David Dickinson, Author at Universe Today

August 19, 2015December 23, 2015 by David Dickinson

Cassini’s Farewell Look at Dione

NASA’s Cassini spacecraft paid a visit to Saturn’s moon Dione this week, one final time.

Cassini passed just 474 kilometers (295 miles) above the surface of the icy moon on Monday, August 17^th at 2:33 PM EDT/18:33 UT. The flyby is the fifth and final pass of Cassini near Dione (pronounced dahy-OH-nee). The closest passage was 100 kilometers (60 miles) in December 2011. This final flyby of Dione will give researchers a chance to probe the tiny world’s internal structure, as Cassini flies through the gravitational influence of the moon. Cassini has only gathered gravity science data on a handful of Saturn’s 62 known moons.

“Dione has been an enigma, giving hints of active geologic processes, including a transient atmosphere and evidence of ice volcanoes. But we’ve never found the smoking gun,” said Cassini science team member Bonnie Buratti in a recent press release. “The fifth flyby of Dione will be the last chance.”

Voyager 1 gave us our very first look at Dione in 1980, and Cassini has explored the moon in breathtaking detail since its first flyby in 2005. This final pass targeted Dione’s north pole at a resolution of only a few meters. Cassini’s Infrared Spectrometer was also on the lookout for any thermal anomalies, a good sign that Dione may still be geologically active. The spacecraft’s Cosmic Dust Analyzer also carried out a search for any dust particles coming from Dione. The results of these experiments are forthcoming. In a synchronous rotation, Dione famously displays a brighter leading hemisphere, which has been pelted with E Ring deposits.

The raw images from this week’s flyby are now available on the NASA Cassini website. You can see the sequence of the approach, complete with a ‘photobomb’ of Saturn’s moon Enceladus early on. Dione then makes a majestic pass in front of Saturn’s rings and across the ochre disk of the planet itself, before snapping into dramatic focus. Here we see the enormous shattered Evander impact basin near the pole of Dione, along with Erulus crater with a prominent central peak right along the day/night terminator. Dione has obviously had a battered and troubled past, one that astro-geologists are still working out. Cassini then takes one last shot, giving humanity a fitting final look at Dione as a crescent receding off in the distance.

It’ll be a long time before we visit Dione again.

“This will be our last chance to see Dione up close for many years to come,” said Cassini mission deputy project scientist Scott Edgington. “Cassini has provided insights into this icy moon’s mysteries, along with a rich data set and a host of new questions for scientists to ponder.”

Cassini also took a distant look at Saturn’s tiny moon Hyrrokkin (named after the Norse giantess who launched Baldur’s funeral ship) earlier this month. Though not a photogenic pass, looking at the tinier moons of Saturn helps researchers better understand and characterize their orbits. Even after more than a decade at Saturn, there are tiny moons of Saturn that Cassini has yet to see up close.

Next up for Cassini is a pass 1,036 kilometers (644 miles) from the surface of Titan on September 28^th, 2015.

Launched in 1997, Cassini has given us over a decade’s worth of exploration of the Saturnian system, including the delivery of the European Space Agency’s Huygens lander to the surface of Titan. The massive moon may be the target of a proposed mission that could one day sail the hazy atmosphere of Titan, complete with a nuclear plutonium powered MMRTG and deployable robotic quadcopters.

Cassini is set to depart the equatorial plane of Saturn late this year, for a series of maneuvers that will feature some dramatic passes through the rings before a final fiery reentry into the atmosphere of Saturn in 2017.

Astronomer Giovanni Cassini discovered Dione on March 21^st, 1684 from the Paris observatory using one of his large aerial refracting telescopes. About 1,120 kilometers in diameter, Dione is 1.5% as massive as Earth’s Moon. Dione orbits Saturn once every 2.7 days, and is in a 1:2 resonance with Enceladus, meaning Dione completes one orbit for every two orbits of Enceladus.

In a backyard telescope, Dione is easily apparent along with the major moons of Saturn as a +10.4 magnitude ‘star.’ Saturn is currently a fine telescopic target in the evening low to the south on the Libra-Scorpius border, offering prime time observers a chance to check out the ringed planet and its moons. Fare thee well, Dione… for now.

August 19, 2015December 23, 2015 by David Dickinson

Watch HTV-5 Chase the International Space Station From Your Backyard

A JAXA H-IIB rocket departs Tanegashima Space Center in a dramatic night shot. Image credit: JAXA/NASA TV

It’s away… and the hunt is on. The Japanese Space Agency’s H-II Transfer Vehicle Kounotori automated cargo spacecraft rocketed out of the Tanegashima Space Center today, headed for the ISS.

Loaded with over 6,000 kilograms of experiments and supplies, HTV-5 is on a five day odyssey that you can follow from your backyard, starting tonight. Kounotori stands for ‘white stork,’ or the purveyor of joyful things in Japanese, and in this instance, the name is appropriate, as the HTV-5 is delivering much needed supplies to the International Space Station.

Launch occurred this morning at 11:50 UT/7:50 AM EDT, hitting an instantaneous window to chase after the International Space Station for grapple and berthing on Monday.

Unlike the Progress and Soyuz spacecraft, which have the capability to rendezvous and dock with the ISS, the HTV-5 and Dragon spacecraft are grappled with the Canadian Space Agency’s Canadarm 2, and stowed or ‘berthed’ in place.

Grapple with berthing to the nadir node of the Harmony module is set for Monday, August 24th, at 11:54 UT/7:54 AM EDT.

Unlike other vehicles that periodically visit the International Space Station, the HTV does not incorporate deployable solar panels, but instead, has panels wrapped around its body. This can also lend itself to some pretty bright flares as it passes overhead.

Grapple of HTV-4 by the Canadarm 2. Image credit: NASA/JAXA

The H-IIB is a two stage rocket, and ground observers should keep an eye out for the second stage booster during ISS passes as well. Debris was also jettisoned during last weeks’ spacewalk, and there’s no word as of yet if this has reentered as well, though ground-spotters have yet to report any sightings. This is a typical EVA maneuver, and cosmonauts conducted the release in such a fashion as to pose no danger to the ISS or HTV. Debris jettisoned from the ISS typically reenters the Earth’s atmosphere after about a week or so.

