Observing Archives

March 6, 2013December 23, 2015 by Nancy Atkinson

Rare Eclipsing Binary Stars Provide Refined Measurements in the Universe

The Large Magellanic Cloud, a neighboring galaxy to the Milky Way. The positions of eight faint and rare cool eclipsing binary stars are marked with crosses. Credit: ESO/R. Gendler

Precise observations of a rare class of binary stars have now allowed a team of astronomers to improve the measurement of the distance to one of our neighboring galaxies, the Large Magellanic Cloud, and in the process, refine the Hubble Constant, an astronomical calculation that helps measure the expansion of the Universe. The astronomers say this is a crucial step towards understanding the nature of the mysterious dark energy that is causing the expansion to accelerate.

The team used telescopes at ESO’s La Silla Observatory in Chile, the Las Campanas Observatory also in Chile and two from the University of Hawaii at Manoa, and the Las Campanas Observatoryas well as others around the globe. These results appear in the 7 March 2013 issue of the journal Nature.

The new distance to the LMC is 163,000 light-years. The LMC is not the closest galaxy to the Milky Way; Canis Major Dwarf Galaxy, discovered in 2003 is considered the actual nearest neighbor at 42,000 light-years from the Galactic Center, and the Sagittarius Dwarf Elliptical Galaxy is about 50,000 light-years from the core of the Milky Way.

Astronomers ascertain the scale of the universe by first measuring the distances to close-by objects and then using them as standard candles — objects of known brightness — to pin down distances farther and farther out in the universe.

Up to now, finding an accurate distance to the LMC has proved elusive. Stars in that galaxy are used to fix the distance scale for more remote galaxies, so it is crucially important.

“This is a true milestone in modern astronomy. Because we know the distance to our nearest neighbor galaxy so precisely, we can now determine the rate at which the universe is expanding — the Hubble constant — with much better accuracy. This will allow us to investigate the physical nature of the enigmatic dark energy, the cause of the accelerated expansion of the universe,” says Dr. Rolf-Peter Kudritzki, an astronomer at the University of Hawaii’s Institute for Astronomy.

“For extragalactic astronomers,” said Dr. Fabio Bresolin, also from UH, “the distance to the Large Magellanic Cloud represents a fundamental yardstick with which the whole universe can be measured. Obtaining an accurate value for it has been a major challenge for generations of scientists. Our team has overcome the difficulties using an exquisitely accurate method, and is already working to cut the small remaining uncertainty by half in the next few years.”

The team worked out the distance to the LMC by observing rare close pairs of stars known as eclipsing binaries. As these stars orbit each other, they pass in front of each other. When this happens, as seen from Earth, the total brightness drops, both when one star passes in front of the other and, by a different amount, when it passes behind.

Read another recent article about studies that used eclipsing binaries to study the Light-travel-time Effect

By tracking these changes in brightness very carefully, and also measuring the stars’ orbital speeds, it is possible to work out how big the stars are, what their masses are, and other information about their orbits. When this is combined with careful measurements of the total brightness and colors of the stars, remarkably accurate distances can be found.

“Now we have solved this problem by demonstrably having a result accurate to 2%,” states Wolfgang Gieren (Universidad de Concepción, Chile) and one of the leaders of the team.

Sources: University of Hawaii, ESO

March 5, 2013December 23, 2015 by Bob King

Comet PANSTARRS Crosses Paths With Zodiacal Light

The tapering wedge of the zodiacal light reaches from the western horizon on March 3, 2013 toward the bright Planet Jupiter at top. Credit: Bob King

With the much-anticipated PANSTARRS comet emerging into the evening sky this week, we might keep our eyes open to another sight happening at nearly the same time. If you live where the sky to the west is very dark, look for the zodiacal light, a tapering cone of softly-luminous light slanting up from the western horizon toward the bright planet Jupiter near twilight’s end.

It makes its first appearance about 75 minutes after sunset and lingers for an hour and a half. Sunlight reflected from countless dust particles shed by comets and to a lesser degree by colliding asteroids is responsible for this little-noticed phenomenon. Comets orbiting approximately in the plane of the solar system between Jupiter and the sun are its key contributors. Jupiter’s gravity stirs the works into a pancake-like cloud that permeates the inner solar system.

The zodiacal is formed of dust left behind by comets orbiting between Jupiter and the sun and forms a pancake-like structure in the plane of the planets. Illustration: Bob King

More of us would be more aware of the zodiacal light if we knew better when and where to look. While a dark sky is essential, you don’t have to move to the Atacama Desert. I live 9 miles from a moderate-sized, light-polluted city; the western sky is terrible but the east is plenty dark and ideal for watching the morning zodiacal light in the fall months.

Near its base, the cone easily matches the summer Milky Way in brightness and spans about two fists held horizontally at arm’s length. At first glance you’d be tempted to think it was the lingering glow of twilight until you realize it’s nearly two hours after sunset. The farther you follow up the cone, the fainter and narrower it becomes. From top to bottom the light pyramid measures nearly five fists long. In other words, it’s HUGE.

The pyramid-shaped zodiacal light cone is centered on the same path the sun and planets take across the sky called the ecliptic. This map shows the sky 90 minutes after sunset in early March facing west. Created with Stellarium — The pyramid-shaped zodiacal light cone is centered on the same path the sun and planets take across the sky called the ecliptic. This map shows the sky facing west 90 minutes after sunset in early March. Created with Stellarium

The zodiacal light is centered on the same path the sun and planets take through the sky called the ecliptic, an imaginary circle that runs through the familiar 12 constellations of the zodiac. Every spring, that path intersects the western horizon at dusk at a steep angle, tilting the light cone up into clear view. A similar situation happens in the eastern sky before dawn in October. Of course the light’s there all year long, but we don’t notice it because it’s slanted at a lower angle and blends into the hazy air near the horizon.

