Universe Today

October 8, 2013December 23, 2015 by David Dickinson

A Tale of a Lost Moon: Hubble Spies Neptune’s Moons and Its Rings

Neptune's system of moons and rings visualized. Credit: SETI

“That’s no moon…”

-B. Kenobi

But in this case, it is… a lost moon of Neptune not seen since its discovery in the late 1980’s.

A new announcement from the 45^th Meeting of the Division for Planetary Sciences of the American Astronomical Society being held this week in Denver, Colorado revealed the recovery of a moon of Neptune that was only briefly glimpsed during the 1989 flyby of Voyager 2.

The re-discovery Naiad, the innermost moon of Neptune, was done by applying new processing techniques to archival Hubble images and was announced today by Mark Showalter of the SETI institute.

Collaborators on the project included Robert French, also from the SETI Institute, Dr. Imke de Pater of UC Berkeley, and Dr. Jack Lissauer of the NASA Ames Research Center.

The findings were a tour-de-force of new techniques applied to old imagery, and combined the ground-based 10 meter Keck telescope in Hawaii as well as Hubble imagery stretching back to December 2004.

The chief difficulty in recovering the diminutive moon was its relative faintness and proximity to the “dazzling” disk of Neptune. At roughly 100 kilometres in diameter and an apparent magnitude of +23.9, Naiad is over a million times fainter than +8th magnitude Neptune. It’s also the innermost of Neptune’s 14 known moons, and orbits once every 7 hours just 23,500 kilometres above the planet’s cloud tops. Neptune itself is about 49,000 kilometres in diameter, and only appears 2.3” in size from Earth. From our Earthly vantage point, Naiad only strays about arc second from the disk of Neptune, a tiny separation.

“Naiad has been an elusive target ever since Voyager left the Neptune system,” Showalter said in a recent SETI Institute press release. Voyager 2 has, to date, been the only mission to explore Uranus and Neptune.

To catch sight of the elusive inner moon, Showalter and team applied new analyzing techniques which filtered for glare and image artifacts that tend to “spill over” from behind the artificially occulted disk of Neptune.

Other moons, such as Galatea and Thalassa — which were also discovered during the 1989 Voyager 2 flyby — are also seen in the new images. In fact, the technique was also used to uncover the as of yet unnamed moon of Neptune, S/2004 N1 which was revealed earlier this year.

Naiad is named after the band of nymphs in Greek mythology who inhabited freshwater streams and ponds. The Naiads differed from the saltwater-loving Nereids of mythology fame, after which another moon of Neptune discovered by Gerard Kuiper in 1949 was named.

It’s also intriguing to note that Naiad was discovered in a significantly different position in its orbit than expected. Clearly, its motion is complex due to its interactions with Neptune’s other moons.

“We don’t quite have enough observations to establish a refined orbit,” Mr. Showalter told Universe Today, noting that there may still be some tantalizing clues waiting to be uncovered from the data.

I know the burning question you have, and we had as well during the initial announcement today. Is it REALLY Naiad, or another unknown moon? Showalter notes that this possibility is unlikely, as both objects seen in the Hubble and Voyager data are the same brightness and moving in the same orbit. To invoke Occam’s razor, the simplest solution— that both sightings are one in the same object —is the most likely.

“Naiad is well inside Neptune’s Roche Limit, like many moons in the solar system,” Mr. Showalter also told Universe Today. Naiad is also well below synchronous orbit, and is likely subject to tidal deceleration and may one day become a shiny new ring about the planet.

The labeled ring arcs of Neptune as seen in newly processed data. The image spans 26 exposures combined into a equivalent 95 minute exposure, and the ring trace and an image of the occulted planet Neptune is added for reference. (Credit: M. Showalter/SETI Institute). — The labeled ring arcs of Neptune as seen in newly processed data. The image spans 26 exposures combined into an equivalent 95 minute exposure. The ring trace and an image of the occulted planet Neptune is added for reference. (Credit: M. Showalter/SETI Institute).

