Will you see it? Comet Jacques will pass about 3.5 degrees north of brilliant Venus tomorrow morning July 13. This map shows the sky facing northeast about 1 hour before sunrise. Stellarium
Comet C/2014 E2 Jacques has returned! Before it disappeared in the solar glow this spring, the comet reached magnitude +6, the naked eye limit. Now it’s back at dawn, rising higher each morning as it treks toward darker skies. Just days after its July 2 perihelion, the fuzzball will be in conjunction with the planet Venus tomorrow morning July 13. With Mercury nearby, you may have the chance to see this celestial ‘Rat Pack’ tucked within a 8° circle.
First photo of Comet Jacques on its return to the morning sky taken on July 11. Two tails are visible – a short, dust tail pointing to the lower left of the coma and longer gas or ion tail to the right. Credit: Gerald Rhemann
While I can guarantee you’ll see Venus and probably Mercury (especially if you use binoculars), morning twilight and low altitude will undoubtedly make spotting Comet Jacques challenging. A 6-inch telescope might nail it. Look for a small, fuzzy cloud with a brighter core against the bluing sky. Patience is the sky observer’s most useful tool. It won’t be long before the comet’s westward motion combined with the seasonal drift of the stars will loft it into darkness again.
Use this map to follow Comet Jacques as it moves west across Taurus and Auriga over the next few weeks. Planet positions are shown for July 13 with stars to magnitude +6. Jacques’ position is marked every 5 days. Click to enlarge. Source: Chris Mariott’s SkyMap
A week from now, when the moon’s slimmed to half, the comet will be nearly twice as high and should be easily visible in 50mm binoculars at the start of morning twilight.
Comet Jacques is expected to remain around magnitude +6 through the remainder of July into early August and then slowly fade. It will be well-placed in Perseus at the time of the Perseid meteor shower on Aug. 12-13. Closest approach to Earth occurs on August 29 at 52.4 million miles (84.3 million km). Good luck and let us know if you see it.
The perigee Full Moon of June 22nd, 2013. Credit: Russell Bateman (@RussellBateman1)
‘Tis the season once again, when rogue Full Moons nearing perigee seem roam the summer skies to the breathless exhortations of many an astronomical neophyte at will. We know… by now, you’d think that there’d be nothing new under the Sun (or in this case, the Moon) to write about the closest Full Moons of the year.
But love ‘em or hate ‘em, tales of the “Supermoon” will soon be gracing ye ole internet again, with hyperbole that’s usually reserved for comets, meteor showers, and celeb debauchery, all promising the “biggest Full Moon EVER…” just like last year, and the year be for that, and the year before that…
How did this come to be?
What’s happening this summer: First, here’s the lowdown on what’s coming up. The closest Full Moon of 2014 occurs next month on August 10th at 18:11 Universal Time (UT) or 1:44 PM EDT. On that date, the Moon reaches perigee or its closest approach to the Earth at 356,896 kilometres distant at 17:44, less than an hour from Full. Of course, the Moon reaches perigee nearly as close once everyanomalistic month (the time from perigee-to-perigee) of 27.55 days and passes Full phase once every synodic period (the period from like phase to phase) with a long term average of 29.53 days.
Moon rise on the evening of July 11th, 2014 as seen from latitude 30 degrees north. Credit: Stellarium.
And the August perigee of the Moon only beats out the January 1st, 2014 perigee out by a scant 25 kilometres for the title of the closest perigee of the year, although the Moon was at New phase on that date, with lots less fanfare and hoopla for that one. Perigee itself can vary from 356,400 to 370,400 kilometres distant.
But there’s more. If you consider a “Supermoon” as a Full Moon falling within 24 hours of perigee, (folks like to play fast and loose with the informal definitions when the Supermoon rolls around, as you’ll see) then we actually have a trio of Supermoons on tap for 2014, with one this week on July 12th and September 9th as well.
What, then, is this lunacy?
Well, as many an informative and helpful commenter from previous years has mentioned, the term Supermoon was actually coined by an astrologer. Yes, I know… the same precession-denialists that gave us such eyebrow raising terms as “occultation,” “trine” and the like. Don’t get us started. The term “Supermoon” is a more modern pop culture creation that first appeared in a 1979 astrology publication, and the name stuck. A more accurate astronomical term for a “Supermoon” is a perigee-syzygy Full Moon or Proxigean Moon, but those just don’t seem to be able to “fill the seats” when it comes to internet hype.
One of the more arcane aspects set forth by the 1979 definition of a Supermoon is its curiously indistinct description as a “Full Moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit.” This is a strange demarcation, as it’s pretty vague as to the span of distance (perigee varies, due to the drag of the Sun on the Moon’s orbit in what’s known as the precession of the line of apsides) and time. The Moon and all celestial bodies move faster near perigee than apogee as per Kepler’s 2nd Law of planetary motion.
A photo essay comparing Full Moon sizes and appearance from one Supermoon to the next, spanning 2011-2012. Credit: Marion Haligowski/RadicalRetinscopy. Used with permission.
We very much prefer to think of a Proxigean Moon as defined by a “Full Moon within 24 hours of perigee”. There. Simple. Done.
And let’s not forget, Full phase is but an instant in time when the Moon passes an ecliptic longitude of 180 degrees opposite from the Sun. The Moon actually never reaches 100% illumination due to its 5.1 degree tilt to the ecliptic, as when it does fall exactly opposite to the Sun it also passes into the Earth’s shadow for a total lunar eclipse.
-Check out this animation of the changing size of the Moon and its tilt — known as libration and nutation, respectively — as seen from our Earthly perspective over the span of one lunation.
