After taking us to Comet Catalina's doorstep, the Moon covers Venus in a spectacular daytime occultation visible from most of North and Central America on Monday.

Warm-up Band
The Moon joins Venus prior to the occultation in the company of Comet Catalina (C/2013 US10) just before the start of dawn on December 7th.

Mark your calendars. In less than a week, we're in for a double treat. Before dawn on Monday, December 7, 2015, the crescent Moon parks right next to Venus with Comet Catalina a stone's throw away. From the central United States, the comet lies just 4° northeast of Venus and 5° from the lunar crescent. Hours later, the Moon occults Venus for most of North and Central America and the Caribbean.

With a nearby Moon and the comet currently around magnitude 6, you're not likely to see it with the naked eye, but it will be an easy sight in binoculars from suburban and rural skies. Bonus! Wide-field glasses will corral all three celestial bodies in one field of view.

To make sure you see Catalina, first focus sharply on the Moon then ease it just outside the field of view to the right; now look for a fuzzy spot with a brighter center on the opposite (left) side of the field.

A similar occultation of Venus by the waning crescent Moon happened on August 13, 2012. Compare the brightness intensity of the planet with the comparatively dim crescent.
Bob King

Now go back to bed and get some rest. Or have breakfast and go to work, but don't forget to sneak out for a coffee break shortly that morning or early afternoon (depending on your time zone) when the bright limb of the waning crescent Moon begins to nibble away at the gibbous Venus. It will take about 30 seconds for Venus to "set" behind the Moon, a sight reserved for those with a small telescope or large binoculars. You'll find the Moon about 40° west of the Sun and either in the southwestern sky (from the eastern half of the viewing area) or in the south-southeastern sky (from the western half).

Moon and Venus Phase to Phase at last
Simulated view of the crescent Moon closing in on Venus shortly before the start of Monday's occultation. Venus will be 69% illuminated and 16.6 arcseconds across.

Most of us will either be in school or at work on a Monday, so bring along those binoculars. Finding Venus with the naked eye will be easy thanks to the Moon being so close. Look immediately to the left and a little above (north) of the crescent. Will you be able to see the planet right up to and during occultation? I suspect you will.

Get ready
Simulated view of the start of the December 7th occultation seen from the central U.S. around 11 a.m. CST. The lunar crescent will appear faint at mid-day. Look about 40° or "four fists" to the right (west) of the Sun to find it.

Overall, the Moon will be brighter at magnitude –8.8 versus –4.2 for Venus, but the planet always wins out because of its much higher surface brightness; swaddled in clouds, it makes a far better reflector than the Moon's charcoal-toned dust and rocks. The contrast between them is quite striking to the eye.

Pin-up Poster
Venus is pinned to the edge of the waning crescent moments before the start of the April 22, 2009, occultation. Skywatchers in the far northwestern U.S. and Canada will see Monday's event in a similar dark sky.
Wes Stone

Some lucky skywatchers will get to see the entire event in a dark sky. If you're reading this from northwestern North America including Alaska, Yukon, British Columbia, and the Northwest Territories, that's you! Darkness will add dramatic contrast to the occultation. A low Moon at those far northern latitudes also means abundant celestial-meets-terrestrial landscape photo opportunities. Don't forget an extra set of fresh (warm) batteries.

Occultation Footprint
This color-coded map shows where the Venus-Moon occultation will be visible. Cyan = occultation at moonrise/moonset; red dotted = daytime occultation; blue = twilight occultation and white = nighttime occultation. Click photo for disappearance and reappearance times for many cities in the far northwest where it will be dark.
Occult 4.1

Here are occultation start times and end times (in parentheses), accurate to 1-2 minutes, for 20 U.S. cities on December 7th. Venus disappears at the Moon's bright limb and emerges from behind the dark limb as the Moon travels from west to east across the sky. The Moon will be too low to see emersion from cities in the northeastern U.S. and eastern Canada.

