Sunday’s Supermoon sweetens August skies

Tomorrow night August 10 we’ll witness the closest full moon of the year. Credit: Bob King

OK, it’s not the Super Bowl exactly. No, this is better. Tickets are free, there’s plenty of parking and you can watch all night commercial-free. Yes, it’s time for the supermoon!

Tomorrow night, the Full Sturgeon Moon occurs at the same time the moon is closest to the Earth or as astronomers like to say, at perigee. The moon passes through perigee and its distant counterpart, apogee, once every 27.3 days, the time it takes the moon to orbit once around the Earth.

Sometimes perigee happens at first quarter moon or crescent phases and no one pays any attention. But when it occurs at full moon, we sit up and notice.

A sexy new term has even been coined in the past 30 years to describe the perigean full moon. Supermoon.

The moon’s orbit around Earth is an ellipse with one end closer to the planet (perigee) and the other farther (apogee). The year’s most distant lunar apogee happened two weeks ago; its closest perigee takes place during tomorrow night’s supermoon. Credit: Bob King

It’s hard not to be seduced by a big bright ball of pure bling. What’s more, the full moon rises at sunset and remains out all night unlike those skittish crescent moons that quickly hide behind trees and set. Its brilliance lights the otherwise dark road at night and adds an ethereal dimension to drabbest of landscapes.

July’s full moon as well as September’s will occur around the time of perigee, but tomorrow night’s will nearly coincide, making it the closest full moon of 2014.

Tom Ruen created this wonderful illustration showing the three supermoons of July, August and September compared to the ‘submoons’ or distant full moons coming up in 2015. You can easily see the difference in moon size comparing the top row to the bottom. The numbers give the moon’s diameter in arc minutes. 30 ‘minutes’ equals 1/2 degree. Credit: Tom Ruen

How close?  221,764 miles (356,896 km). That’s compared to an average distance of 238,855 miles, so the moon will be a smidge more than 17,000 miles closer to your doorstep than normal. Not only will it appear slightly brighter but 7% larger. Unfortunately, the difference, though real, will be nearly impossible to discern because we have no way to compare simultaneous side-by-side near and far full moons. Only after the fact, say by taking a picture of a distant full moon and placing it alongside a photo of a close one, could you tell.

Lots of us connect the dark spots or lunar ‘seas’ to make the face of the ‘man in the moon’ but how many have seen the rabbit? The ears form the strip over the top, the bright crater Aristarchus is the rabbit’s eye, there are two sets of legs and even a tail. Credit: Luc Viatour

2014′s most distant or apogean moon occurred just two weeks ago on July 27. No surprise given that the closest moon should naturally happen on the opposite end of the moon’s orbit or about two weeks later. The super thin crescent on that date was 252,629 miles (406,568 km) from Earth or nearly 31,000 miles farther than tomorrow night’s full moon – a difference of 13%.

Enough with numbers. They’re only a backdrop for the real show. Go out and enjoy a moonrise tonight and tomorrow night.  Not sure when the moon comes up? Head over to timeanddate.com and type in or search for your city. Since the moment of full moon happens early Sunday afternoon for U.S. and Canadian locations, tonight’s moon will be nearly as full.

I walked a mile in the moonlight last night and hope to do it again tonight. Is there a better month for moonwalking than August?

Rosetta in orbit, shoots incredible close-up views of comet

Boulders, cliffs, craters and smooth plains stand out in striking detail in this photo taken from only 81 miles (137 km) away. All photos credits: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

I know I’ve said this before, but WOW! I’ll step out of the way so you can enjoy these spectacular photos taken today when the Rosetta spacecraft arrived at comet 67P/Churyumov-Gerasimenko. Congratulations to all those at the European Space Agency (ESA) for a fantastic job!

Full view of the comet’s nucleus shows amazing details. Come November, ESA will land the small probe Philae on the comet.

Another full view of 67P/Churyumov-Gerasimenko.

Here the comet is overexposed to capture vaporizing ice and gases jetting away from the nucleus.

