Posted on by David Dickinson

Summer Astronomy, Minimoon & Saturn Opposition 2017

Saturn from June 1st. Image credit and copyright: Peter on the Universe Today Flickr forum.
Saturn on June 1st, nearing opposition. Image credit and copyright: Peter on the Universe Today Flickr forum

Summertime astronomy leaves observers with the perennial question: when to observe? Here in Florida, for example, true astronomical darkness does not occur until 10 PM; folks further north face an even more dire situation. In Alaska, the game in late July became “on what date can you first spot a bright planet/star? around midnight.

And evening summer thunder showers don’t help. Our solution is to get up early (4 AM or so) when the roiling atmosphere has settled down a bit.

But there’s one reason to stay up late, as the planet Saturn reaches opposition next week on June 15th and crosses into the evening sky.

Southern hemisphere observers have it best this year, as the ringed planet loiters in southern declinations for the next few years. In fact, Saturn won’t pop up over the celestial equator again until April, 2026. You’ll still be able to see Saturn from mid-northern latitudes, looking low to the south.

First, a brief rundown of the planets this summer. Mars is currently on the far side of the Sun and headed towards solar conjunction of July 26th. Meanwhile, Mercury is headed towards greatest eastern (dusk) elongation on June 21st. Early AM viewers, can follow Venus, which has just passed greatest elongation west of the Sun on June 3rd, just last week. Finally, Jupiter joins Saturn in the dusk sky, high to the south at sunset and headed towards quadrature 90 degrees east of the Sun on July 6th.

Looking eastward on the evening of June 9th. Credit: Stellarium.

There’s another astronomical curiosity afoot this coming weekend: the MiniMoon for 2017. This is the Full Moon nearest to lunar apogee, a sort of antithesis of the over-hyped “SuperMoon.” Lunar apogee occurs on Thursday, June 8th and the Full Moon occurs just 14 hours after.

2017 sees Saturn traveling from the dreaded “13th constellation” of zodiac Ophiuchus the Serpent Bearer into Sagittarius. This also means that Saturn is headed towards bottoming out near 23 degrees southern declination next year in late 2018. Saturn truly lives up to its “father time” namesake, marking up its slow 29 year passage once around the zodiac. This struck home to us a few years back when Saturn passed Spica in the constellation Virgo, right back where I first started observing the planet as a teenager three decades before.

The path of Saturn through the last half of 2017. Credit: Starry Night Education Software.

The rings are also at their widest tilt in 2017, making for an extra photogenic view. 27 degrees wide as seen from our Earthly vantage point is as wide as Saturn’s ring system ever gets. Saturn isn’t really “tipping” back and forth as much as it’s orbiting the Sun and dipping one hemisphere towards us, and then another. In 2017, it’s the planet’s northern hemisphere time to shine.

Saturn: the changing view. Image credit and copyright: Andrew Symes (@failedprotostar)

Here’s the last/next cycle rundown:

-Rings wide open: (southern pole of Saturn tipped earthward): 2003

–Rings edge on: 2009

–Rings wide open: (northern pole of Saturn tipped earthward): 2017

-Rings edge on: 2025

-Rings wide open: (southern pole of Saturn tipped earthward): 2032

Even a small 60 mm refractor and a low power eyepiece will reveal the most glorious facet of Saturn: its glorious rings. Galileo first saw this confounding view in 1610, and sketched Saturn as a curious double-handled world. In 1655 Christaan Huygens first correctly deduced that Saturn’s rings are a flat plane, fully disconnected from the planet itself.

Crank up the magnification a bit, and the large Cassini Gap in the rings and the shadow play of the rings and the planet becomes apparent. This gives the view an amazing 3-D effect unparalleled in observational astronomy. The shadow cast by the bulk of the planet disappears behind it during opposition, then slowly starts to reemerge to one side after. Other things to watch for include the retro-reflector Seeliger Effect ( also known as opposition surge) as the planet brightens near opposition. And can you spy the bulk of the planet through the Cassini gap?

The moons of Saturn. Image credit and copyright: John Chumack

Hunting for Saturn’s moons is also a fun challenge. Saturn has more moons visible to a backyard telescope than any other planet. Titan is easiest, as the +8 magnitude moon orbits Saturn once every 16 days. In a small to medium-sized (8-inch) telescope, six moons are readily visible: Enceladus, Mimas, Rhea, Dione, Iapetus and Tethys. Large light bucket scopes 10” and larger might just also tease out the two faint +15th magnitude moons Hyperion and Phoebe.

