Tiptoe into the twilight zone to see Mercury at its best

Mercury stands alone low in the sky over grain elevators and freeways in this picture taken last night Jan. 27, 2014 in Duluth, Minn. Credit: Bob King

This week and next Mercury will be brightest and highest in the evening sky. Not until May will skywatchers in mid-northern latitudes have as good an opportunity to spy the planet that spins closest to the sun. That’s what makes it so tricky to see in the first place. Mercury never gets far enough from the sun to appear in a dark sky, forever lurking in the twilight zone.

Mercury will be visible for the next week low in the west-southwest sky at dusk. Start looking about 40-45 minutes after sundown. On Friday, a thin day-old moon will join the scene. Stellarium

Still, I was surprised how easy it was to see last night. Higher up than expected too. I bundled up and went out to look 45 minutes after sunset. Nothing. Where was Mercury? It turned out I was looking too low. Once I raised my gaze a bit, a solitary “star” popped into view about a fist above the southwestern horizon.

While the planet shines tonight at magnitude -0.5 (brighter than Vega and Arcturus) the hazier, thicker air near the horizon robs it of 1.2 magnitudes, dimming Mercury to magnitude +0.7 or about as bright as Altair in the Summer Triangle.  Still plenty easy to see with the naked eye.

I kept the planet in view until around 6:20 p.m. or more than an hour past sunset before subzero temps and 20 mph winds forced a retreat back into the car. If you’re in a mercurial mood, start looking about 45 minutes after sunset to the upper left of the brightest part of the lingering solar glow in the southwest. The planet hovers about 10-12 degrees (a little more than one fist held at arm’s length) high. Since Mercury has no bright company, if you see a single star in that direction, you’ve nailed it.

Only a spruce tree separates Venus from the crescent moon this morning Jan. 28, 2014. A similar but thinner crescent will be near Mercury in the evening sky on Friday Jan. 31. Credit: Bob King

To be on the safe side, you might consider toting along a pair of binoculars. I guarantee that once you find it with optical aid, you’ll quickly see Mercury with the naked eye.

Once you’ve fixed in your mind where Mercury is located along your local horizon, get ready for a really fine event. This Friday the 31st, an incredibly thin one-day-old moon will sidle up some 5 degrees to the lower right of the planet. Are you thinking pictures? So I am.

Place your camera on a tripod – or at least wedge it firmly against something – compose a scene including moon and planet and take a series of photos with your lens set anywhere from f/2.8 to 4.5. ISO 400 speed should be fine with exposures ranging from 2 seconds to 1/15 second. While you’ll get a decent photo with a standard lens, a 100-200mm telephoto lens will make for a tighter, more dramatic image.

As you stand in the cold clicking away or simply admiring Mercury, here are some interesting facts about the planet to warm your brain cells:

Color image of Mercury made by the MESSENGER probe. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

* At 3,032 miles (4,880 km) across, Mercury is smaller than Jupiter’s moon Ganymede and Saturn’s moon Titan.

* Mercury’s orbit is the most eccentric or least circular of all the planets. Its distance from the sun ranges from 29 to 44 million miles (46-70 million km).

* While Venus is slightly hotter, Mercury has one of the most extreme temperature ranges of any body in the solar system. With virtually no atmosphere to capture and distribute the sun’s heat, the sun-facing dayside of the planet tops out around 800 degrees Fahrenheit while the nightside dips to -297 F.

All the dayside heat leaks right back into space during the long night. And it is a L-O-N-G night. The sun’s enormous gravity has locked the little planet in a 3:2 rhythm or “resonance”. For every two orbits around the sun, Mercury rotates three times on its axis.

Since the planet completes an orbit in 88 days (one Mercury year), its day is twice as long as its year or 176 Earth days. Mercury’s sunny side bakes for nearly six months and then chills for another six. No wonder it experiences such extremes of hot and cold.

