Odd glows around sun may be caused by Canadian forest fires

A large, pale blue aureole or disk surrounds the sun this morning July 18 in a sky filled with high-altitude smoke from forest fires burning in Canada’s Northwest Territories. Wide-angle 15mm lens view. Credit: Bob King

It happens every summer. Forest fires in Canada pump out vast quantities of smoke which are carried by winds to the south and east. Arriving days later over the northern Great Plains and Midwest, the blue sky soon turns a pallid gray.

Smoke from forest fires near Faber Lake in the Northwest Territories streams south in this photo taken July 7, 2014 by NASA’s Terra satellite. Credit: NASA

The smoke spreads in subtle ripples and bands and dims sun and stars alike. Technically, the sky is clear, and that’s what you’ll hear from the weather service, but the smoky haze creates an overcast of its own. Sunlight is less intense, while the solar disk glows pale yellow-orange compared to its normal white-yellow. It may even disappear from view well before sunset, fading away in the fiery haze.

Wide-angle photo this morning showing the blue aureole and brownish outer ring around the sun. Could smoke particles be responsible for the appearance? Credit: Bob King

Early this morning, under faux clear skies, I noticed an unusual pale blue disk or aureole around the sun about four fists (40 degrees) wide. Beyond that lay a wide, darker ‘ring’ tinted a pale gray-brown. Forest fires release gobs of minute smoke particles and oil droplets into the atmosphere which, like the ash from volcanic eruptions, can occasionally color the sun or moon blue.

Patches and bands of smoke from forest fires are seen in this National Weather Service satellite photo taken this morning July 18, 2014. Credit:NASA

It works like this. Particles that are about 1 micron across (1/1000 of a millimeter) are the same size as the wavelength of red light. The sun pours out all colors of light, but when the red portion strikes the ash or smoke, it’s scattered about the sky. The shorter wavelength blue light isn’t affected and continues to pass directly to our eyes, coloring the sun a pale blue. In effect, the particles act like a blue filter.

Bishop’s Ring around the sun due to volcanic ash of the Eyjafjallajökull volcano on Iceland. Photographed from Leiden, the Netherlands on May 18, 2010. Credit: Marco Langbroek

I’ve seen no blue moons or suns yet, but I wonder if the blue aureole might be the result of smoke particles. It resembles a phenomenon called Bishop’s Ring seen around the sun during volcanic eruptions and created by ash and sulfur droplets. Notice though the ball of the sun remains red-orange, indicating that the smoke particles are not the right size to create a blue sun. At least not yet.

A red sky sunset Friday evening July 18. Colors are enhanced from airborne smoke. Credit: Bob King

If you live where the sky is affected by the smoke of distant fires, keep an eye on the sun, moon and sky for unusual colors, disks and rings. We’d love to hear what you’re seeing.

Abundant high altitude dust on Mars scatters red light away from the sun, lending both the solar disk and sky near it a pale blue. Photo taken on May 19, 2005 by the Spirit Rover. Credit: NASA/ JPL-Caltech

My blue disk this morning also reminded me of the blue aureole around the rising sun on Mars taken by the Spirit Rover. Dust in the Martian atmosphere scatters red light like much like ash and fire smoke do on Earth. Blue sunrises and sunsets there are probably fairly common.

Supermoon fun / Mars-Spica conjunction tonight / Venus visits Mercury at dawn

Passing clouds create a colorful corona around last night’s full moon. Credit: Bob King

The moon coaxed many of us out for a look last night. We had clear if hazy skies in my town which made for a striking display of lunar crepuscular rays. Lunar what? If you’ve ever seen sunbeams poking through clouds in the afternoon or evening, you’re looking at crepuscular rays. Crepuscular comes from the Latin word for ‘twilight’ as the beams are often noticed during early evening hours around sunset.

A delicate display of crepuscular rays radiates across the sky above a cloud-shrouded moon. Credit: Bob King

Bright rays shining through gaps in the clouds alternate with shadows cast by other clouds to form a spreading fan of light and dark columns. The dustier or smokier the air, the more vivid the crepuscular display. Notice how they appear to converge on the moon. This is an optical illusion. The rays are perfectly parallel just like endless rows of beans on a farm that appear to merge together in the distance.