Saturn
Cassini looks back across Saturn’s rings. NASA/Cassini/JPL-Caltech/Space Science Institute

There’s also something else special about Saturn in 2017 in the world of space flight: the venerable Cassini mission comes to an end this September. Hard to believe, this mission soon won’t be with us. Launched in 1997, Cassini arrived at Saturn in in July 2004, and has since provided us with an amazing decade plus of science. The internet and science writing online has grown up with Cassini, and it’ll be a sad moment to see it go.

All thoughts to ponder, as you check out Saturn at the eyepiece this summer.

Posted on by David Dickinson

Movie Review – Alien: Covenant

Promotional poster for Alien: Covenant. Credit: 20th Century Fox
Promotional poster for Alien: Covenant. Credit: 20th Century Fox

Warning: mild plot spoilers ahead for the upcoming summer film Alien: Covenant, though we plan to focus more on the overall Alien sci-fi franchise and some of the science depicted in the movie.

So, are you excited for the 2017 movie season? U.S. Memorial Day weekend is almost upon us, and that means big ticket, explosion-laden sci-fi flicks and reboots/sequels. Lots of sequels. We recently got a chance to check out Alien: Covenant opening Thursday, May 18th as the second prequel and the seventh film (if you count 2004’s Alien vs. Predator offshoot) in the Alien franchise.

We’ll say right up front that we were both excited and skeptical to see the film… excited, because the early Alien films still stand as some of the best horror sci-fi ever made. But we were skeptical, as 2012’s Prometheus was lackluster at best. Plus, Prometheus hits you with an astronomical doozy in the form of the “alien star chart” right off the bat, not a great first step. Probably the best scene is Noomi Rapace’s terrifying self-surgery to remove the alien parasite. Mark Watney had to do something similar to remove the antenna impaled in his side in The Martian. Apparently, Ridley Scott likes to use this sort of scene to really gross audiences out. The second Aliens film probably stands as the benchmark for the series, and the third film lost fans almost immediately with the death of Newt at the very beginning, the girl Sigourney Weaver and crew fought so hard to save in Aliens.

How well does Alien: Covenant hold up? Well, while it was a better attempt at a prequel than Prometheus, it approaches though doesn’t surpass the iconic first two. Alien: Covenant is very similar to Aliens, right down to the same action beats.

The story opens as the crew of the first Earth interstellar colony ship Covenant heads towards a promised paradise planet Origae-6. En route, the crew receives a distress signal from the world where the ill-fated Prometheus disappeared, and detours to investigate. If you’ve never seen an Alien film before, we can tell you that investigating a mysterious transmission is always a very bad idea, as blood and gore via face-hugging parasites is bound to ensue. As with every Alien film, the crew of the Covenant is an entirely new cast, with Katherine Waterston as the new chief protagonist similar to Sigourney Weaver in the original films. And like any sci-fi horror film, expect few survivors.

Alien: Covenant is a worthy addition to the Alien franchise for fans who know what to expect, hearkening back to the original films. As a summer blockbuster, it has a bit of an uphill battle, with a slower opening before the real drama begins.

So how does the science of Alien: Covenant hold up?

The Good: Well, as with the earlier films, we always liked how the aliens in the franchise were truly, well, alien, not just human actors with cosmetic flourishes such as antennae or pointed ears. Humans are the result of evolutionary fortuity, assuring that an alien life form will trend more towards the heptapods in Arrival than Star Trek’s Mr. Spock. Still more is revealed about the parasitic aliens in Alien: Covenant, though the whole idea of a inter-genetic human alien hybrid advanced in the later films seems like a tall order… what if their DNA helix curled the wrong way? Or was triple or single, instead of double stranded?

Spaceships spin for gravity in the Alien universe, and I always liked Scott’s industrial-looking, gray steel and rough edges world in the Alien films, very 2001: A Space Odyssey.