Prospects for Seeing HTV-5 this Weekend

Grapple of the HTV-5 will occur Monday over central Asia. Keep in mind, the HTV-5 will have to perform several burns to reach the elevation of the ISS: this means its orbit will evolve daily. Heavens-Above and NASA’s Spot the Station tracker typically publish sighting predictions for cargo vehicles such as the HTV-5 along with ISS sighting opportunities online.

And we’ll be posting daily updates and maps as @Astroguyz on Twitter. We see the best prospects for spotting the ISS and HTV5 over the next few days leading up to Monday’s berthing are for latitudes 25-45 north (dusk) and latitudes 30-50 south (dawn). That covers a wide range of observers in Europe, North America, South Africa and Australia/New Zealand.

A capture of the passage of HTV-4. Image credit and copyright: Fred Locklear

We’ve caught sight of JAXA’s HTV on previous missions, and contest to it being a conspicuous object.

Pro-tip: the trick to a successful sighting is to start watching early. The HTV-5 will be fainter than the brilliant ISS, but still visible to the naked eye at about magnitude +1 to +2 or so when directly overhead. The HTV-5 will follow the same orbital trace as the station. Spot the ISS and still don’t see HTV-5? Linger for a bit and keep watching after the ISS has passed, as the HTV might follow shortly. And the darker the skies you can find to carry out your HTV-5 vigil under, the better!

Aug 19 — Initial estimations for the passage of the HTV-5 about 10 minutes ahead of the ISS on Wednesday, August 19th. Image credit: Orbitron

Here’s a sampling of ISS passes for Washington D.C. for the next few days:

Wednesday, August 19^th: 8:46 PM EDT (Elevation 65 degrees NE)

Thursday, August 20^th: 9:29 PM EDT (Elevation 23 degrees SW)

Friday, August 21^st: 8:35 PM EDT (Elevation 48 degrees SW)

Clouded out? You can still watch the grapple and berthing action online courtesy of NASA TV.

Want more? Other orbital alumni that have placed a port of call at humanity’s orbital outpost include: SpaceX’s Dragon, the U.S. Space Shuttle fleet (excepting the Columbia orbiter), Progress, ATV, HTV, Soyuz, and Orbital Science’s Cygnus spacecraft. And while the shuttle and the European Space Agency’s ATV fleet are retired, you can follow the next launch of a crewed Soyuz (TMA-18M) on September 2^nd from the Baikonur Cosmodrome on a four-orbit fast-track docking.

JAXA plans to launch one HTV a year, out to HTV-9 in 2019.

Good luck, and good sat-spotting… next time we park the Jeep Liberty in the garage, we’re going to refer to it as a ‘grapple and berthing…’ it just sounds cool.

Got a picture of the International Space Station and friends? Be sure to send ‘em in to Universe Today.

August 18, 2015September 23, 2016 by David Dickinson

Late Summer Tales of Tanabata

The August Milky Way graced with the occasional Perseid. Image credit: Andre van der Hoeven

One of the surest signs that late summer is here in the northern hemisphere is the arrival of the Milky Way in the early evening sky. As darkness falls ever earlier each night, the star-dappled plane of our home galaxy sits almost due south and stretches far to the north. This is also why we refer to the triangular shaped asterism formed by the bright stars of Altair, Deneb and Vega as the Summer Triangle. Two of these stars are the focus of a fascinating mythos from the Far East, and a poetic celestial configuration that commemorates star-crossed lovers lost.

We first heard of tales of Tanabata while stationed in Japan in the U.S. Air Force. Meaning ‘the seventh evening of the seventh month’ — sometimes simply abbreviated to ‘the seventh-seventh,’ — Tanabata is the summer Star Festival of Japan and dates back to about the 7^th century AD. Korean and Chinese cultures also have a version of the tale, and the festival that was once considered a rite for the elite gained popularity during the Edo period in the 17^th century to become a nationwide celebration.

Tanabata 2010. Wikimedia Commons/Hanasakijijii/3.0 license

The origin story of Tanabata involves the romance between the weaver’s daughter Orihime and the cow-herder’s son Kengyuu. As lovers will do, both began to neglect family duties — namely, weaving and cow-herding — until the two were separated by Orihime’s father, Tentei, represented by the Pole Star Polaris. The vast river of heaven, represented by the Milky Way, now separates the two. Orihime (Vega) sits on one side, while Kengyuu (Altair) is alone and unreachable on the other. The Emperor relented to Orihime’s pleading, however, and allows the two to meet once a year, on the seven day of the seventh month. And thus, Tanabata was born.

In late August, Vega and Altair are easily visible high to the east at dusk. You’re looking out along the Orion Spur — of which our solar system is a member — which traverses the Perseus and Cygnus arms of the galaxy beyond. We’re headed roughly in the same direction, towards a point known as the solar apex which is located near the bright star Vega, 25 light years distant. Remember the movie Contact? Vega was the fictional source of an extraterrestrial signal detected by Jodi Foster in the film.

our location in the Orion Spur of the Milky Way galaxy. image credit: Roberto Mura/Public Domain — You are here: our location in the Orion Spur of the Milky Way galaxy. Image credit: Roberto Mura/Public Domain

The modern Japanese calendar actually marks Tanabata on several different dates. The timing of the festival can vary from village to village, depending on which local convention is observed.

The original Japanese calendar was lunisolar, and very similar in convention to the modern Chinese festival calendar. A lunisolar calendar attempts to keep the cycles of the synodic period (29.5 days) of the Moon in sync with the solar calendar year, and must add an extra lunar month every 2-3 years to keep up. The modern Jewish calendar is another example of a lunisolar calendar, whereas the Islamic calendar follows the cycles of the Moon only.

The Summer Triangle. Image credit: Stellarium

Modern Japan has adapted the western Gregorian calendar, which is exclusively solar and reconciles the tropical and sidereal periods of the Sun. Though Tanabata was traditionally held in August, many Japanese communities simply transcribe the ‘seventh day of the seventh month’ onto the modern Gregorian calendar to mean July 7^th. Still other villages use the ‘one-month delay’ rule, to center Tanabata on August 7^th.

