David Dickinson, Author at Universe Today

August 9, 2016 by David Dickinson

Get Ready for the 2016 Perseids

Out camping under the August sky? The coming week gives us a good reason to stay up late, as the Perseid meteor shower graces the summer sky. An ‘old faithful’ of annual meteor showers, the Perseids are always sure to produce.

The 2016 Perseids present a few challenges, though persistent observers should still see a descent show. The Perseids are typically active from July 17^th to August 24^th, with the peak arriving this year right around 13:00 to 15:30 Universal Time on Friday, August 12^th. This will place the radiant for the Perseids high in the sky after local midnight for observers in the northern Pacific, though observers worldwide should be vigilant over the next week. Meteor showers don’t read predictions and prognostications, and an arrival of the peak just a few hours early would place North America in the cross-hairs this coming Friday. The Perseids typically produce an average Zenithal Hourly Rate of 60-200 per hour, and the International Meteor Organization predicts a ZHR of 150 for 2016.

Looking to the northeast from latitude 50 degrees north at 1AM local on the morning of August 12th. Image credit: Stellarium.

The nemesis of the 2016 is the Moon, which reaches Full on August 18^th, six days after the shower’s peak. The time to start watching this shower is now, before the waxing Moon becomes a factor. The farther north you are, the earlier the Moon sets this week:

Moonset on the evening of August 11/12^th:

Latitude versus Moonset ( in local daylight saving time)

20 degrees north – 1:30 AM

30 degrees north – 1:14 AM

40 degrees north – 0:56 AM

50 degrees north – 0:30 AM

Early morning is almost always the best time to watch any meteor shower, as the Earth-bound observer faces in to the meteor stream head on. The December Geminids only recently surpassed the Perseids in annual intensity in the past few years.

The orientation of the Earth's shadow versus, the Sun, Moon and the radiant of the Perseids at the start of the projected peak on August 12th. Image credit: Orbitron. — The orientation of the Earth’s shadow versus the Sun, Moon and the radiant of the Perseids at the start of the projected peak on August 12th. Image credit: Orbitron.

The radiant of the Perseids drifts through the constellations of Cassiopeia, Perseus and Camelopardalis from late July to mid-August. The Perseids could just as easily have received the tongue-twisting moniker of the ‘Cassiopeiaids’ or the ‘August Camelopardalids.’ The source of the Perseids is comet Comet 109P/Swift-Tuttle discovered by Lewis Swift and Horace Tuttle in 1862. Comet Swift-Tuttle reached perihelion on 1992, and visits the inner solar system once again in 2126.

The Perseids are also sometimes referred as the “Tears of Saint Lawrence” who was martyred on a hot grid iron on August 10th, 258 AD.

The Perseids have been especially active in recent decades, following the perihelion passage of Comet Swift-Tuttle. Meteor showers come and go. For example, the Andromedids were a shower of epic storm proportions until the late 19^th century. We have records of the Perseids back to 36AD, but on some (hopefully) far off date, the debris path of Comet Swift-Tuttle will fail to intersect the Earth’s orbit annually, and the Perseids will become a distant memory. During previous years, the Perseids exhibited a peak of ZHR= 95 (2015), 68 (2014), 110 (2013), 121 (2012) and 58 (2011). Keep in mind, the Perseids have also sometimes displayed a twin peak during previous years, as well.

An early snapshot of the activity for the 2016 Perseids. image credit: The International Meteor Organization. — An early snapshot of the activity for the 2016 Perseids. Image credit: The International Meteor Organization.

Observing the Perseids

The best instrument to observe the Perseids with is a pair of old fashioned, ‘Mk-1 eyeballs.’ Simply lay back, warm drink in hand, and watch. Remember, the quoted ZHR is an ideal rate that we all strive for, though there are strategies to maximize your chances of catching a meteor. Watching early in the morning when the radiant rides highest (around sunrise in the case of the Perseids), seeking out dark skies, and enlisting a friend to watch in an opposite direction can raise your hourly meteor count.

Keep a pair of binoculars handy to examine any persistent glowing trains and lingering smoke trails from bright fireballs. Monitoring the FM band for the pings of accompanying radio meteors can add another dimension to an observation session. The ionized trail of a meteor can very occasionally reflect the signal of a distant radio station, bringing it through clear for a few seconds before fading out.

@Astroguyz I wasn’t aiming for #Perseid images, wanted to grab Milky Way shots and it sneaked into one of the frames pic.twitter.com/BuGE8xrsVH

— irv (@irvb) August 9, 2016

Also, keep an ear out for an even stranger phenomenon, as bright meteors are sometimes accompanied by a hissing or crackling sound. Long thought to be a psychological phenomenon, a team of Japanese astronomers managed to catch recordings of this strange effect during the 1988 Perseid meteors.

