A Spectacular Grazing Occultation for Aldebaran at Dawn

aldebaran moon
aldebaran moon
Aldebaran versus the crescent Moon from April 2017, post grazing occultation. Image credit and copyright: frankastro.

An unusual celestial spectacle unfolds for observers around the Great Lakes region next Tuesday at dawn. The Moon has been faithfully occulting (passing in front of) the bright star Aldebaran for every lunation now since January 29th, 2015. These split-second events have touched on nearly every farflung corner of the Earth. Now the United States and Canada get to see the penultimate event, as the waning crescent Moon occults Aldebaran one last time for North America.

Many news outlets are advertising this as the “last occultation of Aldebaran until 2033” which isn’t entirely true: the Moon will occult Aldebaran twice more worldwide, once on August 6th and September 3rd. Both of these events, however, involve a thin crescent Moon and occur over high Arctic climes, so I wouldn’t be surprised if they go unwitnessed by human eyes. The next cycle of Aldebaran occultations then resumes on August 18th, 2033.

July 10th occultation
The footprint for the July 10th occultation of Aldebaran by the Moon. Note that this is a daytime event across the Arctic, except for the tiny lower left corner of the footprint falling over the Great Lakes region at dawn. Credit: Occult 4.2.

Four stars brighter than +1st magnitude lie along the Moon’s celestial path in our current epoch: Antares in Scorpius, Regulus in Leo, Spica in Virgo, and Aldebaran in the eye of Taurus the Bull. Fun fact: this celestial situation is also slowly changing, partly because of the slow 26,000 year-plus long top-like wobble of the Earth’s axis known as the Precession of the Equinoxes, but also because of stellar proper motion, which is slowly bringing stars into and out of the Moon’s path over millennia. For example, until 117 BC, the Moon could also occult Pollux in the constellation of Gemini the Twins.

The circumstances for the July 10 event: The morning of July 10th sees the 11% illuminated, waning crescent Moon meet the +0.9 magnitude star Aldebaran under pre-dawn skies. When the Moon is waning, the bright limb leads the way, covering up the star during ingress and revealing once again during egress. The Moon moves its own half a degree (30 arcminute) diameter once every hour, and how long you’ll see Aldebaran covered up depends on your location. The geographic “sweet spot” for the occultation is eastern Minnesota, northeastern Iowa, northern Wisconsin, Lake Superior, the Upper Peninsula of Michigan, Ontario and northern Quebec… though the farther east you are, the brighter the skies will be, until the occultation begins under dark to twilight dawn skies and ends after sunrise.

Tales from the Graze Line

Folks based along a narrow path running for Iowa, across Wisconsin and Michigan into Ontario and Quebec are in for a very special treat, as Aldebaran just grazes in southern limb of the Moon. Instead of one single wink out, Aldebaran will flash multiple times, as it shines down through the jagged valleys along the limb of the Moon, an amazing sight to witness and catch on video.

Graze line
A close study of the southern graze line for the July 10th event. Credit: IOTA/Google Maps

Here are some times and circumstances for selected cities in the path of the occultation:

Location Ingress Egress Moon altitude Sun altitude Duration
Minneapolis 8:30 8:47 1deg/3deg -16deg/-14deg 17 minutes
Green Bay 8:39 8:40 5deg/5 deg -13deg <1 minute
Thunder Bay 8:32 8:54 5deg/8 deg -12deg/-9 deg 22 minutes
Fort Dodge, Iowa N/A 8:37 0.1 deg -18 deg <1 minute

Notes: all locations listed are in the Central (CDT) time zone (UT-5 for summer time). All times listed are in Universal Time (UT), with the Moon and Sun altitude listed for the beginning and end of the event, rounded to the nearest minute.

Not on the graze line? Well, the rest of us will see a very photogenic near miss on the morning of July 10th… and you might just be able to track Aldebaran up into the daytime sky (make sure you physically block the Sun out of view) if you’ve got clear blue, high contrast skies.