Now, for a very few pedantic nit picks. You knew they were coming, right? In the opening scenes, the Covenant gets hit with a “neutrino burst” dramatically disabling the deployed solar array and killing a portion of the hibernating crew. Through neutrinos are real, they, for the most part, pass right through solid matter, with nary a hit. Millions are passing through you and me, right now. The burst is later described as due to a “stellar ignition event” (a flare? Maybe a nova?) Though the crew states there’s no way to predict these beforehand… but even today there is, as missions such as the Solar Dynamics Observatory and SOHO monitor Sol around the clock. And we do know which nearby stars such as Betelgeuse and Spica are likely to go supernova, and that red dwarfs are tempestuous flare stars. An interstellar colonization mission would (or at least should) know to monitor nearby stars (if any) for activity. True, a similar sort of maguffin in the form of the overblown Mars sandstorm was used in The Martian to get things rolling plot-wise, but we think maybe something like equally unpredictable bursts high-energy cosmic rays would be a bigger threat to an interstellar mission.

The crew also decides to detour while moving at presumably relativistic speeds to investigate the strange signal. This actually happens lots in sci-fi, as it seems as easy as running errands around town to simply hop from one world to the next. In reality, mass and change of momentum are costly affairs in terms of energy. In space, you want to get there quickly, but any interstellar mission would involve long stretches of slow acceleration followed by deceleration to enter orbit at your destination… changing this flight plan would be out of the question, even for the futuristic crew of the Covenant.

Expect a high body count: the crew of the Covenant. Credit: 20th Century Fox

Another tiny quibble: the Covenant’s computer pinpoints the source of the mysterious signal, and gives its coordinates in right ascension and declination. OK, this is good: RA and declination are part of a real coordinate system astronomers use to find things in the sky… here on Earth. It’s an equatorial system, though, hardly handy when you get out into space. Maybe a reference system using the plane of the Milky Way galaxy would be more useful.

But of course, had the crew of the Covenant uneventfully made it to Origae-6 and lived happily ever after stomach-exploding parasite free, there would be no film. Alien: Covenant is a worthy addition to the franchise and a better prequel attempt than Prometheus… though it doesn’t quite live up to the thrill ride of the first two, a tough act to follow in the realm of horror sci-fi.

Posted on by David Dickinson

See Comet C/2015 ER61 PanSTARRS at its Best

ER61 PanSTARRS
Comet C/2015 ER61 PanSTARRS shortly after outburst on April 8th. Image credit and copyright: John Purvis.
ER61 PanSTARRS
Comet C/2015 ER61 PanSTARRS shortly after outburst on April 8th. Image credit and copyright: John Purvis.

Have you been following the springtime parade of bright comets? Thus far, the Oort cloud has offered up several fine binocular comets, including Comet 2/P Encke, 41/P Tuttle-Giacobini-Kresak, 45/P Honda-Mrkos-Pajdusakova, C/2016 U1 NEOWISE and C/2017 E4 Lovejoy. Now, another comet joins the dawn ranks, as it brightens up ahead of expectations: 2015 ER61 PanSTARRS.

Discovered on March 15th, 2015 by the prolific PanSTARRS-1 NEO survey atop Haleakala in Maui, Hawaii, Comet ER61 PanSTARRS made our who’s-who list of bright comets to watch for in 2017. The odd “ER61” designation stems from the early identification of the object as an asteroid, before it presented observers with a cometary appearance.

ER61 PanSTARRS Skychart
The path of Comet C/2015 ER61 PanSTARRS through the sky from early May through mid-August. Credit: Starry Night Education software.

Late northern hemisphere Spring through Summer sees the comet maintaining a decent elevation above the eastern horizon at dawn, gliding north and parallel to the ecliptic plane through the constellations Pisces, Aries and Taurus from May through mid-August. The comet passed 1.08 AU from the Earth last month on April 4th, and is now racing away from us. The comet’s location near the March equinoctial point on the celestial hemisphere assures an equally good apparition for both the northern and southern hemisphere. As seen from latitude 30 degrees north, the comet sits 30 degrees above the eastern horizon, through the remainder of May. Venus also makes a brilliant beacon to track down Comet ER61 PanSTARRS, as the planet heads towards greatest elongation 46 degrees west of the Sun on June 3rd.

The orbit of Comet ER61 PanSTARRS through the inner solar system. Credit: NASA/JPL.

