST) tonight. That’s when the Sun arrives at its southernmost point in the sky in the constellation Sagittarius. For those of us in the northern hemisphere it rises late, never climbs very high in the south and sets early, making today the shortest day and tonight the longest night of the year.

Earth’s tipped axis is responsible for the seasons. On one side of Earth’s orbit, the northern hemisphere is tilted away from the Sun and we experience winter; on the other side it’s tilted toward the Sun and we experience summer. Fall and spring are in-between times when the entire planet is broadside to the Sun and all places on the globe receive equal amounts of sunshine. From places like Australia, which is bisected by the Tropic of Capricorn, the Sun is high in the sky. For them and all other southern hemisphere locations, today marks the first day of summer. Credit: Wikipedia with additions by the author

Seen from the Tropic of Capricorn, that imaginary circle touching every location with a latitude of 23.5 degrees south, the Sun will be directly overhead at noon today. On the summer solstice, anyone living on the Tropic of Cancer at 23.5 degrees north latitude sees the Sun overhead at noon. The number 23.5 is special because it’s how many degrees the Earth’s axis is tilted from the vertical.

Because of the 23.5 tilt of Earth’s axis, the altitude of the sun varies with the seasons. In winter it’s 23.5 degrees below the celestial equator and shines over the Tropic of Capricorn, while in summer it’s 23.5 degrees above and shines over the Tropic of Cancer.  Source: Stellarium

At the winter solstice, the northern hemisphere is tilted away from the Sun, which makes it appear low in the sky. Not only are the Sun’s precious rays more spread out (less direct), but the days are short. Cold soon follows. In summer we experience exactly the opposite – the top of the globe is canted in the Sun’s direction. With our star high overhead, days are long and temperatures steamy.

Map of the continental U.S. showing the time of the average coldest day of the year. Click to enlarge. Credit: NOAA

While the start of winter can be cold, it’s rarely the coldest time of the season. Most places see their coldest days in mid to late January even as the days slowly grow longer and the Sun climbs higher. This seasonal delay occurs because the land is still losing more heat than what the feeble Sun can resupply, while the oceans, which effect climate worldwide, take more time than the land to cool down and warm up.

Likewise we don’t feel the hottest day of summer until the land and oceans heat up from day after day of a high-rolling Sun. That happens in July.

Because the Sun’s at its lowest point in the sky, your noontime shadow is longest this time of year. And if you’re paying close attention, you’ll notice that the earliest sunset occurred two weeks ago – not on the shortest day. However, the Sun will continue to rise later up to about January 4th.

The earliest sunsets happened two weeks ago. The sun sets about 3 minutes later today than it did in early December. Credit: Bob King

The reasons for the discrepancy have to do with both the tilt of the Earth’s axis and the planet’s varying speed due to its oblong, non-circular orbit. For a nice explanation of the phenomenon, head over to Prof. Kirk Korista’s Sunrise, Sunset and the Solstice page.

Christmas and other important holidays and celebrations happen at this darkest time of year to keep our spirits up and fan our hopes for the return of the light. They’re a time to revisit our deepest beliefs, spend time with family or just fall asleep in a soft chair next to a roaring fire.

A fire in the woodstove on the winter solstice. What could be better? Credit: Bob King


Aurora alert through Sunday night Dec. 20-21 / Aurora link updates

The auroral oval has been expanding southward toward the northern U.S. overnight. If you live in the border states, there’s a good chance you’ll see some activity tonight-tomorrow morning. This map shows the oval around 12:45 a.m. Sunday morning Dec. 21st. Credit: NOAA

Auroras are on the prowl. A glancing punch from a coronal mass ejection on December 17th coupled with a more direct hit from another blast on the 18th are already goosing Earth’s magnetic bubble this evening and will continue through Sunday evening. NOAA predicts the latter will cause moderate to major storming starting early Sunday morning (Dec. 21)  through midnight Sunday night. Judging from the map, we’d see aurora here in Duluth, Minn. were the sky clear.

Tomorrow beginning at 5:03 p.m. (CST) marks the start of winter, the shortest day and longest night of the year. Wouldn’t it be nice to fill that night with auroras?