Imaging meteors is also pretty straight forward. Simply tripod mount a DSLR with a wide field lens, take some test exposures of the sky to get the ISO, f-stop and exposure combination just right, and begin taking exposures 30 seconds to five minutes long. An intervalometer can automate the process, freeing you up to kick back and watch the show.

Got science? Be sure to send those meteor counts into the International Meteor Organization (IMO) and watch their live updated graph as the shower progresses.

Also, be sure to tweet those meteor sightings to #Meteorwatch.

August 1, 2016August 2, 2016 by David Dickinson

Lights in the Sky: Meteors, Reentry, or E.T.?

A fireball lights up the skies over Dayton, Ohio. Image credit and copyright: John Chumack.

It happens a few times every year.

Last week, we poured our morning coffee, powered up our laptop and phone, and prepared to engage the day.

It wasn’t long before the messages started pouring in. ‘Bright fireball over the U.S. West Coast!’ ‘Major event lights up the California skies!’ and variations thereof. Memories of Chelyabinsk came immediately to mind. A bit of digging around ye ole web revealed video and a few authentic stills from the event.

Now, I always like to look these over myself before reading just what other experts might think. Chelyabinsk immediately grabbed our attention when we saw the first videos recording the shock wave of sound generated by the blast. ‘That sucker was close,’ we realized.

Thursday’s (Wednesday evening Pacific Time) event was less spectacular, but still interesting: the nighttime reentry of the Long March CZ-7 rocket body NORAD ID 2016-042E as it broke up over the U.S. West Coast.

How do we know this, and what do we look for? Is that flash a meteor, bolide, reentry or something stranger still?

Most good meteor footage comes from video recorders that are already up and running when the event occurs, to include security and dashboard cameras, and mobile phones already recording another event, such as a concert or game. How fast can YOU have your smartphone camera out and running? We only recently learned that a quick double tap of the home button will bring the camera on our Android to bear, no unlock needed.

If the event occurs on a Friday or Saturday night with lots of folks out on the town on a clear evening, we might see multiple captures come streaming-in of the event. Just such a fireball was witnessed over the United Kingdom on Friday evening, September 21st, 2012.

Likewise, the fakes are never far behind. We’ve seen ’em all, though you’re welcome to try and stump us. Such ‘meteor-wrongs’ that are commonly circulated as authentic are the reentry of Mir, the 1992 Peekskill meteor, Chelyabinsk, the reentry of Hayabusa, and screen grabs from the flick Armageddon… has anyone ever been fooled by this one?

Meteors generally have a very swift motion, and occur with a greater frequency as the observer rotates forward into the path of Earth’s motion around the Sun past local midnight. Remember, it’s the front of the windshield that picks up the bugs rolling down the highway.

Evening meteors, however, can have a dramatic slow, stately motion across the sky, as they struggle to catch up with the Earth. If they reach a brilliance of magnitude -14 — about one whole magnitude brighter than a Full Moon — said meteor is known as a bolide.

Sometimes, such a fireball can begin shedding fiery debris, in a dramatic display known as a meteor train or meteor precession. Such an event was witnessed over the northeastern United States on July 20^th, 1860.

The 1860 meteor train. Painting by Frederic Church.

Bright meteors may exhibit colors, hinting at chemical competition. Green for nickel (Not kryptonite!) is typically seen. MeteoriteMen’s Geoffrey Notkin once told us a good rule of thumb: if you hear an accompanying sonic boom a few minutes after seeing a meteor, it’s close. Folks often think what they saw went down behind a hill or tree, when it was actually likely more than 50 miles distant — if it hit the ground at all.

Is that a meteor or a reentry? Reentries move slower still, and will shed lots of debris. Here’s what we’re looking at to judge suspect sighting as a reentry:

Heavens-Above: A great clearing house for satellite passes by location. One great tool is that Heavens-Above will generate a pass map for your location juxtaposed over a sky chart.

Aerospace Corp current reentries: Follows upcoming reentries of larger debris with refined orbits.

Space-Track: The U.S. Joint Space Operations Command’s tracking center for artificial objects in orbit around Earth. Access is available to backyard satellite spotters with free registration. The most accurate source for swiftly evolving orbital elements.

SeeSat-L: This message board always lights up with chatter whenever a possible reentry lights up the skies worldwide.

Stranger Skies

Bizarre sights await the keen eyed. A tumbling rocket booster can often flare in a manner similar to Iridium satellites. Satellites way out in geostationary orbit can flare briefly into naked eye visibility during ‘GEOSat flare season’ near the weeks surrounding either equinox.

