A Fine Pair of Lunar Occultations for North America This Weekend

Pi Sagittarii moments before it was occulted by the Moon on August 10th, 2011. (Photo by Author).

Heads up, North American residents: our Moon is about to blot out two naked eye stars on Friday and Saturday night.

Such an event is known as an occultation, an astronomical term that has its hoary roots in astronomy’s pseudoscience ancestor of astrology. An occultation is simply when one astronomical body passes in front of another from our line of sight. There’s nothing quite like watching a star disappear on the dark limb of the Moon. In a universe where events often transpire over periods of time longer than a human life span, occultations are abrupt affairs to witness.

Close double stars have also been teased out of occultation data, winking out in a quick, step-wise fashion. If an occultation such as the two this weekend occurs while the Moon is waxing towards Full, we get the added advantage of watching the action on the leading dark limb of the Moon during convenient early evening hours.

Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).
Beta Capricorni on the dark limb of the Moon Saturday night. (Created by the author using Starry Night).

First up is the occultation of the +3.9th magnitude star Rho Sagittarii on Friday night, October 11th. Central conjunction for this occultation occurs at 00:40 Universal Time (UT) early on the morning of the 12th. The Moon will be at a 51% illuminated waxing gibbous phase, having passed First Quarter just prior to the start of the occultation at 7:02 PM EDT/23:02 UT on the 11th. The sunset terminator line at the start of the occultation will bisect the central U.S., and observers east of the Mississippi will get to witness the entire event. The southern graze line will cross Cuba and Guatemala. Note that the Moon will also pass its most southern declination for this lunation just two days prior on October 9th at 23:00 UT/7:00 PM EDT, at a declination of -19.6 degrees.  This is one of the Moon’s most southern journeys for 2013, meaning that it will still ride fairly far to the south in the sky during this weekend’s occultations.

The occultation of Rho Saggitarii by the Moon for the night of October 11th. (rendered using Occult 4.1.02 software).
The occultation of Rho Sagittarii by the Moon for the night of October 11th. the dashed line indicates where the occultation will occur in the daytime; east of this region, the occultation occurs after sunset. (rendered using Occult 4.1.02 software).

Rho Sagittarii is an F-type star 122 light years distant. Stick around until February 23rd, 2046, and you’ll get to see an even rarer treat, when the planet Venus occults the very same star. Just south of the Rho Sagittarii pair lies the region from which the Wow! Signal was detected in 1977.

The Moon moves at an average speed of just over a kilometre a second in its orbit about the Earth, and traverses roughly the apparent distance of its angular size of 30’ in one hour. The duration of occultations as seen from their center line take about an hour from ingress to egress, though its much tougher to watch a star reappear on the bright limb of the Moon!

And the night of Saturday, October 12th finds the 62% illuminated waxing gibbous Moon occulting an even brighter star across roughly the same region. The star is +3.1 magnitude Beta Capricorni, which also goes by the Arabic name of Dabih, meaning “the butcher.”  Dabih is also an interesting double star with a +6th magnitude component 3.5’ away from the +3rd magnitude primary. Dabih is an easy split with binoculars, and it will be fun to watch the two components pass behind the Moon Saturday night. This occultation also occurs the night of October 12th which is traditionally Fall Astronomy Day. If you’re hosting a star party this coming Saturday night, be sure to catch the well-timed occultation of Beta Capricorni! The central conjunction for this event occurs at 01:27 UT on the morning of the 13th, and North American observers east of the Rockies will get to see the entire event.

(Rendered using Occult software).
The occultation footprint of Beta Capricorni for the night of October 12th. (Rendered using Occult software).

Beta Capricorni is 328 light years distant, putting the physical separation of the B component at about a third of a light year away from the primary star at 21,000 astronomical units distant. “Beta B” thus takes about 700,000 years to orbit its primary! It’s also amazing to think that those fusion-born photons took over three centuries to get here, only to be rudely “interrupted” by the bulk of our Moon in the very last second of their journey.

And be sure to keep an eye on the primary star as it winks out, as it’s a known spectroscopic triple star with unseen companions in respective 9 and 1374 day orbits. Dabih may just appear to “hang” on the jagged lunar limb as those close companions wink out in a step-wise fashion.

Both occultations are bright enough to watch with the naked eye, although a standard set of 10x 50 binoculars will provide a fine view. The ingress of an occultation is also an excellent event to catch on video, and if you’ve got WWV radio running audio in the background, you can catch the precise time that the star disappears from your locale.