An ‘in your face’ close-up taken from 75 miles (120 km) away. Click photo to watch a 101-image animation of the comet during Rosetta’s approach.

Rosetta Mission main control room this morning August 6. Credit: S. Bierwald

For updates and more photos, click HERE. For live streaming reports, click HERE.

Sunrise and sunset – nature’s most beautiful illusions

Earth turns on its axis to greet the sun at sunrise each morning of the year. Credit: Bob King

Every day the sun rises, crosses the sky and sets. And it does it again and again and again like the perpetually repeating cycle of events in the movie Groundhog Day.

Except perhaps for a few remaining Flat-Earthers, we know what’s going on here. The sun’s not doing the moving. Instead, the Earth’s rotation causes the apparent motion of the sun across the sky. Yet the sense of the sun’s movement is so powerfully ingrained in our experience you might balk if I told you it’s essentially sitting still in the sky.

Every day the turning Earth causes the nearly static sun to rise in the east at sunrise and set in the west at sunset. Credit: Canadian Space Agency

For you to see a sunrise, Earth must rotate on its axis until your location faces the sun as it crests above the planet’s curvature. The following morning, when Earth rolls around after another 24 hours, the sun is very nearly in the same place in the celestial sphere as the previous morning. Once again, we see the sun ‘rise’. Ditto for the next morning and the next. It’s like turning over in your bed each and every morning and seeing your spouse in the same spot. Or very nearly.

If the Earth spun but stood in one spot never circling the sun, we would meet the rising sun at precisely the same time and place every day ad infinitum – a true Groundhog Day scenario. But the Earth orbits or revolves around the sun as surely as it rotates. Just like our daily spin, our planet’s revolution is reflected in the sun, which appears to slowly crawl across the sky, inching its way from one background zodiac constellation to the next, during the course of a year.

The orbiting and titled Earth cause slow but continuous changes in the times of sunrise and sunset during the course of a year. Credit: Thomas G. Andrews, NOAA Paleoclimatology

The ever-changing times of sunrise and sunset stem from the Earth’s orbital travels combined with the shifting seasonal tilt of the planet. From December 21 until June 21, as the amount of daylight increases in the northern hemisphere, the sun appears to travel slowly northward in the sky and we meet its welcome rays a couple minutes earlier each morning.

The sun’s yearly motion across the sky during the year traces out a path called the ecliptic. The top of the curve, at right, is the sun’s position during the summer. The low part of the curve is the sun’s location during winter. The up-and-down path is a reflection of the 23 1/2-degree tilt of the Earth’s axis. Illustration and animation by Dr. John Lucey, Durham University

Then from June 22 to December 20, Earth’s orbital motion causes the north polar axis to slowly point away from the sun. The sun appears to slide south as the hours of daylight wane, and we meet the sunrise a minute or two later each morning.

The sun, located some 26,000 light years from the center of the Milky Way galaxy, takes about 220 million years to make one revolution around its core moving at 483,000 mph. Credit: ESO

Earth moves along its orbit at an average speed of 67,000 mph (108,000 km/hr).

How about the sun? If I left the impression that it’s totally static I apologize. Yesiree, it’s moving too – at the astonishing speed of 483,000 miles per hour (792,000 km/hr) around the center of the galaxy.

Don’t look now, but you and I are going on the ride of our lives.The only reason stars remain static in the sky over the span of many generations despite the sun’s hurry is because nearly all of them are too far away to show a shift in position with the human eye. Telescopes, which magnify everything including motion, do show very subtle changes in the positions of nearby stars over much shorter time intervals.

Rising each morning to the same old sun, I try to remind myself that with every rotation comes a new opportunity to spin some joy into the day.

Tomorrow’s new moon foretells October’s solar eclipse

Tomorrow July 26, 2014, the invisible new moon will pass a few degrees south of the sun in the daytime sky. Stellarium

New moons aren’t much to look at. You can’t even see them most months of the year. That’s true for tomorrow’s new moon which will invisibly accompany the sun in its journey across the sky.