And speaking of which, the tenuous rings of Neptune have also evolved noticeably since the 1989 Voyager flyby. First discovered from the ESO La Silla Observatory in 1984, data using the new techniques show that the knotted ring segments named the Adams and Le Verrier have been fading noticeably.

“In a decade or two, we may see an ‘arc-less’ ring,” Showalter noted during today’s Division for Planetary Sciences press conference. The two ring segments observed are named after Urbain Le Verrier and John Couch Adams, who both calculated the position of Neptune due to orbital perturbations of the position of Uranus. Le Verrier beat Adams to the punch, and Neptune was first sighted from the Berlin Observatory on the night of September 23^rd, 1846. Observers of the day were lucky that both planets had undergone a close passage just decades prior, or Neptune may have gone unnoticed for considerably longer.

The rings of Neptune as seen from Voyager 2 during the 1989 flyby. (Credit: NASA/JPL).

Neptune has completed just over one 164.8 year orbit since its discovery. It also just passed opposition this summer, and is currently a fine telescopic object in the constellation Aquarius.

Unfortunately, there aren’t any plans for a dedicated Neptune mission in the future. New Horizons will cross the orbit of Neptune in August 2014, though it’s headed in the direction of Pluto, which is currently in northern Sagittarius. New Horizons was launched in early 2006, which gives you some idea of just how long a “Neptune Orbiter” would take to reach the outermost ice giant, given today’s technology.

This represents the first time that Naiad has been imaged from the vicinity of Earth, and demonstrates a new processing technique capable of revealing new objects in old Hubble data.

“We keep discovering new ways to push the limit of what information can be gleaned from Hubble’s vast collection of planetary images,” Showalter said in the SETI press release.

Congrats to Showalter and team on the exciting recovery… what other moons, both old and new, lurk in the archives waiting to be uncovered?

– Read today’s SETI Institute press release on the recovery of Naiad.

-Be sure to follow all the action at the 45th DPS conference in Denver this week!

October 8, 2013December 23, 2015 by Bob King

Observing Alert: Rare Triple Transit Of Jupiter’s Moons Happens Friday Night (Oct. 11-12)

Jupiter with polka dot shadows cast by Io, Europa and Callisto as depicted around 1 a.m. EDT Oct. 12. Watch for the Great Red Spot to come into view during the transit. Created with Claude Duplessis' Meridian software

Talk about a great fall lineup. Three of Jupiter’s four brightest moons plan a rare show for telescopic observers on Friday night – Saturday morning Oct. 11-12. For a span of just over an hour, Io, Europa and Callisto will simultaneously cast shadows on the planet’s cloud tops, an event that hasn’t happened since March 28, 2004.

Who doesn’t remember their first time looking at Jupiter and his entourage of dancing moons in a telescope? Because each moves at a different rate depending on its distance from the planet, they’re constantly on the move like kids in a game of musical chairs. Every night offers a different arrangement.

*Jupiter and its four brightest moons seen in a small telescope. Credit: Bob King*

Some nights all four of the brightest are strung out on one side of the planet, other nights only two or three are visible, the others hidden behind Jupiter’s “plus-sized” globe. Occasionally you’ll be lucky enough to catch the shadow of one of moons as it transits or crosses in front of the planet. We call the event a shadow transit, but to someone watching from Jupiter, the moon glides in front of the sun to create a total solar eclipse.

Since the sun is only 1/5 as large from Jupiter as seen from Earth, all four moons are large enough to completely cover the sun and cast inky shadows. To the eye they look like tiny black dots of varying sizes. Europa, the smallest, mimics a pinprick. The shadows of Io and Callisto are more substantial. Ganymede, the solar system’s largest moon at 3,269 miles (5,262 km), looks positively plump compared to the others. Even a small telescope magnifying around 50x will show it.

Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter's clouds. Credit: John Chumack — *Jupiter on Sept. 24 with its moon Europa (at left) casting a pinhead black shadow on Jupiter’s clouds. Credit: John Chumack*

The three inner satellites – Io, Europa and Ganymede – have shadow transits every orbit. Distant Callisto only transits when Jupiter’s tilt relative to Earth is very small, i.e. the plane of the planet’s moons is nearly edge-on from our perspective. Callisto transits occur in alternating “seasons” lasting about 3 years apiece. Three years of shadow play are followed by three years of shadowless misses. Single transits are fairly common; you can find tables of them online like this one from Project Pluto or plug in time and date into a free program like Meridian for a picture and list of times.

Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede's one) a "quadruple transit" is impossible. Credit: Matma Rex / Wikipedia — Because Io, Europa and Ganymede orbit in a 4:2:1 resonance (Io revolves four times around Jupiter in the time it takes Ganymede to orbit once; Europa completes two orbits for Ganymede’s one) it’s impossible for all three to line up – along with Callsto – for a “quadruple transit”. Credit: Matma Rex / Wikipedia

Seeing two shadows inch across Jupiter’s face is very uncommon, and three are as rare as a good hair day for Donald Trump. Averaged out, triple transits occur once or twice a decade. Friday night Oct. 11 each moon enters like actors in a play. Callisto appears first at 11:12 p.m. EDT followed by Europa and then Io. By 12:32 a.m. all three are in place.

Catch them while you can. Groups like these don’t last long. A little more than an hour later Callisto departs, leaving just two shadows. You’ll find the details below. All times are Eastern Daylight or EDT. Subtract one hour for Central time and add four hours for BST (British Summer Time):

* Callisto’s shadow enters the disk – 11:12 p.m. Oct. 11
* Europa – 11:24 p.m.
* Io – 12:32 a.m.
** TRIPLE TRANSIT from 12:32 – 1:37 a.m.
* Callisto departs – 1:37 a.m.
* Europa departs – 2:01 a.m.
* Io departs – 2:44 a.m.

Looking at Jupiter from high above the plane of the solar system, we can picture better how shadow transits and eclipses happen. Credit: Garrett Serviss from "Pleasures of the Telescope" (annotations: Bob King) — Looking at Jupiter from high above the plane of the solar system in this diagram from more than a century ago, we can better picture how shadow transits and eclipses happen. The tiny disk of Io and the shadow of Ganymede are seen in transit; Callisto is about to be eclipsed by Jupiter’s shadow. Credit: Garrett Serviss from “Pleasures of the Telescope” (annotations: Bob King)

The triple transit will be seen across the eastern half of the U.S., Europe and western Africa. Those living on the East Coast have the best view in the U.S. with Jupiter some 20-25 degrees high in the northeastern sky around 1 a.m. local time. Things get dicier in the Midwest where Jupiter climbs to only 5-10 degrees. From the mountain states the planet won’t rise until Callisto’s shadow has left the disk, leaving a two-shadow consolation prize. If you live in the Pacific time zone and points farther west, you’ll unfortunately miss the event altogether.

From the Eastern Time Zone Jupiter will be well-placed in the eastern sky around the time of mid-transit. Created with Stellarium — *From the Eastern Time Zone Jupiter will be well-placed in the eastern sky during the transit. Created with Stellarium*

Key to seeing all three shadows clearly, especially if Jupiter is low in the sky, is steady air or what skywatchers call “good seeing”. The sky can be so clear you’d swear there’s a million stars up there, but a look through the telescope will sometimes show dancing, blurry images due to invisible air turbulence. That’s “bad seeing”. Unfortunately, bad seeing is more common near the horizon where we peer through a greater thickness of atmosphere. But don’t let that keep you inside Friday night. With a spell of steady air, all you need is a 4-inch or larger telescope magnifying around 100x to spot all three.

