Posted on by David Dickinson

Looking for Lunar Letters

Lunar W
Do you see the 'Lunar W,' just below Mons Rümker on the lunar limb? Image credit: Apollo 15/NASA

Ready for some astro-pareidolia? This week, we look no further than Earth’s Moon, which reaches 1st Quarter phase this coming Sunday.

The Moon reaches First Quarter phase for lunation 1156 (which dates synodic cycles of the Moon using what’s called the Brown Lunation Number all the way back to January 17, 1923) this weekend on Sunday, June 12th, at 9:10 EDT/13:10 UT.

Every culture sees something different in the face of the Moon. The Chinese saw a rabbit, and named the Yutu ‘Jade Rabbit’ rover in honor of the myth. In Longfellow’s The Song of Hiawatha, it’s the body of the Iroquois Indian chief’s grandmother we see, flung up against the Moon. The Greeks believed the Moon was a large polished mirror, reflecting back a view of the Earth below. Of course, if this were the case, it would be hard to explain just how the image doesn’t shift during the night, as the Moon moves across the sky.

Moon Map
The annotated features on the lunar nearside. Image credit: Wikimedia Commons/ Peter Freiman(Cmglee). Background photograph by Gregory H. Revera.

A cosmic Rorschach test, the Moon is tidally locked in the Earth’s embrace, keeping its far side forever hidden from our terrestrial vantage point. The subtle rocking motions known as libration and nutation allow us to peer over the edge just a bit, allowing us to see 59% of the Moon’s total surface. A glimpse of the far side had to wait until the Soviet Luna 3 spacecraft flew past the Moon on October 7th, 1959 and returned the first blurry images.

One of the most famous of the lunar letters is the Lunar X, also referred to as the Werner X or Purbach Cross. This is the confluence of the rims of the craters La Caille, Blanchinus and Purbach located in the lunar highlands. The Lunar X becomes visible as the waxing gibbous Moon reaches seven days illumination, about 6 to 10 hours (depending on the incident sun angle) after First Quarter phase, and 6 to 10 hours before Last Quarter. The Lunar X can stand out in dramatic contrast against the darkness just beyond the lunar terminator, if you can catch it just as the first rays of sunlight hits the top of the ridge. Remember, the span of sunrise to sunset lasts two weeks on the Moon, and looking Earthward, you’d see the Earth in an opposite phase.

All hail the 'Lunar X'... image credit: Dave Dickinson.
All hail the ‘Lunar X’… image credit: Dave Dickinson.

Sometimes, the Curtiss Cross feature is referred to as a lesser known Lunar X; the confluence of two or more crater rims on the battered surface of the Moon is far from uncommon.

The Lunar X and the Lunar V features. Image credit and copyright: Mary Spicer
The Lunar X and the Lunar V features. Image credit and copyright: Mary Spicer

Sweeping northward, the Lunar V feature in the Mare Vaporum is also sometimes prominent around the same time as the Lunar X, and it’s possible to nab both in the same image.

Other lunar letters of note include the Lunar S in Sinus Asperitatis (visible at 47% illumination just before First Quarter), the Lunar W located near Mons Rümker on the lunar limb in the Oceanus Procellarum, and our favorite of the lesser known lunar letters, the Lunar Q of crater Kies in the Mare Nubium reaching favorable illumination 10 days after New. You can see a partial listing of lunar letters in the WikiMoon article here.

The 'Lunar Q' feature... Image credit: NASA/LROC.
The ‘Lunar Q’ feature… Image credit: NASA/LROC.

Of course, circular craters provide a wealth of candidates for the ‘Lunar O,’ and straight line features such as the Rupes Recta lunar straight wall feature in the Mare Nubium could easily pass for the ‘Lunar I’. Veteran lunar observer Charles Wood made a call in Sky and Telescope magazine to fill out the visual lunar alphabet in a similar fashion akin to Galaxy Zoo… hey, who wouldn’t love to spell out their name in craters? Maybe some of the recently mapped worlds such as Mercury, Pluto or Ceres could come to the rescue, filling in the final letters?