Last night’s supermoon shines back from a mobile phone. I took the picture by holding the phone’s camera lens directly over the eyepiece. Credit: Bob King

Many of us like to take pictures of the moon through a telescope using nothing more than a mobile phone. If you’ve tried this, you know how tricky it is to hold the phone camera in the right spot over the telescope eyepiece. It takes a few tries, but the results can be remarkable. Phones do well on bright celestial object like the planets, moon and sun (with a safe filter). Despite what some ads might tout, phones can’t yet record fainter things like galaxies, nebulae and the like.

Orion Telescopes makes an adaptor to hold a phone securely over the telescope. While it gets mixed reviews, you might want to consider it if you don’t want to invest in a separate camera but would still like to create an album of your own astrophotos.

Mars (top) and Spica last night July 12. The difference in color between the rusty planet and blue-white star was very easy to see. Mars will remain near the star the next few nights but change its position like the hour hand on a clock. Credit: Bob King

I know we’ve all been moonstruck the past few nights, but did you happen to notice how close Mars and Virgo’s brightest star Spica have become? Last night they were separated by only 1.5 degrees; tonight they’ll be in conjunction a squinch closer at 1.3 degrees. Watch for the duo in the southwestern sky near the end of evening twilight.

Mars moves eastward and soon departs Spica en route to its next notable appointment, a conjunction with Saturn on August 25. Have you been up at 5 a.m. lately? Me neither. But my crystal ball a.k.a. Stellarium program tells me that Venus and Mercury are playing tag an hour before sunrise in the eastern sky.

Venus and Mercury shine together low in the northeastern sky during morning twilight the next couple weeks. This map shows the view tomorrow morning 45 minutes before sunrise. Venus will be about 10 degrees (one ‘fist’) high, Mercury half as much. Source: Stellarium

Mercury reached greatest elongation (distance) west of the sun yesterday and now appears about five degrees high in the northeast some 45 minutes before sunrise. Look for it about the same distance below brilliant Venus. This is a good apparition of Mercury, and having Venus nearby makes it easy to spot.

The swiftest-moving planet will hang near the goddess planet for the next two weeks, all the while growing in brightness as its phase fills out from crescent to full.

Giant cave found on Mars

A beautifully conical crater pit divots the flank of ancient volcano Pavonis Mons on Mars. This digital terrain model is color coded for elevation with red for higher terrain and blue lower. Click to enlarge. Credit: NASA/JPL/University of Arizona

Caves are nothing new to the Red Planet, but a recent photo taken by NASA’s Mars Reconnaissance Orbiter (MRO) reveals a particularly large example on the flanks of the shield volcano Pavonis Mons.

Highest resolution image of the crater pit cropped and enhanced so you can see the opening at the bottom and a hint of the debris pile. Credit: NASA/JPL/University of Arizona

The walls of the pit are very steep –  if they were any steeper, debris would crumble off the walls and roll down through the hole at the crater’s base. Material that once filled the pit drained down the walls to form a pile of debris in a subterranean chamber below. The top of this debris pile can be seen through the opening about 92 feet (28 meters) farther down, although only a hint of it appears in these photographs.

An approximate cross-section of the pit showing the tall pile of rock and soil on the floor of a possible lava tube cavern hidden beneath the extinct volcano Pavonis Mons. Credit: Bob King

Based on a digital model of the ancient volcano’s terrain, scientists can estimate how much material was once in the pit and how big the pile below must be. The results are amazing – a huge hill of soil and rocks some 203 feet (62 meters) tall stands below the opening in the crater’s floor. Given that the top of this pile is 92 feet below the rim of the central hole, this tells us that the empty cavity was once 295 feet deep (90 meters) deep, prior to collapse and infilling.

Natural light view of the crater pit and its central opening to a cavern below. Credit: NASA/JPL/University of Arizona

Only a few caves on Earth are this deep. Most of those are created when water dissolves limestone. Limestone remains elusive on Mars, so planetary astronomers look to lava tubes as the most likely source of the subterranean cavern beneath the pit.

A skylight over a lava tube still coursing with lava on Kilauea in Hawaii. Credit: Martin Ruzek, USGS Hawaiian Volcano Observatory

Most Martian volcanoes are built up from multiple lava flows pouring down their flanks eruption after eruption. Sometimes the surface lavas cool and solidify to form a roof over lavas that continue to flow in underground lava tubes.