The comet is also on a 7,591 year long orbit inbound, which takes it out nearly 2,500 AU from the Sun. That’s 190 times the Pluto-Sun distance, and the fourth most distant aphelion of any solar system object known. The 2015-2017 passage of the comet through the inner solar system actually shortened the orbit of Comet ER61 PanSTARRS down to an aphelion of ‘only’ 854 AU due to a 0.9 AU pass near Jupiter last year on March 28th, 2016. A similar orbital shortening by Jove occurred for Comet Hale-Bopp in 1996, which came in on an 4,200 year orbit and departed the inner solar system on a shorter 2,500 year path around the Sun.

The projected light curve for Comet C/2015 ER51 PanSTARRS. The purple line denotes perihelion, and the black dots are actual observations. Adapted from Seiichii Yoshida’s Weekly Information for Bright Comets.

Prospects and Prognostications

Observers reported an outburst from the comet last month in the first week of April, causing it to jump about 2 magnitudes in brightness. Right now, it’s holding steady at +7th magnitude. Unfortunately, the Moon reaches Full phase this week on May 10th, though you’ve still got a slim window to hunt for the comet after Moonset and before sunrise. Once the Moon moves towards a slender crescent phase next late week, we’ll once again have dark predawn skies ideal for comet hunting.

Here are some key dates for Comet C/2015 ER61 PanSTARRS as it glides through the dawn sky:

(Stars highlighted are brighter than +5th magnitude, and passes are less than a degree unless otherwise noted.)

May 10th: Reaches perihelion at 1.04 astronomical units (AU) from the Sun.

May 12th: Passes near the +4.9 magnitude star 19X Piscium.

May 20-23rd: Passes less than 10 degrees from Venus.

May 21st: The waning crescent Moon passes less than 10 degrees to the south.

June 10th: Passes near the +3.6 magnitude star Eta Piscium.

June 11th: Passes near the galaxy M74.

June 16th: Passes into the constellation Aries.

June 19th: The waning crescent Moon passes 9 degrees to the south.

July 13th: Passes near (less than 5′) the +4.6 magnitude star Epsilon Arietis.

July 18th: The waning crescent Moon passes 9 degrees to the south.

July 23rd: Passes near the +4.8 star Zeta Arietis.

The comet versus Venus in the dawn sky – looking eastward on May 15th. Credit: Stellarium.

August 2nd: Crosses into the constellation Taurus.

August 15th: The waning crescent Moon passes 8 degrees to the south.

August 16th: Passes near M45 (The Pleiades)

After mid-August, Comet 2015 ER61 PanSTARRS will drop back down below +10th magnitude, not to return for several millennia to come.

Observing a comet like ER61 PanSTARRS is as simple as knowing where and when to look, then starting to slowly sweep the suspect area with binoculars for a little fuzzball looking like a globular cluster stubbornly refusing to snap into focus. In pre-telescopic times, ER61 PanSTARRS would’ve entered and exited the inner solar system unrecorded.

April ER61 PanSTARRS
Comet C/2015 ER61 PanSTARRS from April 12th. Image credit and copyright: Joseph Brimacombe.

Next up: We’ve got one more predicted comet on tap for 2017, as C/2015 V2 Johnson brightens up to +7th magnitude in mid-June. Keep watching the skies, as the next great comet of the century could always appear unannounced at any time.

Posted on by David Dickinson

An Impalpable Penumbral Eclipse

penumbral eclipse
The March 2016 penumbral lunar eclipse seen from Calliope, Australia. Image credit and copyright: Teale Britstra.

Hey, how ’bout that annular eclipse last week? Some great images flooded in to Universe Today, as the final solar eclipse for 2016 graced the African continent. This not only marked the start of the second and final eclipse season for 2016, but it also set us up for the final eclipse of the year next week.

The path of next week's penumbral eclipse through the Earth's shadow. Adapted from NASA/GSFC/F. Espenak.
The path of next week’s penumbral eclipse through the Earth’s shadow. Adapted from NASA/GSFC/F. Espenak.

We’re talking about the penumbral lunar eclipse coming up next week on September 16th, 2016. this sort of eclipse occurs when the Moon just misses the dark inner core (umbra) of the Earth’s shadow, and instead, drifts through its relatively bright outer cone, known as the penumbra. Though not the grandest show as eclipses go, astute observers should notice a subtle light tea-colored shading of the Full Moon, and perhaps the ragged dark edge of the umbra on the northwestern limb of the Moon as it brushes by around mid-eclipse.

The visibility map for next week's eclipse. Image credit: NASA/GSFC/Fred Espenak.
The visibility map for next week’s eclipse. Image credit: NASA/GSFC/Fred Espenak.