Some rural villages, however, still use the older lunisolar custom. By this reckoning, Tanabata always falls seven days after the New Moon at the end of seven full lunar cycles, when the Moon is a fat crescent not quite at first Quarter phase.

A table for future dates of Tanabata using the traditional lunisolar calendar for the next decade. Image credit: Dave Dickinson

In 2015, this happens this Thursday on August 20^th. Like Easter, Tanabata can fall early or late by about one lunar cycle, the earliest being August 1st, which happens on 2014 and 2033, and the latest being August 30th, which happens on 2006 and 2044.

Think of the crescent Moon as the boat, which once a year, brings the two lovers together across the celestial river of the Milky Way.

Late to the party? the waxing crescent Moon versus the plane of the galaxy on the evening of August 20th, 2015. Image credit: Starry Night Education Software (Click image to enlarge)

You may notice on the evening of the 20^th that the boat no longer makes its portage to the river, completing the scene. In fact, the cosmic lineup of the Milky Way and the fat waxing crescent Moon is now more of a September/October affair. What gives? Well, they once did align, way back when Tanabata first became a tradition over a millennia ago.

Blame our friend, the Precession of the Equinoxes for conspiring to keep our happy couple apart. The 26,000-odd year wobble is enough to move the equinoctial points about one degree along the ecliptic during a normal 70 year human life span. That all adds up, making the ferryman about one synodic period late to the party in modern times.

Enjoy the show, and happy Tanabata, whenever you may celebrate it in space and time.

August 12, 2015December 23, 2015 by David Dickinson

Revealed: Mars to Appear Larger Than a Full Moon!

A recipe for a three ring circus? Image credit:

We can finally reveal the truth.

A massive conspiracy, spanning over a decade, has been revealed at last by basement bloggers, YouTubers and Facebook users everywhere, implicating ‘big-NASA’ and the powers that be in a massive cover-up.

Yes, it’s the month of August once again, and the Red Planet Mars is set to appear ‘larger than a Full Moon’ over the skies of Earth, as it apparently does now… every year.

Um, no. Stop. Just… stop.

Sure, by now, you’ve had the hoax forwarded to you by that certain well-meaning, but astronomically uninformed family member/co-worker/anonymous person on Facebook.

What’s new under the Sun concerning the August Mars Hoax? To see where the hoax was born, we have to journey all the way back to the close opposition of Mars on August 27^th, 2003. Hey, we actually took two weeks leave in the Fall of 2003 just to sketch and image Mars each night from our backyard lair in the Sonoran desert south of Tucson, Arizona from the then known Very Small Optical Observatory. Those were the days. We measured dial-up internet speeds in kbit/s, ‘burned CDs,’ and Facebook and Twitter were still some years away. Even spam e-mail was still sorta hip.

Two years later in 2005, we were all amused, as the ‘August Mars Hoax’ chain email made its first post-2003 appearance in our collective inboxes. Heck, we were even eager in those halcyon days to take to the nascent web, and do that new hipster thing known as ‘blogging’ to explain just exactly why this couldn’t be so to the masses.

Later in 2006, 2007, and 2008, it wasn’t so funny.

The Mars Hoax just wouldn’t die. “One more unto the breach,” the collective astro-blogging community sighed, as we all dusted off last year’s post explaining how the Red Planet could never approach our own fair world so closely.

It. Just. Couldn’t. Because orbital mechanics. Because physics.

Even the advent of social media couldn’t kill in annual onslaught of the Mars Hoax, and over a Spiderman movie reboot later, we’re now seeing it shared across Facebook, Twitter and more.

Sure, the Mars Hoax is as fake as Donald Trump’s hair. If there’s any true science lesson to learn here, it’s perhaps the mildly interesting social science study of just how the Mars hoax weathers the lean months of winter, to reemerge every August.

Here’s the skinny (again!) on just why Mars can’t appear as large as the Full Moon:

-The Moon is 3,474 kilometers in diameter, and orbits the Earth at an average distance of just under 400,000 kilometers.

-At this distance, the Moon can only appear about 30’ (half a degree) across.

-Think that’s a lot? Well, you could ring the 360 degree circle of the local horizon with 720 Full Moons.

-Mars, like the Earth, orbits the Sun. Even with Earth at aphelion (its most distant point) and Mars at perihelion, we’re still 206.7 – 151.9 = 54.8 million km apart. Sure, aphelion and perihelion of our respective worlds don’t quite line up in our current epochs, but we’ll indulge imagination and fudge things a bit.

-Though Mars is just over 2x times larger in diameter than the Moon, it’s also more than 143 times farther away, even at its said hypothetical closest.

Credit Dave Dickinson — Mars vs Earth; oppositions from 2003 to 2018, including perihelion and aphelion positions. Image credit: Dave Dickinson

-Still want to see Mars as big as a Full Moon? Perhaps one day, astronauts will, though they’ll have to be orbiting just over a 800,000 km from the Red Planet to do it.

If we sound a little pessimistic in our characterizing the Mars Hoax as a recurring non-story, it’s because we see many truly fantastic things in space news that get far from their far shake. Real stories, of collapsing stars, rogue exoplanets, and intrepid rovers exploring distant worlds. Tales of humanoids, exploring space and doing the very best and noble things humanoids as a species can do.

Want to trace the history the Mars Hoax?

Here’s the saga of Universe Today’s coverage of all things ‘Mars Hoax’ since those olden days of the early web:

2005- No, Mars Won’t Look as Big as the Moon

2006- No, Mars Won’t Look as Big as the Moon in August

2007- Will Mars Look as Big as the Moon on August 27? Nope

2008- Please (Again) – Mars Will NOT Look as Big as the Full Moon

2009- Mars Will NOT Look as Big as the Full Moon… But You Can Watch it Get Closer

2010- Tonight’s the Night Mars Will NOT Look as Big as the Full Moon

2011- Is the Moon Mars Myth Over?

2013- The Cyber Myth that Just Won’t Die

2016- ????