As the tubes drain, they can leave empty caverns – caves as it were. Sections of the roof can later collapse forming openings into an underground network of skylights.

Perhaps that’s what were seeing here – a window into the past when lava coursed across the thickening slopes of Pavonis Mons. One wonders whether geothermal springs might still bubble and trickle within the cave’s recesses. Could thermophilic (heat-loving) bacteria have evolved on Mars as they did on Earth and gained a foothold there? And might their descendants still be holed up as the rest of the planet became a desert sterilized by ultraviolet light from the sun?  In my crystal ball I see future mini-drone missions to Martian caves followed by visits from astronauts.

Maybe someday we’ll see what’s up down that hole.

Celestial fireworks light up the sky on the Fifth of July

The crescent moon shines in the southwestern sky tonight July 2 not far from Leo’s brightest star Regulus. It’s headed for two fine conjunctions later this week. Stellarium

We celebrate Independence Day this Friday the 4th with parades and good food topped off with colorful fireworks. Consider that the opening act. Festivities continue into the weekend with two spectacular conjunctions of the moon and planets.

Saturday evening July 5 allow your gaze to wander up to the first quarter moon. Levitating above it will be a bright red light – the planet Mars! They’ll be close. From most of the central and eastern U.S. and Canada the two are separated by just a half degree or one moon diameter. Look a short distance to the left of moon and you’ll also spot Virgo’s brightest star Spica.

The first quarter moon pays a close visit to Mars on Saturday July 5 and then passes Saturn two nights later. The views show the scene from the central U.S. around the start of nightfall. Stellarium

If you live farther south, the moon will inch closer to Mars. From sizzling Miami, the duo’s only a 1/3 of a moon apart, while the moon will completely cover or occult Mars for up to an hour across a wide swath of South America. Click HERE for a map and times showing where and when the occultation will occur.

Though Mars isn’t quite as bright as it was at opposition in April, it’s still brighter than its color rival Betelgeuse in Orion. With haze-free skies and a pair of binoculars you might be able to see it atop the moon a short time before sunset. Certainly worth a try.

Everybody loves an encore after a great performance, and the moon’s happy to oblige. Two nights later on July 7 it glides about a degree (two diameters) directly below Saturn. Once again, the moon will occult the planet as seen from the southern half of South America. While these sky events aren’t exactly stars exploding before our very eyes, their quiet beauty is worth our admiration.

Two asteroids approach in the night / See Saturn’s elusive moon Iapetus

Map showing Ceres and Vesta as they approach each other closely this coming week. Both asteroids are near the easy-to-find star Zeta in Virgo not far from bright Mars (see map below). Although the asteroids appear very close together in the sky, they’re really about 51 million miles apart with Vesta in the foreground. Click to enlarge. Source: Chris Marriott’s SkyMap

This coming week there will be something for everyone in the night sky whatever instrument you choose: telescope, binoculars or naked eyeballs.

The biggest asteroid, Ceres, and brightest, Vesta, have been on converging paths since early spring. Right now they’re about a moon diameter (1/2 degree) apart and closing with each passing night. Saturday night July 5 – one week from today –  they’ll be three times closer yet, separated by just 10 arc minutes. To see this double asteroid treat a pair of 35 or 50mm binoculars should do the trick.

Use this wider view to help get oriented. Our two featured asteroids are near the 3rd magnitude star Zeta Virginis just above the bright pair of Mars and Spica. The map shows the sky around 10 p.m. local time tonight June 28, 2014 for the central U.S. Stellarium

Just as moon routinely has conjunctions with bright planets and stars during its monthly round through the zodiac, Vesta and Ceres will be in conjunction one directly atop the other on July 5. Vesta will shine at 7th magnitude and be easy to spot in binoculars; fainter Ceres at magnitude 8.3 will take a little more effort. Since asteroids are too small and far away to show as disks in most telescopes, the pair will look like a temporary ‘double star’ in all instruments.

Double your conjunction fun on Saturday night July 5. The same night Ceres and Vesta are closest, the moon and Mars form a tight duo nearby. From parts of South America, the moon will cover or occult the Red Planet. Stellarium

Another celestial duo debuts on the very same night the asteroids are closest. For observers in the U.S. and Canada, the moon, some 7 degrees south of Vesta-Ceres, passes only a half degree from Mars. Two conjunctions in the same small pocket of sky on the same night!