The Moon also occults several fainter stars across the V-shaped Hyades open star cluster around the same time worldwide, as well. One such notable event is the occultation of the +3.7 magnitude star Gamma Tauri for the United Kingdom:

Gamma tauri
The footprint for the July 10th Gamma Tauri event. Credit: Occult 4.2

You can follow the July 10th occultation using nothing more than a Mk-1 eyeball, as you can see both the star and the Moon… though binoculars or a telescope will definitely help, as Aldebaran will be tough to pick out against the bright limb of the Moon. Occultations—especially grazing events—really lend themselves to video astrophotography and are simple to capture through a telescope. Just be sure to balance the exposure setting so you can follow the star all the way up to the bright limb of the Moon.

moon graze
The grazing occultation of Aldebaran on July 10th. The direction of motion for the Moon spans one hour. Credit: Stellarium.

Occultations have inspired those who witnessed them back through pre-telescopic times. A Greek coin from 120 BC may depict an occultation of Jupiter by the Moon. Sultan Alp Arslan was said to have been inspired by a close pairing of Venus and the crescent Moon after the Battle of Manzikert in 1071 AD, adopting the celestial spectacle of the star and crescent which adorns several national flags today.

Also, keep an eye out for an optical illusion described in The Rime of the Ancient Mariner (the poem, not the song by Iron Maiden inspired by the epic tale of the same name), where the protagonist witnesses:

“While clome above the Eastern Bar,

The horned Moon, with one bright Star,

Almost atween the tips.”

This illusion is often referred to as the Coleridge Effect.

Don’t miss this fine occultation of Aldebaran… it’ll be awhile before we see the Moon meet the star again.

-Extra credit: if anyone is planning a live stream of the occultation next Tuesday, let us know.

-The International Occultation Timing Association (IOTA) welcomes observations of any occultations worldwide… in the case of a lunar graze, observations can be used to map out the profile of mountains and valleys along the edge of the Moon.

Catch a Fine Lunar Planetary Grouping This Weekend

Phew! Our eyes and thoughts have been cast so far out into the outer reaches of the solar system following New Horizons and Pluto this week, that we’re just now getting to the astronomical action going on in our own backyard.

You’ll recall that Venus and Jupiter have made a fine pairing in the evening sky since their close approach on July 1st. Despite some of the incredulous ‘Star of Bethlehem’ claims that this was a conjunction that happens ‘once every two thousand years,’ this sort of pairing is actually quite common. In fact, Venus and Jupiter are set to meet up again in the dawn sky later this year on October 25th. Continue reading “Catch a Fine Lunar Planetary Grouping This Weekend”

Conjunctions to Watch For in July

The planets are slowly returning into view this month, bashfully peeking out from behind the Sun in the dawn & dusk sky. This month offers a bonanza of photogenic conjunctions, involving the Moon, planets and bright stars.

The action begins tonight on July 8th, as the waxing crescent Moon joins the planet Venus in the dusk sky. The razor thin Moon will be a challenge on Monday night, as it just passed New on the morning of the 8th at 3:14AM EDT/7:14 Universal Time (UT). The record for spotting the thin crescent with the naked eye currently stands at 15 hours and 32 minutes, completed by Stephen O’Meara on May 1990. Binoculars help considerably in this endeavor.  Wait until 15 minutes after local sunset, and then begin patiently sweeping the horizon.

Mr. Thierry Legault completed an ultimate photographic challenge earlier today, capturing the Moon at the precise moment of  New phase!

The Moon & Venus on the evening of July 9th from latitude 30 degrees north, about 30 minutes after sunset. (Created by the author using Stellarium).
The Moon & Venus on the evening of July 9th as seen from latitude 30 degrees north, about 30 minutes after sunset. (Created by the author using Stellarium).

This week  marks the start of lunation 1120. The Moon will be much easier to nab for observers worldwide on Tuesday night, July 9th for observers worldwide. The sighting of the waxing crescent Moon will also mark the start of the Muslim month of Ramadan for 2013. Due to the angle of the ecliptic in July, many northern hemisphere observers may not spot the Moon until Wednesday night on July 10th, about 6.7 degrees south west of -4.0 magnitude Venus.

Did you know? There are Guidelines for the Performance of Islamic Rites for Muslims aboard the International Space Station. It’s interesting to note that the timing of the rituals follows the point from which the astronaut originally embarked from the Earth, which is exclusively the Baikonur Cosmodrome in Kazakhstan for the foreseeable future of manned spaceflight.