Hey, it looks like the hoax did take a break in 2012 and 2014, so that’s encouraging at least…

The great Mars opposition of 2003. image credit: Dave Dickinson — The great Mars opposition of 2003. Image credit: Dave Dickinson

Now, I’m going to do my best to truly terrify all of science blogger-dom, and leave you with one final thought to consider. Mars reaches opposition (otherwise known in astronomical circles as ‘when it’s really nearest to the Earth’) once roughly every 26 months. All oppositions of Mars are not created equal, owing mostly to the eccentric orbit of the Red Planet. We have another fine opposition of Mars coming right up next year on May 22^nd, 2016, followed by one that’s very nearly as favorable as the historic 2003 opposition in 2018, falling juuuuust shy of August on July 28^th of that year…

Will the Mars Hoax meme find a new unwitting audience, and with it, new life?

Sleep tight…. we’ll be covering real science stories in the meantime, ’til we’re called to do battle with the Mars Hoax once again.

August 11, 2015December 23, 2015 by David Dickinson

A Thrift Store Find Yields an Astronomical Mystery

A good mystery is often where you find it. Photographer Meagan Abell recently made a discovery during a thrift store expedition that not only set the internet abuzz, but also contains an interesting astronomical dimension as well. This is an instance where observational astronomy may play a key role in pinning down a date, and we’d like to put this story before the Universe Today community for further insight and consideration.

Meagan first discovered the set of four medium format negatives at a thrift store on Hull Street in Richmond, Virginia. Beyond that, they have no provenance. Meagan was amazed at what see saw when she scanned in the negatives: the images of a woman walking into the surf have an ethereal beauty all their own. Obviously the work of a skilled photographer, the photos appear to date from the late 1940s or 1950s.

Meagan turned to social media for help, and cyber-sleuths responded in a big way. #FindTheGirlsOnTheNegatives became a viral hit, but thus far, who the women in the images are and the story behind them remains a mystery.

We do know one tantalizing bit of information: several Facebook users have pinned down the location as Dockweiler Beach, California near Los Angeles International Airport. Keen-eyed observers noted the similarity of the outline of the distant hills seen to the north in one of the images.

A few things caught our eye upon reading the mystery of the girls in the negatives this past weekend. One shot clearly shows the notch of the Sun just below the twilight horizon. A second, even more intriguing image shows a tiny sliver of Moon just to the subject’s upper left.

Could a date, or set of dates, be estimated based on these factors alone?

Let’s slip into astro-detective mode now. A few things are obvious right off the bat. First, the Moon is a waxing crescent, meaning the shots would have to be set in the evening. This also lends credence to the ocean being the Pacific, because the sunset is occurring over water. The similarity in cloud formations across all of the images seen also strongly suggests the photographer took all of the pictures on the same evening, during one session.

Can that crescent Moon tell us anything? It’s tiny and indistinct, but we have a few things to go on. The Moon looks to be a 5-6 day old waxing crescent about 30-40% illuminated. Not all waxing crescent Moons are created equal, as the ‘horns of the Moon’ can point in various directions based on the angle of the ecliptic to the local horizon at different times of the year.

A typical sampling of the orientation of the horns of the waxing crescent Moon throughout the year as seen from latitude 34 degrees north. Image credit: Dave Dickinson

The horns of the Moon appear to be oriented about 35 degrees from horizontal. Assuming the subject in the red dress is elevated slightly and about 20 feet from the observer, the Moon would be about 25-30 degrees above the horizon in the shot.

Now, Dockweiler Beach is located at latitude 33 degrees 55’ 20” north, longitude 118 degrees 26’ 3” west. The beach itself faces a perpendicular azimuth of 240 degrees out to sea, or roughly WSW.

Already, we can rule out winter and spring, because of the unfavorable angle of the dusk ecliptic. We want a time of year with A) a shallow southward ecliptic and B) a sunset roughly due west.

Turns out, late July through early October fit these ideal conditions for the location.

Can we narrow this even further? Well, here’s one possibility. Remember, this next step is what gumshoe PIs call a ‘hunch’…

The motion of the Moon is a wonderfully complicated affair. The path of the Moon is inclined about five degrees relative to the ecliptic, meaning that the Moon can ride anywhere from declination 28 degrees south, to 28 degrees north. From latitude 34 degrees north, this puts the mid-July ecliptic at about 33 degrees elevation across the meridian at sunset.

The nodal points where the path of the Moon crosses the ecliptic also precess slowly around the celestial sphere. This motion completes one revolution every 18.6 years, meaning that the Moon reaches those maximum declination values (sometimes referred to as a ‘long nights’ or the Major Lunar Standstill of the Moon) just under once every 19 years.

This occurred last in 2006, and will occur next in 2025. Incidentally, we’re at a shallow mid-point (known as a Minor Lunar Standstill) between the two dates this coming Fall.

A good fit? A comparison of the Moon in the image (left) with a simulated view in Stellarium from August 19th, 1950 (click to enlarge). Image credit: Dave Dickinson/Meagan Abell

This also puts the late summer 1^st quarter Moon as far south ‘in the weeds’ as possible. Extrapolating back in time, this sort of wide-ranging Moon occurred around 1949. Looking at the celestial scene in Stellarium, three dates nail the horn angle and elevation of the Moon seen in the photograph pretty closely around this time:

-August 11^th, 1948

-August 29^th, 1949

-August 19^th, 1950

Of course, this is just a hunch. Perhaps the subject was standing on a westward facing spit of rocks. Or maybe the photographer was closer or farther away than estimated. Or maybe the negative was inverted left to right along the way… that’s why I’d like to invite, you, the astute sky watcher, to weigh in.

And even if we pinned down the date, the mystery remains. Who are the girls in the negatives? What became of the photo shoot? And how did the negatives end up in a thrift store in Virginia?

Read another astronomical mystery sleuthed out by Dave Dickinson, with The Downing of Spirit ‘03: Did the Moon Play a Role?

Update: an sharp-eyed reader noticed that if you boost the contrast, you can see an additional ‘speck’ in the Moon image (see comment discussion below):

Update: Meagan responds: “The object along the horizon in the crescent Moon image is actually just a transparency defect.” A second image from the same strip does not show the white speck (arrowed above) near the horizon.

August 10, 2015December 23, 2015 by David Dickinson

The 2015 Perseids: Weather Prospects, Prognostications and More

The venerable ‘old faithful of meteor showers’ is on tap for this week, as the August Perseids gear up for their yearly performance. Observers are already reporting enhanced rates from this past weekend, and the next few mornings are crucial for catching this sure-fire meteor shower.