Some gamma ray bursts, such as GRB 080319B flare up briefly above magnitude +6 into naked eye visibility from far across the Universe. As of yet, there’s never been a reliable observer sighting of such an event, though it should be possible… probably someone far back in humanity’s history witnessed just such a brief flash in the sky, pausing silently to wonder just what it was…

Kaboom! Image credit: NASA/Pi of the Sky.

Going further back still, a nearby supernova or gamma-ray burst would leave a ghostly blue afterglow from Cerenkov radiation as it pummeled our atmosphere… though it would be a deadly planet-sterilizing indigo glow, not something you’d want to see. Thankfully, we live in the ‘Era of Mediocrity,’ safely outside of the 25-50 light year ‘kill zone’ for any potential supernova.

And what if those lights in the sky really were the vanguard of an alien invasion force? Well, if they really did land rayguns ablaze on the White House lawn, you’ll read it first here on Universe Today!

July 26, 2016 by David Dickinson

Celestial Photobomb: Rare Occultation of Mercury by the Moon Set for Next Week

Mercury and the Moon over the ramparts of Assilah, Morocco. Photo by author

Have you caught sight of Mercury yet? This coming week is a good time to try, looking low to the west at dusk. We just managed to to nab it with binoculars for the first time during the current apparition this past Sunday from the rooftop of our Air BnB in Casablanca, Morocco.

Mercury is a tough grab under any circumstance, that’s for sure. Brilliant Venus and Jupiter make great guides to finding the elusive planet in late July, as it ping-pongs between the two. The waxing crescent Moon joins the scene in the first week of August, and for a very lucky few, actually occults (passes in front of ) the diminutive innermost world shortly after passing New.

Mercury (arrowed) near the Moon on the morning of June 3rd, 2016. Image credit: Dave Dickinson.

Here’s the low down on everything Mercurial, and circumstances for the coming weeks.

Mercury passes 18′ from the star Regulus on Saturday, July 30^th at 19:00 Universal Time (UT), representing the closest passage of a planet near a first magnitude star for 2016.

The Moon then reaches New phase, marking the start of lunation 1158 on August 2^nd at 20:45 UT. The Moon then moves on to occult Mercury on Thursday, August 4^th at 22:00 UT, just over 48 hours later. The occultation is visible at dusk for observers based in southern Chile and southern Argentina. The rest of us see a close pass. Note that although it is a miss for North America, viewers based on the continent share the same colongitude and will see Mercury only a degree off of the northern limb of the Moon on the night of August 4^th. Mercury shines at magnitude +0.01, and presents a 67% illuminated disk 6.3” in size, while the Moon is a slender 5% illuminated.

Occultations of Mercury for 2016. Credit: Occult 4.2. (click image to enlarge).

How early can you see the waxing crescent Moon? Catching the Moon with the naked eye under transparent clear skies isn’t usually difficult when it passes 20 hours old. This cycle, first sightings favor South Africa westward on the night of August 3^rd.

Mercury reaches greatest elongation 27.4 degrees east of the Sun 12 days after this occultation on August 16^th.

How rare is it? Well occultations of Mercury by the Moon are the toughest to catch of all the naked eye planets, owing to the fact that the planet never strays far from the Sun. Nearly all of these events go unwitnessed, as they occur mainly under daytime skies. And while you can observe Mercury in the daytime near greatest elongation with a telescope, safety precautions need to be taken to assure the Sun is physically blocked from view. Astronomers of yore did exactly that, hoping to glimpse fleeting detail on Mercury while it was perched higher in the sky above the murk of the atmosphere low to the horizon.

In fact, a quick search of ye ole web reveals very few convincing captures of an occultation of Mercury (see the video above). The closest grab thus far comes from astrophotographer Cory Schmitz on June 3^rd 2016 based in South Africa:

Image credit: — Can you see it? The Moon about to occult Mercury on June 3rd. Image credit and copyright: Cory Schmitz.

Can’t wait til next week? The Moon crosses the Hyades open star cluster this week, occulting several stars along the way. The action occurs on the morning of Friday, July 29^th culminating with an occultation of +1 magnitude Aldebaran by the 23% illuminated Moon. Texas and Mexico are well-placed to see this event under dark skies. A small confession: we actually prefer occultations of planets and stars by the waxing Moon, as the dark edge of the Moon is leading during ingress, making it much easier to witness and the exact moment the Moon blots out the object.

Still want more? The Moon actually goes on to occult Jupiter on August 6^th for the South Pacific. Viewers farther west in southeast Asia might just spy this one in the daytime. This is the second occultation of Jupiter by the Moon in a series of four in 2016.

Looking west on the evening of August 4th. Image credit: Stellarium.

Keep and eye on those planets in August, as they’re now all currently visible in the dusk sky. The Moon, Regulus and Venus also form a tight five degree triangle on the evening of August 4^th, followed by a slightly wider grouping of Venus, Jupiter and the Moon around August 25^th.