The truth is, the Moon does vary from 356,400 to 406,700 kilometres in its wonderfully complicated orbit about our fair world, and a discerning eye can tell the difference in its size from one lunation to the next. This means the apparent size of the Moon can vary from 29.3’ to 34.1’ — a difference of almost 5’ — from perigee to apogee. And that’s not taking into account the rising “Moon illusion,” which is actually a variation of an optical effect known as the Ponzo Illusion. And besides, the Moon is actually more distant when its on the local horizon than overhead, to the tune of about one Earth radius.
Like its bizarro cousin the “minimoon” and the Blue Moon (not the beer), the Supermoon will probably now forever be part of the informal astronomical lexicon. And just like recent years before 2014, astronomers will soon receive gushing platitudes during next month’s Full Moon from friends/relatives/random people on Twitter about how this was “the biggest Full Moon ever!!!”
The perigee Full Moon of May 5th, 2012. Credit: Stephen Rahn (@StephenRahn13)
Does the summer trio of Full Moons look bigger to you than any other time of year? It will be tough to tell the difference visually over the next three Full Moons. Perhaps a capture of the July, August and September Full Moons might just tease out the very slight difference between the three.
And for those preferring not to buy in to the annual Supermoon hype, the names for the July, August and September Full Moons are the Buck, Sturgeon and Corn Moon, respectively. And of course, the September Full Moon near the Equinox is also popularly known as the Harvest Moon.
And in case you’re wondering, or just looking to mark your calendar for the next annual “largest Full Moon(s) of all time,” here’s our nifty table of Supermoons through 2020, as reckoned by our handy definition of a Full Moon falling within 24 hours of perigee.
So what do you say? Let ‘em come for the hype, and stay for the science. Let’s take back the Supermoon.
Got clear skies this July 4th weekend? The Moon passes some interesting cosmic environs in the coming days, offering up some photogenic pairings worldwide and a spectacular trio of occultations for those well placed observers who find themselves along the footprint of these events.
The path of the Moon on July 5th, 6th and 7th. Credit: Stellarium
First, let’s look at our closest natural neighbor in space. The Moon reaches first quarter phase on Saturday, July 5th at 11:59 Universal Time (UT)/7:59 AM EDT. First Quarter is a great time to observe the Moon, as the craters along the jagged terminator where the Sun is just starting to rise stand out in stark profile. Watch for the Lunar Straight Wall and the alphabet soup of elusive features known as the Lunar X or Purbach Cross and Lunar V on evenings right around First Quarter phase.
Mars off of the limb of the Moon as seen from North America on the evening of July 5th. Credit: Starry Night.
Our first conjunction stop on this weekend’s lunar journey is the planet Mars. Although the Moon occults — that is, passes in front of a given planet from our Earthly perspective — exactly 16 naked eye planets in 2014 (24 if you add in Uranus events and 1 Ceres and 4 Vesta on September 28th), the Moon will only occult Mars once in 2014, on the night of July 5th/6th. Northern South America and southern Central America will have a front row seat, while the rest of North America will see a close pass less than one degree from the lunar limb. This will still present a fine photographic opportunity, as it’ll be possible to snag Mars and the limb of the Moon in the same field of view. The Moon will be 56% illuminated during the conjunction, and Mars will present an 88% illuminated disk 9.2” across shining at magnitude +0.3.
The occultation path for Mars. Graphics created using Occult 4.0.
Both will be 96 degrees east of the Sun during geocentric (Earth-centered) conjunction, which occurs around 1:00 UT on July 6th or 9:00 PM EDT on the evening of the 5th. For those positioned to catch the occultation, it’ll take about a minute for “Mars set” to occur on the lunar limb. The last occultation of Mars occurred on May 9th, 2013 and the next won’t happen ‘til March 21st, 2015.
The footprint of Lambda Virginis…
Next up, the Moon occults the +4.5th magnitude star Lambda Virginis on July 7th centered on 8:26 UT. This event is well placed for observers in Hawaii on the evening of July 6th. Located 187 light years distant, the light that you’re seeing departed the far-flung star on 1827, only to be interrupted by the pesky limb of our Moon a second prior to arrival on Earth. This star is also of note as it’s a spectroscopic binary, and while you won’t be able to resolve the pair at a tiny separation of just 0.0002” apart, you just might be able to see the pair “wink out” in a step wise fashion that betrays its binary nature. The Moon misses the brightest star in Virgo (Spica) this month, as it’s wrapped up a series of occultations of the star in early 2014 and won’t resume until 2024. Aldebaran, Antares and Regulus also lie along the Moon’s path on occasion, and the next cycle of bright star occultations resume with Aldebaran in January 2015. You can check out a list of fainter naked eye stars occulted by the Moon this year here courtesy of the International Occultation Timing Association.
… and the occultation footprint for Saturn.
And finally, the Moon visits Saturn, now residing just over the border in the astronomical constellation of Libra. This occultation occurs just 49 hours after the Mars event at 2:00 UT on July 8th (10:00 PM EDT on the evening of July 7th) and favors observers in the southernmost tip of South America. As with Mars, North America will see a close miss, although it will also be possible to squeeze Saturn in the same field of view as the Moon at low power, though it’ll sit about a degree of off its limb. We’re in a cycle of occultations of Saturn this year, with 11 occurring in 2014 and the next on August 4th. The reason for this is that Saturn moves much more slowly across the sky than Mars from our perspective, making for a relatively sluggish moving target for the Moon. Saturn shines at +0.6 magnitude as the 75% illuminated Moon passes by and subtends 42” with rings and will take about five minutes to pass fully behind the Moon.