First, here’s a quick rundown on prospects for 2015. The peak of the shower as per theoretical modeling conducted by Jérémie Vaubaillon projects a broad early maximum starting around Wednesday, August 12th at 18:39 UT/2:39 PM EDT. This favors northeastern Asia in the early morning hours, as the 1862 dust trail laid down by Comet 109P Swift-Tuttle — the source of the Perseids — passes 80,000 km (20% of the Earth-Moon distance, or about twice the distance to geostationary orbit) from the Earth. This is worth noting, as the last time we encountered this same stream was 2004, when the Perseids treated observers to enhanced rates up towards 200 per hour. Typically, the Perseids exhibit a Zenithal Hourly Rate (ZHR) of 80-100 per hour on most years.

This translates into a local peak for observers worldwide on the mornings of August 12th and 13th. Comet 109P Swift-Tuttle orbits the Sun once every 120 years, and last reached perihelion in 1992, enhancing the rates of the Perseids throughout the 1990s.

Don’t live in northeast Asia? Don’t despair, as meteor showers such as the Perseids can exhibit broad multiple peaks which may arrive early or late. Mornings pre-dawn are the best time to spy meteors, as the Earth has turned forward into the meteor stream past local midnight, and rushes headlong into the oncoming stream of meteor debris. It’s a metaphor that us Floridians know all too well: the front windshield of the car gets all the bugs!

The flight of the Perseid radiant through August. Image credit: Dave Dickinson/Stellarium

Weather prospects — particularly cloud cover, or hopefully, the lack of it — is a factor on every observer’s mind leading up to a successful meteor hunting expedition. Fortunately here in the United States southeast, August mornings are typically clear, until daytime heating gives way to afternoon thunder storms. About 48 hours out, we’re seeing favorable cloud cover prospects for everyone in the CONUS except perhaps the U.S. northeast.

Weather and cloud cover prospects for the mornings of August 12th and August 13th. Image credit: NOAA

The Moon is also under 48 hours from New on Wednesday, allowing for dark skies. This is the closest New Moon to the peak of the Perseids we’ve had since 2007, and it won’t be this close again until 2018.

Fun fact: the August Perseids, October Orionids, November Leonids AND the December Geminids are roughly spaced on the calendar in such a way that if the Moon phase is favorable for one shower on a particular year, it’ll nearly always be favorable (and vice versa) on the others as well.

Sky watchers have observed the annual Perseid meteors since antiquity, and the shower is often referred to as ‘The Tears of Saint Lawrence.’ The Romans martyred Saint Lawrence on a hot grid iron on August 10^th, 258 AD. The radiant crosses from the constellation Perseus in early August, and sits right on the border of Cassiopeia and Camelopardalis on August 12^th at right ascension 3 hours 10’ and declination +50N 50.’ Technically, the shower should have the tongue-twisting moniker of the ‘Camelopardalids’ or perhaps the ‘Cassiopeiaids!’

The last few years have seen respectable activity from the Perseids:

2014- ZHR = 68 (Full Moon year)

2013- ZHR = 110

2012- ZHR = 120

2011- ZHR = 60 (Full Moon year)

2010- ZHR = 90

You can see the light-polluting impact of the nearly Full Moon on the previous years listed above. Light pollution has a drastic effect on the number of Perseids you’ll see. Keep in mind, a ZHR is an ideal rate, assuming the radiant is directly overhead and skies are perfectly dark. Most observers will see significantly less. We like to watch at an angle about 45 degrees from the radiant, to catch meteors in sidelong profile.

Imaging the Perseids is as simple as setting up a DSLR on a tripod as taking long exposures of the sky with a wide angle lens. Be sure to take several test shots to get the combination of f-stop/ISO/and exposure just right for current sky conditions. This year, we’ll be testing a new intervalometer to take automated exposures while we count meteors.

Clouded out? NASA TV will be tracking the Perseids live on Wednesday, August 12^th starting at 10PM EDT/02:00 UT:

Remember, you don’t need sophisticated gear to watch the Perseids… just a working set of ‘Mark-1 eyeballs.’ You can even ‘hear’ meteor pings on an FM radio on occasion similar to lightning static if you simply tune to an unused spot on the dial. Sometimes, you’ll even hear a distant radio station come into focus as it’s reflected off of an ionized meteor trail:

And if you’re counting meteors, don’t forget to report ‘em to the International Meteor Organization and tweet ‘em out under hashtag #Meteorwatch.

Good luck and good meteor hunting!

August 6, 2015December 23, 2015 by David Dickinson

Stealing Sedna

An artist's conception of Sedna. this assumes that Sedna has a tiny as yet undiscovered moon. Image credit; NASA/JPl-Caltech

Turns out, our seemly placid star had a criminal youth of cosmic proportions.

A recent study out from Leiden Observatory and Cornell University may shed light on the curious case of one of the solar system’s more exotic objects: 90377 Sedna.

Distant Sedna (circled) moving against the starry background). Image credit: NASA/Hubble

A team led by astronomer Mike Brown discovered 90377 Sedna in late 2003. Provisionally named 2003 VB12, the object later received the name Sedna from the International Astronomical Union, after the Inuit goddess of the sea.

From the start, Sedna was an odd-ball. Its 11,400 year orbit takes it from a perihelion of 76 astronomical units (for context, Neptune is an average of 30 AUs from the Sun) to an amazing 936 AUs from the Sun. (A thousand AUs is 1.6% of a light year, and 0.4% of the way to Proxima Centauri, the closest star to our solar system). Currently at a distance of 86 AU and headed towards perihelion in 2076, we’re lucky we caught Sedna as it ‘neared’ (we use the term ‘near’ loosely in this case!) the Sun.

But this strange path makes you wonder what else is out there, and how Sedna wound up in such an eccentric orbit.

Zooming out; the inner solar system (upper left), the outer solar system (upper right), the orbit of Sedna (lower right) and the inner edge of the Oort cloud (lower left). Image credit: NASA

The study, entitled How Sedna and family were captured in a close encounter with a solar sibling looks at the possibility that Sedna may have been snatched from another star early on in our Sun’s career (of interstellar crime, perhaps?) The team used supercomputer simulations modeling 10,000 encounters to discover which types of near stellar passages might result in an ice dwarf world in a Sedna-like orbit.

