The Martian moon Phobos as it crossed in front of the Sun, as seen by NASA's Curiosity Mars rover on Sunday, March 26, 2019 (Sol 2359). Credit: NASA/JPL-Caltech/MSSS
Ever since the Curiosity rover landed on Mars in 2012, it has provided NASA scientists with invaluable data about the planet’s past, as well as some breathtaking images of the planet’s surface. Much like its predecessors, the Spiritand Opportunityrover, many of these images have shown what it is like to look up at the sky from the surface of Mars and witness celestial events.
Of these events, one of the most intriguing has to be the many Martian solar eclipses that have taken place since the rover’s landed. Last month, the Curiosity rover witnessed two eclipses as the moons of Phobos and Deimos both passed in front of the Sun. These latest eclipses will allow scientists to fine-tune their predictions about Mars’ satellites and how they orbit the Red Planet.
A blood red moon captured during the total lunar eclipse of January 31st, 2018. Image credit and copyright: Eliot Herman
A blood red moon captured during the total lunar eclipse of January 31st, 2018. Image credit and copyright: Eliot Herman
The Blood Moon cometh.
One of the top astronomy events of 2018 occurs on the evening of Friday, July 27th, when the Moon enters the shadow of the Earth for a total lunar eclipse. In the vernacular that is the modern internet, this is what’s becoming popularly known as a “Blood Moon,” a time when the Moon reddens due to the refracted sunlight from a thousand sunsets falling upon it. Standing on the surface of the Moon during a total lunar eclipse (which no human has yet to do) you would see a red “ring of fire” ’round the limb of the eclipsed Earth.
This is the second total lunar eclipse for 2018, and the middle of a unique eclipse season bracketed by two partial solar eclipses, one on July 13th, and another crossing the Arctic and Scandinavia on August 11th.
The path of the Moon through the Earth’s shadow Friday, along with visibility prospects worldwide. Credit: NASA/GSFC
The July 27th total lunar eclipse technically begins around 17:15 Universal Time (UT), when the Moon enters the bright penumbral edge of the Earth’s shadow. Expect the see a slight shading on the southwest edge of the Moon’s limb about 30 minutes later. The real action begins around 18:24 UT, when the Moon starts to enter the dark inner umbra and the partial phases of the eclipse begin. Totality runs from 19:30 UT to 21:13 UT, and the cycle reverses through partial and penumbral phases, until the eclipse ends at 23:29 UT.
Centered over the Indian Ocean region, Africa, Europe and western Asia get a good front row seat to the entire total lunar eclipse. Australia and eastern Asia see the eclipse in progress at moonset, and South America sees the eclipse in progress at moonrise just after sunset. Only North America sits this one out.
Now, this total lunar eclipse is special for a few reasons.
First off, we’ll have the planet Mars at opposition less than 15 hours prior to the eclipse. This means the Red Planet will shine at a brilliant magnitude -2.8, just eight degrees from the crimson Moon during the eclipse, a true treat and an easy crop to get both in frame. We fully expect to see some great images of Mars at opposition along with the eclipsed Moon.
Mars versus the eclipsed Moon on Friday. Credit: Stellarium
How close can the two get? Well, stick around until April 27th, 2078 and you can see the Moon occult (pass in front of) Mars during a penumbral lunar eclipse as seen from South America.
And speaking of occultations, the Moon occults some interesting stars during totality Friday, the brightest of which is the +5.9 magnitude double star Omicron Capricorni (SAO 163626) as seen from Madagascar and the southern tip of Africa. Omicron Capricorni has a wide separation of 22″.
The occultation path of Omicron Capricorni during Friday’s eclipse. Credit: Occult 4.2.
The second unique fact surrounding this eclipse is one you’ve most likely already heard: it is indeed the longest one for this century… barely. This occurs because the Moon reaches its descending node along the ecliptic on July 27th at 22:40 UT, just 21 minutes after leaving the umbral shadow of the Earth. This makes for a very central eclipse, nearly piercing the umbral shadow of the Earth right through its center.
Totality on Friday lasts for 1 hour, 42 minutes and 57 seconds. This was last beat on July 16th, 2000 with a duration of 1 hour, 46 minutes and 24 seconds (2001 is technically the first year of the 21st century). The duration for Friday’s eclipse won’t be topped until June 9th 2123 (1 hour 46 minutes six seconds), making it the longest for a 123 year span.
