February 26, 2020

Astro-Event: A September Occultation Bonanza.

Jupiter & the Moon the morning of September 8th as seen from Central Florida.

(All graphics unless otherwise noted where created by the author using Starry Night).

I love the term occultation. Use it around the astronomically uninitiated, and it just confirms every suspicion they’ve ever had that you’re REALLY a secret astrologer, further confusing the pseudoscience with astronomy in their minds. I sometimes think that even many astronomers feel a bit odd using the term, as it hints at astronomy’s astrological roots before it became a respectable science.

The weeks of mid-September 2012 give us lots of cause to say the term “occultation” in the sense of one object passing in front of another. You can “occult” the latest sky-high electric bill in an act of astronomical denialism, simply by passing a hand in front of it. The Latin term occultus means “to hide,” so you can kinda see how they went there.

The sky offers something for everyone worldwide in the coming week, whether it’s a lunar, planetary, or asteroid occultation or just a photogenic near miss.

First up is an occultation of Jupiter on September 8th at ~11:00UTC. This will occur just past sunrise for viewers in South America from Ecuador southward; the rest of us will see a less than one degree pass of the pair. The Moon will be 51% illuminated during the event and reaches Last Quarter phase on the same day at 13:15 UTC. What’s interesting is that Jupiter should be bright enough at magnitude -2.4 to spy just above the Moon with binocs or perhaps even the naked eye in the broad daylight.

The path of the occultation of Ceres by the Moon on September 9th.

(Created by the Author using Occult V4.0,9.40).

Then, not even 24 hours later, the 42% illuminated waning crescent Moon occults the +7.7 magnitude asteroid Ceres on its way out of the constellation Taurus. This will be around ~09:00 UTC under dark skies for viewers in Canada, Alaska & most of the CONUS; Florida will see a close pass the morning of September 9th. If you’ve never seen the first asteroid to be discovered on the first day of the 19th century, now is a good time to try. It should be especially visible as it egresses from behind the dark limb of the Moon… perhaps 974 kilometer diameter Ceres will “linger” a bit on the dark limb as it reappears behind the lunar hills, revealing its tiny disk? We’ll get our first good close up look at Ceres when NASA’s Dawn spacecraft, departing Vesta this week, arrives there in 2015.

But wait, there’s more… Pluto & its Moon Charon occult a +14.6 magnitude star on the night of September 8th-9th. The event occurs at 03:04 UTC September 9th and will be visible across the central U.S. and Mexico on a line running east of Arizona to North Dakota. Of course, such an occultation of a distant object is only approximate; this path could shift considerably. Pluto itself isn’t much brighter than said star at magnitude +14.1 in the constellation Sagittarius; expect to have to use a large (8” or bigger) scope under dark skies to catch this one. Still, accurate positioning of Pluto and Charon are high value items with NASA’s New Horizons spacecraft closing in on the system in July 2015; this would be a fun and potentially useful occultation to catch.

The coordinates of Pluto the night of the occultation are;

Right Ascension: 18 Hours 28’ 47”.

Declination: -19° 36’ 37.

Pluto’s rough location in Sagittarius.

Finally, one of the more unusual occultations for this year occurs this month. The +14.8 magnitude asteroid 363 Padua occults the +2.7 magnitude star Zuben El Genubi on the evening of September 16th. The path stretches across the U.S. from the Pacific Northwest through central Florida (and Astroguyz HQ!) across the Atlantic to western Africa; the trouble is, it occurs in broad daylight for all ”under the shadow of the asteroid” except those far flung African climes. Too bad, as this is the brightest star occulted by an asteroid for 2012. There is even a tour to see the event scheduled to head to the Republic of Mali, although it’s unclear at the moment of this writing if this will indeed occur due to current civil unrest. The occultation of Zuben El Genubi 2012 may well go unnoticed… the maximum length is projected to be 2.6 seconds. We may run some experiments to see if it’s possible to track a +2 magnitude star telescopically into the daytime sky (thoughts?) Also designated Alpha Librae, Zuben El Genubi is the “Southern Claw” of the zodiac constellation we now know of as the Scales. In ancient times, Libra was seen as an extension of nearby Scorpius, with Alpha and Beta (Zuben Eschamali) known as the Southern & Northern claws. Alpha Librae is a wide double, with a 5th magnitude companion 231” away in a wide 4800 A.U. orbit; both are 65 light years distant. Zuben El Genubi is also famous for being one of the very few stars in the sky that is purported to exhibit a green tint, for reasons unclear; the magnitude contrast alone shouldn’t induce a strong influence ala the Purkinje Effect. What color do you see?

Mars & Zuben El Genubi on Sept 14th.

A colorful object does lie very near Zuben El Genubi (the name just rolls right off the tongue!) this week in the form of the Red Planet Mars. Mars passes just one degree south of the star on the evening of September 14th, shining magnitude +1.2. Can you squeeze both into the same field at low power?

Be sure to catch some or all of these events worldwide; there’s no shortage of “things-passing-in-front-of-other-things” as seen from our Earthly vantage point. Also, be sure to join us for the first star party of the school year this Saturday September 8th at Starkey Park in New Port Richey, Florida at 8PM EDT! It’s free, and we love nothing more than to discuss/debate/ponder Life, Occultations, and Everything under dark skies!


  1. [...] Alpha Librae) at 20:09 UT, visible from Western Africa and the US in daylight. This is the brightest star to be occulted by an asteroid in [...]

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