More to come on that soon. Be sure to check the planet Mercury off of your life list this coming week, using the nearby waxing crescent Moon as a guide.

July 19, 2016July 23, 2016 by David Dickinson

See All Five Naked Eye Planets in the Dusk Sky at Once

Solar System — An Iphone solar system family portrait. Image credit and copyright: Andrew Symes (@Failedprotostar)

Hosting an evening star party this summer? You’re in for a treat. Starting later this week, all five naked eye planets (Mercury, Venus, Mars, Jupiter and Saturn) are visible in the evening sky at dusk for a brief few weeks. We had a similar lineup in the dawn sky earlier in 2016, as the Earth had all the inner planets in its forward-facing view — now, we see these same planets in our collective rear view mirror, as we lap Mars, Jupiter and Saturn on the inner track, while Mercury and Venus race to catch up with us.

Dusk on the evening of August 8th. Image credit: Stellarium. — Dusk on the evening of August 8th, looking to the southwest. Image credit: Stellarium.

At their narrowest, the planets from Saturn to Mercury fit within a span just 75 degrees wide in the last half of August. A wide field all-sky shot should catch ’em all in the same frame at once. This isn’t a ‘grand conjunction’ in a strict sense. To have all five planets visible, you need the slowest and outermost of the five — Jupiter and Saturn, with orbital periods of 11.9 and 29.5 years respectively — in the same general swath of sky. Both are headed towards conjunction on December 21^st, 2020, making such groupings more frequent as they race past the other three. The next true quintuple grand conjunction occurs on September 8^th, 2040, when all 5 planets span just 9.3 degrees of the sky… the closest span since September 18^th, 1186!

Can you see 'em? Five planets from Monte Mario in Rome on February 2nd, 2016. Image credit: Gianluca Masi/The Virtual Telescope project. — Can you see ’em? Five planets from Monte Mario in Rome on February 2nd, 2016. Image credit: Gianluca Masi/The Virtual Telescope project.

There’s a lot to watch out for in the next few weeks. Here’s a who’s who of planets this July and August, from east to west:

Saturn: shining at magnitude +0.4 in the constellation Ophiuchus, Saturn is fresh off of opposition on June 3rd. Riding high in the southeast at dawn, Saturn makes a close 4.4 degree pass near Mars on August 24^th, and the pair makes a straight line completed by the bright star Antares on the same date.

Mars: High to the south in the constellation Libra at dusk, Mars begins its slow dive into the dusk during the last half of 2016. Currently shining at a respectable magnitude -0.9, Mars passed opposition on May 22nd and is headed towards a grand opposition in 2018, nearly as close as the historic close pass of 2003.

Jupiter: Sitting in the constellation Leo, Jupiter shines at magnitude -1.6 and is about 20-30 degrees above the southwestern horizon at dusk. Jupiter passed quadrature 90 degrees east of the Sun on June 4^th and opposition for 2016 on March 8th.

Venus: The bashful planet of the group, Venus is slowly appearing from behind the Sun low in the dusk and headed for a brilliant dusk apparition later in 2016 and early 2017. Currently 3 degrees east of the Sun on July 31^st, Venus reaches greatest elongation 47 degrees east of the Sun on January 12^th, 2017. We’ve just been able to begin spying Venus using binocs last week from the rooftop of our Casablanca Air BnB. Follow that planet, as Venus makes a close 6′ pass near Jupiter on August 27th.

Mercury: And the innermost planet makes five, as Mercury reaches greatest elongation 27 degrees east of the Sun on August 16th. When can you first catch sight of Mercury, completing the fivesome? Jupiter and Venus actually make great bookends in the hunt, as +0.5 magnitude Mercury wanders between them through early August. It’s too bad dusk twilight obscured the view this past weekend, as both Mercury and Venus photobombed the Beehive Cluster M44 in Cancer. Mercury also passes 20′ from the bright star Regulus on July 30^th.

Looking west on the evening of July 19th, 2016. Credit Starry Night Education Software.

But wait, there’s more. The Moon passes New on August 2nd, entering back into the dusk sky. The one day old Moon will pass the grouping of Venus, Regulus and Mercury on the evening of August 4^th, actually occulting (passing in front of) Mercury for the southernmost tip of South America. The Moon then moves on to occult Jupiter for good measure on August 6^th for the South Pacific and southeast Asia in the daytime. Finally, the waxing gibbous Moon makes a wide pass near Mars, Antares and Saturn on the evening of August 12^th, on the same evening that the 2016 Perseids are due to occur.

The footprint of the August 4th occultation of Mercury by the Moon. Image credit: Occult 4.2 software.