Note: WWV radio is still indeed broadcasting through the ongoing U.S. government shutdown, though they’re operated by NOAA & the NIST.

The International Occultation and Timing Association is always interested in reports of occultations carried out by amateur astronomers. Not only can this reveal or refine knowledge of close double stars, but a series of occultation observations from precisely known locations can map the profile of the lunar limb.

Be sure to catch both events this U.S. Columbus Day/Canadian Thanksgiving Day weekend, and send those pics in to Universe Today!

Precise timings for the ingress and egress of each lunar occultations for major North American cities can be found at the following pages:

– Rho Sagittarii

– Beta Capricorni

Spectacular Views: The Moon Occults Jupiter

Caption: July 15 2012 occultation, taken with Canon 550D on Newton 200/1200 mounted on NEQ6Pro. Credit: Andrei Juravle

Astrophotographers in Northern Africa, Europe and the Middle East were treated to a beautiful sight in the early morning hours of July 15, 2012. A lunar occultation of Jupiter took place just before dawn, as the waning crescent Moon slid in front of the planet Jupiter. Venus was hanging around nearby, too. Several astrophotographers were able to capture the event, and some got a bonus look at Jupiter’s Galilean moons, as well! Above is a lovely image by Andrei Juravle.

More below!

Caption: The Moon, Venus and Jupiter. Credit Thierry Legault.

Astrophotographer extraordinaire Thierry Legault took this great shot of Venus, Jupiter and the Moon from Saint-Cloud, France with a Canon 5D mark II and 135mm lens. But look closely: the satellites of Jupiter are visible:

Caption: A closer look reveals Jupiter’s moons! Credit: Thierry Legault.

And as always, you should check out Thierry’s website for more incredible images.

Caption: Jupiter and the Moon hover over Dolmabahce Mosque in Istanbul, Turkey. Credit: Rasid Tugral.

Caption: Clouds nearly covered the view in Mombaroccio, Marche, Italy. Credit: Niki Giada.

Caption: A series of images of the Moon’s occultation of Jupiter as seen in Saida, Lebanon. Credit: astroZ1 on Flickr.

Caption: Occultation of Jupiter by the Moon as seen from Smolyan, Bulgaria. Credit: Zlatan Merakov.

More images are still coming in, and you can see more on Universe Today’s Flickr page. Thanks to everyone who submitted their gorgeous images!

Top Astronomy Events Coming Up in 2012

Stargazing Credit: http://twitter.com/VirtualAstro


As 2011 is drawing to a close, the festive season is here and many of us are winding down and looking forward to the holidays. But this is a great time to look ahead to 2012 and pencil into our calendar and diaries the top astronomical events we don’t want to miss next year.

2012 is going to be a great year for astronomy observing, with some rare and exciting things taking place and a good outlook with some of the regular annual events.

So what top wonders should we expect to see and what will 2012 bring?

Conjunction of Venus and Jupiter

Venus & Jupiter Conjunction Credit: Anthony Arrigo UtahSkies.org

On March 15th the Planets Venus and Jupiter will be within 3 degrees and very close to each other in the early evening sky. This will be quite a spectacle as both planets are very bright (Venus being the brightest) and the pair will burn brightly together like a pair of alien eyes watching us after the Sun sets.

This conjunction (where planets group close together as seen from Earth) will be a fantastic visual and photographic opportunity, as it’s not often you get the brightest Planets in our Solar System so close together.

Transit of Venus

Transit of Venus Credit: Australian Space Alliance

For many, the transit of Venus is the year’s most anticipated astronomical event and it takes place on June 5th – 6th. The Planet Venus will pass between the Earth and the Sun and you will see Venus (a small black circle) slowly move across, or “transit” the disc of the Sun.

Transits of Venus are very rare and only a few have been witnessed since the dawn of the telescope. Be sure not to miss this very rare event as the next one isn’t visible for over another 100 years from now in 2117 and the next after that is in 2125.

The full transit of Venus in 2012 will be visible in North America, the northwest part of South America, Western Pacific, North East Asia, Japan, Australia and New Zealand. Other parts of the world will see a partial transit such as observers in the UK, who will only be able to see the last part of the transit as the Sun rises.

First contact will be at 22:09 UT and final contact will be at 04:49 UT

Take note! You have to use the right equipment for viewing the Sun, such as eclipse glasses, solar filters, or projection through a telescope. Never ever look directly at the Sun and never look at it through a normal telescope or binoculars – You will be permanently blinded! The transit of Venus will be a very popular event, so contact your local astronomy group and see if they are holding an event to celebrate this rare occasion.

