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

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.
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 30th 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 2nd at 20:45 UT. The Moon then moves on to occult Mercury on Thursday, August 4th 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 4th. Mercury shines at magnitude +0.01, and presents a 67% illuminated disk 6.3” in size, while the Moon is a slender 5% illuminated.

Credit: Occult 4.2
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 3rd.

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

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 3rd 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 29th 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 6th 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.
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 4th, followed by a slightly wider grouping of Venus, Jupiter and the Moon around August 25th.

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.

The Moon Occults Jupiter This Weekend

The Moon occults Jupiter

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 9th, 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.
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 6th, September 2nd and 30th before the relative motions of the Moon and Jupiter carry them apart, not to meet again until October 31st, 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.
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
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!

Jupiter and the Moon Have a Close Encounter in the Sky February 18, 2013

The movement of the Moon makes a fascinating study of celestial mechanics. Despite the light pollution it brings to the nighttime sky, we’re fortunate as a species to have a large solitary satellite to give us lessons in “Celestial Mechanics 101″

This weekend, we’ll get to follow that motion as the Moon crosses into the constellation Taurus for a near-pass of the planet Jupiter, and for a very few citizens of our fair world, occults it.

The Moon versus Jupiter during the previous occultation of the planet last month. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).
The Moon versus Jupiter during the previous occultation of the planet last month. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).

In astronomy, the term “occultation” simply means that one astronomical body passes in front of another. The term has its hoary roots in astronomy’s ancient past; just like the modern day science of chemistry sprung from the pseudo-science of alchemy, astronomy was once intertwined with the arcane practice of astrology, although the two have long since parted ways. When I use the term “occultation” around my non-space geek friends, (I do have a few!) I never fail to get a funny look, as if I just confirmed every wacky suspicion that they ever had about us backyard astronomers…

But those of us who follow lunar occultations never miss a chance to observe one. You’ll actually get to see the motion of the Moon as it moves against the background planet or star, covering it up abruptly. The Moon actually moves about 12° degrees across the sky per 24 hour period.

The position of the Moon & Jupiter as seen from Tampa (Feb 18th, 7PM EST), Perth, (Feb 18th 11:30UT) & London  (Feb 18th at 19UT). Created by the author using Stellarium.
The position of the Moon & Jupiter as seen from Tampa (Feb 18th, 7PM EST), Perth, (Feb 18th 11:30UT) & London (Feb 18th at 19UT). Created by the author using Stellarium.

On the evening of Monday, February 18th, the 56% illuminated waxing gibbous Moon will occult Jupiter for Tasmania and southern Australia around 12:00 Universal Time (UT). Folks along the same longitude as Australia (i.e., eastern Asia) will see a close pass of the pair. For North America, we’ll see the Moon approach Jupiter and Aldebaran of February 17th (the night of the Virtual Star Party) and the Moon appear past the pair after dusk on the 18th.

Orientation of Jupiter, the Moon & Vesta on the evening of February 18th for North America. (Created by the author in Starry Night).
Orientation of Jupiter, the Moon & Vesta on the evening of February 18th for North America. (Created by the author in Starry Night).

But fret not; you may still be able to spot Jupiter near the Moon on the 18th… in the daytime. Daytime planet-spotting is a fun feat of visual athletics, and the daytime Moon always serves as a fine guide. Jupiter is juuuuuust bright enough to see near the Moon with the unaided eye if you know exactly where to look;

Jupiter captured during a close 2012 pass in the daytime! (Photo by author).
Jupiter captured during a close 2012 pass in the daytime! (Photo by author).

To see a planet in the daytime, you’ll need a clear, blue sky. One trick we’ve used is to take an empty paper towel tube and employ it as a “1x finder” to help find our target… binoculars may also help! To date, we’ve seen Venus, Jupiter, Sirius & Mars near favorable opposition all in the daylight… Mercury and Vega should also be possible under rare and favorable conditions.

This week’s occultation of Jupiter is the 3rd and final in a series that started in December of last year. The Moon won’t occult a planet again until an occultation of Venus on September 8th later this year, and won’t occult Jupiter again until July 9th, 2016. We’re also in the midst of a long series of occultations of the bright star Spica (Alpha Virginis) in 2013, as the Moon occults it once every lunation from somewhere in the world. Four major stars brighter than +1st magnitude lie along the Moon’s path near the ecliptic; Spica, Aldebaran, Regulus, and Antares which we caught an occultation of in 2009;

Also of note: we’re approaching a “plane-crossing” of the Jovian moons next year. This means that we’ll start seeing Callisto casting shadows on the Jovian cloud tops this summer on July 20th, and it will continue until July 21st, 2016. The orbits of the Jovian moons appear edge-on to us about every five years, and never really deviate a large amount. Callisto is the only moon that can “miss” casting a shadow on the disk of Jupiter in its passage.  The actual plane crossing as seen from the Earth occurs in November 2014. Jupiter reaches solar conjunction this year on June 19th and doesn’t come back into opposition until early next year on January 5th. 2013 is an “opposition-less” year for Jupiter, which occurs on average once per every 11-12 years. (One Jovian orbit equals 11.8 Earth years).

The Moon plus Jupiter during last month's close conjunction. (Photo by author).
The Moon plus Jupiter during last month’s close conjunction. (Photo by author).

But wait, there’s more… the Moon will also occult +7.7th magnitude 4 Vesta on February 18th at~21:00 UT. This occultation occurs across South America and the southern Atlantic Ocean. It would be fun to catch its ingress behind the dark limb of the Moon, and we bet that a precisely timed video might just show evidence for Vesta’s tiny angular diameter as it winks out. For North American observers, Vesta will sit just off the northern limb of the Moon… if you have never seen it, now is a great time to try!

Finally, we realized that also in the field with 4 Vesta is an explorer that just departed its environs, NASA’s Dawn spacecraft. Although unobservable from Earth, we thought that it would be an interesting exercise to see if it gets occulted by the Moon as well this week, and in fact it does, for a very tiny slice of the planet;

The occultation of the Dawn spacecraft as seen from Earth. Created by the author using Occult 4.0.
The occultation of the Dawn spacecraft as seen from Earth. Created by the author using Occult 4.0.

Hey, calculating astronomical oddities is what we do for fun… be sure to post those pics of Jupiter, the Moon and more up to our Universe Today Flickr page & enjoy the celestial show worldwide!

See more of Luis Argerich’s astrophotography at Nightscape Photography.

Graphics created by author using Stellarium, Starry Night and Occult 4.0 software.