Many of these are optical illusions, tricks of lighting as the angle of the rising Sun slowly changes, casting shadows across the lunar landscape. Two illumination effects that are at work here straight out of art class are what’s known as the Clair-obscur or chiaroscuro phenomenon of light and shadow, and the Trompe l’Oeil effect, a three-dimension illusion of forced perspective. Follow features such as the Lunar X night to night as the Moon heads towards Full, and you’ll notice they nearly vanish amid the glare, as the Sun shines down from high overhead. The vanishing ‘face on Mars‘ was the result of the same trick of light seen in the early Viking 1 orbiter images. The ‘face’ vanished once the Mars Global Surveyor re-imaged the region during a pass at near-full illumination in 2001. Hey, why don’t conspiracy theorists ever cite the ‘Man in the Moon‘ as an artificial construct?

Why lunar letters? Well, I think its neat, to see something as familiar yet improbable as a gleaming letter on the lunar surface staring back at you at the eyepiece. If you look long and hard enough, the universe will produce just about anything, including telescope-building primates with language, and an accidental alphabet written in the heavens.

Posted on by David Dickinson

This Friday: The Moon Meets Mercury in the Dawn Sky

The waxing crescent Moon setting over Cadiz, Spain. Image credit: Dave Dickinson

So, have you been following the path of the waning Moon through the dawn sky this week? The slender Moon visits some interesting environs over the coming weekend, and heralds the start of Ramadan across the Islamic world next week.

First up, the planet Mercury rises an hour before the Sun in the dawn this week. Mercury reaches greatest elongation west of the Sun on Sunday, June 5th at 9:00 Universal Time (UT).

Image credit
The Moon meets Mercury on the morning of June 3rd. Image credit: Stellarium.

The slender waning crescent Moon passes less than one degree from +0.8 magnitude Mercury (both 24 degrees from the Sun) on the morning of Friday, June 3rd at 10:00 UT. While this is a close shave worldwide, the Moon will actually occult (pass in front of) Mercury for a very few observers fortunate enough to be based on the Falkland Islands in the southern Atlantic.

Image credit
The occultation footprint of the June 3rd event. Image credit Occult 4.0.

The Moon is 5.2% illuminated and 41 hours from New during the occultation. Meanwhile, Mercury shines at magnitude +0.8 and displays an 8.6” 33.5% illuminated disk during the event. Also, watch for ashen light or Earthshine faintly lighting up the nighttime side of the Moon. You’re seeing sunlight, bounced off of the land, sea and (mostly) cloud tops of the fat waxing gibbous Earth back on to the lunar surface, one light-second away. The Big Bear Solar Observatory has a project known as Project Earthshine which seeks to measure and understand the changes in albedo (known as global dimming) and its effects on climate change.

The Moon occults Mercury three times in 2016. Occultations of the innermost planet are especially elusive, as they nearly always occur close to the Sun under a daytime sky. This week’s occultation occurs less than 48 hours from greatest elongation; the last time one was closer time-wise was March 5th, 2008, and this won’t be topped until February 18th, 2026, with an occultation of Mercury by the Moon just 18 hours prior to greatest elongation. And speaking of which, can you spy +0.8 magnitude Mercury near the crescent Moon on Friday… during the daytime? Use binocs, note where Mercury was in relation to the Moon before sunrise, but be sure to physically block that blinding Sun behind a building or hill!

Mercury reaches greatest elongation six times in 2016: three in the dusk (western), and three in the dawn (eastern).

The Moon also passes less than five degrees from the planet Venus on June 5th at 2:00 UT, though both are only 2 degrees from the Sun. Fun fact: the bulk of the Sun actually occults Venus for 47 hours as seen from the Earth from June 6th through June 8th.

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Venus in SOHO’s view. Image credit: SOHO/NASA

You can observe the passage of Venus through the 15 degree wide field of view of SOHO’s LASCO C3 camera over the next few weeks until July 5th.

Venus reaches superior conjunction on the far side of the Sun 1.74 astronomical units (AU) from the Earth at 21:00 UT on Monday, June 6th.

New Moon occurs at 4:00 UT on Sunday, June 5th, marking the start of lunation 1156.

The Moon and Ramadan

The first sighting of the slim crescent Moon also marks the start of the month of Ramadan (Ramazan in Turkey) on the Islamic calendar. Unlike the western Gregorian calendar, which is strictly solar-based, and the Jewish calendar, which seeks to reconcile lunar and solar cycles, the Islamic is solely based on the 29.5 synodic period of the Moon. This means that it moves forward on average 11 days per Gregorian year. The hallmark of Ramadan is fasting from dawn to dusk, and Ramadan 2016 is an especially harsh one, falling across the northern hemisphere summer solstice (and the longest day of the year) on June 20th. The earliest sunrise occurs on June 14th, and latest sunset on June 27th for latitude 40 degrees north. Finally, the Earth reaches aphelion or its farthest point from the Sun on July 4th at 1.01675 AU or 157.5 million kilometers distant.