These events will make for some great pics and animation sequences for sure… can you spot Saturn or Mars near the lunar limb with binoculars or a telescope before sunset? Or catch ‘em in the frame during a local fireworks show? Let us know, if enough pics surface on Universe Today’s Flickr page, we may do a post weekend roundup!
Pluto passing near the star cluster M25 in late 2013. Credit: Dave Walker.
Are you ready for 2015? On July 14th, 2015 — just a little over a year from now — NASA’s New Horizons spacecraft with perform its historic flyby of Pluto and its retinue of moons. Flying just 10,000 kilometres from the surface of Pluto — just 2.5% the distance from Earth to the Moon on closest approach — New Horizons is expected to revolutionize our understanding of these distant worlds.
And whether you see Pluto as a much maligned planetary member of the solar system, an archetypal Plutoid, or the “King of the Kuiper Belt,” you can spy this denizen of the outer solar system using a decent sized backyard telescope and a little patience.
New Horizons in the clean room having its plutonium-fueled MMRTG installed. (Credit: NASA).
Pluto reaches opposition for 2014 later this week on Friday, July 4th at 3:00 Universal Time (UT), or 11:00 PM EDT on July 3rd. This means that Pluto will rise to the east as the Sun sits opposite to it in the west at sunset and transits the local meridian high to the south at local midnight. This is typically the point of closest approach to Earth for any outer solar system object and the time it is brightest.
The location of Pluto at dusk on July 4th, the night of opposition. Credit: Stellarium.
But even under the best of circumstances, finding Pluto isn’t easy. Pluto never shows a resolvable disk in even the largest backyard telescope, and instead, always appears like a tiny star-like point. When opposition occurs near perihelion — as it last did in 1989 — Pluto can reach a maximum “brilliancy” of magnitude +13.6. However, Pluto has an extremely elliptical orbit ranging from 30 to 49 Astronomical Units (A.U.s) from the Sun. In 2014, Pluto has dropped below +14th magnitude at opposition as it heads back out towards aphelion one century from now in 2114.
The path of Pluto from July to December 2014. Created using Starry Night Education Software.
Another factor that makes finding Pluto challenging this decade is the fact that it’s crossing through the star-rich plane of the galaxy in the direction of the constellation Sagittarius until 2023. A good finder chart and accurate pointing is essential to identifying Pluto as it moves 1’ 30” a day against the starry background from one night to the next.
In fact, scouring this star-cluttered field is just one of the challenges faced by the New Horizons team as they hunt for a potential target for the spacecraft post-Pluto encounter. But this has also meant that Pluto has crossed some pretty photogenic regions of the sky, traversing dark Bok globules and skirting near star clusters.
Pluto (marked) imaged by Jim Hendrickson @SkyscraperJim on the morning of June 28th.
You can use this fact to your advantage, as nearby bright stars make great “guideposts” to aid in your Pluto-quest. Pluto passes less than 30” from the +7th magnitude pair BB Sagittarii on July 7th and 8th and less than 3’ from the +5.2 magnitude star 25 Sagittarii on July 21st… this could also make for an interesting animation sequence.
Though Pluto has been reliably spotted in telescopes as small as 6” in diameter, you’ll most likely need a scope 10” or larger to spot it. We’ve managed to catch Pluto from the Flandrau observatory situated in downtown Tucson using its venerable 14” reflector.
The path of Pluto June 28th-August 8th. (click here for an inverted white background view). Created using Starry Night Education Software.
Pluto was discovered by Clyde Tombaugh from the Lowell Observatory in 1930 while it was crossing the constellation Gemini. It’s sobering to think that it has only worked its way over to Sagittarius in the intervening 84 years. It was also relatively high in the northern hemisphere sky and headed towards perihelion decades later during discovery. 2014 finds Pluto at a southern declination of around -20 degrees, favoring the southern hemisphere. Had circumstances been reversed, or Pluto had been near aphelion, it could have easily escaped detection in the 20th century.
We’re also fortunate that Pluto is currently relatively close to the ecliptic plane, crossing it on October 24th, 2018. Its orbit is inclined 17 degrees relative to the ecliptic and had it been high above or below the plane of the solar system, sending a spacecraft to it in 2015 might have been out of the question due to fuel constraints.
The current location of New Horizons. (Credit: NASA/JPL).
And speaking of spacecraft, New Horizons now sits less than one degree from Pluto as seen from our Earthly vantage point. And although you won’t be able to spy this Earthly ambassador with a telescope, you can wave in its general direction on July 11th and 12th, using the nearby waxing gibbous Moon as a guide:
The Moon, Pluto and New Horizons as seen on July 11th. (Created Using Starry Night Education Software).
All eyes will be on Pluto and New Horizons in the coming year, as it heads towards a date with destiny… and we’ll bet that the “is Pluto a planet?” debate will rear its head once more as we get a good look at these far-flung worlds.
And hey, if nothing else, us science writers will at last have some decent pics of Pluto to illustrate articles with, as opposed to the same half-dozen blurry images and artist’s renditions…
Ceres and Vesta are converging in Virgo not far from Mars and Spica. On July 5, the duo will be just 10' apart and visible in the high power telescope field of view. Positions are shown every 5 days for 10 p.m. EDT and stars to magnitude +8.5. Created with Chris Marriott's SkyMap software
I bet you’ve forgotten. I almost did. In April, we reported that Ceres and Vesta, the largest and brightest asteroids respectively, were speeding through Virgo in tandem. Since then both have faded, but the best is yet to come. Converging closer by the day, on July 5, the two will make rare close pass of each other when they’ll be separated by just 10 minutes of arc or the thickness of a fat crescent moon.
