Curiosity rover reaches the sublime Mt. Sharp

The next goal for NASA’s Mars Curiosity Rover – the beautiful layered rocks at the base of Mt. Sharp. Credit: NASA/JPL

You’ve seen it looming in the background of so many photo for more than two years. Finally, we’re there. NASA’s Curiosity rover rolled up to Mount Sharp in Gale Crater. With a peak 2.7 miles (4.4 km) high, Mt. Sharp stands more than a half mile higher than Mt. Ranier in Washington.

Orbital view of the 96-mile-wide Gale Crater, the peak Mt. Sharp and Curiosity’s landing site. The rover now begins its journey up the mountain’s slope. Credit: NASA

The mountain is built of layer upon layer of stratified rocks deposited by water and wind after the massive impact that excavated Gale Crater more than 3 billion years ago. From orbit, scientists have detected clays in some of the layers, an indication that water flowed here in the past.

Curiosity’s route up Mt. Sharp will first take it through the Pahrump Hills, which make up part of the Murray Formation of layered rocks. The white dashed line represents the border between rocks of Gale Crater’s plains, which Curiosity has investigated since landing, and those at the base of Mt. Sharp. Click to enlarge. Credit: NASA

As Curiosity begins its trek up the mountain’s slope, it will first trundle across the Pahrump Hills, a region of layered rocks that’s part of the Murray Formation. At some point within this broad expanse of soft rock, the rover will drill a sample and analyze it before continuing upslope. Several miles later, it will encounter a ridge of hematite-bearing rocks. Hematite is a gray version of iron oxide (rust) that precipitates in hot springs or in pools of standing water.

Orbital view of the 96-mile-wide Gale Crater showing Curiosity’s planned path up Mt. Sharp. The rover has traversed 5.5 miles to reach the mountain’s base. Credit: NASA image with illustration by T. Reyes

An intriguing layer of clay-bearing rocks that lies further upslope and offers the best opportunity of finding organic, carbon-containing minerals. A region containing sulfates, found earlier by Curiosity in the form of gypsum (calcium sulfate) extends beyond the clay layer higher yet. Gypsum is the same material used to make drywall back on Earth.

More detailed view of a potential path up Mt. Sharp from an earlier study this year showing the different terrains Curiosity will traverse. Credit: NASA/JPL

Scientists hope to study the transition between the two. Sulfates point to a time when the ancient, more watery Mars evolved from a wet, fresh-water climate to a drier one with acidic waters that favored the formation of sulfates instead of clays.

We all hope Curiosity’s wheels, poked and torn by sharp rocks, will be up for the long journey ahead.

“In late 2013, the rover team realized a region of Martian terrain littered with sharp, embedded rocks was poking holes in four of the rover’s six wheels. This damage accelerated the rate of wear and tear beyond that for which the rover team had planned. The team altered the rover’s route to a milder terrain, bringing the rover farther south, toward the base of Mount Sharp”, according to NASA.

A view of Mars taken on September 12, 2014 by the Curiosity rover’s hazard avoidance camera. Inset shows a big hole in one of the rover’s aluminum wheels from 2013. Looks rough out there! Credit: NASA/JPL

Curiosity has already fulfilled its initial goal of determining whether Mars ever offered an environment suitable for the formation and development of early life. Clay-bearing rocks in the Yellowknife Bay site revealed an ancient lakebed that once lapped with fresh water and contained the key elemental ingredients for life - sulfur, nitrogen, hydrogen, oxygen, phosphorus and carbon – as well as a sulfate energy source potential life could use to thrive.

Moon, Mars, Saturn and Antares gather at dusk tonight

The crescent moon, Saturn and Mars will form a compact triangle in the southwestern sky in this evening August 31st. 3.5º separate the moon and Saturn; Mars and Saturn will be 5º apart. Antares is about two ‘fists’ to the east or left. Stellarium

Don’t miss tonight’s sweet gathering of crescent moon and evening planets. Just look to the southwest in late twilight to spot the trio.

Both Saturn and Mars happen to be exactly the same brightness, shining equally at magnitude 0.8, but each with a distinctly different hue. Can you see the contrast between rusty red Mars and vanilla-white Saturn?

Antares is a red supergiant that’s blowing a powerful stellar wind into space at the rate of several solar masses every million years. One day it’s likely to explode as a supernova. Credit: Wikimedia

All this happens in Libra, a dim zodiac constellation preceding the brighter and better know Scorpius. Scorpius brightest star, Antares, is similar to Mars in color and just a tad fainter.

Visually, this red supergiant star doesn’t even hint of its true proportions because it’s 620 light years away, too far to appear as anything more than a shifting point of light. Measuring in at three times the diameter of Earth’s orbit, if Antares were put in place of the sun, its bubbly surface extending beyond the orbit of Mars.

How Antares would appear if we could get close enough to see it based on simulations by A. Chiavassa and team. Huge convective cells of rising and sinking gas crinkle its surface. Click to read the group’s 2010 research paper on the star. Credit: A. Chiavassa et. all

Recent research shows the star dominated by enormous bubbles of incandescent hydrogen gas called convective cells. Although it has a mass some 18 times that of the sun, the star’s powerful winds – from convection and sheer radiant energy – blast away something like 3 solar masses of material into space every million years. Unless Antares slims down through mass loss, it’s destined to grow a core of iron, collapse and explode as a supernova in the future.

Mars and Saturn boogaloo with Zubenelgenubi

Mars and Saturn are now only about 7 degrees apart (a little more than three fingers) low in the southwestern sky at dusk. This view shows the sky about 90 minutes after sunset. Between the two, you can spot the dimmer star Zubenelgenubi, the brightest star in the constellation Libra the Scales. Stellarium

Evening planets Saturn and Mars are fading and dropping lower in the western sky as August ticks toward September. Remember when Mars was brighter than Arcturus this spring? Planets. They never sit still. Their light’s never constant. We love watching them change, which is why our ancient ancestors knew immediately they were different from the static stars.