Image credit
The Moon meets Mercury (arrowed) in 2012. Image credit: Dave Dickinson

In 2016, the Moon will first likely be spotted from the west coast of South America on Sunday night June 5th, though many locales worldwide may not see the Moon until June 6th. There can be some disparity as to just when Ramadan starts based on the first sighting of the crescent Moon. The Islamic calendar is also unique in that it still relies on direct observation of the waxing crescent Moon. Other calendars often use an estimated approximation in a bid to keep their timekeeping in sync with the heavens. The computus estimation (not a supervillain, though it certainly sounds like one!) used by the Catholic Church to predict the future date of Easter, for example, fixes the vernal equinox on March 21st, though it actually falls on March 20th until 2048, when it actually slips to March 19th.

Ramadan has been observed on occasion in space by Muslim astronauts, and NASA even has guidelines stipulating that observant astros will follow the same protocols as their departure point from the Earth (in the foreseeable future, that’s the Baikonur Cosmodrome in Kazakhstan.

Can you see the open cluster M35, just six degrees north (right) of the thin crescent Moon on the evening of Monday, June 6th?

Image credit
Looking west on the evening of Monday, June 6th. Image credit: Starry Night Education Software.

We think its great to see direct astronomical observation still having a hand in everyday human affairs. This also holds a special significance to us, as we’re currently traveling in Morocco.

Don’t miss the meeting of Mercury and the Moon on Friday morning, and the return of the Moon to the dusk skies next week.

Posted on by Evan Gough

Mars At Closest Point To Earth in 11 Years May 30, 2016

Mars in all its red-hued glory. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)
Mars in all its red-hued glory. Image: NASA, ESA, the Hubble Heritage Team (STScI/AURA), J. Bell (ASU), and M. Wolff (Space Science Institute)

If you have a telescope, (What?! You don’t have one?) you’re in for a visual treat tonight. Mars will be at its closest point to Earth in 11 years on May 30. This event is worth checking out, whether with a telescope, astronomy binoculars, or online.

While today is when Mars is at its closest, you actually have a couple weeks to check this out, as the distance between Mars and Earth gradually becomes greater and greater. Today, Mars is 76 million kilometers (47.2 million miles) away, but up until June 12th it will still be no further than 77 million kilometers (48 million miles) away.

The furthest Mars can be from Earth is 401 million kilometers (249 million miles), when the two planets are on the opposite side of the Sun from each other.

For most of us with backyard ‘scopes, it’s difficult to make out much detail. You can see Mars, and at the most you can make out a polar cap. But it’s still fascinating knowing you’re looking at another planet, one that was totally unknowable for most humans who preceded us. A planet that we have rovers on, and that we have several craft in orbit around.

If you don’t have a scope, have no fear. There will be a flood of great astro-photos of Mars in the next few days. There are also options for live streaming feeds from powerful Earth-based telescopes.

The last time Mars was this close to Earth was 2005. A couple years before, the distance shrank to 55.7 million km (34.6 million miles.) That was the closest Mars and Earth have been in several thousand years. In 2018, the two planets will be nearly that close again.

This event is often called “opposition”, but it’s actually more correctly called “closest approach.” Opposition occurs a couple weeks before closest approach, when Mars is directly opposite the Sun.

A top-down image of the orbits of Earth and Mars. Image: NASA
A top-down image of the orbits of Earth and Mars. Image: NASA

But whether you call it opposition, or closest approach, the event itself is significant for more than just looking at it. Missions to Mars are planned when the two planets are close to each other. This reduces mission times drastically.

Mars Express, the mission being conducted by the European Space Agency (ESA) was launched in 2003, when the two planets were as close to each other as they’ve been in thousands of years. All missions to Mars can’t be so lucky, but they all strive to take advantage of the orbital cycles of the two planets, by nailing launch dates that work in our favour.