NOAA recently updated many of the space weather websites including changing the addresses. Here are the new links for you to bookmark:

* 30-minute Aurora Forecast (the old Ovation oval)
* Planetary K-index (the old 3-day Kp index)
* ACE Real-time solar wind
* 3-day forecast

The X1.8 flare around 6:45 p.m. (CST) Friday evening is a brilliant beacon in the light of far ultraviolet light as seen by NASA’s Solar Dynamics Observatory. Credit: NASA

Meanwhile, sunspot region 2242 erupted with a strong X1.8 flare on Friday evening December 20th (CST). Lots happening.

Cloudy or not I’ll be monitoring the upcoming bumpy weather and post updates as necessary. Let us know if you see anything.


Comet Finlay outburst another present under the Christmas tree

Morphing from obscurity to prominence, Comet 15P/Finlay shows off a beautiful finger-shaped tail, a bright nucleus and several rays in this photo taken December 19th. It orbits the Sun every 6.5 years. Credit: Damian Peach

Surprise! An obscure comet that only amateur astronomers would pay attention to experienced a sudden outburst in brightness earlier this week putting it within range of telescopes as small as 4.5 inches.

Comet 15P/ Finlay hunkered along at a dim 11th magnitude successfully avoiding the limelight until about December 16th. That’s when Czech comet observer Jakub Cerny and his team took a photo revealing the comet had surged in brightness by some 8 times to magnitude 8.7. Suddenly, Finlay became a minor celebrity.

Comet Finlay on December 16th shows a bright coma and short tail. Its sudden rise to 9th magnitude was confirmed on December 18th by Australian comet observers. The moderately condensed object is about 3 arc minutes in diameter. Credit: J. Cerny, M. Masek, K. Honkova, J. Jurysek, J. Ebr, P. Kubanek, M. Prouza, M. Jelinek

It still remains in outburst visible low in the southwestern sky very close to the planet Mars, which serves as a convenient “pointer” to help us find it. From mid-northern latitudes, Comet Finlay is best viewed as soon as evening twilight ends, when highest in the sky. The moon, ever a spoiler when it comes to viewing fuzzy stuff like comets and galaxies, won’t be over-bright until after Christmas, leaving us almost a nearly week-long window for finding and tracking the comet before it fades.

Use the general map to take you to Mars and then the more detailed version to pinpoint the comet’s location. Finlay will look like a small, fuzzy spot with perhaps a faint tail to the east visible depending on the size of your telescope.

To find the comet, first find Mars. Face west toward the brilliant star Vega and shoot a line from it through Altair and straight to Mars, low in the southwestern sky in Capricornus. Map time is around 6:15 p.m. CST, end of evening twilight in late December. Source: Stellarium

Planet and comet paths are currently converging toward conjunction. On December 23rd and 24th Mars and Finlay will be separated by just 10 arc minutes or 1/3 the diameter of the Full Moon. By December’s end they’ll gradually separate as each follows its own orbital path around the Sun. The close pairing is line of sight only.

Comet Finlay tracks alongside Mars through early January. On December 23rd, they’ll come together in a remarkably close conjunction. This map shows the nightly position of the comet from Dec. 18th through Jan. 12th. Mars’ location is shown every 5 nights. Positions plotted for 6:15 p.m. (CST). Stars shown to magnitude 8. Star magnitudes are underlined. Click for a large version you can print for outside use. Source: Chris Marriott’s SkyMap software

We’ve known about Comet Finlay since September 26, 1886, when William Henry Finlay happened across it with his 7-inch telescope from the Cape of Good Hope in South Africa. He described humanity’s first view of the object as round, 1 arc minute in diameter and “very slightly more condensed towards the centre.”

Animated movie showing the expansion of the coma of Comet 17P/Holmes over 9 nights during its spectacular outburst in November 2007. Credit: 3.6-meter Canada-France-Hawaii telescope on Mauna Kea / David Jewitt

Finlay reaches perihelion or closest approach to the Sun on December 27th and was expected to brighten to magnitude +10 when nearest Earth in mid-January at 130 million miles (209 million km). This month’s outburst may change that prediction.