The Moon also reaches the nearest apogee (think ‘closest far point’) of the year, at 404,265 kilometers from the Earth on August 10th and reaches Full on August 18^th, featuring a subtle penumbral eclipse and the start of eclipse season 2 of 2 for 2016.

More on all of these events in the coming weeks. So, if you find yourself out hunting Pokémon G0 creatures ’til the late dusk hours this summer, don’t forget to look up at the greatest show in the solar system!

July 6, 2016July 6, 2016 by David Dickinson

The Moon Occults Jupiter This Weekend

So, are you catching sight of the waxing crescent Moon returning this week to the early PM sky? The start of lunation 1157 gives folks observing Ramadan here in Morocco a reason to celebrate, as it marks the end of dawn-to-dusk fasting. Follow that Moon, as it’s about to meet up with the king of the planets this weekend.

On July 9^th, the 5-day old waxing crescent Moon will pass Jupiter. You can see ’em both Saturday night, high in the western sky at dusk. For a very few observers in the southern Indian Ocean and Antarctica, the Moon will actually occult (pass in front of) Jupiter, centered on 10:11 Universal Time (UT). The Moon will be 32% illuminated crescent during the pass, and Jupiter will present a disk 34” across, just over a month past quadrature on June 4th with a current elongation of 60 degrees east of the Sun. Jupiter just passed opposition for 2016 on March 8th, and is now headed towards solar conjunction on the far side of the Sun on September 26th.

The occultation footprint for the July 9th event. Image credit: Occult 4.2 software.

2016 Planetary Occultations

This is the first of four occultations of Jupiter by the Moon in 2016; the next occur over subsequent lunations on August 6^th, September 2^nd and 30^thbefore the relative motions of the Moon and Jupiter carry them apart, not to meet again until October 31^st, 2019. And though most observers will miss this weekend’s occultation, we’ll all get a good view of the pairing worldwide. Unfortunately, the view gets successively worse (though more central) for the next few lunations, as the occultations of Jupiter by the Moon occur close to the Sun.

Looking west on the evening of July 9th. Image credit: Stellarium.

Here’s another reason to celebrate and show off Jupiter at this weekend’s star party: NASA’s Juno spacecraft has just entered orbit around the gas giant world. This is only the second time a mission has orbited Jupiter (the first was Galileo) though lots have performed brief flybys, using the enormous pull of the planet for a gravitational boost en route to elsewhere. Juno is currently the only spacecraft in operation around Jove, and will conduct 36 looping science orbits around the planet before meeting its fiery end in February 2018.

A montage of daytime planets. Image credit and copyright: Shahrin Ahmad (@shahgazer). — A montage of daytime planets (and one Moon and one star). Image credit and copyright: Shahrin Ahmad (@shahgazer).

Yay, humans. Here’s another feat of visual athletics you can attempt this weekend: can you spy Jupiter near the waxing crescent Moon… in the daytime? It’s not that tough, if you know exactly where to look. Deep blue skies for maxim contrast are key, and don’t be afraid to cheat a bit and use binoculars or a wide-field DSLR shot to tease bashful Jupiter out of the daytime sky. Your best bet might be to start hunting for Jupiter 30 minutes prior to local sunset. Hey, if the Sun is still above the local horizon, it still counts! We’ve actually managed to nab Jupiter and Venus before sundown at public star parties on occasion, kicking things off a bit early.

Hunting for Jupiter in the daytime on July 9th. Image credit: Starry Night

Now for the ‘wow’ factor. The Moon is 3,474 kilometers across, and on average, 400,000 kilometers or 1.25 light seconds distant. Jupiter, at 140,000 kilometers across, is currently 5.9 Astronomical Units (AU) or 880 million kilometers away, 2,200 times more distant at 49 light minutes away. You could fit Jupiter and all of the other planets in the solar system – excluding Saturn’s rings — between the Earth and the Moon… not that you’d want such mayhem, of course. Hey; then, for the very first time in the history of human astronomy, Jupiter could occult our puny Moon…

Occultations are abruptly swift affairs in a glacially slow universe. The leading edge of the Moon moves about 30” a minute, taking 17 seconds to cover the disk of Jove. Follow Jupiter this summer, as it’ll pass just 4′ from Venus in the dusk sky on August 27th.

More to come on that soon. Here’s a final thought: has anyone ever tried to observe a radio occultation of Jupiter by the Moon? It’s certainly possible, as Jupiter is a prominent amateur radio source, crackling in the sky. And hey, the daytime sky thing wouldn’t be an issue…

We’d be thrilled to hear that, against all odds, someone on a remote windswept island or on a ship in the distant Indian Ocean actually managed to catch this weekend’s occultation!