As for finding Mars in the night sky, it’s not that difficult. If you have clear skies where you are, Mars will appear as a bright, fire-yellow star.
“Just look southeast after the end of twilight, and you can’t miss it,” says Alan MacRobert, a senior editor of Sky & Telescope magazine, in a statement. “Mars looks almost scary now, compared to how it normally looks in the sky.”

This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech
This image shows how Mars appears at different times of the year in a typical backyard telescope. Image: NASA/JPL-Caltech

Although Mars is the closest thing in the sky to Earth right now, other than the Moon, it isn’t the brightest thing in the night sky. That honour is reserved for Jupiter, even though it’s ten times further away. Jupiter is twenty times larger in diameter than Mars, so it reflects much more sunlight and appears much brighter. (Obviously, everything in the night sky pales in comparison to the Moon.)

The reason for such a variation in distances between the planets lies in their elliptical orbits around the Sun. There’s a great video showing how their orbits change the distance between the two planets, here.

If you don’t have a telescope, you can still check Mars out. Go to slooh.com to check out live feeds from a proper telescope.

Posted on by David Dickinson

A Lord of Rings: Saturn at Opposition 2016

Saturn 2016
Saturn in early May 2016. Image credit: Efrain Morales.

They’re back. After a wintertime largely devoid of evening worlds, the planets are once again in the evening sky. First Jupiter, then Mars have crossed opposition over the past few months, and now Saturn is set to take center stage later next week, reaching opposition at 7:00 Universal Time (UT) on the night of June 2/3rd. This places the ringed world in a position of favorable evening viewing, rising in the east as the Sun sets in the west, and riding highest near local midnight across the meridian.

Opposition 2016 sees the planet Saturn looping through the southern realm of the constellation Ophiuchus, making a retrograde run this summer at the Scorpius border before looping back and resuming eastward motion. That’s right: Saturn currently occupies the dreaded ‘13th house,’ of Ophiuchus, for all you Snake-Bearers out there. Saturn is currently at bright as it can be, at magnitude +0.04.

Saturn rising on the night of June 2nd. Image credit: Starry Night Education Software.
Saturn rising on the night of June 2nd. Image credit: Starry Night Education Software.

Saturn reaches opposition once every 378 days, as it orbits the Sun at a leisurely pace every 29.5 years. 2016 and the next few oppositions sees Saturn ‘bottoming out,’ sitting around -20 degrees south. Saturn won’t peek northward across the celestial equator again until March 2026. This places the 2016 appearance of Saturn high in the sky south of the equator, transiting about 30 degrees above the southern horizon around midnight for folks observing around 40 degrees north latitude. Saturn also begins looping towards the star-rich region of the galactic equator for a crossing it late next year in December 2017. Saturn sits 9 Astronomical Units (AU) or 1.4 billion kilometers distant on June 3rd, a slightly larger distance than usual, owing to the fact that the planet is headed towards aphelion on April 17th, 2018.

The waxing gibbous Moon passes 3.2 degrees north from Saturn on Sunday, June 19th, just a day before reaching Full.

Watch for a sudden brightening of the planet in early June, known as an ‘opposition surge’ due to what is known as the Seeliger effect. This is a coherent back-scattering of light, focusing it similar to highway retro-reflectors shining your headlights back at you at night. In this case, the Sun is the ‘headlight,’ and the millions of snowball moonlets hiding their shadows from view reaching 100% illumination are the highway retro-reflectors. The effect is subtle, to be sure, but serves to raise the brightness of the planet by about half a magnitude. This should be apparent in an animation sequence shot before, during and after over the span of a about a week. Any takers?

Almost there... the widening tilt of Saturn's rings. image credit and copyright: Andrew Symes (@failedprotostar).
Almost there… the widening tilt of Saturn’s rings. image credit and copyright: Andrew Symes (@failedprotostar).

And speaking of the rings, here’s another reason to check out Saturn this opposition 2016 season. The tilt of rings is about 26 degrees wide as seen from our Earthly perspective… about as wide as they can be. Saturn’s rings were last edge on in 2009, and reach a maximum width of 27 degrees on October 16th, 2017 before slowly heading towards edge on again in 2025.

The path of Saturn through the last half of 2016. Image credit: Starry Night Education software.
The path of Saturn through the last half of 2016. Image credit: Starry Night Education software.