What causes a comet to quickly and unpredictably surge in brightness still baffles astronomers. Unlike most rocky asteroids, comets are friable creatures. They crumble easily. It’s thought that sub-surface ices, warmed by a comet’s approach to the Sun, vaporize, creating pressurized pockets of gas that break through the overlying ice above, sending fragments flying and exposing fresh new ice.

Sunlight gets to work vaporizing both the newly exposed vents and aerial shrapnel. Large quantities of dust trapped in the ice are released and glow brightly in the Sun’s light, causing the comet to suddenly brighten.

Comet Lovejoy Q2 looks like a spectacular aerial burst in this photo taken December 20, 2014. The comet’s still low in the southern sky from mid-northern latitudes but will be soon be well-placed for binocular viewing in a few days. Credit: Martin Mobberley

So now we have two fairly bright comets during the holidays – Finlay and Comet C/2014 Q2 Lovejoy. Lovejoy has been steadily brightening and now glows at around magnitude 5.5, bright enough for observers with dark skies to see it with the naked eye. Click HERE for more information and a finder chart for it.

While this means we have two cometary gifts under the Christmas tree, by all means, don’t wait until Christmas to unwrap either. Have at them the next clear night!

Who or what passed gas on Mars?

A photo taken today, December 19th, of sand dunes and rock outcrops around the Curiosity rover through the fisheye lens of one of its Hazard Avoidance Cameras. Colorized by the author. Credit: NASA/JPL-Caltech

What a tantalizing week it’s been for organic chemistry on Mars. We learned that NASA’s Curiosity rover measured a tenfold spike in methane, an organic chemical, in the atmosphere around it and detected other organic molecules in a rock-powder sample collected by its drill.

Scatalogical references to the contrary, methane is a colorless and odorless gas. While it’s a component of both human and bovine flatulence, what gives human “gas” its odor are sulfur compounds, principally hydrogen sulfide and methyl mercaptan, which by the way we share with skunks.

But I digress.

This image illustrates possible ways methane might be added to Mars’ atmosphere and removed from it and stored in “sinks”. The Curiosity rover has detected changes in methane concentration in the atmosphere, implying both types of activity occur on modern Mars. More details of methane’s formation and movement on the planet are given below. Credit: NASA/JPL-Caltech/SAM-GSFC/Univ. of Michigan

“This temporary increase in methane — sharply up and then back down — tells us there must be some relatively localized source,” said Sushil Atreya of the University of Michigan, Ann Arbor, and Curiosity rover science team. “There are many possible sources, biological or non-biological, such as interaction of water and rock.”

Methane molecule

The sudden increase and decrease immediately gets the heart palpitating. Sure sounds like the work of a living being, but methane, a simple organic molecule made of one carbon atom festooned by four hydrogen atoms, can be created in a number of different ways. Bacteria make methane by combining carbon dioxide and hydrogen; the energy liberated in the process powers their minute lives.

Chemical reactions between water and the minerals olivine and pyroxene in rock also release methane as does the action of ultraviolet light from the Sun on organic materials like comet dust and other meteoric material on Mars. Whether manufactured through living or non-living processes, methane generated underground can become trapped within the crystal structure of water to form a curious substance called clathrate, a form of methane ice.

This 98-foot-wide (30-meter) crater spotted in Siberia this past summer was probably caused by the release of methane gas from permafrost. Click to learn more about it. Credit: Yamalo-Nenets Autonomous Okrug Governor

Meteor impacts, faults or cracks in the Martian crust and simple outgassing can then release methane at a later date. Earth has abundant methane clathrates buried beneath deep ocean sediments and stored in permafrost. We hope it stays there. Methane is a powerful greenhouse gas that already plays a role in climate change. Unlike chocolate, more of it isn’t a good thing.

Since Mars is a windy planet, any methane released is likely to quickly thin out and be dispersed. Methane can be removed from the atmosphere through “photochemistry” or the sunlight’s UV light sparking chemical reactions among molecules. These reactions can oxidize the methane, through intermediary chemicals such as formaldehyde and methanol, into carbon dioxide, the predominant ingredient in Mars’ atmosphere.

