regulus occultation Archives

October 12, 2017 by David Dickinson

Tales of the King: Watch as the Moon Occults Regulus for North America This Weekend

The Moon occults Regulus on July 25th, 2017. The Moon also occulted the star shortly after the August 21st total solar eclipse. Credit and copyright; @Shahgazer (Shahrin Ahmad).

Up early Sunday morning? Or perhaps, as we often do, you’re “pulling an all-nighter,” out observing until the break of dawn. Well, the clockwork celestial mechanics of the Universe has a treat in store on the morning of October 15^th, as the waning crescent Moon occults (passes in front of) the bright star Regulus (Alpha Leonis, the “Little King” or “Heart of the Lion”) for the contiguous United States, Mexico and southern Canada.

The visibility footprint for Sunday’s occultation. The white solid lines show where the occultation occurs under dark skies, blue marks twilight, and broken lines represent where the event occurs under daytime skies. Credit: Occult 4.2.

You might call this one the “Great American Occultation,” as it takes a similar track to a certain total solar eclipse and another occultation of the bright star Aldebaran earlier this year. The Moon is a 20% illuminated waning crescent during Sunday’s occultation, about the best phase for such an event, as you’ll also get a nice contrasting Earthshine or Ashen light on dark nighttime limb of the Moon. That’s sunlight from the waxing gibbous Earth, illuminating the (cue Pink Floyd) Dark Side of the Moon.

Moon versus Regulus shortly after Sunday’s occultation as seen from Spring Hill, Florida. Stellarium.

Early morning occultations always see the target star or planet ingress (passing behind) the oncoming bright limb of the waning Moon, then egress (reappearing) from behind its dark limb. During waxing evening occultations, the reverse is true, as the dark limb of the Moon leads the way. The Moon will be 53 degrees west of the Sun during the event, and folks in the western U.S. will see the occultation lower to the eastern horizon under dark skies, while observers from Florida to the Great Lakes will see the event transpire under twilight skies and observers in the U.S. northeast will see the occultation finish up after sunrise. Shining at magnitude +1.4, you’ll be able to see the disappearance and reappearance of Regulus with the unaided eye, though events on the dark limb are always more dramatic. And you may just be able to spy Regulus in the daytime post sunrise near the Moon after the occultation, using binoculars or a telescope.

The northern limit graze line path for Sunday’s occultation. Click here for a Google interactive map. Credit: IOTA

Observers along a line running from Oregon through Lake of the Woods, above the Great Lakes and north of New Brunswick are also in for a treat as you just might be able to catch a rare grazing occultation of Regulus, (see the video below) as the star’s light shines down through those lunar valleys and gets blocked by mountain peaks along the limb of the Moon. Such an event can be quite dramatic to watch, as the star light winks in and out during the very last second of its 79 light year journey.

A look at the occultation circumstances for selected locations tells the story. The International Occultation Timing Association has a full list for locales across North America.

	Ingress	Egress	Moon Alt start/end
Boise, Idaho	9:48 UT	10:03 UT	3 deg / 6 deg
Tuscon, Arizona	(before Moonrise)	10:14 UT	NA / 10 deg
Mexico City, Mexico	9:19 UT	10:06 UT	6 deg / 17 deg
Tampa, Florida	9:24 UT	10:32 UT	23 deg / 39 deg
St. Louis, Missouri	9:29 UT	10:26 UT	18 deg / 29 deg
Boston, Massachusetts	9:50 UT	10:44 UT	36 deg / 45 deg
Toronto, Canada	9:47 UT	10:32 UT	29 / 37 deg

The Moon is in the midst of a cycle of occultations of Regulus running from December 18^th, 2016 to the final one for the cycle on April 24^th, 2018. This is number 12 in a series of 19 events, and the best pre-dawn occultation of Regulus for the United States in the current cycle.

US cloud cover percentages, a few hours before the occultation. Credit: NOAA

The Moon can occult four bright +1^st magnitude stars during the current epoch: Regulus, Antares, Spica and Aldebaran. And though Regulus lies closest to the ecliptic plane, it actually gets occulted the least of any 1^st magnitude star in the 21^st century, with only 220 events. The Moon actually also occulted the bright star Pollux up until almost two millennia ago, and will resume doing so again in the future.