For U.S. observers, this all happens the night after the July 4 Independence Day fireworks. Could July start with more of a bang?

Another telescopic delight is happening a stone’s throw from Mars around the planet Saturn. Of the 62 known moons of the ringed planet, one of the most peculiar is 907-mile-wide Iapetus, which orbits well beyond the more familiar telescopic moons Titan, Rhea, Tethys and Dione.

Ever seen Saturn’s peculiar moon Iapetus? Right now it’s west of the planet and bright — second only to the moon Titan. Click to enlarge. Source: Starry Night

Iapetus has two faces really. One is shiny white and bright as snow, the other dark as the sky above Gotham City. The moon takes 79 days to complete one orbit around Saturn and like our own moon, keeps one face locked toward the planet. When it orbits east of Saturn, Iapetus shines dimly at magnitude +12 because its dark side faces us. But when it’s off to the west of the planet, the brilliant side turns our way and we see it shine two magnitudes brighter.

Saturn’s moon Iapetus, 907 miles (1,460 km) in diameter, has a dual personality. One hemisphere is covered with bright ice, the other with darker material possibly ejected by impacts on the more distant moon Phoebe. Credit: NASA / JPL / Space Science Institute

Greatest brightness occurs at the time of greatest distance west of the planet which happens on July 3. You can use the map above to help you follow the moon through its cycle of bright to dim. For more information, please see this recent article in Sky and Telescope.

Mars and moon are mates tonight / Binocular comet eludes the Lion’s bite

Mars is in conjunction with the moon tonight. Watch for the pair during early evening hours. For U.S. observers the two will be separated by about four moon diameters. Stellarium

As twilight gives way to darkness tonight, look up at the waxing moon in the south. Just above it you’ll see the planet Mars. If you’re game, whip out a pair of binoculars and see if you can spot Mars before sunset using the moon as guide.

It’s been two months now since Mars made its most recent closest approach to Earth. While the planet has faded a full magnitude and shrunk in size since opposition, it will remain the brightest ‘star’ in the evening sky until June 27, when Arcturus will outshine it by a hair.

Mars has resumed its normal eastward motion across the sky and is now on the move across Virgo. Watch for it to glide above bright Spica in mid-July and below Saturn in late August.

Mars looks very much out of round this month. It’s only about 90% illuminated and in gibbous phase. Outer planets – especially Mars – show a gibbous phase when illuminated by the sun from a very different angle than we see it on Earth. Credit: Giorgio Rizzarelli

Through a telescope it’s easy to see that its phase has changed from full to gibbous.

The inner planets Venus and Mercury show phases from crescent to half to full as they alternatively pass between Earth and sun, but the outer planets are limited to full and gibbous phases because they’re forever outside the orbit of our own planet. No passing between the sun and Earth for them.

Left: Inner planets Venus and Mercury pass through all phases from crescent to full. Outer planets appear full around opposition and gibbous when viewed from the side. The effect is most extreme at quadrature when a planet is 90 degrees from the sun. Credit: Univ. of Tennessee-Knoxville

Full phases happens around the time of opposition when Earth and an outer planet like Mars are lined up on the same side of the sun and nearest each other. We face the planet square-on and it appears fully illuminated. Several months past opposition, sunlight strikes Mars at a very different angle than what we see on Earth. We look ‘off to one side’ instead of directly at the planet; from our perspective a portion of its globe is hidden in shadow and we see it as little gibbous ‘egg’.

The shadowing effect is most extreme at ‘quadrature’ when an outer planet lies 90 degrees from the sun, ie. it’s due south at sunrise or sunset. Mars reaches eastern quadrature on July 19.

Jupiter and Saturn also show a phase effect but it’s very, very slight because they’re so far away that Earth and sun appear in nearly the same direction from their perspective. There’s very little ‘looking off to one side’ perspective compared to much closer Mars.

8th magnitude comet K1 PANSTARRS travels above the head of Leo the Lion this month. This map shows its position every 5 days with stars to magnitude 8. The stars marked Mu and Lambda are two of the bear’s claws in Ursa Major. Leo is mid-way up in the southwestern sky at nightfall. Click to enlarge. Created with Chris Marriott’s SkyMap software

Although the moon is getting brighter by the night as it approaches full phase on June 13, I see it’s time for a new map showing the ramblings of comet C/2012 K1 PANSTARRS. This reliable comet has been slowly getting brighter all spring and now has a nice 1/2-degree tail visible in 6-inch and larger telescopes. At magnitude +8, I’ve seen it plainly with 40mm binoculars from a dark sky.