New moons occur about once a month when the moon passes between the sun and Earth. We can’t see them for two reasons: first, no sunshine touches the Earth-facing side when the moon lies in the same direction as the sun. It’s completely dark. From our perspective, the out-of-view lunar farside gets all the sunlight. Second, since the moon is nearly in line with the sun, it’s utterly lost in the glare of daylight.

The moon seesaws 5 degrees north and south of Earth’s orbit during its monthly cycle because its orbit is tilted with respect to Earth’s. Only when the moon crosses the plane of Earth’s orbit at the same time as a new moon do we see a solar eclipse. Illustration: Bob King

We normally have to wait two days after new moon – when the moon’s orbital motion carries it to the left (east) of the sun – to see it as a thin crescent at dusk.

Most of the time the moon passes north or south of the sun at new phase because its orbit is tilted 5 degrees with respect to Earth’s. But 2.4 times a year on average, new moon coincides with the time the moon’s seesawing path slices through the plane of Earth’s orbit. For a brief time during that crossing, all three bodies are aligned and happy earthlings witness a solar eclipse.

If the alignment is imprecise, the moon blocks only a part of the sun, giving us a partial solar eclipse.  If dead-on, we see a rarer total solar eclipse.

View of the partial solar eclipse across the Upper Midwest a half hour before sunset on October 23. By coincidence, Venus will be near conjunction at the same time and only a couple moon diameters north of the pair. Seeing the planet in a telescope will still be challenging because of daylight glare.  Stellarium

On October 23 this year, the lineup at new moon will be a good if imperfect one with a maximum of 81% of the sun covered. The partial eclipse will be visible across much of North America; from the eastern half of the U.S. and Canada the event will occur near sunset, adding a touch of drama to the scene.

I wrote earlier that we can’t see a new moon. That’s only partly true. We mostly pay attention to the sun’s changing shape during solar eclipses, but the dark, curving bite working its way slowly across the sun’s disk is none other than the new moon seen in silhouette.

Supermoon feast begins – it’s three in a row, baby!

Overnight tonight we’ll see the first of three supermoons in July, August and September. Credit: Gary Hershorn / Reuters

If the moon’s orbit were circular there’d be no such thing as ‘supermoons’, the occasional, extra-large full moons we see about once every 13 months. But circular orbits are exceedingly rare. Most celestial bodies dance about each other in ellipses. At one end of the ellipse, the two bodies are closest; at the other end, farthest.

The moon revolves around Earth in an elliptical orbit, passing through perigee (closest point to Earth) and apogee about once each month. When perigee occurs at full moon, we see a supermoon. Credit: Bob King

When the full moon coincides with its time of closest approach to Earth – called perigee – its disk can be up to 14% bigger and 30% brighter than typical full moons. In 2014 we get three consecutive perigee or supermoons in a row. The first occurs tomorrow morning July 12 at 3:28 a.m. CDT about 3 hours before the moment of full moon. Not a perfect match but close.

The next supermoons happen on August 10 (1 p.m. CDT) and September 8 (10:30 p.m.)

“Generally speaking, full moons occur near perigee every 13 months and 18 days, so it’s not all that unusual,” said Geoff Chester of the US Naval Observatory. “In fact, just last year there were three perigee Moons in a row, but only one was widely reported.”

The size difference between an apogee (foreground) and perigee or supermoon. Would that we could see them simultaneously to truly appreciate their different sizes. Credit: Tom Ruen

Supermoons get a lot of press because the word ‘super’ attached to anything these days naturally attracts attention.

While the phenomenon is very real, it’s also really hard to see because there are no rulers you can hold up to the sky to compare the size of one full moon to another. They ALL look big especially when the full moon’s near the horizon. That’s when the infamous ‘moon illusion’ kicks in and psychologically inflates the lunar disk up another notch.

Still, there’s every reason to go out and enjoy a full moon, super or not. The striking beauty of a moonrise, the curious mix of light and dark areas representing ancient crust (light) and titanic impact craters (dark) and the soft, yet stark illumination of the landscape where mystery abounds in every shadow. I could go on and on.