Occultations are easy to observe, and one of the few times (including eclipses) were you can see the motion of the Moon, in real time. The Moon moves its own diameter (30′ or half a degree) per hour, and the reemergence of the bright star will be an abrupt “lights back on” for Regulus. Does it seem to linger a bit between the horns of the crescent Moon? This often reported optical illusion is called the Coleridge Effect, from a line from Samuel Coleridge’s (not Iron Maiden’s) Rime of the Ancient Mariner:

While clome above the Eastern bar

The horned Moon, with one bright star

Almost atween the tips.

Happen to see Regulus “a clome ‘atween the tips?” We also like to refer to this as the ‘Protor and Gamble effect’ due to the company’s traditional star-filled logo.

Occultations also adorn the flags of many Middle Eastern countries. The star and crescent of Islam traces back to antiquity, but was said to have been adapted for the Turkish flag after Sultan Alp Arslan witnessed a close pairing shortly after the Battle of Manzikert on August 26^th, 1071 AD. Though Venus is usually stated as the legendary “star,” Regulus was in fact, just a few degrees away from the Moon on the very same morning… perhaps adding some credence to a major legend vexing vexillology?

The Moon and Regulus on the morning of August 26th, 1071 AD. Stellarium.

Of course, we may never truly know just what Sultan Arsulan saw. A more recent occultation tale was featured in the November 2017 issue of Sky and Telescope, positing the an occultation of Aldebaran by the Moon on March 7^th, 1974 was the source of William Wilkins’ alleged “Volcano on the Moon…” the timing is certainly right, though one wonders how a skilled observer like Wilkins could be fooled by a prominent star (wistful thinking, maybe?)

Recording an occultation is as easy as aiming a video camera at the Moon through a telescope and letting it run. Start early, and make sure you’ve got the contrast between the bright limb of the Moon and the star adjusted, so both appear in the frame. We like to have WWV radio running in the background for an accurate time hack on the video.

Regulus also has a suspected (though never seen) white dwarf companion. Such a star should shine at +12^th magnitude or so… and just might make a very brief appearance on the dark limb of the Moon during egress. One total unknown is its position angle, which is a big wild card, but you just never know… its worth examining that video afterwards, especially if you’re shooting at a high frame rate.

…and speaking of occultations, we’re in the midst of combing through near double occultations of bright stars and planets out to 3000 A.D… hey, it’s what we do for fun. Anyhow, we’re tweeting these out as @Astroguyz as we find ’em, one per day. As a teaser, I give you this grazing occultation of Venus and Regulus over Siberia coming right up in 2025:

The Moon occults Venus and Regulus in 2025. Stellarium.

If nothing else, the cosmic grin of a planet, star and crescent Moon does hint at the Universe’s strange sense of humor.

February 9, 2017February 9, 2017 by David Dickinson

Watch the Moon Make a Pass at Earth’s Shadow, Then Kiss Regulus This Valentine’s Weekend

Regulus Occultion — The Moon occults Regulus of January 15th, 2017. Image credit and copyright: Lucca Ruggiero

In the southern hemisphere this weekend in the ‘Land of Oz?’ Are you missing out on the passage of Comet 45/P Honda-Mrkos-Pajdušáková, and the penumbral lunar eclipse? Fear not, there’s an astronomical event designed just for you, as the Moon occults (passes in front of) the bright star Regulus on the evening of Saturday, January 11th.

The entire event is custom made for the continent of Australia and New Zealand, occurring under dark skies. Now for the bad news: the waning gibbous Moon will be less than 14 hours past Full during the event, meaning that the ingress (disappearance) of Regulus will occur along its bright leading limb and egress (reappearance) will occur on the dark limb. We prefer occultations during waxing phase, as the star winks out on the dark limb and seems to slowly fade back in on the bright limb.

The footprint for the February 11th occultation of Regulus by the Moon. Image credit: Occult 4.2 software

The International Occultation Timing Association has a complete list of precise ingress/egress times for cities located across the continent. An especially interesting region to catch the event lies along the northern graze line across the sparsely populated Cape York peninsula, just north of Cairns.

The northern grazeline for the February 11th occultation of Regulus by the Moon. Graphic by author.

The Moon occults Aldebaran and then Regulus six days later during every lunation in 2017. This is occultation number three in a cycle of 19 running from December 18, 2016 to April 24, 2018. The Moon occults Regulus 214 times in the 21st century, and Regulus is currently the closest bright star to the ecliptic plane, just 27′ away.

