2016 astronomy Archives

July 26, 2016 by David Dickinson

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

January 18, 2016January 18, 2016 by David Dickinson

Watch the Moon Occult Aldebaran Tuesday Night

Now you see it... the December 23rd 2015 occultation of Aldebaran. Image credit and copyright: Roger Hutchinson

“That’s no moon…”

But in this case, it is (sorry Ben), and that Moon is headed to temporarily obliterate (occult) the view of the bright star Aldebaran as seen from the Earth on the evening of January 19^thand into the morning of the 20^th.

Here are the specifics. Not to be confused with Princess Leia’s homeworld of Alderaan of Star Wars science fiction fame, the occultation of the bright star Aldebaran in the astronomical constellation Taurus occurs on the night of Tuesday, January 19^th and finds the waxing gibbous the Moon 82% illuminated and four days from the first Full Moon of the year on January 24th. This is also the first of 13 occultations of Aldebaran for the year 2016, one for even lunation. Evening occultations are particularly favorable, as the star in question always disappears along the leading edge dark limb of the Moon, to reappear along its daytime limb. Once the Moon is waning, the reverse is true, as the bright limb then leads towards New phase.

We’ve caught occultations of bright stars very near Full, and can attest that it is indeed possible to follow a +1st magnitude star all the way to the lunar limb.

The occultation footprint runs across the nighttime northern hemisphere from the early morning hours in western Europe and the United Kingdom across the northern Atlantic, across the contiguous ‘lower 48’ states of of U.S. to Canada and northern Mexico. It actually juuuust misses us here down in sunny Florida, one of the few states that will miss out on the event. This is the best placed occultation of Aldebaran for 2016 for most North American viewers, falling during early evening prime time hours high in the post twilight sky.

Here’s the timing for the ingress (beginning) and egress (end) for the occultation for selected cities; the International Occultation Timing Association (IOTA) has an extensive table of times for cities within the occultation path. (all quoted using Universal Time(UT), plus altitude (alt) in degrees (deg) :

London

Ingress: 3:25 UT/alt: 6 deg

Egress: 3:57 UT/alt: 2 deg

Atlanta

Ingress: 2:22 UT/73 deg

Egress: 3:06 UT/70 deg

Boston

Ingress: 2:35 UT/60 deg

Egress: 3:47 UT/50 deg

Los Angeles

Ingress: 1:05 UT/40 deg

Egress: 2:13 UT/54 deg

Montreal

Ingress: 2:28 UT/59 deg

Egress: 3:42 UT/51 deg

Halifax

Ingress: 2:46 UT/53 deg

Egress: 3:57 UT/43 deg

Note that precise times for the event change slightly due to the position of the observer within various time zones, as well as the parallax shift of the Moon as seen from the Earth.

Occultations always give us a chance to analyze the target star for any possible close in binary companions, as the star winks out in a tell tale step-wise fashion. Aldebaran has no known close companion star, though spurious claims have been made for planets orbiting the star over the years. 65 light years distant, Aldebaran is in the direction of the Hyades star cluster in the distant galactic background, though it is physically unrelated to the group, which is 153 light years from the Earth. This also means that several bright stars in the Hyades get occulted by the Moon as well on Tuesday night, as the Moon makes its way to Aldebaran and its date with astronomical destiny.

An occultation of a bright star by the Moon also allows selenographers to map out the profile of the jagged lunar limb, as light from the distant star is alternately shines through the valleys and is occluded mountain peaks along the edge of the relatively nearby Moon. This effect can be especially dramatic for observers positioned along the graze line, which on Tuesday night runs from southern Georgia through southern Texas into northern Mexico, across to Baja California.

Recording the occultation is as simple as aiming a video camera coupled to a telescope at the Moon at the appointed time, and running video. Start early, and you may want to overexpose the waxing gibbous Moon a bit to bring out Aldebaran. We managed to nab the 2008 occultation of Antares by the nearly Full Moon using a simple JVC video camera and an 8” Schmidt-Cassegrain telescope.

The event will be easily visible using binoculars, and should even be noticeable to the unaided eye.

That’s it for this week in ‘things passing in front of each other…’ In astronomy, lots can be learn just from analyzing light, or in this case, the absence of it. What good are occultations? Well, they might just save your not-so-secret rebel base from immediate annihilation:

And watch that Moon, as there will be another good occultation of Aldebaran shifted just slightly westward next lunation on February 16th, 2016.

More to come!

December 3, 2015December 23, 2015 by David Dickinson

Astro-Challenge: Watch the Moon Occult Venus in the Daytime

The Moon meets Venus on February 26th, 2014. Image credit and copyright: Konstantinos Spanos

The year 2015 saved one of the best astronomical events for last, as the waning crescent Moon occults (passes in front of) the planet Venus as seen from North America on Monday, December 7^th.

This is the final of seven naked eye occultations of planets by the Moon in 2015, three of which involve Venus. It’s also the best of the year, well positioned for North America. Continue reading “Astro-Challenge: Watch the Moon Occult Venus in the Daytime”