Close flyby of asteroid 2014 KH39 June 3 / Camelopardalid meteor shower ‘radar rich’

Diagram showing the orbit of 2014 KH39. Yellow shows the portion of its orbit above the plane of Earth’s orbit (grey disk); blue is below the plane. When farthest, the asteroid travels beyond Mars into the asteroid belt. It passes closest to Earth around 3 p.m. CDT June 3. Credit: IAU Minor Planet Center

Next Tuesday afternoon June 3, asteroid 2014 KH39 will silently zip by Earth at a distance of just 272,460 miles (438,480 km) only a little farther than the moon. To be exact, it will miss us by 1.14 lunar distances (LDs). Close as flybys go but not record-breaking. The hefty space rock will buzz across the constellation Cepheus near the Little Dipper at the time. Pity it will be too faint to spot in amateur telescopes, but astrophotographers might want to give it a whirl.

2014 KH39 was discovered on May 24 by the automated Mt. Lemmon Sky Survey. Further observations by the survey and additional telescopes like the Pan-STARRS 1 observatory in Hawaii nailed down its orbit as an Earth-approacher with an approximate size of 72 feet (22-m). That’s a tad larger than the 65-foot Chelyabinsk asteroid that exploded into thousands of small stony meteorites over Russia in Feb. 2013. Three large fragments weighing a total of 1,442 lbs. were also found at the bottom of Chebarkul Lake.

Cool infographic depicting asteroids that will make close approaches to Earth in the next 200 years. Vertical axis shows distance in thousands of km from the asteroid to Earth’s center. Click it to see a larger, easy-to-read version. Credit: Rianovosti

Since this asteroid is not on a collision course with Earth we have nothing to fear from the flyby. I only report it here to point out how common near-Earth asteroids are and how remarkable it is that we can spot them at all. While we’re a long ways from finding and tracking all potentially hazardous asteroids, dedicated sky surveys turn up dozens of close-approaches every year.

Take today for instance. 2014 KF22, estimated at 56 feet across (17-m) is making its closest approach to Earth at 2.67 LDs as I write this sentence. On June 8, 2014 HQ124 will pass 3.3 LDs away. That one’s BIG with a diameter estimated at more than 2,100 feet (650-m) and close enough to glow at magnitude +13.7. Amateur astronomers with good maps should be able to track it in 8-inch and larger scopes.

This all-sky radar map by the Canadian Meteor Orbit Radar (CMOR) shows a hot spot of meteor activity at the ‘Cams’ radiant near Polaris on May 24. The shower produced about 100 meteors per hour as seen by radar. Credit: Dr. Peter Brown /CMOR

While we’re on the topic of things buzzing through space, more results from the May 24 Camelopardalid meteor shower have been published. You’ll recall that rates of at least 100 per hour were predicted but most of us saw 1/10 that rate at best. Guess what? We really did get the higher number except they were about a magnitude too faint to see with the eye even from a dark sky site.


Video clip by John Chumack of bright Cams flashing over Dayton, Ohio on May 24, 2014

The Canadian Meteor Orbit Radar facility picked up plenty of Cams with ‘underdense’ echoes, according to Dr. Peter Brown of the University of Western Ontario. Underdense means faint – most Cams were magnitude 6-7 — at and below the naked eye limit. Larger particles, which produce brighter meteors, had been forecast, but now we know that the shower’s parent comet, 209P/LINEAR, shed finer debris more like dust than pebbles.

We’ll have to wait until 2022 and 2045 for the Cams to return. Maybe by then Google Glass will be available in a radar version.

Prepare for sleepless nights – space station marathon starts this week!

The International Space Station cuts across sky and clouds alike in this time exposure image. Starting later this week, the station will be in continuous sunlight and be visible on passes all night long. Credit: Bob King

I love watching the space station. It’s the brightest satellite and makes frequent passes. It’s also unique. Most satellites are either spent rocket stages or unmanned science and surveillance probes. The ISS is inhabited by a crew of astronauts. Real people. Every time I see that bright, moving light I think of them up there taking pictures of ‘down here’, performing experiments, cracking jokes and pondering the meaning of it all while staring out the panoramic cupola windows.