The longest total lunar eclipse over the span of 5,000 years from 2000 BC to 3000 AD was on May 31st, 318 AD at 106.6 minutes in duration.
A Minimoon Eclipse
Finally, a third factor is assisting this eclipse in its longevity is the onset of the MiniMoon: The Moon reaches apogee at July 27th, 5:22 UT, 14 hours and 37 minutes prior to Full and the central time of the eclipse. This is the most distant Full Moon of the year for 2018 (406,222 km at apogee) the 2nd most distant apogee for 2018. Apogee on January 15th, beats it out by only 237 kilometers. This not only gives the Moon a slightly smaller size visually at 29.3′, versus 34.1′ near perigee, less than half of the 76′ arcminute diameter of the Earth’s shadow. This also means that the Moon is moving slightly slower in its orbit, making a more stately pass through the Earth’s shadow.
Going, going… the stages of a lunar eclipse. Credit: Dave Dickinson.
What will the Moon look like during the eclipse? Not all total lunar eclipses are the same, but I’d expect a dark, brick red hue from such a deep eclipse. The color of the Moon during a eclipse is described as its Danjon number, ranging from a bright (4) to dark murky copper color (0) during totality.
Tales of the Saros
This particular eclipse is member 38 of the 71 lunar eclipses in saros series 129, running from June 10th, 1351 all the way out to the final eclipse in the series on July 24th, 2613 AD. If you caught the super-long July 16th, 2000 eclipse (the longest for the 20th century) then you saw the last one in the series, and the next one for the series occurs on August 7th, 2036. Collect all three, and you’ve completed a triple exeligmos series, a fine word in Scrabble to land on a triple word score.
Photographing the Moon
If you can shoot the Moon, you can shoot a total lunar eclipse, though a minimum focal length lens of around 200mm is needed to produce a Moon much larger that a dot. The key moment is the onset of totality, when you need to be ready to rapidly dial the exposure settings down from the 1/100th of a second range down to 1 second or longer. Be careful not to lose sight of the Moon in the viewfinder all together!
Are you watching the eclipse during moonrise or moonset? This is a great time to shoot the eclipsed Moon along with foreground objects… you can also make an interesting observation around this time, and nab the eclipsed Moon and the Sun above the local horizon at the same time in what’s termed a selenelion. This works mainly because the Earth’s shadow is larger than the apparent diameter of the Moon, allowing it to be cast slightly off to true center after sunrise or just before sunset. Gaining a bit of altitude and having a low, flat horizon helps, as the slight curve of the Earth also gives the Sun and Moon a tiny boost. For this eclipse, the U2-U3 umbral contact zone for a selenelion favors eastern Brazil, the UK and Scandinavia at moonrise, and eastern Australia, Japan and northeastern China at moonset.
Incidentally, a selenelion is the second visual proof you see during a lunar eclipse that the Earth is indeed round, the first being the curve of the planet’s shadow seen at all angles as it falls across the Moon.
Another interesting challenge would be to capture a transit of the International Space Station during the eclipse, either during the partial or total phases… to our knowledge, this has never been done during a lunar eclipse. This Friday, South America gets the best shots at a lunar eclipse transit of the ISS:
ISS transit paths (revised) during Friday’s eclipse, including times in UT and Moon phases. The northern and southern limits of the paths mark the point where the Moon is no longer visible. Created by the author using CalSky. (Thanks to PAHLES in comments below for pointing out the errors in the first map!)
Watch Friday’s eclipse live online. Credit: Gianluca Masi/Virtual Telescope Project.
Live on the wrong continent, or simply have cloudy skies? Gianluca Masi and the Virtual Telescope Project 2.0 have you covered, with a live webcast of the eclipse from the heart of Rome, Italy on July 27th starting at 18:30 UT.
Be sure to catch Friday’s total lunar eclipse, either in person or online… we won’t have another one until January 21st, 2019.
Learn about eclipses, occultations, the motion of the Moon and more in our new book: Universe Today’s Guide to the Cosmos: Everything You Need to Know to Become an Amateur Astronomer now available for pre-order.