Comet K1 PANSTARRS on June 1, 2014 displays a bright head and two tails – a brighter dust tail pointing east and a faint gas or ion tail. Credit: Gianluca Masi

This month it moves from the obscure constellation Leo Minor into Leo the Lion and will continue to slowly brighten. The best time to view K1 PANSTARRS is at nightfall when it’s highest in the southwestern sky.

Moonlight won’t interfere too much with viewing tonight but will be an issue in the coming nights. Dark skies return around June 15.

Give it a try – we’ve got until mid-July. After that northern hemisphere observers won’t see the comet again until morning twilight in early September.

Mars got a black eye this March

A large, fresh crater on Mars resulting from an impact sometime on March 27-28 this year. The main crater’s 159 by 143 feet (49-meter diameter). It’s surrounded by secondary craters (circled) probably formed from impact debris crashing down on the surface after the crater was excavated. Click to enlarge. Credit: NASA/JPL/Univ. of Arizona

Let’s face it. We’re all sitting ducks. Planets get whacked routinely by space debris. Most of it gets burned up in our atmosphere; a few pieces occasionally fall to the ground every year as meteorites. Mars is in the same boat. With a difference. It’s atmosphere is much thinner than Earth’s, allowing smaller meteoroids to penetrate to the surface.

This pair of images was taken 1 day apart by the lower resolution weather camera on NASA’s Mars Reconnaissance Orbiter (MRO). The left image was taken during Martian afternoon on March 27, 2012; the right one on the afternoon of March 28, 2012.The dark area in the “after” image is about 5 miles (8 kilometers) wide and marks the spot of the new crater. Credit: NASA/JPL-Caltech/MSSS

NASA’s orbiters have to date discovered about 400 fresh craters on the Red Planet using before and after photos taken from orbit. Recently, the largest ever impact crater in the solar system confirmed by this method was spotted on Mars by a scientist Bruce Cantor who studies the daily images taken with the Mars Reconnaissance’s weather-monitoring camera. His eye caught a dark spot in late March that wasn’t there the last time he looked.

Before and after pictures taken with the Context camera on MRO. Left photo was taken on Jan. 16, 2012; right photo on April 6. The dual-impact crater stands out clearly. Credit: NASA/JPL-Caltech/MSSS

When the more powerful cameras on Mars Reconnaissance Orbiter zoomed in for a look, they revealed a fresh impact scar half as long as a football field (49-meters) with a good-sized secondary crater biting into the main crater’s south rim. Scientists suspect the original meteoroid broke up into many pieces on atmospheric entry creating not only the secondary crater but a smattering of smaller craters (circled above) in the vicinity. It’s also possible that chunks of crust blown out by the impact fell back and gouged out some of the smaller depressions.

Fresh landslides created by the shock wave from the impact darkened the slopes in the 5-mile area surrounding the new craters. Credit: NASA/JPL-Caltech/MSSS

Working through older images, Cantor was able to narrow the time of the crater’s formation to sometime between the afternoon of March 27 and the following afternoon March 28. This is the narrowest time interval in which a crater-forming event has ever been observed.

Alfred McEwen, principal investigator MRO’s high resolution camera, estimates the impact object measured about 10 to 18 feet (3 to 5 meters) long, or less than a third the estimated length of the asteroid that hit Earth’s atmosphere near Chelyabinsk, Russia last year.

Saturn disappears, Mercury appears during ‘night of the planets’

Saturn covered and uncovered by the moon earlier today by Dave Herald, Murrumbateman, Australia

Enjoy the video. Dave Herald did a great job recording this morning’s Saturn occultation. The images are very sharp. I always find it remarkable how atmosphere-less the moon is. There’s not a hint of softness in the planet as it’s devoured by the lunar limb. If there were substantial air, the planet would gradually soften and fade.