At the eyepiece, Saturn shows a yellowish disk 18” extended to 43” across if you count the rings. Crank up the magnification to over 100x under good seeing, and the black thread of the Cassini division jumps into view. Saturn has 62 moons in all, with +9th magnitude Titan being the brightest. You’re looking at the most distant surface outpost of humanity, the site of the 2005 landing of the European Space Agency’s Huygens lander. Six moons are readily visible in a small telescope, while the fainter moons Hyperion and Phoebe present a challenge to owners of extreme light buckets. Also, as Saturn heads past opposition and towards eastern quadrature 90 degrees from the Sun on September 2nd, 2016, watch for the shadow of the bulk of the planet, cast back across the rings.

A sampling of the Moons of Saturn. Image credit: Stellarium.
A sampling of the Moons of Saturn. Image credit: Stellarium.

We never miss a chance to observe Saturn if it’s above the horizon. Saturn is a sure-fire crowd-pleaser for any sidewalk astronomy session, and no one forgets their first glimpse of the glorious ringed world. You can just imagine how much consternation this bizarre-looking planet must have caused Galileo. You can tell just how primitive his first telescope was, as his sketches show off Saturn as more of a two-handled ‘coffee cup’ in appearance. Christaan Huygens first deduced something of the true nature of Saturn’s rings in 1655, correctly claiming that they are physically separated from the disk.

Don’t miss Saturn at opposition next week!

Posted on by Bob King

Hubble Telescope Zooms In On Mars

Mars snapped with the Hubble Space Telescope on May 12 just days before opposition. Credit: NASA/ESA
This image shows our neighbouring planet Mars, as it was observed shortly before opposition in 2016 by the NASA/ESA Hubble Space Telescope. Some prominent features of the planet are clearly visible: the ancient and inactive shield volcano Syrtis Major; the bright and oval Hellas Planitia basin; the heavily eroded Arabia Terra in the centre of the image; the dark features of Sinus Sabaeous and Sinus Meridiani along the equator; and the small southern polar cap.
On May 12, the Hubble Space Telescope took this photo of Mars. Some prominent features of the planet are clearly visible: the ancient and inactive shield volcano Syrtis Major (far right and partly covered by clouds); the heavily eroded Arabia Terra in the center of the image; the dark features of Sinus Sabaeous and Sinus Meridiani below center and the small north polar cap (top).

We’re in store for an exciting weekend as the Earth and Mars get closer to each other than at any time in the last ten years. To take advantage of this special opportunity, the Hubble Space Telescope, normally busy eyeing remote galaxies, was pointed at our next door neighbor to capture this lovely close-up image.

Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together at that time. Mars opposition occurs on May 22, when the planet will shine at magnitude -2.0 and with an apparent diameter of 18.6 arc seconds, its largest in years. Credit: Bob King
Opposition occurs when Mars and Earth line up on the same side of the Sun. The two planets are closest together around that time. Mars opposition occurs on May 22, when the planet will shine at magnitude -2.0 and with an apparent diameter of 18.6 arc seconds, its largest in over 10 years. Credit: Bob King

As Universe Today writer David Dickinson described in his excellent Mars guide, the planet reaches opposition on Sunday morning May 22. That’s when the planet will be directly opposite the Sun in the sky and rise in the east around the same time the Sun sets in the west. Earth sits squarely in between. Opposition also marks the planet’s close approach to Earth, so that Mars appears bigger and brighter in the sky than usual. A perfect time for detailed studies whether through both amateur and professional telescopes.

Although opposition for most outer planets coincides with the date of closest approach, that’s not true in the case of Mars. If Mars is moving away from the Sun in its orbit when Earth laps it, closest approach occurs a few days before opposition.  But if the planet is moving toward the Sun when our planet passes by, closest approach occurs a few days after opposition. This time around, Mars is headed sunward, so the date of closest approach of the two planets occurs on May 30.

It’s all goes back to Mars’ more eccentric orbit, which causes even a few days worth of its orbital travels to make a difference in the distance between the two planets when Earth is nearby.  On May 22, Mars will be 47.4 million miles away vs. 46.77 million on the 30th, a difference of about 700,000 miles.