A dusty view of Mars from July 11th. Image credit and copyright: Waskogm.
A dusty view of Mars from July 11th as Mars opposition 2018 nears. Image credit and copyright: Waskogm.
Have you checked out Mars this season? Mars reaches opposition on July 27th at 5:00 Universal Time (UT) shining at magnitude -2.8 and appearing 24.3” across—nearly as large as it can appear, and the largest since the historic opposition of 2003. We won’t have an opposition this favorable again until September 15th, 2035.
Mars starts this week near the +4th magnitude star Psi Capricorni, loops westward through retrograde briefly into the astronomical constellation of Sagittarius the Archer in late August before heading back into Capricornus in September.
Mars opened up 2018 just 4.8” across, trekking through the early dawn sky. What a difference a few months make: Mars broke 15” arc seconds—a maximum size for an unfavorable opposition near aphelion—on May 30th, and now dominates the summer sky around midnight.
The path of Mars from July through September 2018. Credit: Starry Night.
There’s one downside, however, to the 2018 opposition of Mars: it’s occurring very nearly as far south along the ecliptic as it can. This is great news for observers in Australia, South Africa and South America, as the Red Planet rides high near the zenith at local midnight. Up north, however, we are still looking at Mars through the murk of the atmosphere lower to the horizon. For example, here in Norfolk, Virginia at latitude 37 degrees north, we never see Mars rise more than 29 degrees altitude above the southern horizon this season.
Down with Dust Storms
Does Mars seem a bit… peachy colored to you this season? It’s not your imagination: a planetary dust storm is indeed underway. It’s the middle of autumn for northern hemisphere of Mars, and this seems to be shaping up to be one of those oppositions where the planet, though at its closest, presents a featureless, dust-shrouded disk. This seems to be the case roughly every third opposition or so… our best hope now is that it may clear in the coming final weeks of July. We checked out Mars over the past weekend, and could just spy the pole cap and some slight detail under a veil of haze.
The Curiosity rover’s dusty view from late June. Credit: NASA
Despite the depiction of Martian dust storms in science fiction blockbusters such as The Martian as furious and unrelenting, these storms are actually pretty mild-mannered, barely able to chase a leaf before them through the tenuous Martian atmosphere, if deciduous trees grew on Mars. One thing Martian dust storms can do, however, is coat solar panels with a battery-killing film, and it has yet to be seen if the aging Opportunity rover will awaken and phone home from Meridiani Planum.
Unlike the Earth, Mars has a markedly elliptical orbit, varying from 1.7 (AU) astronomical units from the Sun at aphelion to 1.4 AU near perihelion. This all means that not every opposition of Mars is equal; in fact, Mars can range from 55 million to 102 million kilometers from the Earth near opposition and appear 13.8” to 25.1” across, depending on where it’s at in its orbit. And although Mars laps the Earth roughly every 26 months, a cycle of favorable oppositions repeat every 15 years.
Still dusty… Mars from July 16th. Image credit and copyright: Shahrin Ahmad.
In 2018, Mars reaches opposition on July 27th at 5:00 UT/1:00 AM EDT 57.8 million kilometers from the Earth, then makes its closest approach four days later on July 31st at 8:00 UT/4:00 AM EDT, 57.6 million kilometers distant. Why the discrepancy? Well, opposition is simply reckoned as the point where an outer planet reaches an ecliptic longitude of 180 degrees opposite from the Sun. Mars, however, is still headed inward towards perihelion on September 16th, while Earth just came off of aphelion on July 6th.
Visually, Mars can on occasion “go yellow” and present a saffron color even to the naked eye if a planetary wide sandstorm is underway. At the eyepiece, the most prominent feature is always the pole cap, a white dollop on the planet’s pumpkin hued limb. Crank up the magnification, and dark patches come into view, as Mars is the only planet in the solar system presenting an actual surface available for amateur scrutiny. Mars has a day very similar to Earth’s at only 37 minutes longer in duration, meaning that if you observe Mars at the same time every evening, you’ll see nearly the same longitude of the planet turned towards you, shifted 10 degrees westward. A great tool for comparing what features on Mars are currently turned Earthward is Mars Previewer.