Vesta (left) and Ceres. Vesta was photographed up close by the Dawn spacecraft from July 2011-Sept. 2012, while the best views we have to date of Ceres come from the Hubble Space Telescope. The bright white spot is still a mystery. NASA will plunk Dawn into orbit around Ceres next February. Credit: NASA
Both asteroids are still within range of ordinary 35mm and larger binoculars; Vesta is easy at magnitude +7 while Ceres still manages a respectable +8.3. From an outer suburban or rural site, you can watch them draw together in the coming two weeks as if on a collision course. They won’t crash anytime soon. We merely see the two bodies along the same line of sight. Vesta’s closer to Earth at 164 million miles (264 million km) and moves more quickly across the sky compared to Ceres, which orbits 51 million miles (82 million km) farther out.
Ceres and Vesta lie near an easy naked eye star, Zeta Virginis, which forms an isosceles triangle right now with Mars and Spica. The map shows the sky around 10 p.m. local time tonight facing southwest. Stellarium
Right now the two asteroids are little more than a moon diameter apart not far from the 3rd magnitude star Zeta Virginis. Happily, nearby Mars and Spica make excellent guides for finding Zeta. Once you’re there, use binoculars and the more detailed map to track down Ceres and Vesta.
Virgo will be busy Saturday night July 5, 2014 when the waxing moon passes about 1/2 degree from Mars as Ceres and Vesta squeeze closest. Stellarium
In early July they’ll look like a wide double star in binoculars and easily fit in the same high power telescopic view. Vesta has always looked pale yellow to my eye. Will its color differ from Ceres? Sitting side by side it will be easier than ever to compare them. Vesta is a stony asteroid with a surface composed of solidified (and meteoroid-battered) lavas; Ceres is darker and covered with a mix of water ice and carbonaceous materials.
On the night of closest approach, it may be difficult to spot dimmer Ceres in binoculars. By coincidence, the 8-day-old moon will be very close to the planet Mars and brighten up the neighborhood. We’ll report more on that event in a future article.
With so much happening the evening of July 5, let’s hope for a good round of clear skies.
It’s one of the most iconic images of the modern Space Age. In 1995, the Hubble Space Telescope team released an image of towering columns of gas and dust that contained newborn stars in the midst of formation. Dubbed the “Pillars of Creation,” these light-years long tendrils captivated the public imagination and now grace everything from screensavers to coffee mugs. This is a cosmic portrait of our possible past, and the essence of the universe giving birth to new stars and worlds in action.
Now, a study out on Thursday from the 2014 National Astronomy Meeting of the Royal Astronomical Society has shed new light on just how these pillars may have formed. The announcement comes out of Cardiff University, where astronomer Scott Balfour has run computer simulations that closely model the evolution and the outcome of what’s been observed by the Hubble Space Telescope.
The ‘Pillars’ lie in the Eagle Nebula, also known as Messier 16 (M16), which is situated in the constellation Serpens about 7,000 light years distant. The pillars themselves have formed as intense radiation from young massive stars just beginning to shine erode and sculpt the immense columns.
The location of Messier 16 and the Pillars of Creation in the night sky. Credit: Stellarium.
But as is often the case in early stellar evolution, having massive siblings nearby is bad news for fledgling stars. Such large stars are of the O-type variety, and are more than 16 times as massive as our own Sun. Alnitak in Orion’s belt and the stars of the Trapezium in the Orion Nebula are examples of large O-type stars that can be found in the night sky. But such stars have a “burn fast and die young” credo when it comes to their take on nuclear fusion, spending mere millions of years along the Main Sequence of the Hertzsprung Russell diagram before promptly going supernova. Contrast this with a main sequence life expectancy of 10 billion years for our Sun, and life spans measured in the trillions of years — longer than the current age of the universe — for tiny red dwarf stars. The larger a star you are, the shorter your life span.
A capture from the simulation, showing a cross-section 25 by 25 light years square and 0.2 light years thick. The simulation shows how the O-type star “sculpts” its surroundings over the span of 1.6 million years, carving out, in some cases, the famous “pillars”. Credit: S. Balfour/ University of Cardiff.
Such O-Type stars also have surface temperatures at a scorching 30,000 degrees Celsius, contrasted with a relatively ‘chilly’ 5,500 degree Celsius surface temperature for our Sun.
This also results in a prodigious output in energetic ultraviolet radiation by O-type stars, along with a blustery solar wind. This carves out massive bubbles in a typical stellar nursery, and while it may be bad news for planets and stars attempting to form nearby any such tempestuous stars, this wind can also compress and energize colder regions of gas and dust farther out and serve to trigger another round of star formation. Ironically, such stars are thus “cradle robbers” when it comes to potential stellar and planetary formation AND promoters of new star birth.
In his study, Scott looked at the way gas and dust would form in a typical proto-solar nebula over the span of 1.6 million years. Running the simulation over the span of several weeks, the model started with a massive O-type star that formed out of an initial collapsing smooth cloud of gas.
That’s not bad, a simulation where 1 week equals a few hundred million years…
As expected, said massive star did indeed carve out a spherical bubble given the initial conditions. But Scott also found something special: the interactions of the stellar winds with the local gas was much more complex than anticipated, with three basic results: either the bubble continued to expand unimpeded, the front would expand, contract slightly and then become a stationary barrier, or finally, it would expand and then eventually collapse back in on itself back to the source.
The study was notable because it’s only in the second circumstance that the situation is favorable for a new round of star formation that is seen in the Pillars of Creation.