July 4, 2016July 4, 2016 by David Dickinson

Earth at Aphelion 2016

Sunset over Naples, Florida. Image credit: Dave Dickinson

Having a great July 4^th? The day gives us another cause to celebrate, as the Earth reaches aphelion today, or our farthest point to our host star.

Aphelion is the opposite of the closest point of the year, known as perihelion. Note that the ‘helion’ part only applies to things in solar orbit, perigee/apogee for orbit ’round the Earth, apolune/perilune for orbit around the Moon, and so on. You’ll hear the words apijove and perijove bandied about this week a bit, as NASA’s Juno spacecraft enters orbit around Jupiter tonight. And there are crazier and even more obscure counterparts out there, such as peribothron and apobothron (orbiting a black hole) and apastron/periastron (orbiting a star other than our Sun). And finally, there’s the one-size fits all generic periapsis and apoapsis, good for all occasions and ending pedantic arguments.

In the 21^st century, aphelion for the Earth can actually fall anywhere from July 2nd to the 7th. The once every four year leap day is the primary driver in this oscillation, and the exclusion of a century leap day in 2100 — the first such exclusion since 1900 — will reset things even farther astray.

Aphelion versus perihelion. (orbits exaggerated). Image credit: NOAA/NASA.

In 2016, the Moon reaches New on July 4^that 11:01 Universal Time (UT) just over five hours prior to aphelion, marking the start of lunation 1157. The sighting of the waxing crescent Moon also marks the end of the Muslim fasting month of Ramadan.

Earth reaches aphelion at 16:24 UT today, 1.0168 AU from the Sun. This year’s close occurrence of aphelion versus a New Moon won’t get topped until 2054, with an aphelion versus New Moon just 5 hours 6 minutes apart. The 2016 coincidence is also the closest since the start of the 21^st century.

Fun fact: we’re headed towards an aphelion maximum just 6,590 kilometers off of the mean on July 4^th, 2019, the widest for the 21st century. Mean distance from the Sun at aphelion is 1.0167 AU (152,097,701 km). Aphelion for the Earth can range over a variation of 21,225 kilometers for the 21^st century.

It’s a happy circumstance that Earth reaches aphelion in our current epoch in the midst of northern hemisphere summer, and just a few weeks after the June solstice. The eccentricity of the Earth’s orbit actually varies from near-circular to 0.0679 and back over the span of 413,000 years. In our current epoch, the eccentricity of our orbit is 0.017 and decreasing. Add this variation to changes in the axial tilt of our planet and orbital obliquity, and you have what are known as Milankovitch Cycles. One only has to look at Mars’s wacky orbit with an eccentricity of 0.0934 to see what a difference it makes. Ironically, Mars reaches perihelion in October 29^th, 2016, and will make a very close pass near next opposition pass in 2018.

The orbits of Mercury, Earth and Mars compared. image credit: NASA

Want to prove it for yourself? You can indeed ‘observe’ aphelion. The trick is to image the solar disk using the same rig and settings… about six months apart. At aphelion, the solar disk is 31.6′ across, versus 32.7′ across at perihelion. This variation is slight, but you can indeed see the subtle difference side by side:

The Sun as seen from the Earth: perihelion vs aphelion. The red circles are the size of the opposing solar disk transposed on the other. Image credit: Dave Dickinson.

Aphelion means a smaller apparent Sun, a good target for a total solar eclipse. Stick around until July 2^nd, 2019 and you’ll see just that, as a total solar eclipse occurs near aphelion for South America and the southern Pacific at 4 minutes and 33 seconds in central duration.

Aphelion versus perihelion 2008. Image credit and copyright: Alex Conu.

This month also sees another special treat, as all classical planets enter the evening sky.

More to come on that soon. For now, happy 4^th of July, and merry aphelion!

June 20, 2016June 25, 2016 by David Dickinson

Seeking the Summer Solstice

A summer solstice sunset. Image credit and copyright: Sarah and Simon Fisher.

Can you feel the heat? If you find yourself north of the equator, astronomical summer kicks off today with the arrival of the summer solstice. In the southern hemisphere, the reverse is true, as today’s solstice marks the start of winter.

Thank our wacky seasons, and the 23.4 degree tilt of the Earth’s axis for the variation in insolation. Today, all along the Tropic of Cancer at latitude 23.4 degrees north, folks will experience what’s known as Lahiana Noon, as the Sun passes through the zenith directly overhead. Eratosthenes first noted this phenomena in 3^rd century BC from an account in the town of Syene (modern day Aswan), 925 kilometers to the south of Alexandria, Egypt. The account mentioned how, at noon on the day of the solstice, the Sun shined straight down a local well, and cast no shadows. He went on to correctly deduce that the differing shadow angles between the two locales is due to the curvature of the Earth, and went on to calculate the curvature of the planet for good measure. Not a bad bit of reasoning, for an experiment that you can do today.