For a moon or planet to be completely without air is next to impossible. The solar wind knocks atoms from minerals on the lunar surface and sends them reeling into the virtual vacuum above the surface. Studies have found potassium, sodium, helium and argon in the moon’s exosphere, the name given to the lunar atmosphere. Bombardment of the moon’s surface rocks by micrometeorites and the solar wind release potassium and sodium; helium and argon probably bubble up from radioactive decay of those same rocks. Helium may also arrive via the sun’s wind.

Glow from sodium in the lunar atmosphere. The light from the moon has been blocked by the telescope, but the size, position and phase of the Moon are shown by the superimposed image in the center. Rayleighs are a measure of brightness. Credit: NASA

At sea level on Earth, we breathe in an atmosphere where each cubic centimeter contains 10,000,000,000,000,000,000 (10 quintillion) molecules; by comparison, the lunar atmosphere has less than a million molecules in the same volume.

Comets and meteoroids striking the surface temporarily enhance the amounts of other atoms and molecules. But the sum total of all the sputtering and interacting is an atmosphere equal to the amount of air you’ll find 250 miles high where the space station plies it orbit. Not much.

Mercury stands all by itself low in the northwest in this photo taken about 50 minutes after sunset last night. Credit: Bob King

At my house, we saw no occultation of Saturn, but the two did stand together in the southeastern sky at dusk. On the opposite end of the heavens, Mercury made a fine naked eye appearance in the northwestern sky.

Jupiter glows over Amity Creek last night. Both the creek and the sky were lit by the light of the full moon. Credit: Bob King

I first caught it around 9:15 p.m. some 40 minutes after sunset and watched it for at least a half hour. Capella and Jupiter – both higher up in a darker sky – made for great sight lines to the planet.See yesterday’s map for details.

Jupiter in Gemini remains the most brilliant object in the western sky at dusk during early evening hours. I watched it from a nearby creek that rushed with water from snow melt and recent rains.

Mars stood between Jupiter and Saturn. This week the ‘boring’ hemisphere – the one with fewest dark markings – is turned toward western hemisphere observers.

The Moon, Mars (upper right), Saturn (lower left), Spica (immediate right of moon) and Arcturus (top) as seen from Dayton, Ohio on May 12. Credit: John Chumack
Dayton, Ohio

But there’s still much to see – enough to easily stay up past your bedtime. The north polar cap on Mars remains visible despite the seasonal summer ‘heat’, and white clouds topping the planet’s major volcanoes are visible along the planet’s western edge. Check it out.

Star trail photo hints at hidden polestars

A 45-minute time exposure of the southern sky taken in early May shows trailed stars. The fat, bright streak is the planet Mars. Credit: Bob King

A week ago I made a 45-minute time exposure of the southern sky featuring the planet Mars. As the Earth rotated on its axis, the stars trailed across the sky. But take a closer look at the photo and you’ll see something interesting going on.

The trails across the diagonal (upper right to lower left) are straight, those in the top third arc upward or north while those in the bottom third curve downward or south.

I’ve drawn part of the imaginary great circle in the sky called the celestial equator. Residents of cities on or near the Earth’s equator see the celestial equator pass directly overhead. From mid-northern latitudes, it’s about halfway up in the southern sky. From mid-southern latitudes, it’s halfway up in the northern sky. Credit: Bob King

I suspect you know what’s happening here. Mars happens to lie near the celestial equator, an extension of Earth’s equator into the sky. The celestial equator traces a great circle around the celestial sphere much as the equator completely encircles the Earth.

On Earth, cities north of the equator are located in the northern hemisphere, south of the equator in the southern hemisphere. The same is true of the stars. Depending on their location with respect to the celestial equator they belong either to the northern or southern halves of the sky.

Earth’s axis points north to Polaris, the northern hemisphere’s North Star, and south to dim Sigma Octantis. Illustration: Bob King

Next, let’s take a look at Earth’s axis and where each end points. If you live in the northern hemisphere, you know that the axis points north to the North Star or Polaris. As the Earth spins, Polaris appears fixed in the north while all the stars in the northern half of the sky describe a circle around it every 24 hours (one Earth spin). The closer a star is to Polaris, the tighter the circle it describes.

Time exposure centered on Polaris, the North Star. Notice that the closer stars are to Polaris, the smaller the circles they describe. Stars at the edge of the frame make much larger circles. Credit: Bob King

Likewise, from the southern hemisphere, all the southern stars circle about the south pole star, an obscure star named Sigma in the constellation of Octans, a type of navigational instrument. Again, as with Polaris, the closer a star lies to Sigma Octantis, the smaller its circle.