The March 28, 2004 triple transit. Shadows from left: Ganymede, Io and Callisto. You can also see the disks of Io (white dot) and Ganymede (blue dot) in this photo taken in infrared light by the Hubble Space Telescope. Credit: NASA/ESA

If bad weather blocks the view, there are two more triple transits coming up soon – a 95-minute-long event on June 3, 2014 starring Europa, Ganymede and Callisto (not visible in the Americas) and a 25-minute show on Jan. 24, 2015 featuring Io, Europa and Callisto and visible across Western Europe and the Americas. That’s it until dual triple transits in 2032.

October 8, 2013December 23, 2015 by Ray Sanders

Book Review: ‘Five Billion Years of Solitude’ by Lee Billings

Over the past few years, the field of astrobiology has made great strides. With missions such as Kepler making exoplanet discoveries commonplace, the question no longer is “Are other planets out there?” but “When will we find a true twin of Earth?”

A new book, “Five Billion Years of Solitude,” takes the reader from the earliest efforts of astrobiology, along with information on how life took hold on Earth, to how we can use that information to help understand how life may flourish on other worlds – all while giving us a glimpse inside the minds of some of the field’s most notable scientists.

Read a Q&A with Billings here.

To say that author Lee Billings tackles only the subject of astrobiology in “Five Years of Solitude” would be selling this book extremely short. While the main focus of the book is life on Earth and the possibility of life elsewhere, readers will find “Five Years of Solitude” incredibly engaging. Combining conversations with such legends like Frank Drake and Sara Seager with in-depth discussions of numerous science topics related to the search for life, Billings has created a book that is not only entertaining, but educational as well.

For those who aren’t well-versed in the details of astrobiology, the casual, “conversational” approach Billings takes to presenting scientific concepts makes for easily digestible reading. While the scientific concepts explained in the book are laid out in good detail, Billings doesn’t present them in an overly dry, or boring manner. Weaving scientific knowledge with interviews from heavy hitters in the world of astrobiology is one of the book’s strongest selling points. The book is both a primer on astrobiology, and a collection of knowlegde from some of the greatest minds in the field.

In the many conversations Billings has with people such as Geoff Marcy, Frank Drake, Sara Seager, and many others, one can get a “feel” for the sometimes insurmountable obstacles scientists face in trying to get their projects approved and funded. Readers will finish “Five Billion Years of Solitude” with a deep appreciation for the miracle of life on Earth, and the hard work and dedication researchers invest in understanding life on Earth, and the possibility of life elsewhere.

Additionally, Billings provides a gold mine of additional materials that readers can dive into if they want to immerse themselves much deeper into the field of astrobiology. If you are interested in the field of Astrobiology, and understanding how life developed on Earth (and possibly elsewhere), you’ll find “Five Billion Years of Solitude” a very engaging book.

Stay Tuned for an interview with the author, Lee Billings, here at Universe Today later this week. ‘Five Billion Years of Solitude” is available now online, and at your local bookstore.

October 8, 2013March 16, 2017 by Fraser Cain

What Color is the Sun?

Ask anyone, “what color is the Sun”? and they’ll tell you the obvious answer: it’s yellow.

But is it really?

Please don’t go check, it’s not safe to look directly at the Sun with your unprotected eyes.

From our perspective it does look a little yellow, especially after sunrise or shortly before sunset,

But don’t be fooled.

If you could travel into space and look at the Sun without going blind, you’d find that it’s actually white, and not yellow.

Using a prism, you can see how sunlight can be broken up into the spectrum of its colors: red, orange, yellow, green, blue, indigo and violet. When you mix all those colors together, you get white.

Here’s the strange part.

If look at all the photons coming in, our star is actually sending the most photons in the green portion of the spectrum,

Our Sun appears yellow to us because of the atmosphere.

Photons in the higher end of the spectrum – blue, indigo and violet – are more likely to be scattered away, while the lower end of the spectrum – red, orange and yellow – are less easily scattered.