* Mercury’s slight axial tilt of just 0.03 degree means that craters at its poles are steeped in perpetual shadow and never heated by the sun, making them perfect places to trap volatile materials like ice and keep them frozen for a long, long time. New data from the MESSENGER spacecraft now gives strong evidence for ice holed up in some of these craters.

* Mercury has a large (by volume) partially molten iron core and a planet-wide magnetic field, a feature lacking on Venus and Mars.

Sesame Street’s Cookie Monster and a crater on Mercury appear to be related. Credit: NASA

* Mercury is the most cratered planet in the solar system. Unlike Earth, Mars and Venus, which have been extensively resurfaced through volcanic and tectonic processes, Mercury’s retains much of its ancient battered surface.

Mercury MESSENGER mission scores 100%

Global maps of Mercury. Half the globe is shown in black & white, the other in color. Each map is composed of thousands of images. Click this and any of the other photos for hi-res versions. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Nice job MESSENGER! After two years in orbit, the entire planet of Mercury has been mapped. Can a cellphone map app be far behind? Prior to MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), human eyes had seen less than half of the planet up close. No spacecraft had dropped by the solar system’s innermost planet since Mariner 10 sent us the first detailed images of Mercury during three brief flyby loops executed in 1974-75.

Craters (from left) Tolkien, Tryggvadottir and Chesterton are located close to the planet’s north pole and have permanently shadowed floors. MESSENGER found evidence for ice in all three. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Over the past two years the probe has taken more than 168,000 pictures of Mercury’s numerous craters, ridges and enigmatic “hollows”, mapped its topography and determined the makeup of minerals on its surface through examination of the light they reflect from the sun.The probe also revealed water ice coated with organic materials within permanently shadowed craters at the planet’s north pole.

The 20.5-mile-diameter crater Kertesz, named for photographer Andre Kertesz. Mercury craters are named for artists. Kertesz’s floor is pocked by enigmatic “hollows” which could be material boiled off by the sun’s heat and radiation. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

With the probe’s original mission extended from one to two years, it’s now coming to an end. Unless a further extension is approval, March 17 would be the last for data gathering. Principal investigator, Sean Solomon of Columbia University’s Lamont-Doherty Earth Observatory, has submitted a proposal that would keep MESSENGER and mission control in business for another two years, about the time it runs out of fuel and crash lands on Mercury.

Waters crater was recently named in honor of blues legend “Muddy Waters” (a.k.a. McKinley Morganfield). The “mud” pouring out below it is melted rock from the impact. A color image at upper right shows it’s appropriately blue-toned. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Keeping the mission running would let scientists continue targeted studies of various features and shoot photos at incredibly high resolution as MESSENGER’s decaying orbit carries it closer and closer to the surface. Not only that, but the spacecraft is ideally placed to study and photograph Comet ISON when it makes it grazes the sun later this fall.

An oblique view of a 174-mile-long escarpment cutting through a crater. The slope is a geologic fault resembling an “overbite” that formed when the planet shrunk due to cooling of its interior. The left side is 1.2 miles higher than the right. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

To celebrate MESSENGER’s milestone, I thought you’d enjoy a selection of images from recent photo shoots.We’ll know in April whether the mission will continue once a science commission makes its decision. Click HERE to browse more photos in the archive.

A closeup view of hollows in an unnamed crater. The pits almost always occur within or surrounding impact features. They’re about 100 feet to a couple miles wide and lack rims. Hollows might be volcanic vents or created when sulfur and other volatile materials escape from the surface during solar wind bombardment. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Jupiter and moon put on a great show at 18 below

The moon and Jupiter through a 400mm telephoto lens last night around 9:30 p.m. (CST) when they were near their closest separation. You can just make out Jupiter’s disk. Photo: Bob King

Jupiter and the moon were fabulous last night. I hope you got to see them. We were clear in Duluth, Minn. though there a price to be paid in frozen fingertips. The temperature hit -18 F at my house.