Eratosthenes' classic experiment. Wikimedia Commons image in the Public Domain. — Eratosthenes’ classic experiment. Wikimedia Commons image in the Public Domain.

And although we call it the Tropic of Cancer, and the astrological sign of the Crab begins today as the Sun passes 90 degrees longitude along the ecliptic plane as seen from Earth, the Sun now actually sits in the astronomical constellation of Taurus on the June northward solstice. Thank precession; live out a normal 72 year human life span, and the solstice will move one degree along the ecliptic—stick around about 26,000 years, and it will complete one circuit of the zodiac. That’s something that your astrologer won’t tell you.

The tilt of the Earth's axis during the June northward solstice. Image credit: NASA. — The tilt of the Earth’s axis during the June northward solstice. Image credit: NASA.

The solstice in the early 21^st century actually falls on June 20th, thanks to the ‘reset’ the Gregorian calendar received in 2000 from the addition of a century year leap day. The actual moment the Sun reaches its northernmost declination today and slowly reverses its apparent motion is 22:34 Universal Time (UT). In 2016, the Moon reaches Full just 11 hours to the solstice. The last time a Full Moon fell within 24 hours of a solstice was December 2010, and we had a total lunar eclipse to boot. Such a coincidence won’t occur again until December 2018. You get a good study in celestial mechanics 101 tonight, as the Full Moon rises opposite to the setting Sun. The Moon occupies the southern region of the sky where the Sun will reside this December during the other solstice, when the Full Moon will then ride high in the night sky, and gets ever higher as we head towards a Major Lunar Standstill in 2025.

The back alley of our Morocco Air BnB mimics Eratosthenes’ well. Image credit: Dave Dickinson

Of course, this motion of the Sun through the year is all an illusion from our terrestrial biased viewpoint. We’re actually racing around the Sun to the tune of 30 kilometers per second. You wouldn’t know it as summer heats up in the northern hemisphere, but we’re headed towards aphelion or the farthest point from the Sun for the Earth on July 4th at 152 million kilometers or 1.017 astronomical units (AU) distant. And the latest sunset as seen from latitude 40 degrees actually occurs on June 27^th at 7:33 PM (not accounting for Daylight Saving Time) go much further north (like the Canadian Maritimes or the UK) and true astronomical darkness never occurs in late June.

And speaking of the Sun, we’re wrapping up the end of the 11 year solar cycle this year… and there are hints that we may be in for another profound solar minimum similar to 2009. We’ve already had a brief spotless stretch last month, and some solar astronomers have predicted that solar cycle #25 may be absent all together. This means a subsidence in aurorae, and an uncharacteristically blank Sol.

But don’t despair and pack it in for the summer. As a consolation prize, high northern latitudes have in recent years played host to electric blue noctilucent clouds near the June solstice. Also, the International Space Station enters a second period of full illumination through the entire length of its orbit from July 26th to 28th, making for the possibility of seeing multiple passes in a single night.

A display of noctilucent clouds over Blackrod, UK. Image credit and copyright: Dave Walker.

And folks in the Islamic world (and travelers such as ourselves currently in Morocco) can rejoice, as the Full Moon means that we’re half way through the fasting lunar month Ramadan. This is an especially tough one, as Ramadan 2016 goes right through the summer solstice, making for only a brief six hour span to break the fast each night and prepare for another 18 hour long stretch… and to repeat this pattern for 29 days straight. It’s a fascinating time of night markets and celebration, but for travelers, it also means odd opening hours and delays.

Searching for the solstice and other strange astronomical alignments at M'Soura, Morocco. Image credit: Dave Dickinson — Searching for the solstice and other strange astronomical alignments at M’Soura, Morocco. Image credit: Dave Dickinson

See any curious solstice shadow alignments in your neighborhood today?

Happy Lahiana Noon… from here on out, northern viewers slowly start to take back the night!

June 14, 2016 by David Dickinson

Peering for Pluto: Our Guide to Opposition 2016

An enviable view, of the most distant eclipse seen yet, as New Horizons flies through the shadow of Pluto. Image credit: NASA/JPL.

What an age we live in. This summer marks the very first opposition of Pluto since New Horizons’ historic flyby of the distant world in July 2015. If you were like us, you sat transfixed during the crucial flyby phase, the climax of a decade long mission. We now live in an era where Pluto and its massive moon Charon are a known worlds, something that even Pluto discoverer Clyde Tombaugh never got to see.

Pluto in 2016

And this summer, with a little skill and patience and a good-sized telescope, you can see Pluto for yourself. Opposition 2016 sees the remote world looping through the star-rich fields of eastern Sagittarius. Hovering around declination 21 degrees south, +14.1 magnitude Pluto is higher in the June skies for observers in the southern hemisphere than the northern, but don’t let that stop you from trying. Opposition occurs on July 7th, when Pluto rises opposite from the setting Sun and rides across the meridian at 29 degrees above the southern horizon for observers based along 40 degrees north latitude at local midnight.