The ISS’s orbit is inclined 51.6 degrees to the equator and passes overhead for anyone living between 51.6 degrees north and 51.6 degrees south latitude. It’s visible well beyond this zone also but never passes through the zenith.

Diagram showing the Earth in late May when the space station’s orbital track is closely aligned with the day-night terminator. The astronauts see the sun 24-hours a day (midnight sun effect) while we on the ground get to watch repeated passes. Credit: Bob King

Most of the time we get one easy-to-see bright pass preceded or followed by a fainter partial pass. ‘Partials’ occur when the space station glides into Earth’s shadow and disappears from view during an appearance. But in late May-early June each year, the space station’s orbit and Earth’s day-night terminator nearly align. From the astronauts’ viewpoint, it’s the time of the midnight sun. From down on the planet between latitudes 40-55 degrees north, the ISS remains in sunlight during every single 90 minute pass.


In late May-early June near the summer solstice, the sun doesn’t set on the International Space Station

Instead of once or twice a night, we’ll see 4-5 passes starting about May 30. For instance, on May 31 from Duluth, Minn. we’re graced with four appearances at 12:12 a.m, 1:44 a.m., 3:20 a.m. and 11:23 p.m. The best nights are June 4 and 6 with five passes. By the 10th, the ISS ‘marathon’ winds down and we return to 2-3 passes a night.

The ISS always appears in the western sky first, rising up contrary to the movement of the stars, and traveling to the east. Low altitude passes put a lot of lateral distance between you and the station, making them fainter. Not by much though. Even on a low arc, the ISS shines as bright as Vega. Overhead passes means the ISS is as close as it can get – straight up at about 250 miles away. When you get one of those, the station’s only a magnitude shy of the planet Venus and absolutely stunning.

The ISS is huge – about the size of a pro football field – and consists of many separate modules linked together like a colossal Tinkertoy creation. Large solar panels power the station. Credit: NASA

If you closely watch the ISS as it moves against the starry sky, it will appear to move jerkily. This would be very bad orbital maneuvering if true. What you’re really seeing are your own jerky eye movements transposed on the sky. Some of my favorite passes are those when the space station fades from view mid-track as it passes into Earth’s shadow. I always keep binoculars handy for these passes so I can watch the station turn orange and red as it experience one of its many orbital sunsets. Try it sometime.

There are many ways to find out when the ISS will pass over your city. My favorite are the listings in Heavens-Above. Login with your city and you’ll see a complete list with links to create maps of the station’s track across the sky. There’s also Spaceweather’s Satellite Flyby tracker. Type in your zip code and hit enter. Couldn’t be easier. You can also have NASA send you an e-mail when the most favorable (highest, brightest) passes occur by adding your e-mail to the Spot the Station site. Be aware though that you won’t be notified on some of the less favorable passes.

Well, I’m going to prep for the marathon. Eat lots of pasta you know and keep a favorite beverage handy. See you in spirit on the course.

The sky is falling! Surprise meteor shower may strike Saturday morning

A brand new meteor shower shooting 100 and potentially as many as 400 meteors an hour may radiate from the dim constellation Camelopardalis below the North Star Saturday morning May 24. This map shows the sky facing north around 2 a.m. from the central U.S. Saturday.  Stellarium

Get ready for what could be the most awesome meteor shower of the year. On Saturday morning May 24 between 1 and 4 a.m. skywatchers across much of North America are in prime position to witness the birth of a brand new meteor shower – the Camelopardalids. At least 100 meteors per hour and possibly as many as 400 meteors per hour are expected with a peak viewing time around 2 a.m. Central Daylight Time. Short but sweet!

If predictions by meteor experts Peter Jenniskens of the SETI Institute and Esko Lyyttinen of Finland hold true, that morning, Earth will pass through multiple filaments of sand and pebble-sized debris trails boiled off comet 209P/LINEAR during previous passages near the sun during the 19th and early 20th centuries.