We’ve also got a very special event just under 14 hours prior, as a penumbral lunar eclipse occurs, visible on all continents… except Australia. Mid-eclipse occurs at 00:45 Universal Time (UT, Saturday morning on February 11^th), or 7:45 PM Eastern Standard Time (EST) on the evening of Friday, February 10th, when observers may note a dusky shading on the northern limb of the Moon as the Moon just misses passing through the dark edge of the Earth’s inner umbral shadow. Regulus will sit less than seven degrees off of the lunar limb at mid-eclipse Friday night.

How often does an eclipsed Moon occult a bright star? Well, stick around until over four centuries from now on February 22nd, 2445, and observers based around the Indian Ocean region can watch just such an event, as the eclipsed Moon also occults Regulus. Let’s see, I should have my consciousness downloaded into my second android body by then…

A graphic study of the simultaneous lunar eclipse and occultation of Regulus in 2445. Credit: NASA/GSFC/Fred Espenak/Occult 4.2/Stellarium.

We’ll be streaming the Friday night eclipse live from Astroguyz HQ here in Spring Hill, Florida starting at 7:30 PM EST/00:30 UT, wifi-willing. Astronomer Gianluca Masi of the Virtual Telescope Project will also carry the eclipse live starting at 22:15 UT on the night of Friday, February 10th.

This eclipse also marks the start of eclipse season one of two, which climaxes with an annular eclipse crossing southern Africa and South America on February 26th. The second and final eclipse season of 2017 starts with a partial lunar eclipse on August 7th, which sets us up for the Great American Eclipse crossing the United States from coast to coast on August 21st, 2017.

A lunar occultation of Regulus also provides a shot at a unique scientific opportunity. Spectroscopic measurements suggest that the primary main sequence star possesses a small white dwarf companion, a partner which has never been directly observed. This unseen white dwarf may – depending on the unknown orientation of its orbit – make a brief appearance during ingress or egress for a fleeting split second, when the dark limb of the Moon has covered dazzling Regulus. High speed video might just nab a double step occlusion, as the white dwarf companion is probably about 10,000 times fainter than Regulus at magnitude +11 at the very brightest. Regulus is located 79 light years distant.

Our best results for capturing an occultation of a star or planet by the Moon have always been with a video camera aimed straight through our 8” Schmidt-Cassegrain telescope. The trick is always to keep the star visible in the frame near the brilliant Full Moon. Cropping the Moon out of the field as much as possible can help somewhat. Set up early, to work the bugs out of focusing, alignment, etc. We also run WWV radio in the background for an audible time hack on the video.

The January 15th, 2017 occultation of Regulus by the Moon. Image credit and copyright: Lucca Ruggiero.

The best occultation of Regulus by the Moon for North America in 2017 occurs on October 15th, when the Moon is at waning crescent phase. Unfortunately, the occultation of Regulus by asteroid 163 Erigone back in 2014 was clouded out, though the planet Venus occults the star on October 1^st, 2044. Let’s see, by then I’ll be…

Comets and eclipses and occultations, oh my. It’s a busy weekend for observational astronomy, for sure. Consider it an early Valentine’s Day weekend gift from the Universe.

Webcasting the eclipse or the occultation this weekend? Let us know, and send those images of either event to Universe Today’s Flickr forum.

Read about eclipses, occultations and more tales of astronomy in our yearly guide 101 Astronomical Events For 2017, free from Universe Today.

December 12, 2016 by David Dickinson

This Week: Occultations of Aldebaran, Regulus vs. the Supermoon

Aldebaran Occultation — The Moon about to occult Aldebaran on December 23rd, 2015. Image credit and copyright: Paul Campbell.

It’s a busy week for the Moon. While our large solitary natural satellite reaches Full and interferes with the 2016 Geminids, it’s also beginning a series of complex bright star occultations of Aldebaran and Regulus, giving us a taste of things to come in 2017.

First up, here’s the lowdown on this week’s occultation of Aldebaran by the Moon, coming right up tonight:

The 99% illuminated waxing gibbous Moon occults the +0.9 magnitude star Aldebaran on Monday, December 12^th. The Moon is just 19 hours and 30 minutes before reaching Full during the event. Both are located 167 degrees east of the Sun at the time of the event. The central time of conjunction is 4:37 Universal Time (UT). The event occurs during the daylight hours over Hawaii at dusk during Moonrise, and under darkness for Mexico, most of Canada and the contiguous United States. The event also includes the United Kingdom and southwestern Europe at Moonset near early dawn. This is the final occultation of Aldebaran by the Moon for 2016; The Moon will next occult Aldebaran on January 9^th, 2017. This is occultation 26 in the current series of 49, running from January 29^th, 2015 to September 3^rd, 2018.