Pluto actually crossed the plane of the galactic equator in 2009, and won’t cross the celestial equator northward until 2109. Fun fact: astronomer Clyde Tombaugh discovered Pluto as it drifted through the constellation Gemini in 1930. Here we are 86 years later, and Pluto has only moved six zodiacal constellations along the ecliptic eastward in its 248 year orbit around the Sun.

A close up look at the path of Pluto for the remainder of 2016. Note the position of New Horizons and KBO 2014 MU69 at the end of the year thrown in as well. Image credit: Starry Night Pro 7.

And Pluto is getting tougher to catch in a backyard scope, as well. The reason: Pluto passed perihelion or its closest point to the Sun in 1989 inside the orbit of Neptune, and it’s now headed out to aphelion about a century from now in 2114. Pluto is in a fairly eccentric orbit, ranging from 29.7 astronomical units (AU) to 49.4 AU from the Sun. This also means that Pluto near opposition can range from a favorable magnitude +13.7 near perihelion, to three magnitudes (16 times) fainter near aphelion hovering around magnitude +16.3. Clyde was lucky, in a way. Had Pluto been near aphelion in the 20^th century rather than headed towards perihelion, it might have waited much longer for discovery.

2016 sees Pluto shining at +14.1, one magnitude (2.5 times) above the usual quoted mean. See Mars over in the constellation Libra shining at magnitude -1.5? It’s 100^3 (a 5-fold change in magnitude is equal to a factor of 100 in brightness), or over a million times brighter than Pluto.

The inner and outermost planet(?) Mercury meets Pluto earlier this year in January. Image credit and copyright: Shahrin Ahmad (@Shahgazer).

You often see Pluto quoted as visible in a telescope aperture of ‘six inches or larger,’ but for the coming decade, we feel this should be amended to 8 inches and up. We once nabbed Pluto during public viewing using the 14” reflector at the Flandrau observatory.

And how about Pluto’s large moon, Charon? Shining at an even fainter +16th magnitude, Charon never strays more than 0.9” from Pluto… still, diligent amateurs have indeed caught the elusive moon… as did Wendy Clark just last year.

Pluto: imaged last year during New Horizons' historic encounter. Image credit and copyright: Wendy Clark — Pluto: imaged last year during New Horizons’ historic encounter. Image credit and copyright: Wendy Clark.

Lacking a telescope? Hey, so are we, as we trek through Morocco this summer… never fear, you can still wave in the general direction of Pluto and New Horizons on the evening of June 21^st, one day after the northward solstice and the Full Moon, which passes three degrees north of Pluto.

The location of Pluto in relation to the rising Full Moon on the night of June 21st. Image credit: Stellarium.

And follow that spacecraft, as New Horizons is set to make a close pass by Kuiper Belt Object 2014 MU69 in January 2019 on New Year’s Day.

A key date to make your quest for Pluto is June 26^th, when Pluto sits just 3′ minutes to the south of the +2.9 magnitude star Pi Sagittarii (Albaldah), making a great guidepost.

Does the region of Sagittarius near Pi Sagittarii sound familiar? That’s because the Wow! Signal emanated from a nearby region of the sky on August 15^th, 1977. Pluto will cross the border into the constellation Capricornus in 2024.

After opposition, Pluto heads into the evening sky, towards solar conjunction on January 7^th, 2017.

Observing Pluto requires patience, dark skies, and a good star chart plotted down to about +15^th magnitude. One key problem: many star charts don’t go down this faint. We use Starry Night Pro 7, which includes online access to the USNO catalog and a database of 500 million stars down to magnitude +21, more than enough for most backyard scopes.

Don’t miss a chance to see Pluto for yourself this summer!

June 6, 2016June 6, 2016 by David Dickinson

Looking for Lunar Letters

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 1^st 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 12^th, 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 7^th, 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

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.

Doubloons! Look for the lunar ‘S’ on the 19th September 2015http://t.co/qhW4krMIba pic.twitter.com/rTnApfKQXg

— blobrana (@blobrana) September 18, 2015

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.

June 1, 2016June 2, 2016 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 5^th at 9:00 Universal Time (UT).

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 3^rd 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.

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 5^th, 2008, and this won’t be topped until February 18^th, 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 5^th 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 6^th through June 8th.

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 5^th, 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.

In 2016, the Moon will first likely be spotted from the west coast of South America on Sunday night June 5^th, though many locales worldwide may not see the Moon until June 6^th. 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 21^st, though it actually falls on March 20^th 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 6^th?

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.