The entirety of the eclipse will be visible from the region surrounding the Indian Ocean on the evening of Friday, September 6th. Viewers in Australia, New Zealand and Japan will see the eclipse transpire at moonset, and the eclipse will get underway at moonrise for observers in western Africa and Europe.

The eclipse runs from first contact at 16:55 Universal Time (UT) to 20:54 UT when the Moon quits the Earth’s shadow almost four hours later. Mid-eclipse occurs at 18:55 UT, with the Moon 91% immersed in the Earth’s outer shadow.

Tales of the Saros

This particular eclipse is member 9 of the 71 lunar eclipses in saros series 147. This saros began on July 2nd 1890 and runs through to the final eclipse in the cycle on May 1st 2990. It will produce its very first partial eclipse next time around on September 28th 2034, and its first total lunar eclipse on June 6th, 2449.

Why penumbrals? Aren’t they the ultimate non-event when it comes to eclipses? Like with much of observational astronomy, a penumbral lunar eclipse pushes our skills as a visual athlete to the limit. Check out the waxing gibbous Moon the night before the eclipse, then the Moon the night of the event. If you didn’t know any better, could you tell the difference from one night to the next? Often, the camera can see what the eye can’t. Photographing the Moon before, during and after a penumbral eclipse will often bring out the subtle shading on post-comparison. You’ll want to photograph the Moon when its high in the sky and free of atmospheric distortion low to the horizon, which tends to discolor the Moon. Such a high-flying Moon during mid-eclipse favors the Indian Subcontinent this time around. We’ve yet to see a good convincing time-lapse documenting a penumbral eclipse, though such a feat is certainly possible.

See anything... shady going on? Here's the penumbral lunar eclipse from this past March. Image credit and copyright: Neeraj Ladia
See anything… shady going on? Here’s the penumbral lunar eclipse from this past March. Image credit and copyright: Neeraj Ladia

When is an eclipse… not an eclipse? By some accounts, the Moon underwent a very shallow penumbral one cycle ago on August 18th, 2016, though the brush past the shadow was so slight that many lists, including the NASA’s GSFC eclipse page omitted it. Three eclipses (a lunar partial and a penumbral, or two penumbrals and one solar) can occur in one eclipse season, if the nodes of the Moon’s orbit where it intersects the ecliptic fall just right. This last occurred in 2013, and will happen again in 2020.

And when there’s a lunar eclipse, there’s also a Full Moon. The September Full Moon is the Harvest Moon, providing a few extra hours of illumination to get the crops in. This year, the Harvest Moon falls just six days from the equinox on September 22nd, marking the start of astronomical Fall in the northern hemisphere and Spring in the southern. The relative ecliptic angle also ensures that moonrise only slides back by a slight amount each evening for observers in mid-northern latitudes around the Harvest Moon.

Can’t wait til the next eclipse? Well, 2017 has four of ’em: an annular on February 26th favoring South America, two lunars (another penumbral on February 11th and a partial on August 7th) and oh yeah, there’s a total solar eclipse crossing the United States on August 21st. And the next total lunar eclipse? The dry spell is broken on January 31st, 2018, when a total lunar eclipse favoring the Pacific Rim occurs. Yeah, we got spoiled with four back-to-back lunar eclipses during the Blood Moon tetrad of 2014-2015…

Read Dave Dickinson’s eclipse-fueled sci-fi tales Exeligmos, Shadowfall, The Syzygy Gambit and Peak Season.

Posted on by David Dickinson

Tales of Two Asteroid Occultations: Io, Nemausa Cast Shadows Over North America

Don't blink... an artist's conception of an asteroid blocking out a distant star. Image credit: NASA.

Up for a challenge? Over the next two weekends, two asteroid occultations pass over North America. These are both occulting (passing in front of) +7th magnitude stars, easy targets for even binoculars or a small telescope. These events both have a probability score of 99-100%, meaning the paths are known to a high degree of accuracy. These are also two of the more high profile asteroid occultations for 2016.

Here’s the lowdown on both events:

Image credit:
The path of the 85 Io event. Image credit: Steve Preston/Asteroid Occultation Updates.