This graphic shows tenfold spike in the amount of methane in the Martian atmosphere surrounding the Curiosity rover as detected by a series of measurements made with the Tunable Laser Spectrometer instrument in the rover’s Sample Analysis at Mars laboratory suite. Credit: NASA/JPL-Caltech

Researchers used Curiosity’s onboard Sample Analysis at Mars (SAM) laboratory a dozen times in a 20-month period to sniff methane in the atmosphere. During two of those months, in late 2013 and early 2014, four measurements averaged seven parts per billion. Before and after that, readings averaged only one-tenth that level.

Whatever its origin, we’re not talking much gas – Earth’s atmosphere, of which methane is a minor constituent, averages 1,800 parts per billion. Cattle belching alone accounts for 16% of that total.

Curiosity also detected different Martian organic chemicals in powder drilled from a rock dubbed Cumberland, the first definitive detection of organics in surface materials of Mars. These Martian organics could either have formed on Mars or been delivered to Mars by meteorites.

There’s abundant evidence for Mars once being a wetter world. These riverbeds, called Nanedi Valles, flowed with water about 3.8 billion years ago. Credit: ESA

As we saw with methane, organic or carbon-containing materials aren’t necessarily an indicator of little green bugs. They can form and be left in rocks through inorganic processes, too. There’s simply no way to know from the Curiosity data how they originated, but they do give us hope that Mars was once (and may still be) a planet favorable to life.

Identifying which specific Martian organics are in the rock is complicated by the presence of perchlorate minerals in Martian rocks and soils. Perchlorates are toxic salts used for propellents here on Earth because they have explosive properties. When heated inside SAM, the perchlorates alter the structures of the organic compounds, masking the identities of the organics in the sample.

Curiosity also revealed some interesting news about the past water in the Martian atmosphere. According to its measurements, the Cumberland rock formed 3.9 to 4.6 billion years ago and contains just half the ratio in water vapor in today’s Martian atmosphere. This suggests that much of the planet’s water loss occurred since that rock formed.

View of a rocky desert-like landscape inside Gale Crater snapped by Curiosity on December 14th. Colorized by the author. Credit: NASA/JPL-Caltech

On the other hand, the ratio is about three times higher than that estimated in the original water supply of Mars. This suggests much of Mars’ original water was lost before the rock formed. More information please!

Additional samples along with data from the NASA’s MAVEN mission, which is conducting a study of the planet’s atmosphere to determine where both the water and air disappeared to, will hopefully give us a clearer picture of the Red Planet’s evolution from a water world like Earth to the present cold, dry desert.

In more recent news, NASA and an international team of planetary scientists have found evidence in meteorites on Earth that indicates Mars had yet another global reservoir of water or ice near its surface. Check out the details HERE.

Source information in today’s blog

Who’d a- thunk it? Mercury May Have Meteor Showers Too

Artist’s concept of Mercury crossing the debris trail of Comet Encke, sparking a recurring meteor shower. New evidence from the MESSENGER mission suggests the planet receives regular doses of Mercurial dust. Credit: NASA’s Goddard Space Flight Center

Of course, of course, it only makes sense. We’re so caught up in watching meteor showers on our own planet, who ever thinks about meteors at Mercury? Or Venus for that matter? This week NASA announced that regular spikes in the amount of calcium in Mercury’s upper atmosphere bespeak a cyclical source. The likely culprit? Comet 2P/Encke.

Like breadcrumbs dropped to mark a path, dust and fragile bits of rock are released through vaporization of a comet’s ice and pushed back by the pressure of sunlight to form a tail. The larger pieces are left behind to fan out along the comet’s orbit. If by good fortune Earth’s orbit happens to intersect the debris trail, we see a shower of meteors in the sky.

This photo, made by NASA’s Spitzer Space Telescope in infrared light, shows Comet Encke’s glowing nucleus/nuclear region and a trail of warm dust and pebbly debris shed by the comet along its orbital path. Credit: NASA

Most recently, the Geminids put on a great show, although their origin lies with the peculiar rock-shedding asteroid 3200 Phaethon.

Comet 109P/Swift-Tuttle brings us the familiar Perseid meteor shower, while 2P/Encke gives rise to several meteor streams - the Southern and Northern Taurids, showers that peak in October and November, and the daytime Beta Taurids in June and July.