Our two celebs were so close together you could easily see the moon’s motion to the east in just 20 minutes. For a change, the air was tranquil overhead, giving steady, sharp images at the telescope. Craters like Copernicus, Plato and Tycho were crisply detailed and Europa’s shadow on Jupiter’s cloud tops looked like the most perfect of points.

Five of the 11-day-old moon’s most prominent craters are visible tonight in 8x (or higher) binoculars and small telescopes. Three of them – Copernicus, Kepler and Tycho – are surrounded by bright rays, which are aprons of impact debris. Plato has a smooth, dark, lava-flooded floor. Credit: Frank Barrett with my annotations

Tonight the moon moves further east into Taurus. As it waxes closer to full, we get more moon for our buck. That means more cool craters and alien terrain to pour over in binoculars and telescopes. I encourage you to take a look even if the weather bites. Just throw on a few more layers and laugh at the cold.

Heavy fog at -20 F over Lake Superior near the Lester River in Duluth, Minn. this morning. Cold air moving over the warmer lake condenses into tendrils of mist which gather into foggy clouds. Photo: Bob King

Go crater crazy this week; Venus and Saturn prep for close conjunction

Tonight the 6-day moon displays a concave (inward curving) terminator. Tomorrow night the terminator will swell further to the left and appear convex (curving outward). The southern or bottom half of the moon displays hundreds of craters visible in small instruments. Click photo for a map to identify lunar features by name with a hover of your mouse.  Photo: Bob King

I tried to observe my usual faint comets and galaxies last night but the bright moon reeled in my eyes like bait dangled before a fish. And why not? Now through about Saturday is the best time to enjoy views of the rugged lunar landscape in the smallest of instruments.

As the moon waxes from nearly half tonight toward full, fresh new territory is exposed to sunlight with each passing night. This line of advancing sunlight is called the lunar terminator and marks the boundary between the bright part of the moon we see and the part that will soon be revealed. What makes the terminator advance? Geometry.

This diagram shows the moon orbiting Earth as seen from far above Earth’s north pole. We see different amounts of the lit side depending on where the moon is in its orbit. Credit: Michele Stark

Because the moon revolves around the Earth, its position with respect to the Earth and sun is constantly changing night to night. When it lines up between the two bodies, we see 0% of the moon illuminated by the sun. When it’s a quarter of the way around its orbit and makes a 90-degree angle with the Earth and sun, we see half a moon or 50%. And when it’s directly opposite or 180 degrees from the sun, we see a full 100% illuminated moon. The phases work in reverse after full moon with a new cycle beginning about a month later at the next new moon.

We see the terminator sweeping from one side of the moon to the other during a full lunar cycle of about 30 days. The wobble, called libration, is due to the moon’s changing orbital speed and the tilt of its orbit. Credit: Tom Ruen

Around the time of half moon or first quarter phase, the terminator “pulls the shade back” on a multitude of craters that face us directly. That makes it easy to look straight down inside them. During other phases, we the lunar landscape sidelong and craters appear stretched out and too crowded together to fully appreciate their individuality.

Around first quarter we can take in fascinating details like cracks in their floors caused by the weight of ancient lava floods, concentric ridges in their walls from material that’s slumped downward over time, overlapping craters, craters within craters and majestic mountain pinnacles found in the centers of many craters from crustal rocks that rebounded after being compressed by the power of the impact that formed the crater in the first place.

The craters Aristillus and Alphonsus show features typical of many lunar craters including concentric inner walls (from slumping due to settling and gravity), central peaks and cracked floors. Click photo to see more examples. Credit: Damian Peach

Low-angled sunlight in the vicinity of the terminator creates long shadows that throws these and other features of the landscape into breathtaking 3-D relief. Time to take the bait.

Venus, Saturn and Virgo’s brightest star Spica tomorrow morning Nov. 20 about an hour before sunrise as you face east. Created with Stellarium

Morning skywatchers can now be on the lookout for the planet Saturn below Venus low in the southeastern sky about an hour before sunrise. Saturn’s rings are really opening up this season with a current tip of about 17 degrees. As with the moon, even a small telescope magnifying around 40x or higher will show the planet as a ball surrounded by at least one bright ring.