Moon Gibraltar — The view from Gibraltar just prior to this week’s occultation of Aldebaran by the Moon. Credit: Stellarium.

Four 1^st magnitude stars are along the Moon’s path in the current epoch: Regulus, Aldebaran, Antares and Spica. In the current century, (2001-2100 AD) the Moon occults Aldebaran 247 times, topped only by Antares (386 times) and barely beating out Spica (220 times). The Moon also occults Regulus 220 times this century, and occultations of Spica and Antares resume on May 2024 and July 2023, respectively.

And yes, this Supermoon 3 of 3 for 2016, though actual perigee occurs at 23:28 UT tonight, 39 minutes past our own ’24 hour from Full’ rule. The Moon reaches Full on Wednesday, December 14^th at just past midnight at 00:07 UT. This is also the closest Full Moon to the December 21^st winter solstice next week, and the Full Moon will ride high in the sky this week for northern hemisphere observers on long winter nights.

Keep an eye out for Geminid meteors tonight as well… sure, 2016 may be an off year for this usually spectacular shower, but a few brighter fireballs may still punch through the lunar light pollution.

Clouded out? Be sure to catch the Supermoon action tomorrow night live online starting at 16:00 UT, courtesy of Gianluca Masi and the Virtual Telescope Project.

And there’s more. This coming weekend marks the start of an upcoming new cycle of occultations of Regulus by the Moon. These run right through 2018, as the Moon visits the bright star Regulus five days after crossing the Hyades and occulting Aldebaran for every lunation pass in 2017.

Here’s the specifics for Sunday’s event:

Moon Regulus — The footprint for Sunday’s occultation of Regulus by the Moon. You can find specific ingress and egress times for major cities near you on the IOTA event page. Credit: Occult 4.2.

The 73% illuminated waning gibbous Moon occults the +1.4 magnitude star Regulus on Sunday, December 18^th. The Moon is just four days past Full during the event. Both are located 117 degrees west of the Sun at the time of the event. The central time of conjunction is 18:38 Universal Time (UT). The event occurs during the daylight hours over Tasmania, and under darkness for the southwestern tip of Australia, including Perth. The Moon will next occult Regulus on January 15^th, 2017. This is the first occultation in a new series of nineteen, running from this weekend to April 24^th, 2018.

It’s worth noting that the graze line for Sunday’s occultation of Regulus by the Moon runs just north of the Australian city of Perth and the Perth Observatory… let us know if anyone ‘Down Under’ witnesses the first occultation of Regulus in the new cycle.

Can you spy Regulus’ white dwarf companion? Located 77 light years distant, the Regulus system has at least four components: a B/C pair shining at a combined magnitude of +8, with an apparent separation of 3”, (5,000 AU physical distance in a ~600 year orbit) and an unseen white dwarf companion in a tight 40 day orbit. We know that said white dwarf companion exists from spectroscopic analysis… and it would shine at an easy magnitude +13, were it not near dazzling Regulus shining over 10,000 times brighter. Could this elusive companion turn up just moments before the reappearance of Regulus from behind the Moon? Remember, the dark limb of the Moon leads the way during waxing phases, then trails as the Moon wanes. These and other amazing facts are included in our forthcoming free guide to 101 Astronomical Events to watch out for in 2017.

Regulus occultations — Every occultation of Regulus for the upcoming cycle. Credit: Occult 4.2.

Follow that Moon, and don’t miss these fine astro-events coming to sky above you this week!

March 10, 2014April 26, 2016 by David Dickinson

How to Watch an Asteroid Occult a Bright Star on March 20th

Live in the New York City tri-state area, or anywhere near the path above? One of the most unusual big ticket astronomical events of 2014 occurs on in the morning hours of Thursday March 20th, when the asteriod 163 Erigone “blocks” or occults the bright star Regulus.

This is brightest star to be occulted by an asteroid for 2014, and has a potential to be observed by millions.

Occultations of stars by asteroids are often elusive events, involving faint stars and often occurring over remote locales. Not so with this one. In fact, the occultation of Regulus on March 20^th will result in an “asteroid shadow” passing over viewers across the populous areas of New York and adjoining states in the U.S. northeast before racing into Canada.