“If I’m right, it means that O-type and other massive stars play a much more complex role than we previously thought in nursing a new generation of stellar siblings to life,” Scott said in a recent press release. “The model neatly produces exactly the same kind of structures seen by astronomers in the classic 1995 image, vindicating the idea that giant O-type stars have a major effect in sculpting their surroundings.”
Such visions as the Pillars of Creation give us a snapshot of a specific stage in stellar evolution and give us a chance to study what we may have looked like, just over four billion years ago. And as simulations such as those announced in this week’s study become more refined, we’ll be able to use them as a predictor and offer a prognosis for a prospective stellar nebula and gain further insight into the secret early lives of stars.
The summer astronomical action heats up this week, as the waning crescent Moon joins the inner planets at dawn. This week’s action comes hot on the tails of the northward solstice which occurred this past weekend, which fell on June 21st in 2014, marking the start of astronomical summer in the northern hemisphere and winter in the southern. This also means that the ecliptic angle at dawn for mid-northern latitude observers will run southward from the northeast early in the morning sky. And although the longest day was June 21st, the earliest sunrise from 40 degrees north latitude was June 14th and the latest sunset occurs on June 27th. We’re slowly taking back the night!
The dawn patrol action begins tomorrow, as the waning crescent Moon slides by Venus low in the dawn sky Tuesday morning. Geocentric (Earth-centered) conjunction occurs on June 24th at around 13:00 Universal Time/9:00 AM EDT, as the 8% illuminated Moon sits 1.3 degrees — just shy of three Full Moon diameters — from -3.8 magnitude Venus. Also note that the open cluster the Pleiades (Messier 45) sits nearby. Well, nearby as seen from our Earthbound vantage point… the Moon is just over one light second away, Venus is 11 light minutes away, and the Pleiades are about 400 light years distant.
Looking east the morning of Tuesday, June 24th at 5:00 AM EDT from latitude 30 degrees north. Created using Starry Night Education software.
And speaking of the Pleiades, Venus will once again meet the cluster in 2020 in the dusk sky, just like it did in 2012. This is the result of an eight year cycle, where apparitions of Venus roughly repeat. Unfortunately we won’t, however, get another transit of Venus across the face of the Sun until 2117!
Can you follow the crescent Moon up in to the daytime sky? Tuesday is also a great time to hunt for Venus in the daytime sky, using the nearby crescent Moon as a guide. Both sit about 32 degrees from the Sun on June 24th. Just make sure you physically block the dazzling Sun behind a building or hill in your quest.
From there, the waning Moon continues to thin on successive mornings as it heads towards New phase on Friday, June 27th at 8:09 UT/4:09 AM EDT and the start of lunation 1132. You might be able to spy the uber-thin Moon about 20-24 hours from to New on the morning prior. The Moon will also occult (pass in front of) Mercury Thursday morning, as the planet just begins its dawn apparition and emerges from the glare of the Sun.
The position of the Moon and Mercury post-sunrise on the morning of June 26th. Credit: Stellarium.
Unfortunately, catching the event will be a challenge. Mercury is almost always occulted by the Moon in the daytime due to its close proximity to the Sun. The footprint of the occultation runs from the Middle East across North Africa to the southeastern U.S. and northern South America, but only a thin sliver of land from northern Alabama to Venezuela will see the occultation begin just before sunrise… for the remainder of the U.S. SE, the occultation will be underway at sunrise and Mercury will emerge from behind the dark limb of the Moon in daylight.
The ground track of the June 26th occultation. Credit: Occult 4.0.
Mercury and the Moon sit 10 degrees from the Sun during the event. Stargazer and veteran daytime planet hunter Shahrin Ahmad based in Malaysia notes that while it is possible to catch Mercury at 10 degrees from the Sun in the daytime using proper precautions, it’ll shine at magnitude +3.5, almost a full 5 magnitudes (100 times) fainter than its maximum possible brightness of -1.5. The only other occultation of Mercury by the Moon in 2014 favors Australia and New Zealand on October 22nd.
This current morning apparition of Mercury this July is equally favorable for the southern hemisphere, and the planet reaches 20.9 degrees elongation west of the Sun on July 12th.
You can see Mercury crossing the field of view of SOHO’s LASCO C3 camera from left to right recently, along with comet C/2014 E2 Jacques as a small moving dot down at about the 7 o’clock position.
Mercury (arrowed) and comet E2 Jacques (in the box) as seen from SOHO. (Click here for animation)
And keep an eye on the morning action this summer, as Jupiter joins the morning roundup in August for a fine pairing with Venus on August 18th.
The Moon will then reemerge in the dusk evening sky this weekend and may just be visible as a 40-44 hour old crescent on Saturday night June 28th. The appearance of the returning Moon this month also marks the start of the month of Ramadan on the Islamic calendar, a month of fasting. The Muslim calendar is strictly based on the lunar cycle, and thus loses about 11 days per year compared to the Gregorian calendar, which strives to keep the tropical and sidereal solar years in sync. On years when the sighting of the crescent Moon is right on the edge of theoretical observability, there can actually be some debate as to the exact evening on which Ramadan will begin.
Don’t miss the wanderings of our nearest natural neighbor across the dawn and dusk sky this week!
The band of the Milky Way stretches from Cygnus (left) to the Sagittarius in this wide-angle, guided photo. Credit: Bob King
Look east on a dark June night and you’ll get a face full of stars. Billions of them. With the moon now out of the sky for a couple weeks, the summer Milky Way is putting on a grand show. Some of its members are brilliant like Vega, Deneb and Altair in the Summer Triangle, but most are so far away their weak light blends into a hazy, luminous band that stretches the sky from northeast to southwest. Ever wonder just where in the galaxy you’re looking on a summer night? Down which spiral arm your gaze takes you?