Malaysia’s first astronaut, Sheikh Muszaphar Shukor observed Ramadan aboard the International Space Station in 2007.

From there, the crescent Moon fattens, meeting up with Saturn and Spica on the evenings of July 15th and 16th. The Moon will actually occult (pass in front of) the bright star Spica on the evening of July 15/16th at ~3:33UT/11:33PM EDT (on the 15th) for observers in Central America and western South America. The rest of us will see a near miss worldwide.

The waxing crescent Moon nearing Spica on the evening of the 15th at 10PM EDT. The Moon reaches 1st Quarter on the same evening at 11:18PM EDT. (Created by the author using Starry Night).
The waxing crescent Moon nearing Spica on the evening of the 15th at 10PM EDT. The Moon reaches 1st Quarter phase on the same evening at 11:18PM EDT. (Created by the author using Starry Night).

This is the 13th in a cycle of 18 occultations of Spica by our Moon spanning 2012-2013. Spica is one of four stars brighter than magnitude +1.4 that lie close enough to the ecliptic to be occulted by our Moon, the others being Antares, Regulus and Aldebaran. Saturn will lie 3 degrees from the Moon on the evening of July 16th.

Can you nab Spica and Saturn near the Moon with binoculars in the daytime around the 15th? It can be done, using the afternoon daytime Moon as a guide. Crystal clear skies (a rarity in the northern hemisphere summertime, I know) and physically blocking the Sun behind a building or hill helps.

The waxing gibbous Moon will also occult +2.8 Alpha Librae for South Africa on July 17th around 17:09UT & +4.4th magnitude Xi Ophiuchi for much of North America on the night of July 19th-20th.

And speaking of Regulus, the brightest star in the constellation Leo lies only a little over a degree (two Full Moon diameters) from Venus only the evenings of July 21st & the 22nd. 77.5 light years distant, Regulus is currently over 100 times fainter at magnitude +1.4. Can you squeeze both into the field of view of your telescope at low power? Venus’s mythical ‘moon’ Neith lives!

Venus can even occult Regulus on rare occasions, as last occurred on July 7th, 1959 and will happen next on October 1st, 2044.

But there’s morning action afoot as well. The planets Mars and Jupiter have emerged from solar conjunction on April 18th and June 19th, 2013 respectively, and can now be seen low in the dawn skies about 30 minutes before sunrise.

Mars and Jupiter in a close conjunction on the morning of July 22nd, about 30 minutes before sunrise as seen from latitude 30 degrees north. (Created by the author using Starry Night).
Mars and Jupiter in a close conjunction on the morning of July 22nd, about 30 minutes before sunrise as seen from latitude 30 degrees north. (Created by the author using Starry Night).

Mars approaches Jupiter in the dawn until the pair is only 0.79 degrees (about 48 arc minutes) apart on Monday, July 22nd. Mars shines at magnitude +1.6 and shows a tiny 3.9” disk, while Jupiter displays a 32.5” disk shining at magnitude -1.9 on this date. Conjunction occurs at about 7:00 UT/3:00 AM EDT, after which the two will begin to race apart. Mercury is visible beginning its morning apparition over 5 degrees to the lower right of the pair (see above).

Jupiter will reach opposition and reenter the evening sky on January 5th, 2014, while Mars won’t do the same until April 8th of next year. Weird factoid alert: neither Jupiter or Mars reach opposition in 2013! What effect does this have on terrestrial affairs? Absolutely none, well unless you’re a planetary imager/observer…

Mars also reaches its most northern declination of 2013 of 24 degrees in the constellation Gemini on July 16th at 7:00 AM EDT/11:00 UT.  Mars can wander as far as declination 27 degrees north, as last happened in 1993.

Finally, are you observing from southern Mexico this week and up for a true challenge? The asteroid 238 Hypatia occults a +7.4 magnitude star from 10:13-10:49 UT on July 10th in the constellation Pisces for up to 29 seconds. This event will be bright enough to watch with binoculars- check out our best prospects for asteroid occultations of stars in 2013 here and here.

Good luck, clear skies, and be sure to post those astro-pics in the Universe Today’s Flickr community!