Meteor Showers

Don't Miss the Major 2012 Meteor Showers Credit: Shooting Star Wallpapers

2011 was a poor year for meteor showers due to the presence of a largely illuminated Moon on all of the major showers; this prevented all but the brightest meteors being seen.

In contrast 2012 brings a welcome respite from the glare of the Moon as it gives little or no interference with this year’s major showers. The only other issue left to contend with is the weather, but if you have clear skies on the evenings of these celestial fireworks, you are in for a treat.

  • The Quadrantid Meteor Shower peak is narrow and just before dawn on January 4th this shower is expected to have a peak rate (ZHR) of around 80 meteors per hour.
  • The Perseid Meteor Shower peak is fairly broad with activity increasing on the evenings of the August 9th and 10th with the showers peak on the morning of the 12th. Perseids are the most popular meteor shower of the year as it tends to be warm and the shower has very bright meteors and fireballs, with rates of 100+ an hour at its peak.
  • The Geminid Meteor Shower is probably the best meteor shower of the year with high rates of slow bright meteors. The peak is very broad and rates of 100+ meteors per hour can be seen. The best time to look out for Geminids is on the evenings of the 12th to 14th December, but they can be seen much earlier or later than the peak.

If you want to find out more and enjoy the meteor showers of 2012, why not join in with a meteorwatch and visit meteorwatch.org

Jupiter and the Moon

Occultation of Jupiter by the Moon on July 15th as seen from Southern England Credit: Adrian West

European observers are in for a very rare treat as the Moon briefly hides the planet Jupiter on the morning of July 15th. This “lunar occultation” can be seen from southern England and parts of Europe at approximately 1:50am UT (dependant on location) and the planet re-emerges from the dark lunar limb at approximately 3:10am UT.

This is a great chance to watch this rare and bright event, and it will also be a fantastic imaging opportunity.

Annular Eclipse

Annular Eclipse Credit: Kitt Peak Observatory

American observers will have treat on May 20th with an annular eclipse of the Sun. The eclipse will be visible from many western US states and a partial eclipse visible from most of North America.

Because the Moon’s orbit is not a perfect circle and is slightly elliptical, it moves closer and further away from us slightly in its orbit by 13% and on July 15th it is at its furthest point away from the Earth as it passes in front of the Sun.

Normally the Moon covers the entire disc of the Sun and creates a total solar eclipse, but because the Moon is at its furthest point in its orbit on the 15th, we get an annular eclipse, where we can still see a ring of bright light around the Sun, but we don’t get totality.

The eclipse starts roughly at 6:20pm local time for the Western US states and lasts for four and a half minutes.

As mentioned earlier; never, ever look at the Sun without proper protection such as eclipse glasses or filters for equipment! This can damage your eyes and permanently blind you. This is the same for cameras; the sensitive chips inside can be damaged.

The World Not Ending

End Of The World

Finally we get to December 21st, in which astronomy-minded folks will celebrate the solstice. But in case you haven’t heard, some have prophesied the end of the world, saying the Mayan calendar ends. This has been the subject of much discussion, comedy and media coverage, and it has even been made into films.

Will the Antichrist press the red button and will there be the Rapture? Will the Earth reverse its magnetic poles, or will we get wiped out by a solar flare, rogue comet or asteroid?

Nope, probably not. You can read our entire series which explains why this whole 2012 end-of-the-world craze is complete hokum.

All I know is 2012 is going to be a great year for astronomy with some very interesting, rare events taking place, with many more regular events to see, as well.

I’m sure it’s not going to end.


Occultation Reveals Distant Kuiper Belt Object is Surprisingly Icy Bright

An artist's rendering of a Kuiper Belt object. Image: NASA
An artist's rendering of a Kuiper Belt object. Image: NASA


How do you study an extremely small planetary body in the dim outer reaches of our solar system? Get all your friends from around the world to wait for a very elusive – if not short-lived – special event. And in doing so, you may find something completely unexpected. Enter James Elliot from MIT, who worked with dozens of observatories and astronomers across the globe, including Jay Pasachoff from Williams College in Massachusetts, in an attempt to make observations of the Kuiper Belt Object 55636, (also known as 2002 TX300) a small body orbiting about 48 AU away from the Sun. Since this KBO is too small and distant for direct observations of its surface, the astronomers tracked and plotted its course, figuring out when it would pass in front of a distant star.