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Every 26 months Mars reaches opposition. This mosaic of photos taken by Hubble show seven different oppositions since 1995. Because of Mars’ elliptical orbit, it shows variations in apparent size from opposition to opposition.  Mars was the closest in 2003 when it came within 34.8 million miles (56 million kilometer) of Earth. The part of Mars that is tilted towards the Earth also shifts over time, resulting in the changing visibility of the polar caps. Clouds and dust storms, as well as the size of the ice caps, can change the appearance of Mars on time scales of days, weeks, and months. Other features of Mars, such as some of the large dark markings, have remained unchanged for centuries. Credit: NASA/ESA

On May 12, Hubble took advantage of this favorable alignment and turned its gaze towards Mars to take an image of our rusty-hued neighbor, From this distance the telescope could see Martian features as small as 18.6 miles (30 kilometers) across. The image shows a sharp, natural-color view of Mars and reveals several prominent geological features, from smaller mountains and erosion channels to immense canyons and volcanoes.

This image shows our neighbouring planet Mars, as it was observed shortly before opposition in 2016 by the NASA/ESA Hubble Space Telescope. Some prominent features on the surface of the planet have been annotated.
Some of the more prominent features in the Hubble photo of Mars are marked here. Limb hazes are visible in modest-sized telescopes as a pale edging around the planet’s rim. The planet’s distinctive red color is created by rust. Billions of years ago, it’s thought that ultraviolet light from the Sun split water in the Martian atmosphere into hydrogen and oxygen. The hydrogen escaped, but the oxygen combined with iron in the planet’s surface rocks to form iron oxide or rust. Many of Earth’s red rock formations are similarly “oxidized.” Credit: NASA/ESA

The orange area in the center of the image is Arabia Terra, a vast upland region. The landscape is densely cratered and heavily eroded, indicating that it could be among the oldest features on the planet.

While the polar caps aren't currently visible, telescope users will be treated to nice views of India-shaped Syrtis Major. The large crater Hellas at the top (south) limb is currently covered in winter clouds. Credit: Christopher Go
While the polar caps aren’t currently visible, telescope users will be treated to nice views of India-shaped Syrtis Major. The large crater Hellas at the top (south) limb is currently covered in winter clouds. Credit: Christopher Go

South of Arabia Terra, running east to west along the equator, is the long dark feature named Sinus Sabaeus that terminates in a larger, dark blob called and Sinus Meridiani. These darker regions are covered by bedrock from ancient lava flows and other volcanic features. An extended blanket of clouds can be seen over the southern polar cap where it’s late winter. The icy northern polar cap has receded to a comparatively small size because it’s now late summer in the northern hemisphere.

Mars on May 2 shows Syrtis Major off to the east (right). Crossing the top of the photo are Mare Tyrrhenum to the right of the planet's central meridian and Mare Cimmerium, to the left. Credit: Christopher Go
Mars on May 2 shows Syrtis Major off to the east (right). Crossing the top of the photo are Mare Tyrrhenum to the right of the planet’s central meridian and Mare Cimmerium, to the left. Credit: Christopher Go

So the question now is how much will you see as we pull up alongside the Red Planet this weekend? With the naked eye, Mars looks like a fiery “star” in the head of Scorpius the scorpion not far from the similarly-colored Antares, the brightest star in the constellation. It’s unmistakable. Even through the haze it caught my eye last night, rising in the southeast around 10 o’clock with its signature hue.

Through a 4-inch or larger telescope, you can see limb hazes/clouds and prominent dark features such as Syrtis Major, Utopia, clouds over Hellas, Mare Tyrrhenum (to the west of Syrtis Major) and Mare Cimmerium (west of M. Tyrrhenum).

Expert imager Damian Peach created this photographic map of Mars labeled with its most prominent features visible in amateur telescopes. Click for a larger version. Credit: Damian Peach
Expert astroimager Damian Peach created this photographic map of Mars labeled with its most prominent features visible in amateur telescopes. Click for a large version. Credit: Damian Peach

These features observers across the America will see this week and early next between about 11 p.m. and 2 a.m. local time. As Mars rotation period is 37 minutes longer than Earth’s, these markings will gradually rotate out of view, and we’ll see the opposite hemisphere in the coming weeks. You can use the map to help you identify particular features or Sky & Telescope’s handy Mars Profiler to know which side of the planet’s visible when.

The Full Moon, Mars only hours before opposition, Saturn and Antares gather in the southern sky for a special, diamond-shaped grouping. Diagram: Bob King, source: Stellarium
The Full Moon, Mars only hours before opposition, Saturn and Antares gather in the southern sky for a special, diamond-shaped grouping. Diagram: Bob King, source: Stellarium

To top off all the good stuff happening with Mars, the Full Flower Moon will join up with that planet, Saturn and Antares Saturday night May 21 to create what I like to call a “diamond of celestial lights” visible all night. Don’t miss it!