Can you spy Mars… daytime? This month is a good time to try, as it currently shines brighter than Jupiter. The easiest thing to do is lock on to it with a telescope near dawn as it sets to the west and the Sun rises in the east, then simply track it into the daytime sky. We’ve seen Mars in 2003 and again this year while the Sun is still above the horizon… having the Moon nearby also helps, though of course, Mars is very close to the horizon at sunset/sunrise right at opposition.
And speaking of which, viewers in Europe, Africa, Asia and Australia are in for a special treat on the evening of July 27th, as a total eclipse of the Moon occurs just 15 hours after Mars passes opposition. Ironically, this is also a Minimoon eclipse, as the Moon also passes apogee just 14 hours prior to entering the Earth’s shadow. Expect to see the Red Planet just seven degrees from the blood red Moon at mid-eclipse (more on the eclipse next week).
Mars versus the total lunar eclipse on the night of July 27th. Credit: Stellarium
The Moon won’t occult (pass in front of) Mars again until November 16th, 2018 for the very southernmost tip of South America. Stick around until July 26th, 2344 AD, and you can witness the Moon occulting the planet Saturn during an eclipse, though you’ll have to journey to southern Japan to do it.
But you may not have to wait that long… stick around until April 27th, 2078, and you can witness the Moon occult Mars… during a penumbral lunar eclipse:
The April 27th, 2078 occultation of Mars… during a penumbral lunar eclipse. Credit: NASA/GSFC/Occult 4.2/Starry Night
This current evening apparition of Mars ends over a year from now on September 2nd, 2019, as Mars reaches solar conjunction on the farside of the Sun.
Finally, opposition is a great time to try and check the tiny Martian moons Phobos and Deimos off of your life list. These two moons were actually discovered by Asaph Hall from the United States Naval Observatory’s newly installed 26-inch refractor during a favorable parihelic apparition of Mars in 1877.
An alien sky… Phobos occults Deimos as seen from the surface of Mars, courtesy of the Curiosity rover. NASA/JPL-Caltech/Malin Space Science Systems/Texas A&M Univ
Shining at magnitude +12.4 (Deimos) and +11.3 (Phobos), seeing these moons would be a cinch… were it not for the presence of Mars shining a million times brighter nearby. Your best bet is to construct an occulting bar eyepiece (we’ve used a thin strip of foil and a guitar string affixed to an eyepiece to accomplish this) or simply place brilliant Mars just out of view. Phobos orbits once every 7.7 hours and substends 20” from the disk of Mars, while Deimos goes around Mars once every 30.35 hours and journeys 66” with each elongation from the Martian disk. PDS rings node or a good planetarium program such as Starry Night or Stellarium will show the current orientation of the Martian moons, aiding in your decision of whether or not to take up the quest.
Don’t miss out on Mars this opposition season… it’ll be almost another two decades before we get another favorable view.
Read all about viewing the planets, from observation to imaging and sketching in our new book: The Universe Today Guide to the Cosmos out October 23rd, now available for pre-order.
Mars as seen on from Aguadilla, Puerto Rico on Mars 25th, 2014, two weeks prior to opposition. Credit-Efrain Morales Rivera.
Did you see it? Last night, the Red Planet rose in the east as it passed opposition for 2014, and astrophotographers the world over were ready to greet it. And although Mars gets slightly closer to us over the coming week, opposition marks the point at which Mars is 180 degrees “opposite” to the setting Sun in Right Ascension as viewed from our Earthly vantage point and denotes the center of the Mars observing season. Opposition only comes around once about every 26 months, so it’s definitely worth your while to check out Mars through a telescope now if you can. We’ve written about prospects for observing Mars this season, and the folks at Slooh and the Virtual Telescope Project also featured live views of the Red Planet last night. We also thought we’d include a reader roundup of pics from worldwide:
Mars and Spica rising over the telescope domes at Kitt Peak, Arizona. The 2.1 metre dome is on the left, and the 0.9 metre dome is to the right. Credit-Rob Sparks @halfastro.
Even near opposition, Mars presents a challenge to observers. In 2014, Mars only reaches 15 arc seconds maximum in apparent size, a far cry from its 25″ appearance during the historic 2003 opposition. Now for the good news: we’re in a cycle of improving oppositions… the next one on May 22nd, 2016 will be better still, and the 2018 opposition will be nearly as favorable as the 2003 appearance!