“We constrained the parent star of Sedna to have between one and two times the mass of the Sun and its closest approach to be 200-400 AUs,” Dr. Lucie Jilkova of Leiden Observatory told Universe Today. “Such a close encounter probably happened while the Sun was still a member of its birth star cluster — a family of about 1,000 stars, so called solar siblings, born at the same time relatively close together — which was about 4 billion years ago.”

The best fit for what we see today in the outer solar system in the case of Sedna, is a close (340 AU) passage from the Sun — that’s over 11 times Neptune’s distance — of a 1.8 solar mass star inclined at an angle of 17-34 degrees to the ecliptic. Sedna’s current orbital inclination is 12 degrees.

Rise of the Sednitos

The paper assigns the term ‘Sednitos’ (also sometimes referred to as ‘Sednoids’) for these Edgeworth-Kuiper Belt intruders with similar characteristics to Sedna. In 2012, 2012 VP113, dubbed the ‘twin of Sedna,’ was discovered by astronomers at the Cerro Tololo Inter-American Observatory in a similar looping orbit. The ‘VP’ designation earned the as yet unnamed remote world the brief nickname ‘Biden’ after U.S. Vice President Joe Biden… hey, it was an election year.

There’s good reason to believe something(s?) out there shepherding these Senitos into a similar orbit with a comparable argument of perihelion. Researchers have suggested the existence of one or several planetary mass objects loitering out in the 200-250 AU range of the outer solar system… note that this is

a separate scientific-based discussion versus any would-be Nibiru related non-sense, don’t even get

us started…

If researchers in the study are correct, Sedna may have lots of company, with perhaps 930 planetesimals predicted in the ‘Sednito region’ of the solar system from 50 to 1,000 AUs and 430 more additional planetesimals littering the inner Oort cloud from the same early event.

“We focused on a particular example of a stellar encounter with characteristics from the ranges mentioned,” Dr. Jilkova said. “For this example, we estimated that there would be about 430 bodies similar to Sedna in the outer solar system (beyond 75 AU).”

Fun fact: One possible controversial candidate for the birth cluster of Sol and our solar system is the open cluster M67 in Cancer. It’s an intriguing notion to try and track down the star we stole Sedna from 4 billion years ago using spectral analysis, though researchers in the study point out that the other more massive star is probably an aging white dwarf by now.

Astronomy from the surface of Sedna is mind-bending to contemplate. Currently 86 AU from the Sun and headed towards perihelion in 2076, Sol would appear only 20” across from the surface of Sedna, but would still shine at magnitude -17 to -18 near perihelion, about 40 to 100 times brighter than a Full Moon. Fast forward about 5,500 years towards aphelion, however, and the Sun would dim to a paltry magnitude -12, a full magnitude (2.5 times) dimmer than the Full Moon.

The view from Sedna looking towards the inner solar system in 2015. Image credit: Starry Night Education Software. — The view from Sedna looking towards the inner solar system in 2015. Note the five degree red field of view marker. Image credit: Starry Night Education Software.

Shining at magnitude +21 in the constellation Taurus, astronomers know little else about Sedna. Based on brightness estimates, Sedna measures about 1,000 km in diameter. It does appear to be the reddest object in the solar system, and may turn out to be the ‘red twin of Pluto’ as recently revealed by NASA’s New Horizons spacecraft, complete with a surface rich in tholins.

And a new generation of observatories may uncover a treasure trove of Sednitos. The European Space Agency’s Gaia astrometry mission should uncover lots of new asteroids, comets, exoplanets and distant Kuiper Belt objects as a spin-off to its primary mission. Then there’s the Large Synoptic Survey Telescope, set to see first light in 2019.

“The key piece of the puzzle is to actually observe more Sedna-like objects.” Dr Jilkova said. “Currently, we know only of two such bodies. More discoveries are expected in the following years and they will shed light on the origin of Sedna and its family and the ‘criminal record’ of the Sun.”

It’s a fascinating story of interstellar whodunit for sure, as our Sun’s early days of wanton juvenile delinquency unravel before the eyes of modern day astronomical detectives.

August 4, 2015December 23, 2015 by David Dickinson

The Dog Days and Sothic Cycles of August

The month of August is upon us once again, bringing with it humid days and sultry nights for North American observers.

You’ll often hear the first few weeks of August referred to as the Dog Days of Summer. Certainly, the oppressive midday heat may make you feel like lounging around in the shade like our canine companions. But did you know there is an astronomical tie-in for the Dog Days as well?

We’ve written extensively about the Dog Days of Summer previously, and how the 1460 year long Sothic Cycle of the ancient Egyptians became attributed to the Greek adoption of Sothis, and later in medieval times to the ‘Dog Star’ Sirius. Like the Blue Moon, say something wrong enough, long enough, and it successfully sticks and enters into meme-bank of popular culture.

Sirius (to the lower right) along with The Moon, Venus and Mercury and a forest fire taken on July 22, 2014. (Note- this was shot from the Coral Towers Observatory in the southern hemisphere). Image credit and copyright: Joseph Brimacombe

A water monopoly empire, the Egyptians livelihood rested on knowing when the annual flooding of the Nile was about to occur. To this end, they relied on the first seasonal spotting of Sirius at dawn. Sirius is the brightest star in the sky, and you can just pick out the flicker of Sirius in early August low to the southeast if you know exactly where to look for it.

Sundown over Cairo during the annual flooding of the Nile river. Image Credit: Travels through the Crimea, Turkey and Egypt 1825-28 (Public Domain). — Sundown over Cairo during the annual flooding of the Nile river. Image Credit: *Travels through the Crimea, Turkey and Egypt 1825-28* (Public Domain).

Sirius lies at a declination of just under 17 degrees south of the celestial equator. It’s interesting to note that in modern times, the annual flooding of the Nile (prior to the completion of the Aswan Dam in 1970) is commemorated as occurring right around August 15th. Why the discrepancy? Part of it is due to the 26,000 year wobbling of the Earth’s axis known as the Precession of the Equinoxes; also, the Sothic calendar had no intercalculary or embolismic (think leap days) to keep a Sothic year in sync with the sidereal year. The Sothic cycle from one average first sighting of Sirius to another is 365.25 days, and just 9 minutes and 8 seconds short of a sidereal year.