Italian astronomer Gianluca Masi will offer up two online Mars observing sessions in the coming week, on May 22 and 30, starting at 5 p.m. CDT (22:00 UT). Yet another opportunity to get acquainted with your inner Mars.

Posted on by David Dickinson

Images of Today’s Transit of Mercury From Around the World

Mercury Transit
Mercury meets the Sun in Hydrogen Alpha. Image credit and copyright: Brendan Martin @HASungazer

Lead image credit: Brendan Martin.

(Note: Awesome images are being added as they come in!)

Update: Here’s two more amazing videos of yesterday’s transit of Mercury that have come our way. First: double solar transits featuring Mercury, the International Space Station and a low flying plane right here in the skies of good old planet Earth courtesy of (who else?) Thierry Legault:

And here’s one of the very few sequences we’ve seen of the transit with foreground, captured at sunset by Gadi Eidelheit based in Israel:

And finally, check out this amazing (and mesmerizing) animation of Mercury racing across the Sun, courtesy of the Big Bear Solar Observatory!

It’s not every day you get to see a planet pass in front of the Sun.

But today, skywatchers worldwide got to see just that, as diminutive Mercury passed in front of the disk of the Sun as seen from the Earth. This was the first transit of Mercury across the face of the Sun since November 8th, 2006, and the last one until November 11th, 2019. Continue reading “Images of Today’s Transit of Mercury From Around the World”

Posted on by David Dickinson

A Summer Comet: Our Guide to Observing X1 PanSTARRS

Comet X1 PanSTARRS
Comet C/2013 X1 PanSTARRS from early January 2016, shortly after a reported outburst. Image credit and copyright: Hisayoshi Kato.

Ready for one of the better binocular comets of 2016? Emerging from behind the Sun and a surprise outburst in January, Comet C/2013 X1 PanSTARRS is about to put on its summer show. The waning crescent Moon just crossed paths with the comet in the dawn sky on its way to New on May 6th, and the time to start tracking it is now as it plunges southward across the ecliptic this weekend. Continue reading “A Summer Comet: Our Guide to Observing X1 PanSTARRS”

Posted on by David Dickinson

An Old Glass Plate Hints at a Potential New Exoplanet Discovery

Polluted white dwarf
An artist's conception of a 'polluted white dwarf' star, plus debris disk. Image credit: NASA.

What’s the value to exoplanet science of sifting through old astronomical observations? Quite a lot, as a recent discovery out of the Carnegie Institution for Science demonstrates. A glass plate spectrum of a nearby solitary white dwarf known as Van Maanen’s Star shows evidence of rocky debris ringing the system, giving rise to a state only recently recognized as a ‘polluted white dwarf.’ Continue reading “An Old Glass Plate Hints at a Potential New Exoplanet Discovery”

Posted on by David Dickinson

Into the Red: Our Complete Guide to Mars Opposition 2016

Mars 2014
Mars from opposition 2014. Image credit and copyright: Paul Stewart.

Ready to explore the Red Planet? Starting in May, Mars invades the evening skies of the Earth, as it heads towards opposition on May 22nd. Not only does this place Mars front and center for prime time viewing, but we’re headed towards a cycle of favorable oppositions, with Mars near perihelion, while Earth is near aphelion. Continue reading “Into the Red: Our Complete Guide to Mars Opposition 2016”

Posted on by David Dickinson

April Lunacy: Getting Ready for the Full ‘Mini-Moon’

2015 Mini-Moon
The March 5th 2015 Mini-Moon. Image credit and copyright: Alan Dyer

Do you welcome the extra evening light of the Full Moon, or curse the additional light pollution? Either way, this week’s Full Moon on Friday April 22nd is special. It’s the smallest Full Moon of 2016, something we here at Universe Today have christened the Mini-Moon.

Mini-Moon 2016: This year’s Mini-Moon falls on April 22nd at 5:25 Universal Time (UT), just 13 hours and 19 minutes after lunar apogee the evening prior at 16:06 UT on April 21st. Though apogee on the 21st is 406,350 km distant – a bit on the far end, but the third most distant for the year by 300 km — this week’s Full Moon is the closest to apogee for 2016 time-wise. The 2015 Mini-Moon was even closer, in the 10 hour range, but you’ll have to wait until December 10th, 2030 to find a closer occurance.