Boston, MA — 12:42 p.m. EST (1:46 p.m.)
Atlanta, GA —12:31 p.m. EST (1:57 p.m.)
Miami, FL —12:51 p.m. EST (2:16 p.m.)
Cleveland, OH —12:29 p.m. EST (1:40 p.m.)
Indianapolis, IN —12:22 p.m. EST (1:39 p.m.)
Jackson, MS —11:21 a.m. CST (12:54 p.m.)
Chicago, IL —11:17 a.m. CST (12:32 p.m.)
Minneapolis, MN —11:03 a.m. CST (12:15 p.m.)
New Orleans, LA —11:24 a.m. CST (12:59 p.m.)
Oklahoma City, OK 10:58 a.m. CST (12:35 p.m.)
Denver, CO — 9:35 a.m. MST (11:12 a.m.)
Billings, MT — 9:24 a.m. MST (10:51 a.m.)
Albuquerque, NM — 9:33 a.m. MST (11:19 a.m.)
Tucson, AZ — 9:23 a.m. MST (11:14 a.m.)
Las Vegas, NV — 8:09 a.m. PST (9:58 a.m.)
Seattle, WA — 7:53 a.m. PST (9:25 a.m.)
San Fransisco, CA — 7:52 a.m. PST (9:37 a.m.)
Los Angeles, CA — 8:03 a.m. PST (9:53 a.m.)
Fairbanks, AK — 6:42 a.m. AKST (7:48 a.m.)
Anchorage, AK — 6:34 a.m. AKST (7:46 a.m.)

Venus by the Slice
Composite image of the daylight occultation of Venus by the waning crescent Moon on August 13, 2012. Taken with a130-mm Astro-Physics refractor and 2× Barlow for f/12 and focal length of 1600 mm, ISO 400, and 1400 second.
Alan Dyer /

Notice how long it takes for Venus to reappear, often more than 90 minutes. There are at least two reasons for this: Venus is also moving east, forcing the Moon to "chase it down," and the Moon is just two days past apogee — the most distant point in its orbit — when it travels at its slowest speed.

Click the image to see the full video of Venus "setting" behind the limb of the Moon during the July 18, 2007, occultation.
Michael Vlasov

To summarize, there are three ways to partake of this eye-catching celestial event: See Venus and the Moon in the company of the comet at daybreak; use the Moon to make a daytime sighting of Venus; or be present at just the right time to witness the occultation.

I know what I want to take — half a day off from work so I can see all three! Clear skies to all on Monday.


Moon Venus


Image of Bruce-McClure


December 2, 2015 at 2:31 pm

Hi Bob.

Just want to double-check. Does the occultation really last for one hour and 50 minutes in Los Angeles (8:03 to 9:53 a.m. PST)? Seems like an extraordinarily long time for a lunar occultation!

Bruce McClure

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December 2, 2015 at 3:09 pm

Bob, I reread your post more carefully and believe I found my answer:

"Notice how long it takes for Venus to reappear, often more than 90 minutes. There are at least two reasons for this: Venus is also moving east, forcing the Moon to "chase it down," and the Moon is just two days past apogee — the most distant point in its orbit — when it travels at its slowest speed."

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Bob King

December 2, 2015 at 10:21 pm

Hi Bruce,
When I was working out the times, I was surprised just like you by the length. I checked and double-checked and then it dawned on me that Venus's motion had to play a part. If you use a planetarium program to speed up the occultation, Venus moves a significant amount. I wasn't satisfied, so I wondered where the moon was in its orbit and discovered the apogee connection. Another factor, which would increase the length of time especially for southern U.S. observers, is how centrally Venus passes behind the moon. It's nearly central for Miami, but considerably north of center from my location in n. Minn.

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December 4, 2015 at 7:15 pm

I'm not sure what counts as a "long" occultation from your perspective, but the fact that it's lunar apogee and the fact that Venus is also moving only increase the duration by about 10% (each).

