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).

 

Seven ways to savor the upcoming total eclipse of the moon

Next Monday night April 14-15, skywatchers across much of North and South America will get to see a total eclipse of the moon. Lunar eclipses last for hours and can be safely viewed with the naked eye. This photo was taken of the June 2011 eclipse. Credit: Muhammed Mahdi Karim

It’s been too long. The moon last slipped into Earth’s shadow for North America in Dec. 2011. Next Monday night’s eclipse will end the current dry spell and make for a thrilling night out.

Map showing where next Monday night’s (April 14-15) eclipse will be visible. The western hemisphere has prime viewing seats. Credit: Fred Espenak

This eclipse is the first of four total lunar eclipses spaced about six months apart that will be visible across most of the Americas. The others occur on Oct. 8 this year, April 4, 2015 and Sept. 27, 2015. This particular sequence of four total lunar eclipses with no partials in between is called a ‘tetrad’. While we all hope for clear skies, if the weather’s uncooperative next week, you won’t have to wait long for another eclipse.


Eclipse tetrads explained

Lunar eclipses unfold slowly, lasting up to five hours. Unlike a total solar eclipse, where the sun disappears at most a few minutes, totality during a lunar eclipse can easily last more than an hour, giving you lots of time to enjoy the spectacle.

The only downside will be the late hour. Try to get some shuteye early as most of the eclipse happens after midnight in the wee hours Tuesday morning.

Because the moon’s orbit is tilted 5 degrees, the full moon normally misses the cone of shadow cast by the Earth and we see no eclipse. But several times a year, the moon’s orbit intersects Earth’s at the time of full moon and we see an eclipse. The Credit: Wikipedia

Lunar eclipses occur during full moon when the sun, Earth and moon line up in a neat row, and the moon passes into the shadow cast by our planet. You’d think eclipses would happen every full moon, but they don’t because the moon’s orbit around the Earth is tipped 5 degrees to Earth’s orbit around the sun.

The moon’s tipped orbit (red) is the reason we only get occasional eclipses at full moon. Most of the time the moon is either a little above or below the ideal alignment. Credit: Bob King

The moon spends most of the time above or below the plane of Earth’s orbit. And since Earth casts a shadow across its orbital plane, a lunar eclipse can only happen if the moon happens to be crossing that plane at the same time it’s full. That’s why eclipses are such a now and again thing.

While total solar eclipses are only visible along a narrow strip of land or ocean, a total lunar can be seen across half the globe wherever the sky is dark and the moon is up.

The moon’s past from west to east (right to left) across the dual shadow cast by Earth. The diagram shows key times (CDT) during the eclipse listed in the table below. Credit: Fred Espenak with additions by the author

Earth’s shadow is composed of two nested components – the inner umbra, where the Earth completely blocks the sun from view, and an outer penumbra, where the planet only partially blocks the sun. Because the penumbra is a mix of shadow and sunlight, it’s nowhere near as dark as the umbra.

An eclipse is divided into stages beginning with the moon’s entry into Earth’s lighter penumbral shadow. Most of us won’t notice any shading at all until about a half hour in, when the moon is deep enough inside to reveal a subtle darkening along its eastern edge. The table below lists the times for each stage of the eclipse across the four time zones:

Eclipse Events                     EDT             CDT                 MDT                PDT

Penumbra visible 1:20 a.m. 12:20 a.m. 11:20 p.m. 10:20 p.m.
Partial eclipse begins 1:58 a.m. 12:58 a.m. 11:58 p.m. 10:58 p.m.
Total eclipse begins 3:07 a.m. 2:07 a.m. 1:07 a.m. 12:07 a.m.
Mid-eclipse 3:46 a.m. 2:46 a.m. 1:46 a.m. 12:46 a.m.
Total eclipse ends 4:25 a.m. 3:25 a.m. 2:25 a.m. 1:25 a.m.
Partial eclipse ends 5:33 a.m. 4:33 a.m. 3:33 a.m. 2:33 a.m.
Penumbra visible  ——– 5:10 a.m. 4:10 a.m. 3:10 a.m.

During a total lunar eclipse (seen on Earth) an astronaut on the moon would instead see the Earth cover the sun, its atmosphere aglow with the combined light of all the sunrises and sunrises “leaking” around the rim of the planet. The light would bathe the moonscape in deep orange light. Stellarium

Partial eclipse begins when the moon treads within the dark umbra. Nibble by nibble the shadow eats away at the lunar disk. When only a sliver of the moon remains in sunlight, you’ll notice the shadowed portion glowing an eerie red or deep copper. To understand why, imagine an astronaut on the moon looking back at Earth during the eclipse.

During the next Tuesday morning’s eclipse, the moon will be just 1.5 degrees from Spica and not far from the planet Mars in the southern sky. Don’t forget to give Saturn a nod, located about two “fists” to the left of the moon. Stellarium

From her perspective, as the Earth passes in front of the sun, it’s surrounded by a glowing red-orange ring of light. Our atmosphere bends the light from all the sunrises and sunsets around the planet’s circumference into the umbra, coloring the moon red. Earth’s shadow isn’t really black after all but more a deep rusty red. Back on Earth, the moon will hang like a ghostly amber globe near the bright star Spica.

After mid-eclipse, the moon slowly exits the Earth’s shadow and performs the whole show in reverse, transitioning back to partial eclipse and finally exiting the penumbra.

Different aspects of a total lunar eclipse from start to near finish photographed in Hefei, China on Dec. 10, 2011. Credit: Reuters

You can take in the eclipse as casually as you like, but are seven cool things you might like to watch for:

#1 – When will you detect the first hint of penumbral shading? Keep an eye on the eastern (left) side of the moon for a “dented” appearance.