Mars as seen from the Netherlands at 0:26 UT… about 3 hours past opposition. Credit- Christian Fröschlin @chrfde.
And you can see just how technology in the amateur astronomy community has improved with each successive appearance of Mars over the years. Early observers were restricted to sketching features glimpsed during fleeting moments of steady seeing. Even during the film era of photography, absurdly long focal lengths were required to yield even a tiny speck of a dot. And even then, the “graininess” of the film tended to smear and yield a blurry image with few details to be seen.
The advent of digital photography opened new vistas on planetary imaging. Now backyard astrophotographers are routinely taking images using stacking techniques and processing to “grab” and align those moments of good seeing. These images are often now better that what you’d see in a text book taken from professional observatories only a few decades ago!
And you can now easily modify a webcam to take decent planetary images that can then be stacked and processed with software freely available on the web.
…And check out this video animation also by Christian Fröschlin that shows the rotation (!) of Mars:
Mars as seen from Ottawa, Canada, taken using an IPhone 4S through a NexStar 8SE telescope on April 4th, 2014. Awesome! Credit-Andrew Symes @FailedProtostar
Shahrin Ahmad made an excellent video from Malaysia that demonstrates just what raw captured images of Mars look like before processing:
Note that the large dark triangular region is Syrtis Major.
Mars annotated, a stack of 1128 frames shot at 666x. Credit-Mike Weasner/Cassiopeia Observatory.
The northern polar cap is currently tipped towards us, as it’s northern hemisphere summertime on Mars. Many images reflect this prominent feature, as well as the orographic clouds skirting the Hellas basin that have been the hallmark of the Mars opposition of 2014. These are also apparent visually at the eyepiece. It’s worth staying up a bit towards local midnight to observe and image Mars, as it transits at its maximum elevation — and is above the murk of the sky low to the horizon — right around this time.
Mars captured through a Celestron C6 SCT telescope on April 5th, 2014. Credit: Joel Tonyan.
Mars: a study of color contrasts on the eve of opposition. Credit-Laura Austin @LAismylady
And Mars observing season doesn’t end this week. Mars makes its closest passage to the Earth for 2014 next Monday on April 14th at 0.618 Astronomical Units (A.U.s) distant. Mars will occupy the evening sky for the remainder of 2014 before finally reaching solar conjunction on June 14th, 2015. Mars will still be greater than a respectable 10″ in apparent size until June 24th and will continue to offer observers a fine view at the eyepiece.
Mars as seen from Rhode Island on the night of opposition. Credit-Cherie @KelieAna
And don’t forget, that waxing gibbous Moon is now homing in on Mars and will only sit a few degrees away from the Red Planet and Spica on the night of the April 14th/15th, 2014 during a fine total lunar eclipse. And no, a “red” planet + a “blood red” eclipsed Moon does not equal doomsday… but it’ll make a great photo op!
Mars imaged using a 150 mm scope. Credit-Sergei Golyshev under a Creative Commons Share-Alike 2.0 Generic License.
… and finally, Mars and the bright blue-white star Spica offered us a fine morning view as the storm front passed over Astroguyz HQ here in Florida this AM:
Mars, Spica, and our partly cloudy terrestrial atmosphere. Photo by author.
Want something more? Have you ever seen Mars… in the daytime? Currently shining at magnitude -1.5, its just possible if you known exactly where to look for it low to the east about 10 minutes or so before local sunset. In fact, near opposition is the only time you can carry this unusual feat of visual athletics out. The best chance in 2014 is on the evening of April 13th and 14th, when the waxing gibbous Moon lies nearby:
Looking east on the evening of April 13th, just before sunset. Credit: Starry Night education software.
Good luck, and thanks to everyone who imaged Mars this season!
Phobos transiting the Sun as seen by the Mars Curiosity rover on Sol 369. (Credit: NASA/JPL-Caltech/Malin Space Science Systems/Texas A & M University).
It’s always interesting to consider the astronomical goings-on that occur under alien skies.
On August 17th, Curiosity wowed us once again, catching the above sequence of images of the Martian moon Phobos transiting the Sun.