From my house, I need to be vigilant to spot Saturn and Mars before they’re lost in the treetops. That means getting out about an hour after sunset in fading twilight and finding an open spot where I can look low in the southwestern sky.

You may have noticed that the two have slowly been drawing together over the past few weeks. Mars, much closer to Earth than Saturn, moves more quickly across the sky. It’s been ‘chasing’ slower Saturn for some time now.

Mars gets closer to Saturn with each passing night until August 25 when they’ll be in conjunction just 3.4 degrees apart (twice as close as tonight). Watching Mars move against much slower Saturn makes a fun and easy observing project. Stellarium

Tonight, the two planets will be 7 degrees apart on either side of Libra the Scales’ brightest star, Zubenelgenubi (zoo-BEN-el-je-NEW-bee). The name, a delight to pronounce, is pure Arabic and means ‘southern claw’. Libra’s stars used to belong to neighboring Scorpius and both it and nearby Zubeneschamali (northern claw) remind of us of times long ago when Libra belonged to Scorpius.

Zubenelgenubi (a.k.a. Alpha Librae) is a double star that observers with keen vision can split with the naked eye. Most of us will find that a pair of binoculars will make the job much easier.

Mars will soon pass its slower brother but not before the two are in conjunction and closest together on the evening of August 25th. Watching two planets pass in the night is fun and instructive – it makes us aware that everything in our solar system’s on the move.

This weekend we’ll look at another even more amazing planetary conjunction coming up very soon – Jupiter and Venus on August 18.

Mars-bound comet scores a galactic ‘ringer’

Comet C/2013 A1 Siding Spring passes the beautiful ring galaxy NGC 1291 in the constellation Eridanus the River on August 2, 2014. Credit: Damian Peach

Comet C/2013 A1 Siding Spring  has been gaining ground on the planet Mars with only 208 million miles separating the two as of today. Discovered in January 2013, astronomers quickly determined the comet would pass only 82,000 miles from the planet on October 19 this year.  That’s more than 10 times closer than any comet has ever been observed to pass by Earth.

Because of the possibility for stray dust particles from the comet’s tail to damage instruments on several of its orbiters, NASA recently initiated orbital maneuvers to place them out of harm’s way on the opposite side of the planet during the time of closest approach.

Meanwhile, observers in the southern hemisphere have been keeping watch on the comet through modest-sized telescopes as have astrophotographers like Damian Peach who shared this remarkably beautiful photo of C/2013 A1 passing by the peculiar galaxy NGC 1291 in Eridanus. No danger of those two ever brushing up against one another –  the galaxy’s about 33 million light years in the background.

When we’re near the orbital plane of a comet, we look across space nearly edge-on into the cloud of dust it sheds. From our perspective, the tails and dust collapse into a flattened streak with the comet’s core or nucleus near the center. An anti-tail is really a dust or gas tail, but it appears to precede the comet instead of trail it, hence the term ‘anti’. Credit: Justin J. McCollum

Two things to notice here – the comet’s peculiar stretched-out shape and the galaxy’s striking interior ring.

Earth recently crossed Siding Spring’s orbital plane, providing with a unique, nearly edge-on view of the comet. Tails as well as dust shed in the its path stack up to form a flattened ‘pancake’ comet for a few brief days or weeks. (see diagram).

Composite image of NGC 1291  from the Galaxy Evolution Explorer and data from the Cerro Tololo Inter-American Observatory in Chile shows brilliant, massive stars firing up inside the ring. Galaxy rings may also form when galaxies pull in material from their surroundings. Shocked and heated through compression, new stars form. Credit: NASA

A number of galaxies show rings but few as symmetrical as NGC 1291. It’s thought that ring galaxies form when another galaxy collides and passes straight through the host galaxy.

While stars rarely crash during such encounters, merging gas clouds and gravitational disruptions can spark waves of star formation. Images taken by NASA’s Galaxy Evolution Explorer ultraviolet telescope clearly shows a ring of massive, young blue stars.

Beauty can be so happenstance.

Crescent moon joins a planet parade / Opportunity ready for marathon run

The moon scoots by two bright stars and two bright evening planets in the next few nights. This map shows the sky facing southwest in late evening twilight. Stellarium

The moon joins a lineup of planets and bright stars hung like tiki lamps across the southwestern sky at dusk. Watch for it to pass near fading Mars Saturday evening and Saturn on Monday.

The Martian landscape photographed by on July 30, 2014. The rover is exploring south along the west rim of Endeavour Crater heading toward a notch called ‘Marathon Valley’ about 1.2 miles (2 kilometers) away. Credit: NASA/JPL

While you’re gazing at the Red Planet, know that the Opportunity rover made news this week when it set a record for the most miles ever driven off-planet, tallying a satisfying 25 miles (40 km) of Martian travels. The previous record was held by the Soviet Union’s Lunokhod 2 rover when it ambled across 24.2 miles of the moon’s surface in 1973.

Out of this world distance records compared. Credit: NASA

Opportunity surpassed that record on Monday July 28 when it registered 25.01 miles en route to a notch called Marathon Valley along the west rim of Endeavour Crater. Mission controllers would like to get a look at clay minerals there that have been spotted from orbit.

Lunokhod 2 crater photographed by Opportunity last spring. The crater’s 20 feet (6 meters) in diameter. Credit: NASA/JPL

When it reaches the Valley it will have completed 26.2 miles (42 km), the official distance of a marathon. When you consider that Opportunity and its sister probe Spirit were only intended to function for 90 days, the current record-breaking feat and upcoming marathon completion are that more remarkable.

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.