Measurements taken by MESSENGER’s Mercury Atmospheric and Surface Composition Spectrometer have revealed seasonal surges of calcium that occurred regularly over the first nine Mercury years (1 year = 88 Earth days) since MESSENGER began orbiting the planet in March 2011. Just as we saw huge spikes in the amounts of metals like magnesium and iron in Mars’ upper atmosphere during Comet’s Siding Spring’s brush with the planet last October, MESSENGER’s instrument detected periodic spikes in the amount of calcium – although with a twist.

A color- enhanced view of Mercury, assembled from images taken at various wavelengths by the cameras on board the MESSENGER spacecraft, shows a cratered composed with a surface composed of a variety of minerals. The circular, orange area near the center-top of the disk is the enormous Caloris impact basin. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington

Mercury’s has only a whiff of an atmosphere, what astronomers term an exosphere, the last thing you could call an atmosphere before encountering the vacuum of space. The shower of small dust particles peppering interplanetary space pass right down to the surface and strike the planet’s rocks, knocking calcium-bearing molecules free from the surface, which are then free to rise to greater heights. This process, called impact vaporization, continually renews the gases in Mercury’s exosphere as interplanetary dust and meteoroids rain down on the planet.

These type of impacts happen all the time, but scientists noticed a pattern in the calcium spikes that pointed to a repeating source. Sounds like a perfect time for a comet to step in. Examination of the handful of comets in orbits that would permit their debris to cross Mercury’s orbit indicated that the likely source of the spikes was Encke.

The Jupiter family of comets were all once long-period objects in the Kuiper the orbits of which were changed to short-period by close passes by Jupiter. The green circle is Jupiter’s orbit, the purple is Earth’s. Notice that when farthest from the Sun, the comets about as far as Jupiter is from the Sun. Credit: Wikipedia with additions by the author

“If our scenario is correct, Mercury is a giant dust collector,” said Joseph Hahn, a planetary dynamist in the Austin, Texas, office of the Space Science Institute and coauthor of the study. “The planet is under steady siege from interplanetary dust and then regularly passes through this other dust storm, which we think is from comet Encke.”

To test their hypothesis, Han and crew created detailed computer simulations and discovered that the MESSENGER were offset from the expected results but in a way that made sense due to changes in Encke’s orbit over time from the gravitational pull of Jupiter and other planets.

Pantheon Fossae – The striking troughs of Mercury’s Pantheon Fossae, the feature that MESSENGER scientists first called “The Spider” when they discovered it. Credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington

Comets get nudged by planets routinely, especially if they pass near Jupiter, the outer Solar System’s gravitational goliath. Jupiter, with the help of Neptune, has re-worked the orbits of countless bodies that once resided in the distant Kuiper Belt into shorter-period comets that swing around the Sun in 20 years or less. Called the Jupiter-family, there are about 400 known and Encke is one of them with an orbital period of just 3.3 years.

Who knows how many other meteor showers might pepper Mercury in a year, but scientists will be looking for potential signs of them in planet’s atmosphere in the months ahead. While they may not leave bold streaks of light as they do on Earth, they create something almost as amazing – a shower of particles that goes up instead of down.

Solar flares and gobs of spots make for fiery fall finale

A freckle-faced Sun earlier this morning December 17 photographed by the Solar Dynamics Observatory. Regions 2242 and 2241 have produced several impressive M-class moderate flares in the past couple days. 2242 has a complex beta-gamma-delta magnetic field ripe for the production of strong flares. Credit: NASA

The Sun cares not for Earth’s seasons. It follows its own cycle of high and low activity. So while winter will soon be underway in the northern hemisphere, things have been heating up in recent days on our home star.

An M8 flare (almost an X-class!) in Region 2242 shines brilliantly in ultraviolet light in this photo taken by the Solar Dynamics Observatory at 10:57 p.m. (CST) last night. Credit: NASA

Nine sunspot groups speckle the Sun today with two of them – regions 2241 and 2242 – still growing and harboring the potential for M-class (moderate) or stronger flares in the coming days. Region 2242 let loose with an M1 flare around 7 p.m. (CST) yesterday evening and a stronger M8 flare at 11 p.m.