#2 – What color and how bright is the totally eclipsed moon? Depending upon the aerosol content of the atmosphere (greatly affected by volcanic eruptions), eclipses range from bright copper to dark brown and even black. Try rating this one on the traditional Danjon scale where “4″ is bright and “0″ is nearly invisible.

#3 – Watch for “the night within the night” phenomenon. If you thought it was dark out at the start of the eclipse, you’ll be amazed at how inky the landscape becomes during totality. As the eclipse progresses, the stars and Milky Way return to view.

#4 – With the entire moon darkened during totality, it will be relatively easy to watch it block or occult any star within its path. Many stars ranging from magnitude +8 and 12 will be occulted when viewed through small to medium telescopes. Click HERE for stars and times.

#5 – Binocular and telescope users should also look for a blue tinge to the encroaching umbral shadow as it slowly envelops the moon caused by light refracted by the upper atmosphere’s ozone layer.

#6 – Variation in the moon’s brightness. The top half will be closer to the center of the umbra and appear darker than the bottom. How obvious will this be?

#7 – Bring home a souvenir with your camera. If you have a telescope, you can hold a cellphone over the eyepiece to get great shots of the bright phases. During total eclipse, longer exposures of 1 to 10 seconds are necessary. For that you’ll need a tripod and a camera that can shoot time exposures. Telephoto lenses will pump up the moon’s size, but even a standard lens can do a great job of recording the sunset-colored moon in a landscape setting. Set your lens to its widest-open setting (f/2.8, 3.5) and expose 10-30 seconds to include the scene.

 

Watch the moon gobble up some Hyades Thursday night

The moon is shown about 15 minutes before passing in front of Delta 1 in the Hyades star cluster for Duluth, Minn. this Thursday night April 3, 2014. The green arrow shows the moon’s direction of motion. Star magnitudes are: Delta 1= 3.8, Delta 2 = 4.8 and Delta 3 = 4.3. Created with Chris Marriott’s SkyMap software

Here’s something very fun and enjoyable to see with a small telescope or even a pair of 50mm binoculars. This Thursday night across North America the crescent moon’s dark, earth-lit edge will cover up to three stars in the familiar V-shaped Hyades star cluster.

Never heard of the Hyades? Its next door neighbor is the Pleiades cluster, the one shaped like a little dipper and better known as the Seven Sisters. At just 153 light years away, the Hyades is the closest star cluster to Earth, one of the reasons it covers a nice-sized chunk of sky and is plainly visible to the naked eye. The bright orange giant Aldebaran helps to complete the cluster’s nifty V-shape, but isn’t a true member; the star simply happens to lie along the same line of sight.

Time exposure of the Hyades star cluster shows bright Aldebaran (left) and many, many stars. Although the “three Deltas” are the highlights, the moon will cover up other fainter cluster members as well. Credit: Bob King

The moon passes near the Hyades every month but only passes through the cluster for a six-year period every 18.6 years, the time it takes the moon’s orbit to precess or cycle once around the ecliptic. This last happened from 1995 to 2001. We begin a new cycle this year.

The sun’s gravity causes the moon’s orbit to slowly rotate westward once every 18.6 years. The nodes in the diagram are the two places where the moon’s tipped orbit intersects the plane of Earth’s orbit called the ecliptic. The line connecting the nodes makes a complete circle every 18.6 years. Credit: Prof. Marcia Rieke

The sun’s gravitational pull on the moon forces its orbit to slowly rotate westward. Combined with the 5-degree tilt of the lunar orbit, the moon’s track across the zodiac constellations varies continuously to the attentive observer over an 18.6 year cycle. During part of that cycle, it crosses the Hyades; during another part it swings north and misses them.

Thursday night the dark edge of the moon will cover one, two or even three bright Hyades depending where you live. Eastern and central U.S. and Canadian observers will see the moon blot out Delta 1 followed by Delta 2 for observers in the northern U.S. and Canada. The final bright star, Delta 3, slides behind the moon for much of the central and western U.S. and Canada.

Because the moon is close to the Earth compared to the planets and stars, observers in different locations see it against a slightly different background of stars. Travel north in North America, the moon slides south. Travel south and the moon’s path shifts north.

By 10 p.m. CDT, the southern edge of the moon has covered Delta 2 and will soon cover Delta 3 as seen from Duluth, Minn. Occulted stars will reappear along the moon’s bright limb, where they’re much harder to see. For Duluth, Minn. U.S. the stars will disappear within a few minutes of 9:03 p.m., 9:56 pm. and 10:35 p.m. Created with Chris Marriott’s SkyMap software

To find out which stars and when they’ll be covered for your city or region, click the links for each below:

* Delta 1
* Delta 2
* Delta 3 

When you visit these sites, select the disappearance times of the star. Note that the times are given in Greenwich or Universal Time for April 4. Subtract 4 hours for Eastern, 5 for Central, 6 for Mountain and 7 for Pacific. For example, 2 hours UT April 4 = 9 p.m. CDT April 3.

The fun in watching occultations is to see how suddenly the star disappears when it touches the edge of the moon. Were there a substantial lunar atmosphere, it would gradually fade away instead. It’s also just plain cool to see the moon move in real time as it approaches and then blinks out the star.

Some of you will be able to see one or more of the Deltas graze the edge of the moon, popping in an out of view as they’re hidden by crater walls and mountains along the lunar profile.

Good luck!