But that does add up over time. German historian Eduard Meyer first described the Sothic Cycle in 1904, and tablets mention its use as a calendar back to 2781 BC. And just over 3 Sothic periods later (note that 1460= 365.25 x 4, which is the number of Julian years equal to 1461 Sothic years, as the two cycles ‘sync up’), and the flooding of the Nile now no longer quite coincides with the first sighting of Sirius.

Such a simultaneous sighting with the sunrise is known in astronomy as a heliacal rising. Remember that atmospheric extinction plays a role sighting Sirius in the swampy air mass of the atmosphere low to the horizon, taking its usual brilliant luster of magnitude -1.46 down to a more than a full magnitude and diminishing its intensity over 2.5 times.

This year, we transposed the seasonal predicted ‘first sightings’ of Sirius versus latitude onto a map of North America:

Another factor that has skewed the date of first ‘Sirius-sign’ is the apparent motion of the star itself. At 8.6 light years distant, Sirius appears to move 1.3 arc seconds per year. That’s not much, but over the span of one Sothic cycle, that amounts up to 31.6’, just larger than the average diameter of a Full Moon.

Sirius has been the star of legends and lore as well, not the least of which is the curious case of the Dogon people of Mali and their supposed privileged knowledge of its white dwarf companion star. Alvan Graham Clark and his father discovered Sirius B in 1862 as they tested out their shiny new 18.5-inch refractor. And speaking of Sirius B, keep a telescopic eye on the Dog Star, as the best chances to spy Sirius B peeking out from the glare of its primary are coming right up around 2020.

Sirius image Credit — The dazzling visage of Sirius. Image credit: Dave Dickinson

Repeating the visual feat of spying Sirius B low in the dawn can give you an appreciation as to the astronomical skill of ancient cultures. They not only realized the first sighting of Sirius in the dawn skies coincided with the annual Nile flooding, but they identified the discrepancy between the Sothic and sidereal year, to boot. Not bad, using nothing but naked eye observations. Such ability must have almost seemed magical to the ancients, as if the stars had laid out a celestial edge for the Egyptians to exploit.

You can also exploit one method of teasing out Sirius from the dawn sky a bit early that wasn’t available to those Egyptian astronomer priests: using a pair of binoculars to sweep the skies. Can you nab Sirius with a telescope and track it up into the daytime skies? Sirius is just bright enough to see in the daytime against a clear blue sky with good transparency if you know exactly where to look for it.

Let the Dog Days of 2015 begin!

July 28, 2015December 23, 2015 by David Dickinson

Faces of the Solar System

Move over, Pluto... Disney already has dibs on Mercury as seen in this MESSENGER photo. Image credit: NASA/JHAPL/Carnegie institution of Washington

“Look, it has a tiny face on it!”

This sentiment was echoed ‘round the web recently, as an image of Pluto’s tiny moon Nix was released by the NASA New Horizons team. Sure, we’ve all been there. Lay back in a field on a lazy July summer’s day, and soon, you’ll see faces of all sorts in the puffy stratocumulus clouds holding the promise of afternoon showers.

Pluto's moon Nix as imaged by New Horizons from 590,000 kilometers distant. Image credit: NASA/JHUAPL/SWRI — Pluto’s moon Nix as imaged by New Horizons from 590,000 kilometers distant. Image credit: NASA/JHUAPL/SWRI

This predilection is so hard-wired into our brains, that often our facial recognition software sees faces where there are none. Certainly, seeing faces is a worthy survival strategy; not only is this aspect of cognition handy in recognizing the friendlies of our own tribe, but it’s also useful in the reading of facial expressions by giving us cues of the myriad ‘tells’ in the social poker game of life.

And yes, there’s a term for the illusion of seeing faces in the visual static: pareidolia. We deal lots with pareidolia in astronomy and skeptical circles. As NASA images of brave new worlds are released, an army of basement bloggers are pouring over them, seeing miniature bigfoots, flowers, and yes, lots of humanoid figures and faces. Two craters and the gash of a trench for a mouth will do.

Now that new images of Pluto and its entourage of moons are pouring in, neural circuits ‘cross the web are misfiring, seeing faces, half-buried alien skeletons and artifacts strewn across Pluto and Charon. Of course, most of these claims are simply hilarious and easily dismissed… no one, for example, thinks the Earth’s Moon is an artificial construct, though its distorted nearside visage has been gazing upon the drama of humanity for millions of years.

Do you see the 'Man in the Moon?' Image credit: Dave Dickinson — Do you see the ‘Man in the Moon?’ Image credit: Dave Dickinson

The psychology of seeing faces is such that a whole region of the occipital lobe of the brain known as the fusiform face area is dedicated to facial recognition. We each have a unique set of neurons that fire in patterns to recognize the faces of Donald Trump and Hillary Clinton, and other celebs (thanks, internet).

Damage this area at the base of the brain or mess with its circuitry, and a condition known as prosopagnosia, or face blindness can occur. Author Oliver Sacks and actor Brad Pitt are just a few famous personalities who suffer from this affliction.

The 'Snowman of Vesta,' as imaged by NASA's Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA — The ‘Snowman of Vesta,’ as imaged by NASA’s Dawn spacecraft. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA

Conversely, ‘super-recognizers’ at the other end of the spectrum have a keen sense for facial identification that verges on a super-power. True story: my wife has just such a gift, and can immediately spot second-string actors and actresses in modern movies from flicks and television shows decades old.

It would be interesting to know if there’s a correlation between face blindness, super-recognition and seeing faces in the shadows and contrast on distant worlds… to our knowledge, no such study has been conducted. Do super-recognizers see faces in the shadowy ridges and craters of the solar system more or less than everyone else?

A well-known example was the infamous ‘Face on Mars.’ Imaged by the Viking 1 orbiter in 1976, this half in shadow image looked like a human face peering back up at us from the surface of the Red Planet from the Cydonia region.

Image credit: The 'Face on Mars': HiRISE vs Viking 1 (inset): Image credit: NASA/JPL — Image credit: The ‘Face on Mars’: HiRISE vs Viking 1 (inset): Image credit: NASA/JPL

But when is a face not a face?