Artist’s conception of the Milky Way galaxy based on the latest survey data from ESO’s VISTA telescope at the Paranal Observatory. A prominent bar of older, yellower stars lies at galaxy center surrounded by a series of spiral arms. The galaxy spans some 100,000 light years. Credit: NASA/JPL-Caltech, ESO, J. HurtTwo different perspectives on our galaxy help us better understand its shape. A face-on artist’s view at left reveals the core, spiral arms and the sun’s position. At right, we see an edge-on perspective photographed by the Cosmic Background Explorer probe. Because the sun and planets orbit in the galaxy’s plane, we’re ‘stuck’ with an edge-on view until we build a fast-enough rocket to take us above our galactic home. Credit: NASA/JPL et. all (left) and NASA
Because all stars are too far away for us to perceive depth, they appear pasted on the sky in two dimensions. We know this is only an illusion. Stars shine from every corner of the galaxy, congregating in its bar-shaped core, outer halo and along its shapely spiral arms. The trick is using your mind’s eye to see them that way.
Employing optical, infrared and radio telescopes, astronomers have mapped the broad outlines of the home galaxy, placing the sun in a minor spiral arm called the Orion or Local Arm some 26,000 light years from the galactic center. Spiral arms are named for the constellation(s) in which they appear. The grand Perseus Arm unfurls beyond our local whorl and beyond it, the Outer Arm. Peering in the direction of the galaxy’s core we first encounter the Sagittarius Arm, home to sumptuous star clusters and nebulae that make Sagittarius a favorite hunting ground for amateur astronomers.
Further in lies the massive Scutum-Centaurus Arm and finally the inner Norma Arm. Astronomers still disagree on the number of major arms and even their names, but the basic outline of the galaxy will serve as our foundation. With it, we can look out on a dark summer night at the Milky Way band and get a sense where we are in this magnificent celestial pinwheel.
The Milky Way band arches across the east and south as seen about 11:30 p.m. in mid-late June. The center of the galaxy is in the direction of the constellation Sagittarius. The dark ‘rift’ that appears to cleave the Milky Way in two is formed of clouds of interstellar dust that blocks the light of stars beyond it. Stellarium
We’ll start with the band of the Milky Way itself. Its ribbon-like form reflects the galaxy’s flattened, lens-like profile shown in the edge-on illustration above. The sun and planets are located within the galaxy’s plane (near the equator) where the stars are concentrated in a flattened disk some 100,000 light years across. When we look into the galaxy’s plane, billions of stars pile up across thousands of light years to create a narrow band of light we call the Milky Way. The same term is applied to the galaxy as a whole.
Since the average thickness of the galaxy is only about 1,000 light years, if you look above or below the band, your gaze penetrates a relatively short distance – and fewer stars – until entering intergalactic (starless) space. That why the rest of the sky outside of the Milky Way band has so few stars compared to the hordes we see within the band.
Here’s the galactic big picture showing the outline of the galaxy with constellations added. In this edge-on view, we see that the summertime Milky Way from Cassiopeia to Sagittarius includes the central bulge (in the direction of Sagittarius) and a hefty portion of one side of the flattened disk:
The outline of the Milky Way viewed edge-on is shown in gray. The yellow box includes the summer portion of the Milky Way from Cassiopeia to Scorpius with a red dot marking the galaxy’s center. This is the section we see crossing the eastern sky in June. Click to enlarge. Credit: Richard Powell with additions by the author
If you enlarge the map, you’ll see lines of galactic latitude and longitude much like those used on Earth but applied to the entire galaxy. Latitude ranges from +90 degrees at the North Galactic Pole to -90 at the South Galactic Pole. Likewise for longitude. 0 degrees latitude, o degrees longitude marks the galactic center. The summer Milky Way band extends from about longitude 340 degrees in Scorpius to 110 in Cassiopeia.
Now that we know what section of the Milky Way we peer into this time of year, let’s take an imaginary rocket journey and see it all from above:
Viewed from above, we can now see that our gaze (red arrows) reaches down the Perseus Arm (toward the constellation Cygnus) and across the Sagittarius and Scutum-Centaurus arms (toward the constellations Scutum, Sagittarius and Ophiuchus) and directly into the central bar. Interstellar dust obscures much of the center of the galaxy. Blue arrows show the direction we face during the winter months. Credit: NASA et. all with additions by the author.
Wow! The hazy arch of June’s Milky Way takes in a lot of galactic real estate. A casual look on a dark night takes us from Cassiopeia in the outer Perseus Arm across Cygnus in our Local Arm clear over to Sagittarius, the next arm in. Interstellar dust deposited by supernovae and other evolved stars obscures much of the center of the galaxy. If we could vacuum it all up, the galaxy’s center – where so many stars are concentrated – would be bright enough to cast shadows.
A view showing the summer Milky Way from mid-northern latitudes with three prominent constellations and the spiral arms we peer into when we face them. Stellarium
Here and there, there are windows or clearings in the dust cover that allow us to see star clouds in the Scutum-Centaurus and Norma Arms. In the map, I’ve also shown the section of Milky Way we face in winter. If you’ve ever compared the winter Milky Way band to the summer’s you’ve noticed it’s much fainter. I think you can see the reason why. In winter, we face away from the galaxy’s core and out into the fringes where the stars are sparser.
Look up the next dark night and contemplate the grand architecture of our home galaxy. If you close your eyes, you might almost feel it spinning.