Transit of Venus from Japan. 'Japanese fishermen before the 'Great Sun of Hiroshima'. Credit: Niki Gaida — Credit: Niki Gaida

When the Sun is close to the horizon, you’re seeing it distorted by more of the Earth’s atmosphere, scattering away the bluer photons and making it appear red.

When there’s smoke and pollution in the air, it enhances the effect and it will look even redder.

If the Sun is high in the sky, where it has the least amount of atmospheric interference, it will appear more blue.

The Sun, with AR1800 on July 28, 2013. This sunspot poses a slim threat for M-class flares the next few days, NASA says. Credit and copyright: César Cantú. — The Sun. Credit and copyright: César Cantú.

We’re so familiar with the Sun being yellowish-orange, that astronomers will artificially change the color of their images to look more yellowy.

But really, the Sun looks like a pure white ball – especially when you’re out in space.

Interestingly, the color of the Sun is very important to astronomers. They use a technique called spectroscopy to stretch out the spectrum of light coming from a star. Dark lines in this spectrum tell you exactly what it’s made of.

You can see which stars have high amounts of metals, or which are mostly hydrogen and helium, leftover from the Big Bang.

This color also tells you the temperature of the star. Cooler stars are actually redder. Betelgeuse is only 3500 Kelvin. Hotter stars, like Rigel, can get above 10000 Kelvin, and they look blue.

Our own Sun has a temperature of almost 5800 Kelvin, and when viewed outside of our atmosphere, appears white. in colour.

October 8, 2013December 23, 2015 by Elizabeth Howell

‘Diamond’ Super-Earth’s Makeup Called Into Question In New Study

Illustration of 55 Cancri e, a super-Earth that’s thought to have a thick layer of diamond Credit: Yale News/Haven Giguere

A precious planet? Don’t think so fast, a new study says. The so-called “diamond super-Earth“, 55 Cancri e, may actually have a different composition than initially expected.

The team examined previous observations of the system, which is 40 light years from Earth, and said that there is less carbon (or what diamonds are made of) than oxygen in the planet’s star.

“In theory, 55 Cancri e could still have a high carbon to oxygen ratio and be a diamond planet, but the host star does not have such a high ratio,” stated University of Arizona astronomy graduate student Johanna Teske, who led the study.

“So in terms of the two building blocks of information used for the initial ‘diamond-planet’ proposal – the measurements of the exoplanet and the measurements of the star – the measurements of the star no longer verify that.”

Absorption of Light — Image Credit: www.daviddarling.info

The difficulty is it’s not so easy to send a spacecraft to a planet that is so far away from us, so we can’t do any close-up observations of it. This means that astronomers rely on methods such as absorption spectra (looking at what chemical elements absorb light at different wavelengths) of a star to see what it is made of.

The astronomers said there had been only a single oxygen line found in the last study, and they feel that 55 Cancri is cooler than the sun and has more metals into it. This conclusion would imply that the amount of oxygen in the star “is more prone to error.”

There are, however, a lot of moving pieces to this study. How do you know if a planet and star have similar compositions? How to accurately model a planet that you can’t see very well with conventional telescopes? How to best measure chemical abundances from afar? Teske acknowledged in a statement that her work may not be the definitive answer on this planet, so it will be interesting to see what comes out next.

The study has been accepted into the Astrophysical Journal. In the meantime, you can read the preprint version on Arxiv.

Source: University of Arizona

October 8, 2013December 23, 2015 by Elizabeth Howell

Higgs Boson Physicists Receive 2013 Nobel Prize

This is the signature of one of 100s of trillions of particle collisions detected at the Large Hadron Collider. The combined analysis lead to the discovery of the Higgs Boson. This article describes one team in dissension with the results. (Photo Credit: CERN)

That was fast! Just one year after a Higgs Boson-like particle was found at the Large Hadron Collider, the two physicists who first proposed its existence have received the Nobel Prize in Physics for their work. François Englert (of the former Free University of Brussels in Belgium) and Peter W. Higgs (at the University of Edinburgh in the United Kingdom) received the prize officially this morning (Oct. 8.)