Now, it’s not an entirely far-fetched idea that an alien entity visiting the solar system would place something (think the monolith on the Moon from Arthur C. Clarke’s 2001: A Space Odyssey) for us to find. The idea is simple: place such an artifact so that it not only sticks out like a sore thumb, but also so it isn’t noticed until we become a space-faring society. Such a serious claim would, however, to paraphrase Carl Sagan, demand serious and rigorous evidence.

But instead of ‘Big NASA’ moving to cover up the ‘face,’ they did indeed re-image the region with both the Mars Reconnaissance Orbiter and Mars Global Surveyor at a much higher resolution. Though the 1.5 kilometer feature is still intriguing from a geological perspective… it’s now highly un-facelike in appearance.

A 'face' or... more fun with 'scifi spacecraft pareidolia. Image credit: NASA/JPL/Paramount Pictures — A ‘face’ or… more fun with ‘scifi spacecraft pareidolia.’ Image credit: NASA/JPL/Paramount Pictures

Of course, it won’t stop the deniers from claiming it was all a big cover-up… but if that were the case, why release such images and make them freely available online? We’ve worked in the military before, and can attest that NASA is actually the most transparent of government agencies.

We also know the click bait claims of all sorts of alleged sightings will continue to crop up across the web, with cries of ‘Wake up, Sheeople!’ (usually in all caps) as a brave band of science-writing volunteers continue to smack down astro-pareidolia on a pro bono basis in battle of darkness and light which will probably never end.

What examples of astro-pareidolia have you come across in your exploits?

July 27, 2015December 23, 2015 by David Dickinson

Blues for the Second Full Moon of July

An artificially created 'Blue Moon,' using the white balance settings on the camera. Image credit and copyright: John Chumack

Brace yourselves for Blue Moon madness. The month of July 2015 hosts two Full Moons: One on July 2^nd and another coming right up this week on Friday, July 31^st at 10:43 Universal Time (UT)/6:43 AM EDT.

In modern day vernacular, the occurrence of two Full Moons in one calendar month has become known as a ‘Blue Moon.’ This is a result of the synodic period (the amount of time it takes for the Moon to return to a like phase, in this case Full back to Full) of 29.5 Earth days being less than every calendar month except February.

In the ‘two Full Moons in one month’ sense, the last time a Blue Moon occurred was on August 31st, 2012, and the next is January 31^st, 2018. The next time a Blue Moon occurs in the month of July is 2034, and the last July Blue Moon was 2004.

We say “once in a blue Moon,” as if it’s a rarity, but as you can see, they’re fairly frequent, occurring nearly once every 2-3 years or so.

Now, we’ll let you in on a secret. Like its modern internet meme cousin the ‘Super-Moon,’ astronomers don’t sit in mountain top observatories discussing the vagaries of the Blue Moon. In fact, astronomers rarely like to observe during the weeks surrounding the light-polluting Full Moon, and often compile data from the comfort of their university offices rather than visit mountaintop observatories these days…

The modern Blue Moon is now more of a cultural phenomenon. We’ve written previously about how an error brought us to the current ‘two Full Moons in one month definition.’ A more convoluted old timey definition was introduced in ye ole Maine Farmer’s Almanac circa 1930s as “the third Full Moon in an astronomical season with four.”

Legend has it that the Maine Farmer’s Almanac denoted this pesky extra seasonal Full Moon with ‘blue’ instead of black ink… to our knowledge, no examples exist to support this intriguing tale. Anyone have any old almanacs in the attic holding such a revelation out there?

The ghostly glow of the gibbous moon in Jean-Francois Millet's The Sheepfold. Image Credit: Public Domain — The ghostly glow of the gibbous moon in Jean-Francois Millet’s The Sheepfold. Image Credit: Public Domain

We’ve also laid out the occurrences for both types of Blue Moons for the remainder of the decade, as well as its New Moon cousin and internet meme to be, the Black Moon.

Untitled — The rising waxing gibbous Moon on the night of September 23rd, 1950. Image credit: Stellarium

Of course, the Moon most likely won’t appear to be physically blue, no matter what friends/family/co-workers/anonymous persons on Twitter say. The Moon can actually appear blue, as it did on September 23^rd, 1950 for much of the eastern United States and Canada through the haze of several forest fires in western Canada. The Moon was actually at waxing gibbous phase on the evening of this phenomenon, and as far as we can tell, no photographic documentation of this event exists. Spaceweather, has, however gathered a gallery of blue moon eyewitness reports over the years, including a few images. This occurs when moonlight is filtered through suspended oil drops about a micrometer in diameter which scattered yellow and red light, leaving a Moon with a ghostly indigo glow.

So there’s definitely another challenge to catch and photograph a truly ‘Blue Moon’ under such rare atmospheric circumstances… and remember, the Moon doesn’t have to be near Full to do it!

Watch that Moon, as we’ve got a few red letter dates coming up through the remainder of 2015. First up: the Supermoon season cometh in August, as we have a series of three Full Moons falling less than 24 hours from perigee on August 29^th, September 28^th, and October 27^th. Our money is on that middle one as having the potential to generate the most online lunacy, as it’s also the last total lunar eclipse of the current tetrad of four total lunar eclipses for 2014 and 2015, a ‘super-blood moon eclipse’ anyone? Though the dead won’t rise from the grave to mark such an occasion, you can be sure that many a sky aficionado will stumble zombie-like into the office the next day after pulling an all-nighter for the last good North American total lunar eclipse until 2018.

And it’s worth noting the path of the Moon, as it reaches its shallow mid-point in the last half of 2015. The Moon’s orbit is tilted about five degrees relative to the ecliptic, meaning that it can ride anywhere from 18 degrees—as it does this year—to 28 degrees from the celestial equator. This cycle takes about 19 years to complete, and a wide-ranging ‘long nights Moon’ last occurred in 2006, and will next occur in 2025.

A 'mock Blue Moon...' — A ‘mock Blue Moon…’ induced by use of a military flashlight filter. Image credit: Dave Dickinson

So don’t fear the Blue Moon, but be sure to take a stroll under its light this coming Friday… and perhaps enjoy a frosty Blue Moon beer on the eve of the sultry month of August.