And unlike most asteroid occultations, you won’t need any special equipment to detect this event. Shining at magnitude +1.3, Regulus is an easy and familiar naked eye object and is the 22nd brightest star in the sky. And heck, it might be interesting just to catch a view of the constellation Leo minus its brightest star!

Finding Regulus: Looking westward from the New York tri-state region at the time of the occultation. Credit: Stellarium.

Asteroid 163 Erigone shines at magnitude+12.4 during the event. At 72 kilometres in diameter and 1.183 A.U.s distant during the occultation, 163 Erigone was discovered by French astronomer Henri Joseph Perrotin on April 26^th, 1876.

There’s a great potential to learn more not only about 163 Erigone during the event, but Regulus itself. Amateur observations will play a key role in this effort. The International Occultation Timing Association (IOTA) seeks observations from this and hundreds of events that occur each year. Not only can such a precise measurement help to pin down an asteroid’s orbit, but precise timing of the occultation can also paint a “picture” of the profile of the asteroid itself.

Example credit: — An example of an asteroid shape profile created by observers during the occultation of a star by asteroid 55 Pandora in 2007. Each cord represents an observer. Credit- The IOTA.

Regulus also has a faint white dwarf companion, and it’s just possible that it may be spied a fraction of a second before or after the event. Does 163 Erigone have a moon? Several asteroids are now known to possess moons of their own, and it’s just possible that 163 Erigone could have a tiny unseen companion, the presence of which would be revealed by a small secondary event. Observers along and outside the track from Nova Scotia down to Kentucky are urged to be vigilant for just such a surprise occurrence:

Wide map (credit) — A widened map of the March 20th event, noting the span over which an unseen “moon” of 163 Erigone could be potentially observed. Credit: IOTA/Ted Blank/Google Earth.

The maximum duration for the event along the centerline is 14.3 seconds, and the rank for the event stands at 99%, meaning the path is pretty certain.

The shadow touches down on Earth in the mid-Atlantic at 5:53 Universal Time (UT), and grazes the island of Bermuda before making landfall over Long Island New York, New Jersey, Connecticut and northeastern Pennsylvania just after 6:06 UT/2:06 AM EDT. From there, the shadow of the asteroid heads to the northwest and crosses Lake Ontario into Canada before passing between the cities of Ottawa and Toronto just before 6:08 UT. Finally, it crosses out over Hudson Bay and Nunavut before departing the surface of our fair planet at 6:22 UT.

The path is about 117 kilometres wide, and the “shadow” races across the surface of the Earth at about 2.8 kilometres per second from the southeast to the northwest.

Timing an occultation can be accomplished via audio or video recording, though accurate time is crucial for a meaningful scientific observation. The IOTA has a complete explanation of tried and true methods to use for capturing and reporting the event.

We had a chance to catch up with veteran asteroid occultation observer Ted Blank concerning the event and the large unprecedented effort underway to capture it.

He notes that Regulus stands as the brightest star that has been observed to have been occulted by an asteroid thus far when 166 Rhodope passed briefly in front of it on October 19^th, 2005.

“This is the best and brightest occultation ever predicted to occur over a populated area, and that covers the entire 40 years of predictive efforts,” Mr. Blank told Universe Today concerning the upcoming March 20^th event.

The general public can participate in the scientific effort for observations as well.

“We’re trying to make a “picket fence” of thousands of observers to catch this asteroid, so the best thing to do is to go out and observe. If they live anywhere near or in the path, just step outside (or watch from a warm house through a window). Make sure they are looking at the right star,” Mr. Blank told Universe Today. “If they can travel an hour or so to be somewhere in the predicted path, by all means do so – they’ll be home and back in bed well before rush hour starts! Then report what they saw at the public reporting page. If no occultation was seen, report a miss. This is more important that people think, since “miss” observations define the edges of the asteroid.”

There is also a handy “Occultation 1.0” timing app now available for IPhone users for use during the event.

Mr. Blank also plans to webcast the occultation live via UStream, and urges people to check the Regulus2014 Facebook page for updates on the broadcast status, as well as the final regional weather prospects leading up event next week. For dedicated occultation chasers, mobility and the ability to change observing locale at the last moment if necessary may prove key to nabbing this one. One of our preferred sites to check the cloud cover forecast prior to observing any event is the Clear Sky Chart.

This promises to be a historic astronomical event. Thanks to Ted Blank and Brad Timerson at the IOTA for putting the public outreach project together for this one, and be sure not to miss the occultation of Regulus on March 20^th!