Though ISON may have fizzled in early 2014, we’ve certainly had a bevy of binocular comets to track this year. Thus far in 2014, we’ve had comets R1 Lovejoy, K1 PanSTARRS, and E2 Jacques reach binocular visibility. Now, and asteroid-turned-comet is set to put on a fine show this summer for northern hemisphere observers.
Veteran stargazer and Universe Today contributor Bob King told the tale last month of how the asteroid formerly known as 2013 UQ4 became comet 2013 UQ4 Catalina. Discovered last year on October 23rd 2013 during the routine Catalina Sky Survey searching for Near Earth Objects based outside of Tucson Arizona, this object was of little interest until early this year.
A recent image of 2013 UQ4 Catalina from June 16th. The development of fine tail structure can be seen. Credit: A. Maury & J.G. Bosch.
As it rounded the Sun, astronomers recovered the asteroid and discovered that it had begun to sprout a fuzzy coma, a very un-asteroid-like thing to do. Then, on May 7th, Taras Prystavski and Artyom Novichonok — of Comet ISON fame — conducted observations of 2013 UQ4 and concluded that it was indeed an active comet.
The orbital path of UQ4 Catalina in early July. Created using the JPL Solar System Dynamics Small Body Database Browser.
Hovering around +13th magnitude last month, newly rechristened 2013 UQ4 Catalina was a southern hemisphere object visible only from larger backyard telescopes. That should change, however, in the coming weeks if activity from this comet holds up.
The light curve of UQ4 Catalina with current observations (dots) noted. Credit: Seiichi Yoshida/Aerith.net.
2013 UQ4 belongs to a class of objects known as damocloids. These asteroids are named after the prototype for the class 5335 Damocles and are characterized as long-period bodies in retrograde and highly eccentric orbits. These are thought to be inactive varieties of comet nuclei, and other asteroids in the damocloid series such as C/2001 OG 108 (LONEOS) and C/2002 VQ94 (LINEAR) also turned out to be comets. Damocloids also exhibit the same orbital characteristics of that most famous inner solar system visitor of them all; Halley’s Comet.
The path of Comet UQ4 Catalina looking towards the NE at 9PM local in early July from latitude 30 degrees north. Credit: Stellarium.
The good news is, 2013 UQ4 Catalina is brightening on schedule and should be a binocular object greater than +10th magnitude by the end of June. Recent observations, including those made by Alan Hale (of comet Hale-Bopp fame) place the comet at magnitude +11.9 with a bullet. The comet is currently placed high in the east in the constellation Pisces at dawn, and will soon speed northward and vault across the sky as it crosses the ecliptic plane this week. In fact, comet 2013 UQ4 Catalina reaches perihelion on July 6th only four days before its closest approach to the Earth at 47 million kilometres distant, when it may well reach a peak magnitude of +7. At that point, the comet will have an apparent motion of about 7 degrees a day — that’s the span of a Full Moon once every 1 hour and 42 minutes — as it rises in the constellation Cepheus to the northeast at dusk in early July. A fine placement, indeed. And speaking of the Moon, our natural satellite reaches New phase later this month on June 27th, another good reason to begin searching for 2013 UQ4 Catalina now.
Here’s a list of notable events to watch out for and aid you in your quest as comet 2013 UQ4 Catalina crosses the summer sky:
June 16th: The comet crosses north of the ecliptic plane.
June 20th: The waning crescent Moon passes 3 degrees from the comet.
The celestial path of the comet from June 16th to July 15th… Credit: Starry Night Education software.
June 29th: Crosses into the constellation of Andromeda.
July 1st: Passes less than one degree from the +2nd magnitude star Alpheratz.
July 2nd: Crosses briefly into the constellation Pegasus before passing back into Andromeda.
July 6th: The comet reaches perihelion or its closest point to the Sun at 1.081 A.U.s distant.
July 7th: Crosses into the constellation of Lacerta and passes the deep sky objects NGCs 7296, 7245, 7226.
July 8th: Crosses into the constellation Cepheus and across the galactic plane.
July 9th: Passes a degree from the Elephant Trunk open star cluster.
July 10th: Passes less than one degree from the stars Eta (magnitude +3.4) and Theta (magnitude +4.2) Cephei.
July 10th: Passes 2 degrees from the +7.8 magnitude Open Cluster NGC 6939.
July 10th: Passes closest to Earth at 0.309 A.U.s or 47 million kilometres distant.
July 11th: Crosses into the constellation Draco.
July 11th: Reaches its most northerly declination of 64 degrees.
July 12th: Photo op: the comet passes 3 degrees from the Cat’s Eye Nebula.
… and the path of the comet from July 15th to August 20th. Credit: Starry Night.
July 17th: The comet passes into the astronomical constellation of Boötes.
July 31st: Passes just 2 degrees from globular cluster NGC5466 (+9th magnitude) and 6 degrees from the famous globular cluster Messier 3.
From there on out, the comet drops below naked eye visibility and heads back out in its 470 year orbit around the Sun. Be sure to check out comet 2013 UQ4 Catalina this summer… what will the Earth be like next time it passes by in 2484 A.D.?
Airglow shows as wavy stripes of pale green across the northeastern sky on May 24, 2014. Andromeda Galaxy at left. the banding was faintly visible with the naked eye as a soft, diffuse glow. The red glow at lower left is airglow from atomic oxygen 90-185 miles up. Details: 20mm lens, ISO 3200, 30". Credit: Bob King
Emerald green, fainter than the zodiacal light and visible on dark nights everywhere on Earth, airglow pervades the night sky from equator to pole. Airglow turns up in our time exposure photographs of the night sky as ghostly ripples of aurora-like light about 10-15 degrees above the horizon. Its similarity to the aurora is no coincidence. Both form at around the same altitude of 60-65 miles (100 km) and involve excitation of atoms and molecules, in particular oxygen. But different mechanisms tease them to glow.