If we consider only the geocentric motion of the Moon around the Earth, the Moon moves by its own apparent diameter across the celestial sphere, about half a degree, in a bit less than an hour on average. So why do occultations last so much longer than an hour? Primarily it's because of the Moon's changing parallax as it crosses the sky. This is like retrograde motion of the outer planets caused by the Earth's annual motion around the Sun except in this case the cause is the observer's motion as the Earth turns. Like the Moon's orbital motion, the Earth's rotation is counter-clockwise as seen from the north, so observers on the Earth are chasing the Moon's motion. This greatly slows the apparent motion of the Moon across the sky relative to stars and planets, like Venus during this occultation on Monday.

The motion of the Moon relative to the Sun, stars, and planets was once the basis for determining longitude at sea, since that motion was like the hand of a great clock in the sky. The technique was called "longitude by lunar distances" or more often just "lunars". Many mathematicians and mathematically-minded navigators investigating the concept of lunars have been confused for a while by this same slowing of the Moon's motion caused by its parallax. On the face of it, it appears to make the process less accurate, but it all washes out in the end.

Frank Reed

PS: I teach classes on the history and science of "lunars" at Mystic Seaport, one of the world's premier maritime museums, located in Mystic, Connecticut. And I should add that there is a fantastic visiting exhibit from the National Maritime Museum in Greenwich, UK at Mystic Seaport right now (through March) which includes many important artifacts from the early history of "lunars" as well as the chronometers which eventually made lunars un-necessary.

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December 5, 2015 at 12:18 pm

Ah, that tricky parallax! Would love to take your course! So one hour and 50 minutes is not an exceptionally long occultation?

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December 6, 2015 at 5:18 pm

Oh it's certainly a long occultation! 🙂

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December 7, 2015 at 8:11 am

Frank, I take it for granted that all lunar occulations are increased by parallax (Earth's rotation). But what additional factors account for extra-long occulations?

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December 4, 2015 at 6:26 am

Perfect storm? I see also that Venus was at perihelion on November 29!

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December 4, 2015 at 6:45 pm

That doesn't actually have any significance for an occultation. The relative motion of the Earth and Venus and especially the distance from Venus to the Earth are the big factors in the angular rate of motion of Venus across the sky. Also note that the orbit of Venus is almost perfectly circular, so perihelion is a non-event --and actually quite difficult to define for such a circular orbit!

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Stub Mandrel

December 4, 2015 at 4:39 pm

Very envious of you in the, states the occulation will be on the far side of the Earth from me in the UK.

Something odd about the video - it appears to show Venus rising...

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December 6, 2015 at 5:34 pm

Any particular reason why you decided not to include the largest metro area in the country, New York, in your list? It can't still be about the 2011 Super Bowl?

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December 7, 2015 at 8:07 am

The longest lunar occulatations of planets exceed those of stars because planets move with respect to the stars. Because of their eastward movement, lunar occultations of the swifter-moving planets (Mercury, Venus and Mars) can easily last more than 2 hours. No lunar occultation of a star can last that long. From what I have been able to gather, the longest central occulatations occur when the moon is near apogee and quarter phase. All else being equal, the moon's orbital speed is least near the quadratures. Source: Mathematical Astronomy Morsels V by Jean Meeus (pages 129 to 139).

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December 7, 2015 at 12:54 pm

6:20 AM...the Moon and Venus have been playing peek-a-boo with me since around 4:30 AM when they first appeared above the local hillside but beneath scattered clouds. Finally, they are beginning to show well as the sky lightens and the clouds break up. The horizon has some orange in it. The pairing is beautiful. Venus is less than the Moon's width to the right and slightly above the crescent. Viewed with 10x32 IS Nikon binoculars December 7th, HST from Lihue, HI.

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Anthony Barreiro

December 7, 2015 at 3:06 pm

I was hoping to watch this occultation (and also to get a first look at Comet C/2013 US10). One of my coworkers graciously agreed to cover my duties for the morning. But, alas, clouds, fog, and drizzle.

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