Along with so many other spot groups now pocking the solar disk, this week will be a good one for anyone with a small telescope and safe solar filter to get a great view of the Sun. This morning I could easily see Regions 2241 and 2242 with the naked eye through a #14 welder’s glass.

Tongue of fire! A coronal mass ejection (CME) of high speed electrons and protons departs the Sun around 2:30 a.m. (CST) today in the wake of last night’s M8 flare. This photo was taken with a coronagraph that blocks the brilliant solar disk so we can see what’s happening near the Sun. Arrow shows the direction of the blast. Credit: NASA/ESA

The more powerful of the two flares launched a large coronal mass ejection in a mostly southernly direction just below the Sun-Earth plane. However, there’s a chance for some spillover in our direction as particles traveling at over 400 miles per second (650 km/sec) arrive on or about Sunday the 21st, the first day of winter.

Quiet conditions in Earth’s ever-dynamic magnetic environment will be the rule the next couple days, but we’ll be keeping our eyes on those big sunspot groups and a possible glancing blow from that CME. A colorful red and green aurora would be so fitting for the season!

Saturn’s back at dawn – follow the moon to the ring-bearer’s lair

Face southeast about an hour fifteen minutes before sunrise to see Saturn and a beautiful, thin lunar crescent this week. Source: Stellarium

While Orion’s stepping into the evening sky followed by Jupiter in Leo, the lord of the rings has returned to punctuate the dawn. It’s great to see Saturn back in view. Along with Venus, which we’ll take a look at later this week, there are now three evening planets (Mars, Jupiter, Venus) and one in the morning.

While still low in the southeast, the delicate crescent moon has a happy meeting with Saturn this Friday the 19th two nights after a conjunction with Virgo’s brightest star Spica. The rings are tilted a hair more than 24° or near the maximum of 27°. Any telescope will show the rings at 30x or higher magnification. You can even see the planet’s oval shape due to the extra girth provided by the rings in a pair of 10x binoculars.

The many ringlets that compose Saturn’s ring system are seen here projected against the planet. This angle shows how translucent they are – you can see one of the planet’s dark belt showing through the rings. Credit: NASA/JPL-Caltech

In honor of the rings, we present a recent photo of Saturn taken by the Cassini spacecraft on August 14 this year. Although Saturn’s rings look solid when viewed from Earth, they’re really translucent, composed of floating chunks of water ice in size from about 1/2-inch (1 cm) to 33 feet (10 meters). I wouldn’t put it past some future entrepreneur to gather up these smaller chunks and market them to those wishing to sip their hard liquor “on the rocks” as it were.

It wasn’t until 1859 that physicist James Clerk Maxwell demonstrated the rings must be made of many individual particles; if they were solid they’d be unstable and break into pieces. Spectroscopic studies in the 1970s, where astronomers determine the composition of an object by examining the light it reflects and absorbs with a spectroscope, proved beyond a shadow that the rings were made of mostly water ice.

One of my favorite astronomical daydreams is to imagine myself in the ring plane gently hopping from one low-gravity ice chunk to the next. Once I arrived at a piece large enough to make for a comfortable seat, I’d tether myself to it so as not to float off and then ponder the millions of small, icy world-lets tumbling across my field of view.

A lovely vision on a wintery afternoon.

The Geminids ain’t over yet! Meteor shower update

Jeff Stephens created this composite of all the Geminids he caught during the peak hours on the morning of December 14th from central Louisiana. His camera faced north. Click for more of Jeff’s images. Credit: Jeff Stephens

An overcast of biblical proportions has hidden the sky at my home for 9 nights in a row. But even without seeing a single Geminid meteor, I can tell you this – the shower’s been fantastic. NASA’s network of all-sky cameras detected more than 200 fireballs and the International Meteor Organization’s quicklook data show a peak of 155 meteors an hour around 10 p.m. (CST) December 13th.