The comet was only discovered in 2004 by the Lincoln Laboratory Near-Earth Asteroid Research (LINEAR) automated sky survey. Unlike Comet Hale-Bopp and the late Comet ISON that swing by the sun once every few thousand years or million years, this one drops by every 5.1 years.

When closest at perihelion, 209P/LINEAR passes some 90 million miles from the sun. At the far end of its orbit it’s about Jupiter’s distance from the sun. In 2012, during a relatively close pass of that planet, Jupiter perturbed its orbit, bringing the comet and its debris trails to within 280,000 miles (450,000 km) of Earth’s orbit, close enough to spark a meteor shower.

When a comet nears the sun, heat vaporizes dust-laden ices from the comet’s nucleus. The solar wind ‘blows’ the dust particles into a tail which spread out along the comet’s orbit. Under the right circumstances, as with returning comet 209P/LINEAR, Earth can pass through the debris stream and we see a meteor shower as comet grit burns up in the atmosphere.

This time around, the comet itself will fly just 5 million miles from Earth on May 29 a little more than 3 weeks after perihelion, making it the 9th closest comet encounter ever observed.

You’d think this close pass would make 209P a bright sight, but it’s only predicted to reach magnitude +11, faint enough to require an 8-inch or larger telescope to see. Most likely the comet is either very small or producing dust at a very low rate or both.

Next week I’ll post maps here on how to find it. For the moment, 209P/LINEAR glows dimly at around magnitude +14 and visible in large amateur telescopes. As it speeds from the Big Dipper south to Crater the Cup over the next couple weeks, we’ll be watching it closely. Check here for updates if the comet experiences any hiccups.

The shaded area shows where the shower will be visible on May 23-24. North of the red line, the moon (a thick crescent) will be up during shower maximum around 2 a.m. CDT May 24. Click for more details. Credit: Mikhail Maslov

Meteors from 209P/LINEAR are expected to be bright and slow with speeds around 40,000 mph compared to an average of 130,000 mph for the Perseids. Most shower meteoroids are minute specks of rock, but the Camelopardalids (Cam-el-o-PAR-duh-lids) – let’s just call them ‘Cams’ –  contain a significant number of particles larger than 1mm, big enough to flare as fireballs.

Viewers in the northern half of the U.S. and southern Canada have the best seats for watching the potential shower because the radiant is midway up in the northern sky during peak viewing time Saturday morning. For points farther north, all-night twilight will blot out the fainter meteors. For observers in the far southern U.S. the radiant will be low in the northern sky, reducing meteor counts.

There’s always the chance the shower won’t materialize, so prepare yourself for that possibility. At worst we may see zero meteors, but even the most conservative estimates predict a show at least as good as the Perseids and Geminids, two of the strongest showers of the year.

But if you’re an optimist – and what skywatcher can’t afford not to be? – plan to be out before the peak and face north in a comfortable lawn chair. Bring a friend and share a cup of your favorite hot drink while you watch this ultimate wild card event.

Shower observing times across Canada and U.S.:

* Eastern Daylight Time 1:30-5 a.m. with the peak around 3 a.m.

* Central Daylight Time 12:30-4 a.m. with a 2 a.m. peak

* Mountain Daylight Time 11:30-3 a.m. with a 1 a.m. peak

* Pacific Daylight Time 10:30-2 a.m. with a peak at midnight

The dark “finger” represents streams of dust and rocks left behind by 209P/LINEAR during passes made from 1803 to 1924. Earth is shown intersecting the debris on May 23-24, 2014. Click for more details. Credit: Dr. Jeremie Vaubaillon

If it’s cloudy or you’re not in the sweet zone for viewing, the SLOOH will cover comet 209P/LINEAR live on the Web with its telescopes on the Canary Islands starting at 5 p.m. CDT (6 p.m. EDT, 4 p.m. MDT and 3 p.m. PDT) May 23 Follow-up live coverage of the new meteor shower starts at 10 p.m. CDT. The broadcast will feature astronomer Bob Berman of Astronomy Magazine; viewers can ask questions during the comet show by using hashtag #slooh.