The two planets will gradually draw together this week as they head toward a close conjunction on Nov. 26 when they’ll be just half a degree apart. More on that later this week.

Cool stuff to see while you’re out tonight

This annotated photo shows the moon as it will appear this evening. The most prominent maria are labeled with numbers; craters and other features are lettered. Photo credit: copyright David Haworth www.stargazing.net/david

I know you’ll all be out there moon gazing tonight in celebration of International Observe the Moon Night. You can use the photo and key above to help you identify some of the gibbous moon’s most prominent features. The seas or “maria” (MAH-ree-uh) are visible with the naked eye, while sharp-eyed sky watchers can pick out the larger rayed craters like Copernicus and Tycho. All the other features are visible in binoculars and small telescopes.

* 1-6: The maria are those largish gray spots that make up the face of the “man in the moon”. They’re ancient impact basins created when asteroids struck the moon some four billion years ago. At that time, they looked like enormous craters, but lava from the mantle bubbled up through cracks and later filled them.
* A: Copernicus is 58 miles across and one of the most magnificent lunar craters. It looks like a bulls-eye surrounded by its bright rays of ejecta.
* B: Kepler is similar to Copernicus in appearance but smaller.
* C: Sinus Iridium or Bay of Rainbows is a large crater, the right half of which was flooded by Mare Imbrium lavas. As a result, we see only half the crater which resembles a bay.
* D: Plato is 68 miles across and a nice even gray color. It’s also been flooded by lavas from within, making it look like a miniature lunar sea.
* E: Gassendi crater is the same size as Plato. Its proximity to the moon’s day-night line, called the terminator, will bring its walls, rough interior and central peak into beautiful relief tonight.
* F: Tycho is 53 miles in diameter and one of the freshest, large lunar craters. Its extensive system of rays has no equal on the moon.
* G: Proclus is a small crater with a brilliant, asymmetric ray system.
* H: Langrenus, at 84 miles across, looks like a smooth white oval. Its “flat” appearance is due to lack of shadows (which show relief) from a high sun.
* I: Directly below or south of Tycho, you’ll see Clavius, one of the largest craters on the near side of the moon. It’s 140 across and home to lots of additional craters within its walls.
* J: The arc-shaped Apennines Mountain range lies along the southeastern border of Mare Imbrium. Peaks here reach to 2.8 miles.

Jupiter and its four bright moons: Io (I), Europa (II), Ganymede (III) and Callisto (IV) as seen around 9:30-10 p.m. tonight in binoculars and telescopes. Uranus is directly above the planet. North is at top, east to the left. Maps created with Stellarium

Jupiter quickly catches the eye low in the southeastern sky after 9 o’clock. There’s nothing else that comes close to its brightness in that region. Binoculars will not only show several of its brightest moons, which happen to be lined up left-to-right in order of increasing true distance from the planet, but also the planet Uranus. It’s the “star” directly above Jupiter and about as bright as the moon Io. Jupiter and Uranus are in conjunction with each other tonight and less than one degree apart. If you’re using a small or medium-sized telescope at its lowest magnification, both planets will fit comfortably in the same field of view. As you look at the pair, consider that Jupiter is 367 million miles from Earth, while Uranus is deep in the background at 1.8 billion miles or four times as distant.

The Summer Triangle is directly above the moon tonight. This map shows the sky looking south about 9 p.m.

Above the moon, stands the Summer Triangle, composed of the three luminaries Deneb, Vega and Altair. Vega is the brightest and will occupy the sky’s overhead spot called the zenith around 8:30 p.m.

The west-northwest is not without its celestial booty. Find the Big Dipper, which is leveling out low in the northwestern sky at nightfall, and follow the arc of its handle to the brilliant, papaya-colored Arcturus. No matter where you look tonight, there’s something for the eye to marvel upon.