On the morning of Saturday, August 27th , the +10th magnitude asteroid 85 Io occults a +7.5 magnitude star (TYC 0517-00165-1). the maximum predicted duration for the event is 28 seconds, and the maximum predicted brightness drop is expected to be 3 magnitudes. The ‘shadow’ will cross North America from the northeast to the southwest starting over Quebec at 4:27 Universal Time (UT), crossing Ontario and Michigan’s upper peninsula at 4:30 UT, and heading south over Oklahoma, Texas, and Mexico at 4:36 UT. The action takes place in the constellation Aquarius, with the Moon at a 28% waning crescent.

Image credit: Stellarium
A wide field finder view for the 85 Io event. Image credit: Stellarium

Discovered by C.H.F. Peters on September 19th, 1865, 85 Io is about 180 kilometers in diameter, as measured by an occultation in late 1995.

Image credit:
The path of the 51 Nemausa event. Image credit: Steve Preston/Asteroid occultation updates.

Next, on the morning of Saturday, September 3rd, the +11.5 magnitude asteroid 51 Nemausa occults a +7.6 mag star (HIP 8524). The maximum duration of the event along the centerline is expected to be 32 seconds in duration, with a maximum drop of four magnitudes. Said shadow will cross western Canada at9:42 UT, and the U.S. crossing runs from 9:49 to 9:55 UT. The action takes place in the constellation Pisces. The Moon phase is a slim 4% waxing crescent during the event.

Image credit: Stellarium
A wide field finder view for the 51 Nemausa event. Image credit: Stellarium

Discovered in 1858 by A. Laurent observing from Nîmes, France, 51 Nemausa occulted a bright star in 1979. In fact, there’s evidence from previous occultation to suggest the 51 Nemausa may possess a tiny moon… could it show up again during the September 3rd event?

Observing asteroid occultations is really a modern sub-specialty of amateur and even professional astronomy. To predict such an occurrence, the orbit of the asteroid or occulting body and the precise position of the star need to be known to a pretty high degree of precision. This required the advent of modern astrometry and massive computing power. If any casual sky observer noticed a naked eye star wink out way back when pre-mid 20th century, it’s lost to history.

The first successfully predicted and observed occultation of a star by an asteroid was the +8.2 magnitude star SAO 112328 by 3 Juno on February 19, 1958. Less than two dozen such events were observed right up through to 1980. Today, hundreds of such events are predicted worldwide each year.

Next month’s expected data release from the ESA’s Gaia mission should refine our stellar position and parallax knowledge even further, and fine-tune predictions of future asteroid occultations.

And speaking of occultations, some great observations were made of the July 29th, 2016 lunar grazing occultation of Aldebaran across the United States. The Moon occults Aldebaran for every lunation in 2016 into 2017, and we get another shot favoring the southern U.S. in the daytime on August 25th.

Observing an asteroid occultation is a challenge, requiring an observer acquiring and monitoring the correct star at the precise time of the event. If possible (i.e. weather permitting) familiarize yourself with the star field a night or two prior to the event. I usually have a precise audio time signal such as WWV radio running in the background.

Image credit: Occult 4.2.
The shape of 51 Nemausa from the 2014 event. Image credit: Occult 4.2.

Why occultations? Well, if enough observations can be gathered, a sort of shadow profile of the occulting space rock can be made, with each observation representing a chord. Even negative ‘misses’ along the edge of the path help. Tiny moons of asteroids have even been discovered this way, as the distant star winks out multiple times.

The International Occultation Timing Association wants your observation. You can, with a little practice, make usable observations visually, though most observers tend to video record events.

Don’t miss these asteroid occultations and more, coming to a sky worldwide near you!

Posted on by David Dickinson

An Old Glass Plate Hints at a Potential New Exoplanet Discovery

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

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

Posted on by David Dickinson

Into the Red: Our Complete Guide to Mars Opposition 2016

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

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

Posted on by David Dickinson

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Posted on by David Dickinson

Prelude to Transit: Catching Mercury Under Dusk Skies

Mercury and the Moon
The waxing gibbous Moon passes Mercury (low to the right). Image credit and copyright: Tavi Greiner

Have you ever seen Mercury? The diminutive innermost world takes the center stage next month, as it transits the Sun as seen from our early perspective on May 9th. This week, we’d like to turn your attention to bashful Mercury’s dusk apparition, which sets up the clockwork celestial gears for this event. Continue reading “Prelude to Transit: Catching Mercury Under Dusk Skies”