Earth at night from the International Space Station showing bright splashes of city lights and the airglow layer created by light-emitting oxygen atoms some 60 miles high in the atmosphere. This green cocoon of light is familiar to anyone who’s looked at photos of Earth’s night-side from orbit. Credit: NASA
Auroras get their spark from high-speed electrons and protons in the solar wind that bombard oxygen and nitrogen atoms and molecules. As excited electrons within those atoms return to their rest states, they emit photons of green and red light that create shimmering, colorful curtains of northern lights.
Green light from excited oxygen atoms dominates the light of airglow. The atoms are 56-62 miles high in the thermosphere. The weaker red light is from oxygen atoms further up. Sodium atoms, hydroxyl radicals (OH) and molecular oxygen add their own complement to the light. Credit: Les Cowley
Airglow’s subtle radiance arises from excitation of a different kind. Ultraviolet light from the daytime sun ionizes or knocks electrons off of oxygen and nitrogen atoms and molecules; at night the electrons recombine with their host atoms, releasing energy as light of different colors including green, red, yellow and blue. The brightest emission, the one responsible for creating the green streaks and bands visible from the ground and orbit, stems from excited oxygen atoms beaming light at 557.7 nanometers, smack in the middle of the yellow-green parcel of spectrum where our eyes are most sensitive.
Airglow across the eastern sky below the summertime Milky Way. Notice that unlike the vertical rays and gently curving arcs of the aurora, airglow is banded, streaky and in places almost fibrous. It’s brightest and best visible 10-15 degrees high along a line of sight through the thicker atmosphere. If you look lower, its feeble light is absorbed by denser air and dust. Looking higher, the light spreads out over a greater area and appears dimmer. Credit: Bob KingA large, faint patch of airglow below the Dippers photographed May 24. To the eye, airglow appears as colorless streaks and patches. Unlike the aurora, it’s typically too faint to excite our color vision. Time exposures show its colors well. This swatch is especially faint because it’s much higher above the horizon. Credit: Bob King
That’s not saying airglow is easy to see! For years I suspected streaks of what I thought were high clouds from my dark sky observing site even when maps and forecasts indicated pristine skies. Photography finally taught me to trust my eyes. I started noticing green streaks near the horizon in long-exposure astrophotos. At first I brushed it off as camera noise. Then I noticed how the ghostly stuff would slowly shape-shift over minutes and hours and from night to night. Gravity waves created by jet stream shear, wind flowing over mountain ranges and even thunderstorms in the lower atmosphere propagate up to the thermosphere to fashion airglow’s ever-changing contours.
An obvious airglow smear across Virgo last month. Mars is the bright object below and right of center. Light pollution from Duluth, Minn. creeps in at lower left. Credit: Bob King
Last month, on a particularly dark night, I made a dedicated sweep of the sky after my eyes had fully adapted to the darkness. A large swath of airglow spread south of the Big and Little Dipper. To the east, Pegasus and Andromeda harbored hazy spots of varying intensity, while brilliant Mars beamed through a long smear in Virgo.
To prove what I saw was real, I made the photos you see in this article and found they exactly matched my visual sightings. Except for color. Airglow is typically too faint to fire up the cone cells in our retinas responsible for color vision. The vague streaks and patches were best seen by moving your head around to pick out the contrast between them and the darker, airglow-free sky. No matter what part of the sky I looked, airglow poked its tenuous head. Indeed, if you were to travel anywhere on Earth, airglow would be your constant companion on dark nights, unlike the aurora which keeps to the polar regions. Warning – once you start seeing it, you
Excited oxygen at higher altitude creates a layer of faint red airglow. Sodium excitation forms the yellow layer at 57 miles up. Airglow is brightest during daylight hours but invisible against the sunlight sky. Credit: NASA with annotations by Alex Rivest
Airglow comes in different colors – let’s take a closer look at what causes them:
* Red – I’ve never seen it, but long-exposure photos often reveal red/pink mingled with the more common green. Excited oxygen atoms much higher up at 90-185 miles (150-300 km) radiating light at a different energy state are responsible. Excited -OH (hydroxyl) radicals give off deep red light in a process called chemoluminescencewhen they react with oxygen and nitrogen. Another chemoluminescent reaction takes place when oxygen and nitrogen molecules are busted apart by ultraviolet light high in the atmosphere and recombine to form nitric oxide (NO).
* Yellow – From sodium atoms around 57 miles (92 km) high. Sodium arrives from the breakup and vaporization of minerals in meteoroids as they burn up in the atmosphere as meteors.
* Blue – Weak emission from excited oxygen molecules approximately 59 miles (95 km) high.
Comet Lovejoy passing behind green oxygen and sodium airglow layers on December 22, 2011 seen from the space station. Credit: NASA/Dan Burbank
Airglow varies time of day and night and season, reaching peak brightness about 10 degrees, where our line of sight passes through more air compared to the zenith where the light reaches minimum brightness. Since airglow is brightest around the time of solar maximum (about now), now is an ideal time to watch for it. Even cosmic rays striking molecules in the upper atmosphere make a contribution.
See lots of airglow and aurora from orbit in this video made using images taken from the space station.
If you removed the stars, the band of the Milky Way and the zodiacal light, airglow would still provide enough illumination to see your hand in front of your face at night. Through recombination and chemoluminescence, atoms and molecules creates an astounding array of colored light phenomena. We can’t escape the sun even on the darkest of nights.