Though past maximum, bits and pieces of the asteroid 3200 Phaethon, the meteor shower’s parent, will continue to zip through the atmosphere over the next few nights. We may even be see some larger fireballs. The Geminids arrive pre-sorted, with the smallest meteoroids appearing early on, followed by larger crumbs and small rocks later.

Diagram of the inner solar system showing the orbits of Geminid fireballs (and a few other bright meteors) on December 14th. They intersect at the blue dot, which represents Earth, and are color-coded by velocity, from slow (red) to fast (blue) based on information from NASA’s all-sky camera network that scans the skies above the U.S. Automated software determines the orbits and other characteristics of the incoming meteors. Credit: NASA/ Bill Cooke

The moon has continued to slim down and is now a crescent rising well after midnight. Best viewing times will be from about 10 p.m. to 3 a.m. There’s also a decent chance for a small auroral display tonight for the northern U.S. and southern Canada.  You’ll find more about the Geminids HERE.

Zoltan Kenwell got a nice auroral surprise when he stepped out to watch the Geminid meteor shower near Edmonton, Alberta, Canada yesterday morning December 14th. Click to see more of Ken’s aurora photography. Credit: Zoltan Kenwell

Heck of a place to watch a meteor shower … and northern lights. Zoltan Kenwell kicks back and takes it all in Sunday morning. Credit: Zoltan Kenwell

Rosetta’s comet – colorful personality but gray as a foggy day

A color photo of Comet 67P/Churyumov-Gerasimenko composed of three images taken by Rosetta’s scientific imaging system OSIRIS in the red, green and blue filters. The images were taken on August 6, 2014 from a distance of 75 miles (120 km) from the comet. Click to enlarge. Credti: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

Is this really a color photo? Yes! And it shows how remarkably gray and colorless the comet truly is. This is just how you’d see 67P/C-G if you could piggyback on Rosetta and whirl around it for a few orbits.

“As it turns out, 67P/C-G looks dark grey, in reality almost as black as coal,” says the instrument’s Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research.

Pictures of Enceladus, the Earth, the Moon, and Comet 67P/C-G showing their relative brightness. Saturn’s icy moon Enceladus reflects back nearly 100% of the sunlight it receives, Earth, 31% , the moon, 12% and 5% for 67P/C-G. Images not to scale. Credit: NASA/JPL/Space Science Institute (Enceladus); ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/ UPM/DASP/IDA and Gordan Ugarkovich (Earth); Robert Vanderbei, Princeton University (Moon); ESA/Rosetta/NAVCAM (67P/C-G).

The intensity of the images has been enhanced to span the full range from black to white and bring out surface details, but the colors haven’t been altered. Shadows are deep black because there’s no atmosphere to significantly diffuse the light as on Earth. Some photos however do show shadow detail from sunlight reflecting off other parts of the comet and into shadowed regions.

The comet – at least at this distance – is nothing more than a hundred shades of gray. A careful analysis shows a small amount of excess red light reflected from 67P due to fine-grained dust on its surface. We can’t see this hint of rouge because our eyes are much more sensitive to the greens, yellows and blues of sunlight, but a camera recording light reflected from the comet through multiple color filters can.

Before Rosetta moved in close to 67P/C-G, Earth-based telescopes had also shown the comet’s gray nature, but I think it’s safe to say scientists were surprised that even close-up, the comet remains a monotonous monochrome megalith.

For instance, any ice on the surface should appear brighter in the blue filter, leading to the appearance of blue-ish patches. This photo contains no indication of any such icy patches, consistent with observations made by some of Rosetta’s instruments.

So what’s up? The same thing that dulls the shine on your computer monitor coats the surface the comet: dust. Dark dust is everywhere and mission scientists are in the process of determining what it’s made of. Ice is surely there – Philae detected ice at its landing site and Rosetta’s MIRO instrument found the comet shedding 2 cups of water a second as icy vapor.

Jets of carbon dioxide blast from beneath the surface of Comet Hartley 2 in this photo taken during the flyby by NASA’s EPOXI/Deep Impact spacecraft in 2010. The jets carry water ice in the form of large snowballs (white dots) and dust particles. Credit: NASA

It would seem logical to assume that some of the dust embedded in that vaporizing ice drifts back down to the surface, quickly covering any exposed material. I’ve seen something similar happen during a winter here in Duluth, Minnesota. Grit and sand accumulate atop fresh snow. Over time, the snow compacts, melts and refreezes to form ice covered by black gunk.