The Brout-Englert-Higgs (BEH) mechanism was first described in two independent papers by these physicists in 1964, and is believed to be responsible for the amount of matter a particle contains. Higgs himself said this mechanism would be visible in a massive boson (or subatomic particle), later called the Higgs boson. Check out more information on what the particle means at this past Universe Today article by editor Nancy Atikinson.

“The awarded theory is a central part of the Standard Model of particle physics that describes how the world is constructed. According to the Standard Model, everything, from flowers and people to stars and planets, consists of just a few building blocks: matter particles. These particles are governed by forces mediated by force particles that make sure everything works as it should,” the Royal Swedish Academy of Sciences said in a statement.

The Standard Model describes the interactions of fundamental particles. The W boson, the carrier of the electroweak force, has a mass that is fundamentally relevant for many predictions, from the energy emitted by our sun to the mass of the elusive Higgs boson. Credit: Fermilab

“The entire Standard Model also rests on the existence of a special kind of particle: the Higgs particle. This particle originates from an invisible field that fills up all space. Even when the universe seems empty this field is there. Without it, we would not exist, because it is from contact with the field that particles acquire mass. The theory proposed by Englert and Higgs describes this process.”

A very thrilled CERN (the European Organization for Nuclear Research) noted that the Standard Model theory has been “remarkably successful”, and passed several key tests before the particle was unveiled last year in ATLAS and CMS experiments at the Large Hadron Collider.

Dark matter in the Bullet Cluster. Otherwise invisible to telescopic views, the dark matter was mapped by observations of gravitational lensing of background galaxies. Credit: X-ray: NASA/CXC/CfA/ M.Markevitch et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/ D.Clowe et al. Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.;

“The discovery of the Higgs boson at CERN last year, which validates the Brout-Englert-Higgs mechanism, marks the culmination of decades of intellectual effort by many people around the world,” stated CERN director General Rolf Heuer.

CERN added that the discovery last year was exciting, but the Higgs boson only explains only the matter that we can see. CERN is among the organizations on the hunt for dark matter and energy, forms that can’t be sensed with conventional observatories but can be seen through their effects — such as gravitational lensing.

Sources: CERN, The Royal Swedish Academy of Sciences

October 8, 2013December 23, 2015 by Elizabeth Howell

Tale Of Two Moons Reveals Asteroid’s Insides

Artist's concept of the triple asteroid system: Sylvia (in the center) is surrounded by two moons, Romulus and Remus. Inset: The differentiated interior of Sylvia. Credit: Danielle Futselaar/SETI Institute

Fluffy, with a core of density. That’s what the interior of the asteroid 87 Sylvia likely looks like, astronomers say. The neatest thing about that observation? It didn’t require a drill or even a spacecraft visit. That came from watching the orbits of the asteroid’s two moons, Romulus and Remus.

The discovery illustrates the power of amateur and professional astronomers working together, the team said. On Jan. 6, dozens of small telescopes across France, Greece and Italy were set up to watch a celestial show: watching Sylvia move in front of an eleventh-magnitude star. The professionals received assistance from European Asteroidal Occultations (EURASTER), a group of professional and amateur observers, for this event.

“Observers at different locations see different parts of the asteroid, or its moons, passing in front of the star,” the team stated in a press release. “Such occultations allow exquisitely precise measurements of the relative positions and sizes of the occulting objects.”

Of the 50 observers watching the show, twelve of them saw the occultation, which lasted anywhere from four to 10 seconds depending on where the observers were.