The KBO occulted, or passed in front of a bright background star, an event which lasted only 10 seconds. But in that short amount of time, the astronomers were able to determine the object’s size and albedo. Both of these results were surprising.

55636 was found to be smaller than previously thought, 300km in diameter, but it is highly reflective, meaning it is covered in fresh, white ice.

Most known KBOs have dark surfaces due to space weathering, dust accumulation and bombardment by cosmic rays, so 55636’s brightness implies it has an active resurfacing mechanism, or perhaps that in some cases, fresh water ice can persist for billions of years in the outer reaches of the Solar System.

One graph of the occultation from the Las Cumbres Observatory. Credit: Elliot, et al.

42 astronomers from 18 observatories located in Australia, New Zealand, South Africa, Mexico and the US were part of the observations, but because of weather and timing, only two observatories, both in Hawaii, were able to detect the occultation. Working with Wayne Rosing, Pasachoff coordinated the observations at the Las Cumbres Observatory Global Telescope Network located at Haleakala Crater on Maui, Hawaii, which made the best observations.

But Pasachoff told Universe Today that having two different angles of view to work with provided the ability to make quite precise measurements of the KBO.

“It was absolutely crucial to have the second observation site,” he said. “Without it, we
would not have known where on a round or elliptical body the chord, the line of occultation, passed and we could not have set an upper limit to the size of the body.”

A chord near the edge of a huge body can be vanishingly small, Pasachoff added, illustrating why they needed at least two chords.

Although the surfaces of other highly reflective bodies in the solar system, such as the dwarf planet Pluto and Saturn’s moon Enceladus, are continuously renewed with fresh ice from the condensation of atmospheric gases or by cryovolcanism that spews water instead of lava, 55636 is too small for these mechanisms to be at work.

“The surprising thing in a billion-year-old object that is so reflective is that it maintained or renewed its reflectivity,” said Pasachoff, “so possibilities include the darkening that we know takes place in the inner solar system is much less way out there; or the object renews its ice or frost from inside. We need new observations or more KBO’s with occultations, and we need more theoretical work.”

This was the first successful “planned” observation of a KBO using the stellar occultation method. In 2009 another team scoured through four and a half years of Hubble data to find on occultation of an extremely small KBO 975 meters (3,200 feet) across and a whopping 6.7 billion kilometers (4.2 billion miles) away.

For several years, Pasachoff and his team from Williams College have worked with Elliot and others from MIT, as well as Amanda Gulbis of the South African Astronomical Observatory to study Pluto by occultation. With careful measurements of a star’s brightness as Pluto hides or occults it, they have shown that Pluto’s atmosphere was slightly warming or expanding. A main goal now is to find out how the atmosphere is changing. This will be especially significant with the New Horizons spacecraft en route to Pluto.

Pasachoff said he knew 55636’s albedo would be bright, but was surprised how bright it was. The origins of this object is believed to come from a collision that occurred one billion years ago between one of the three known dwarf planets in the Kuiper Belt, Haumea and another object that caused Haumea’s icy mantle to break into a dozen or so smaller bodies, including 55636.

“Mike Brown (KBO and dwarf planet hunter from Caltech) told me last year, before the observations, that the object would be reflective since it is in the Haumea family, and Haumea itself has a high albedo,” Pasachoff said.

Pasachoff worked with Brown and his team last year in trying to capture the mutual occultations of transits of Haumea with its moon Namaka using the Palomar 5-meter telescope, but they weren’t successful in detecting the extremely small effect, given Haumea’s rapid rotation period.

Elliot used the occultation method to discover the rings of Uranus decades ago and continues to champion the method.

Pasachoff said the recent observation of 55636 was very rewarding. “It was an incredible observation, and I was very pleased to be part of it.” He said. “I am proud that all three of the graphs in the Nature article, and both of the successful observations, were arranged or made by our Williams College team.”

He added that any such observation includes at least these four elements: astrometric predictions, observations, reduction of data, interpretation.

“We were very fortunate and interested in being successful with observations,” Pasachoff said. “But it is important to note that Jim Elliot and his colleagues at MIT and Lowell Observatory have been working for years to refine the methods of predictions to get them accurate enough for this purpose. And this event was the first time that the predictions had been accurate enough to merit the all-out press of telescopes that we assembled. That we picked up the event, near the center of the prediction to boot, is a credit to the astrometry team.”

Note: This article was updated on 6/20.

The team’s paper was published in the journal Nature.

Sources: Williams College,(and email exchange with Jay Pasachoff), MIT, BBC, Nature