Often, water escapes as a plume of dust-laden vapor through a vent in its surface like a geyser. I’d love to see a close-up of one of those. Imagine the amount and ubiquity of fine dust deposited over millions of years every time the comet swings by the Sun and gets cooked.

If we just get somebody up there to sweep the floor.

Ho-ho-ho! Comet Lovejoy Q2 brings Christmas joy

Comet Lovejoy Q2 on December 12th shows a big glowing coma and faint, 2° long gas tail. The comet becomes an easy binocular object this week for northern skywatchers. Credit: Rolando Ligustri

A naked eye comet for Christmas? Yes, Bobby there is a Santa Claus. Comet C/2014 Q2 Lovejoy, which has been slowly pushing into northern skies this month, has brightened in recent days to magnitude +6.5. That’s the cusp of naked eye visibility. A few observers in Australia, where Lovejoy hovers nearly overhead, reported seeing it faintly with the naked eye last night.

Most of us will view Q2 with ease in binoculars, especially once it gains a bit more elevation at night. Right now, the comet’s in Puppis the Stern, a gangly constellation south of the more familiar Canis Major the Greater Dog, home to Sirius, the brightest star. When best placed for observing around 1-1:30 a.m. local time it climbs to an altitude of 10° (one fist held at arm’s length) for observers in the central U.S. but just 3-5° for the northern states.

Comet Lovejoy Q2 begins its northward trek slowly but picks up speed with each passing night. On the night of December 28-29, the comet will pass 1/3° from the bright globular cluster M79 in Lepus. This map shows the sky and comet’s position facing south from 42° north latitude around 1:30 a.m. CST. Click to enlarge. Source: Chris Marriott’s SkyMap software

That will change soon as Lovejoy swings rapidly northward and rises earlier and earlier in the coming nights. By Christmas, the comet will be even brighter and stand 20° high from places like Kansas City, Denver and Indianapolis shortly before midnight.

Lovejoy Q2 is Australian amateur astronomer Terry Lovejoy’s fifth find. He snagged it while making a photographic search for comets with his 8-inch (20-cm) last August. Q2′s been on a beeline toward the Sun since that time and brightened from a 15th magnitude smudge to a robust, glowing ball with a skinny-necktie tail.

Comet Lovejoy Q2 is a long-period comet, dropping in toward the Sun with an orbital period of about 11,500 years. Here it’s shown when nearest Earth and brightest in early January 2015. The comet follows a steeply tilted orbit that takes it high over the plane of the planets. Credit: NASA/JPL HORIZONS

As it approaches Earth this month and next, Q2′s expected to brighten to 5th magnitude, putting it within naked eye range from the outer ‘burbs of a mid-sized city. Binoculars will provide a clear view of the fat, fuzzy coma and telescopes will add a faint ion tail composed of vaporizing gases fluorescing in solar UV. Cool!

Closest approach to Earth happens on January 7-8th when Lovejoy will be 43.6 million miles (70.2 million km) away. A little more than 3 weeks later on January 30, the comet passes perihelion to the Sun at a distance of 120 million miles.

I’ve included three maps to find and track Comet Lovejoy through early January. The first (top) is a wide view showing the “big picture” to help you get oriented. The others go in tighter and show black stars against a white background. I prefer them for a couple reasons – they use far less ink when making printouts and are cleaner and easier to read at the telescope. Click each to download a larger version.

Detailed map showing the comet night-by-night path starting tomorrow December 14th through December 27th in the early morning hours (CST). Stars shown to magnitude +8.0. Source: Chris Marriott’s SkyMap software

Because Comet Lovejoy moves rapidly into the evening sky by mid-late December, its position on this map is shown for 10 p.m. (CST) nightly. Mark your calendars for the close approach to M79 on Dec. 28-29. Source: Chris Marriott’s SkyMap software

I’m hoping we get out from under our week-long battle with clouds, so I can see the comet for myself. I’ll be updating all along and would love to include your observations in future blogs.