Astrophysicist Gianluca Masi will also have a live feed of the comet at the Virtual Telescope Project website scheduled to begin at 3 p.m. CDT (8 p.m. Greenwich Time) May 22. A second meteor shower live feed will start at 12:30 a.m. CDT (5:30 a.m. Greenwich Time) Friday night/Saturday morning May 24.

No matter what, you’re covered. Later this week I’ll update with a forecast and fresh comet photos and observations. Cross your fingers!

Mercury leaps into dusk – don’t miss it!

The sky facing west about 40 minutes after sunset in mid-May when Mercury will be just shy of one outstretched fist above the northwestern horizon.  It shines brightly at magnitude -0.3 this week. Use higher, brighter Jupiter to make a sight line to the planet. Mercury’s making its best evening appearance of the year for northern hemisphere sky watchers. Stellarium

Now through the end of May is the prime time to look for Mercury in the evening sky. Like the rock star Prince, this small, speedy planet is elusive, making only a few brief appearances a year.  Consider this a personal invite to the show.

To find Mercury, pick out a place with a wide open view to the west-northwest in the direction of sunset. Start looking a half hour after sundown about a fist to the left of the brightest glow left on the horizon by the setting sun. Mercury will be some 8-10 degrees (about one outstretched fist) above the horizon. It looks like a solitary diamond in twilight’s pink glow.

Mercury shows phases as it revolves around the sun as seen from Earth’s perspective outside looking in. Mercury, like Venus, appears largest when nearly lined up between Earth and sun at inferior conjunction. Planets not to scale and phases shown are approximate. Illustration: Bob King

Mercury gets easier to see as the sky darkens … to a point. Once it’s within a few degrees of the horizon, the thicker, dustier air in that direction quenches its light and the planet fades.

The one-day old evening crescent moon with Mercury (upper left) on Jan. 31 this year. Credit: Bob King

It’s amazing that Mercury’s rates as a planet considering how small it is – just 3,021 miles (4,880 km) in diameter. At 2,160 miles across, our own moon is 71% as large. Jupiter’s moon Ganymede is even bigger at 3,275 miles (5,270 km). If it were orbiting the sun instead of Jupiter, Ganymede would easily be considered a planet. Pluto, demoted to dwarf planet status in 2006, spans just 1,430 miles (2,302 km).

Despite Mercury’s diminutive dimensions, its self-gravity easily crushed it into a sphere long ago. That plus the fact that it revolves around the sun and has cleared its orbit of competition from other smaller bodies places it firmly within the realm of the planets.

And there’s no planet quite like it. Mercury hovers near the sun too close to see and a few weeks later leaps into the morning sky. Drifts back down toward the sun in a few weeks and then leaps into the evening sky. So it goes, back and forth like that a half dozen times a year. Northern hemisphere observers see it best at dusk during late winter and spring ‘elongations’ and at dawn in the fall.

It’s easy to guess the reason for its swift maneuvering – a tight orbit around the sun lasting only 88 days keeps Mercury on the move.

Mercury looks like a tiny gibbous moon this week through a small telescope. Use at least 75x to make out its shape.  Illustration: Bob King

Like Venus and the moon, Mercury shows phases. Right now, if you’re lucky enough to train a telescope on it before it atmospheric turbulence near the horizon mushes up the view, the planet would look like a very tiny gibbous moon 66% illuminated.

Its phase changes quickly too. Within a few weeks, as it moves closer to Earth and grows in apparent size, the planet will morph from gibbous to half to a dim crescent. Yes, dim! Mercury is brightest when at ‘full moon’ phase, being nearly as brilliant as Sirius, but fades to 3rd magnitude when a thin crescent. This week we’ll see it brightest; next week the planet will start to fade noticeably.

Orbiting between 28 and 43 million miles (46 and 70 million km) from the sun and possessing no atmosphere, Mercury’s temperature ranges from an extremely hot 800 F (430 C) on the dayside to marrow-chilling -280 F (-170 C) on the nightside.