Image credit and copyright:
The Mini-Moon versus the 2011 Supermoon. Image credit and copyright: Ken Lord.

What is the Mini-Moon, you might ask? As with the often poorly defined Supermoon, we like to eschew the ambiguous ‘90% of its orbit’ definition, and simply refer to it as a Full Moon occurring within 24 hours of lunar apogee, or its farthest point from the Earth in its orbit.

Fun fact: the 29.55 day period from perigee to perigee (or lunar apogee-to-apogee) is known as an anomalistic month.

Image credit: Dave Dickinson
Mini-Moons by year for the remainder of the decade. Note that the 2020 Full Moon is also the 2nd of the month… A ‘Mini-Blue Halloween Moon?’ Image credit: Dave Dickinson

Thank our Moon’s wacky orbit for all this lunacy. Inclined 5.14 degrees relative to the ecliptic plane, the Moon returns to the same phase (say, Full back to Full) every 29.53 days, known as a synodic month. The Moon can appear 33.5′ across during perigee, and shrink to 29.4′ across near apogee.

The appearance of the Moon through one synodic period. Note that in addition to rocking back and forth (libration) and side-to-side (nutation), the Moon appears to swell and shrink in size. Wikimedia Commons graphic in the public Domain.
The appearance of the Moon through one synodic period. Note that in addition to rocking back and forth (libration) and side-to-side (nutation), the Moon appears to swell and shrink in size. Wikimedia Commons graphic in the Public Domain.

And don’t fear the ‘Green Moon,’ and rumors going ’round ye’ ole internet that promise a jaded Moon will occur in April or May; this is 100% non-reality based, seeking to join the legends of Super, Blood, and Full Moons, Black and Blue.

Image faked by: David Dickinson.
No. Just. No. Image faked by: David Dickinson.

The April Full Moon is also known as the Full Pink Moon to the Algonquin Indians. The April Full Moon, can, on occasion be the Full Moon ushering in Easter (known as the Paschal Moon) as per the rule established by the 325 AD council of Nicaea, stating Easter falls on the first Sunday after the first Full Moon after the fixed date of the Vernal Equinox of March 21st. Easter can therefore fall as late as April 25th, as next occurs on 2038. The future calculation of Easter by the Church gets the Latin supervillain-sounding name of Computus.

April 21st. Image credit: Stellarium
Looking east on the evening of April 21st. Image credit: Stellarium

Of course, the astronomical vernal equinox doesn’t always fall on March 21st, and to complicate matters even further, the Eastern Orthodox Church uses the older Julian Calendar and therefore, Easter doesn’t always align with the modern western Gregorian calendar used by the Roman Catholic Church.

The Moon can create further complications in modern timekeeping as well.

Here’s one wonderful example we recently learned of in our current travels. The Islamic calendar is exclusively based on the synodic cycle of the Moon, and loses 11 days a year in relation to the Gregorian solar calendar. Now, Morocco officially adopted Daylight Saving (or Summer) Time in 2007, opting to make the spring forward during the last weekend of March, as does the European Union to the north. However, the country reverts back to standard time during the month of Ramadan… otherwise, the break in the daily fast during summer months would fall towards local midnight.

You can see a curious future situation developing. In 2016, Ramadan runs from sundown June 5th, to July 4th. Each cycle begins with the sighting of the thin waxing crescent Moon. However, as Ramadan falls earlier, you’ll get a bizarre scenario such as 2022, when Morocco springs forward on March 27th, only to fall back to standard time six days later on April 2nd on the start of Ramadan, only to jump forward again one lunation later on April 30th!

Morocco is the only country we’ve come across in our travels that follows such a convoluted convention of timekeeping.

Fun fact #2: the next ‘Mini-Moon’ featuring a lunar eclipse occurs on July 27th 2018.

And the Spring Mini-Moon sets us up for Supermoon season six months later this coming October-November-December. Though lunar perigees less than 24 hours from Full usually occur as a trio, an apogee less than 24 hours from Full is nearly always a solitary affair, owing to the slightly slower motion of the Moon at a farther distance.

Don’t miss the shrunken Mini-Moon rising on the evenings of Thursday April 21st and Friday 22nd, coming to a sky near you.