As a reminder, members of the Arrowhead Astronomical Society will have telescopes set up for looking at the moon and Jupiter in Canal Park in Duluth – weather permitting – between 8 and 11 tonight. Look for us near the Lakewalk at the east end of the parking lot. See you there.

Use the handle of the Big Dipper to guide you to Arcturus, a bright spring star which is now dropping off into the western sky.

Take the plunge into that burnin’ ring of fire

Individual dew drops line a blade of grass this morning. Photo: Bob King

Yesterday on a walk in Hawk Ridge Nature Reserve near my home, a flock of migrating nighthawks blew by headed south. I identified them right away by their white wing patches. Birds on the move, cool mornings lavish with dew. I like these hints of fall. Through the telescope last night, the nearly 12-day-old moon served as an illuminated stage for the passage of yet more birds. Over a period of five minutes, I saw some a dozen silhouetted avians zip across the cratered landscape on their way outta here.

Now through September is an ideal time to point your telescope at the waxing moon — especially around full phase — to watch birds migrate at night. We don’t think about it much, but many birds are busy migrating while you and I are out like a light. Hummingbirds, warblers and others not only avoid the heat of day by doing so but are less likely to get nailed by a predator under cover of darkness. To watch the show, all you need is a small telescope and a big moon. Plunk in your low power eyepiece and just wait. I saw my first bird within a minute. They fly by quickly, but since I’m no bird expert, I couldn’t identify the different species. Craters are my forte.

Numerous white rings, splashy bright patches and ray systems are best visible around the time of full moon. Credit: Frank Barrett

Some amateur astronomers scorn gibbous and full moons as worthy of study because they’re too bright, and the landscape is washed out due to the sun shining almost directly above the moon’s surface. When the sun shines from the side, as it does near sunset and sunrise both here and on the moon, everything casts a shadow and shows minute detail. Every bump, wrinkle and hair on a person’s face stands out in glaring detail. But shine a light directly at a person’s face – equivalent to the sun shining squarely over the full or nearly full moon – and shadows and those disturbing wrinkles disappear, lost in a flood of light.

A full moon offers no sense of depth or relief, but does reveal details otherwise invisible at other lunar phases. That includes many small craters which hardly anyone notices during lesser phases, but which are transformed into brilliant rings during the equivalent of lunar high noon.  Last night I lost count of how many of these “hot rings” I saw through the telescope at low power. They’re so brilliant they resemble white flares or fiery white-hot rings of lava. Johnny Cash’s “Ring of Fire” comes to mind.

What you’re seeing is high-angle sunlight reflected off fresher rocks and soils on crater rims and floors or from the tendrils of long rays (splashed rock) surrounding fresher craters. The rays and lighter soils truly shine around the time of full moon. Once you get into seeing these strange lunar lily pads, you’ll be surprised at how alien they look compared to the more familiar peaks and crater holes seen to advantage at other phases.

Proclus crater photographed by astronauts aboard Apollo 15. Credit: NASA

I was particularly struck by the fiery ring of Proclus crater and its peculiar off-center system of rays. Proclus, at 18 miles in diameter, is a young lunar crater, and the brilliance of its rim is clearly the result of fresh rock exposed by impact that has yet to darken under the influence of solar radiation. It contrasts beautifully with the older, surrounding moonscape called Palus Somni or the Marsh of Sleep. The weird forked appearance of the rays suggests that the asteroid that created Proclus struck the moon at an oblique angle.

Several of the brightest craters and their systems of rays (strings of fresh secondary craters formed by rock ejected during the main crater's creation) around the time of full moon include Tycho and its rays, Aristarchus and Proclus. Credit: Frank Barrett

Other brilliant craters and ray systems include Aristarchus (brightest crater on the moon) and Tycho, and there are many more. Like Proclus, they’re relatively fresh craters compared to most. With binoculars you can see all three of the aforementioned as bright spots, while any telescope will show their ring-like forms and feathery rays in far more detail. Between moon and birds, you may find yourself staying at the telescope side later than you thought tonight.