To the eye, Mercury would appear as shades of dark brown. NASA enhanced the subtle colors to in this photo of the planet, a mosaic of images taken by MESSENGER. Younger craters with their bright rays appear blue. Plains formed form ancient lava eruptions are tan or orange. Credit: NASA

Because the planet’s axis is tilted only .01 degree – it essentially rotates straight up and down perpendicular to the sun – sunlight never reaches into craters in its polar regions. Locked in permanent shadow, NASA’s MESSENGER spacecraft has found strong evidence for abundant water ice and other volatile materials stored there for millions of years.

We could go on and on about this strange little planet, but I’d be holding you back from getting outside to see it for yourself. For more information, check out NASA’s quick-facts summary and a wonderful gallery of photos from MESSENGER.

Brilliant Mars opening act for upcoming total lunar eclipse

Brilliant Mars shines atop dimmer Spica in the constellation Virgo in this photo taken Sunday night April 6. The planet now rises at sunset and is easy to spot around 9:30 p.m. in the southeastern sky. Yes, we still have almost 4 feet of snow here in Duluth, Minn. Credit: Bob King

Mars reaches opposition today, its closest approach to Earth since Dec. 2007 and the brightest we’ve seen it since 2012. What a sight it’s become. Last night, while walking our respective dogs, my daughter took one look at the gleaming pink-orange “star” in the southeastern sky and knew immediately it was Mars.

About every two years, Mars and Earth line up on the same side of the sun at opposition. Because Mars’ orbit is eccentric (less circular than Earth’s) the two planets are closer at some oppositions than others. This year’s opposition is a relatively distant one. Illustration: Bob King

While it sounds like an act of defiance, opposition refers to Mars being on exactly opposite side of the sky as the sun. The planet rises at sunset this evening and sets when the sun pops up tomorrow morning. Not only is Mars out all night long, but being opposite the sun, it’s paired up closely with Earth on the same side of the sun as shown above.


One full rotation of Mars on April 8 created by Tom Ruen. North polar cap at top.

That’s why Mars is so doggone bright – it’s close! Of course we know that’s a relative term in astronomy. Today the Red Planet is 57.7 million miles away, which sounds rather terribly far. But keep in mind that it can be up to 249 million miles away. So yes, Earth and Mars are practically neighbors … for a little while. The same orbital motions that brought them together will also move them farther apart in the coming months.

Now here’s the kicker. Because the orbits of Earth and Mars aren’t perfect circles, the two planets are actually closest on April 14, six days past opposition. That’s the same night as the total eclipse of the moon. Even better, the moon will only be a “fist” away from the planet. What a sight they’ll make – two red orbs aglow in the southern sky.

Mars outshines its neighbors Spica and Arcturus in the east and is ever so slightly brighter than magnitude -1.46 Sirius off to the southwest. The map shows the sky around 9:30 p.m. local time tonight. Stellarium

The Red Planet far outshines the nearby stars Spica and Arcturus and at magnitude -1.5 glows a hair brighter than Sirius, the brightest star in the entire sky. While similar in brightness, their colors are dramatically different. Compare the two and tell us what you think.

One side of Mars, the side turned toward the Americas during the best observing times this week, shows relatively few features. Use the map below to help you identify other dark markings as they rotate into view in the coming days and weeks. North at bottom. Credit: Mark Justice

Mars won’t appear bigger or brighter until its next opposition in May 2016 so take a look at this miniature “eye of Sauron” beaming in the south the next clear night.

If you have a telescope, use a magnification of 150x or higher to look for the planet’s very tiny north polar cap (it’s summer there and the cap has shrunk!) and other dark markings on its surface. This week, the planet’s “blank” hemisphere is presented for observers in the Americas. Be patient. The more obvious features like Mare Erythraeum, Syrtis Major and Mare Acidalium will soon rotate into view (see map below).

Complete Mars map showing many more features. Click to learn more about Mars’ upcoming opposition. Credit: Association of Lunar and Planetary Observers (A.L.P.O).