Stars trail around the dim southern pole star Sigma Octantis as seen from the southern hemisphere. The two smudges are the Large and Small Magellanic Clouds, companion galaxies of the Milky Way. Credit: Ted Dobosz

But what about stars on or near the celestial equator? These gems are the maximum distance of 90 degrees from either pole star just as Earth’s equator is 90 degrees from the north and south poles. They “tread the line” between both hemispheres and make circles so wide they appear not as arcs – as the other stars do in the photo – but as straight lines. And that’s why stars appear to be heading in three separate directions in the photograph.

A view of the entire sky as seen from Quito, Ecuador on the equator this evening. The celestial equator crosses directly overhead while each pole star lies 90 degrees away on opposite horizons. Stellarium

In so many ways, we see aspects of our own planet in the stars above.

Mercury returns, planets align, life is good

Mercury is just entering the picture tonight but by May 10 it will be easy to see, along with three other evening planets, 45 minutes after sunset in the northwestern sky. The pink arc is the ecliptic, the apparent path the sun takes during its yearly travels. It’s also followed closely by the planets and moon. Click to enlarge. Created with Stellarium

Planets are popping up everywhere. We’ve touched on Jupiter and Mars many times the past few months, but recently Saturn and now Mercury have entered the scene. Maybe you’ve noticed Saturn now in the southeastern sky at nightfall. From the northern U.S. and southern Canada, it’s bright but low at nightfall. Saturn reaches opposition a week from now when it will be at its closest and brightest for 2014. Each night that passes, the ringed rises higher and becomes better placed for viewing.

Mars, brilliant and fiery orange-red, now dominates the southern sky before midnight, standing above fainter Spica in the constellation Virgo. Only a month past opposition, we’re smack in the middle of the best time to observe the Red Planet through a telescope. I try to catch a look every clear or partly cloudy night but nearly missed the chance last night.

Two different hemispheres of Mars. The left image from May 2 shows a shrinking north polar cap and clouds blanketing the base of several volcanoes (dark dots) along the left edge of the planet. Right view taken on April 14 shows the hemisphere currently facing U.S. observers at nightfall. Credit: Christopher Go (left) and Anthony Wesley

The sky suddenly cleared after almost a week of overcast. I figured I’d walk my dog first and then set up the telescope, but 15 minutes later, clouds reappeared in the west. I turned around and footed it back home as quickly as I could, catching just five minutes of Mars light before a blanket of clouds suffocated the starry sky. Yeah, it was worth it.

Jupiter on May 2 displays its two most prominent belts visible in small telescopes, the North and South Equatorial Belts. Credit: Christopher Go

You might think it’s crazy to look at a planet night after night. Amateur astronomers do this for several reasons. First, most nights the air is too turbulent for a clear, sharp view. Looking often maximizes your chances of seeing the planet crisply in stable air. Almost nothing in observational astronomy beats viewing Mars or Jupiter or Saturn without air currents gooing things up. At these special times the dross falls away and the planet looks absolutely real. No exaggeration, you feel like you’re right there.

Planets also rotate. One hemisphere faces us one night, another on a different night or different time of night. Repeated observation gives you a certain familiarity with the “landscape” and alerts your eye to any changes happening. Remember, on most planets, weather plays a role in their appearance. Unexpected changes like a newly-spawned dust storm on Mars or the disappearance of a cloud belt on Jupiter lend an air of anticipation to the night’s viewing.

The sky from the central U.S. facing west-northwest this evening May 3 about 25 minutes after sunset. Mercury will be very low (about 3-4 degrees) but bright. The crescent moon passes just north of the star Eta in the constellation Gemini. Stellarium

Let’s talk about Mercury a minute. Skywatchers blessed with a clear view down to the west-northwest horizon can find the little planet as soon as this evening. Face the sunset direction about 20 minutes after sunset and sweep a few degrees above the horizon with your eyes or a pair of binoculars. The planet now shines at magnitude -1.4 or nearly as bright as it can, an equal to Sirius, the brightest star.

If you don’t succeed, try again in a week on the 10th. After the late January show, the period from May 10-23 will be the best time this year to see the planet at dusk.