Such phenomena have been captured by the Curiosity, Opportunity and Spirit rovers before, as the twin Martian moons of Deimos & Phobos cross the face of the Sun. But these recent images taken by Curiosity’s right Mastcam pair are some of the sharpest yet.
Orbiting only an average of 6,000 kilometres above the surface of Mars, Phobos is the closest to its primary of any moon in the solar system. It appears about 11 arc minutes in size when directly overhead, about 3 times smaller than our own Moon does from the Earth.
“This event occurred near noon at Curiosity’s location, which put Phobos at its closest point to the rover, appearing larger against the Sun than it would at other times of the day,” Said co-investigator Mark Lemmon of Texas A&M University in a recent press release. “This is the closest to a total eclipse that you can have on Mars.”
Phobos is 40% more distant from an observer standing on the surface of Mars when it is rising above the local horizon than when it is overhead. The Sun is about 20’ arc minutes across as seen from Mars, 66% of its diameter as seen from the Earth.
The sequence above spans only six seconds in duration. You would easily note the apparent motion of Phobos as it drifted by! Also, since Phobos orbits Mars once every 7.7 hours, it actually rises in the west and sets in the east. The Martian day is over three times this span, at 24.6 hours long. Deimos has a more sedate orbit of 30.4 hours in duration.
The twin Moons of Deimos and Phobos were discovered this month back during the opposition of 1877 by Asaph Hall using the United States Naval Observatory’s newly installed 65 centimetre refractor. The moons are just within the grasp of eagle-eyed amateurs near opposition. You’ve got another opportunity to cross these elusive moons off of your life list coming up in the Spring of 2014.
It’s especially captivating that you can make out the irregular “potato shape” of Phobos in the above images. With low orbital inclinations relative to the equator of Mars of 1.1 degrees for Phobos and 0.9 degrees for Deimos, solar transits are not an uncommon occurrence, transpiring somewhere along the Martian surface with every orbit. If Phobos were twice as close to Mars, it would completely cover the Sun in a total solar eclipse. What Curiosity gave us this month is more akin to an annular eclipse with a ragged central shadow. An annular eclipse occurs when the occulting body is too distant to cover the Sun, leaving a bright, shining ring, or annulus.
On the Earth, we live in an epoch where annular eclipses are slightly more common than total solar eclipses, as the Moon currently recedes from us to the tune of 3.8 centimetres a year. About 1.4 billion years from now, the last total solar eclipse will be seen from the Earth. The next purely annular eclipse as seen from Earth occurs on April 29th, 2014 across Australia and the Antarctic.
Conversely, Phobos is in a “death spiral,” meaning that it will one day crash into Mars about 30-50 million years from now. This also means that in about half that time, it will also be large enough to visually cover the Sun when crossing it near local noon. For a brief time far in the future, jagged total solar eclipses will be visible from Mars. That is, if the gravitational field of Mars doesn’t rip Phobos apart before that!
But beyond just aesthetics, these observations serve a scientific purpose as well. These phenomena serve to refine our understanding of the precise positions of Phobos and Deimos and their orbits.
“This one is by far the most detailed image of any Martian lunar transit ever taken, and it is especially useful because it is annular. It was taken closer to the Sun’s center than predicted, so we learned something.”
The track during the August 17th observation was off by about 2-3 kilometres, allowing for a surprise central transit of the Sun as seen from Curiosity’s location.
Both Phobos and Deimos are captured asteroids only 22.2 & 12.6 kilometres across, respectively. Both must be subject to occasional bombardment from meteorites blasted off of the surface of nearby Mars. Sample return missions to Phobos have been proposed. Russia’s ill-fated Phobos-Grunt mission would’ve done just that.
Will humans ever stand on the surface of the Red Planet and witness an annular eclipse of the Sun by Phobos in person? Well, if we make it there by November 10th, 2084, observers placed on the slopes of Elysium Mons will witness just such an event… with a rare transit of Earth and the Moon to boot!:
Arthur C. Clarke wrote of a transit of Earth from Mars that occurred in 1984 in his science fiction short story Transit of Earth.
Hey, I’m marking my calendar for the 2084 event… assuming, of course, my android body is ready by then!