The path of the occultation of 87 Sylvia and an eleventh-magnitude star on Jan. 6, 2013. On the map, Sylvia is represented by a black line, with its path limits marked by blue lines. Its moons -- Romulus and Remus -- are represented by green and orange lines. Credit: IMCCE — The path of the occultation of 87 Sylvia and an eleventh-magnitude star on Jan. 6, 2013. On the map, Sylvia is represented by a black line, with its path limits marked by blue lines. Its moons — Romulus and Remus — are represented by green and orange lines. Credit: IMCCE

Subsequently, the professional astronomers determined how Sylvia is shaped by using that information and combining it with other data, such as recordings of the asteroid’s light variations that happened as it spun, and some direct images using adaptive optics. The team noted that Romulus and Remus don’t seem to change in their paths in space due to Sylvia’s non-circular shape, making them conclude that it has an interior of different materials.

All told, there were 66 adaptive optics observations of the asteroids using 8 to 10 meter telescopes at the W. M. Keck Observatory, the European Southern Observatory, and Gemini North. Calculations of the system came from the Institute of Celestial Mechanics and Ephemerides Calculations (IMCCE) of the Paris Observatory.

The sun sets on Mauna Kea as the twin Kecks prepare for observing. Credit: Laurie Hatch/ W. M. Keck Observatory

“Four observers detected a two-second eclipse of the star caused by Romulus, the outermost moon, at a relative position close to our prediction. This result confirmed the accuracy of our model and provided a rare opportunity to directly measure the size and shape of the moon,” stated Jérôme Berthier, an IMCCE astronomer.

“Combined observations from small and large telescopes provide a unique opportunity to understand the nature of this complex and enigmatic triple asteroid system,” added Francis Marchis, a senior research scientist at the Carl Sagan Center of the SETI Institute, who led the research. “Thanks to the presence of these moons, we can constrain the density and interior of an asteroid, without the need for a spacecraft’s visit. Knowledge of the internal structure of asteroids is key to understanding how the planets of our solar system formed.”

The results were presented yesterday (Oct. 7) at the American Astronomical Society’s division of planetary sciences meeting in Denver.

Source: W.M. Keck Observatory

October 8, 2013December 23, 2015 by David Dickinson

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).

First up is the occultation of the +3.9^th magnitude star Rho Sagittarii on Friday night, October 11^th. Central conjunction for this occultation occurs at 00:40 Universal Time (UT) early on the morning of the 12^th. 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 11^th. 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 9^th 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 23^rd, 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 12^th 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 +6^th magnitude component 3.5’ away from the +3^rd 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 12^th 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 13^th, and North American observers east of the Rockies will get to see the entire event.

The occultation footprint of Beta Capricorni for the night of October 12th. (Rendered using Occult 4.1.0.2 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

October 7, 2013December 23, 2015 by Nancy Atkinson

Astrophoto: Uranus at Opposition

Uranus, imaged from Italy on October 3, 2013, when the planet was at opposition. Credit and copyright: Giuseppe Petricca.

Last week, we asked if you were looking for an observing challenge: looking for planet Uranus when it reached opposition — where it is opposite the Sun the sky, meaning the planet rises as the Sun sets. Giuseppe Petricca from Italy took the challenge and ran with it. His skies over Sulmona, Abruzzo in Italy cleared, and not even 12 hours after the official time of opposition he got this shot using his new Toucam Pro II on a Newtonian 200/1000 on EQ5 unmotorized mount.

Nice!

Want to get your astrophoto featured on Universe Today? Join our Flickr group or send us your images by email (this means you’re giving us permission to post them). Please explain what’s in the picture, when you took it, the equipment you used, etc.

October 7, 2013December 28, 2015 by Fraser Cain

Astronomy Cast Episode 316: Observational Versus Experimental Science

Sometimes you can do science by watching patiently, and sometimes you’ve just got to get your hands dirty with an experiment or two. These two methods have their advantages and disadvantages for revealing Nature’s secrets. Let’s talk about how and why scientists choose which path to go down.

Visit the Astronomy Cast Page to subscribe to the audio podcast!

We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page.