The zodiacal light we see at dusk is a portion of the larger zodiacal dust cloud that extends at least to Jupiter’s distance (~500 million miles) on either side of the Sun, making it the single biggest thing in the Solar System visible with the naked eye. Under exceptional skies, like those found on distant mountaintops or far from city lights, the cone tapers into the zodiacal band that completely encircles the sky.

The gegenschein is the small, oval glow within the zodiacal band seen in this photo taken at the European Southern Observatory in Chile. Credit: ESO / Yuri Beletsky

Exactly opposite the sun around local midnight, you might see an enhancement in the band called the gegenschein (GAY-gen-shine). This eerie oval glow is caused by sunlight shining directly on interplanetary dust grains and then back to your eye. A similar boost happens for the same reason at the time of full moon.

Deep connections abound throughout the universe. Over time, much of the comet dust in the zodiacal cloud either spirals inward toward the sun or gets pushed outward by solar radiation. The fact that we can still see it today means it’s continually being replenished by the silent comings and goings of comets.

Comet C/2011 L4 PANSTARRS photographed with a 200mm telephoto lens over Bridgetown, Western Australia on March 3. Credit: Jim Gifford — Comet C/2011 L4 PANSTARRS photographed with a 200mm telephoto lens over Bridgetown, Western Australia on March 3.
Credit: Jim Gifford

Consider Comet L4 PANSTARRS. Dribs and drabs of dust sputtered from this comet during its current trip to the inner solar system may find their way into the zodiacal cloud to secure its presence for future sky watchers. How wonderful then the comet and the ghostly light should happen to be at their best the very same time of year.

Zodical light touching the Seven Sisters star cluster also known as the Pleiades March 19, 2012. Credit: Bob King

Now through March 13 is the ideal time for zodiacal light viewing. If you begin your evening with Comet PANSTARRS, stick around until nightfall to spot the light. Face west and cast a wide view across the sky, sweeping your gaze from left to right and back again. Look for a big, hazy glow reaching from the horizon toward the Planet Jupiter. After the 13th, the waxing moon will wash out the subtle light cone for a time. Another “zodiacal window” opens up in late March through mid-April when the moon comes up too late to spoil the view.

As you take in the sight, consider how something as small as a dust mote, when teamed with its mates, can create a jaw-dropping comet’s tail, meet its end in the fiery finale of a meteor shower or span a billion miles of space.

March 5, 2013December 23, 2015 by David Dickinson

Why This Weekend is Perfect for a Messier Marathon

To 'scopes, get set, marathon! (A homemade 14" Gregorian reflector, photo by author).

This coming weekend presents the first window for 2013 to complete a challenge in the realm of backyard astronomy and visual athletics. With some careful planning, persistence, and just plain luck, you can join the vaunted ranks of those seasoned observers who’ve seen all 110 objects in the Messier catalog… in one night.

Observing all of the objects in Messier’s catalog in a single night has become a bit of a sport over the last few decades for northern hemisphere observers, and several clubs and organizations now offer certificates for the same. The catalog itself was a first attempt by French astronomer Charles Messier to catalog the menagerie of “faint fuzzies” strewn about the northern hemisphere sky.

Not that Charles knew much about the nature of what he was seeing. The modern Messier catalog includes a grab bag collection of galaxies, nebulae, open and globular clusters and more down to magnitude +11.5, all above declination -35°. Charles carried out his observations from Paris France at latitude +49° north. Unfortunately, this also means that Messier catalog is the product of Charles Messier’s northern-based vantage point. The northernmost objects in the catalog are Messiers 81 & 82 at declination +69°, which never get above the horizon for observers south of latitude -21°. His initial publication of the catalog in 1774 contained 45 objects, and his final publication contained 103, with more objects added based on his notes after his death in 1817. (Fun fact: Messier is buried in the famous Père Lachaise Cemetery in Paris, site of other notable graves such as those of Chopin and Jim Morrison).

M51, the Whirlpool Galaxy, one of the more photogenic objects in the Messier catalog. (Credit: NASA/Hubble Heritage Project).

There’s a fair amount of controversy on Messier’s motivations and methods for compiling his catalog. The standard mantra that will probably always be with us is that Messier was frustrated with stumbling across these objects in his hunt for comets and decided to catalog them once and for all. He eventually discovered 13 comets in his lifetime, including Comet Lexell which passed only 2.2 million kilometres from Earth in 1770.

No one is certain where the modern tradition of the Messier Marathon arose, though it most likely had its roots in the amateur astronomy boom of the 1970s and was a fixture of many astronomy clubs by the 1980s. There are no Messier objects located between right ascension 21 hours 40 minutes and 23 hours 20 minutes, and only one (M52) between 23 hours 20 minutes and 0 hours 40 minutes. With the Sun reaching the “0 hour” equinoctial point on the March Vernal Equinox (falling on March 20^th as reckoned in Universal Time for the next decade), all of the Messier objects are theoretically observable in one night around early March to early April. Taking into account for the New Moon nearest to the March equinox, the best dates for a weekend Messier marathon for the remainder of the decade are as follows;

Optimal Messier marathon dates for the remainder of the decade. (Compiled by author).

Note that this year’s weekend is very nearly the earliest that it can occur. The optimal latitude for Messier marathoning is usually quoted as 25° north, about the latitude of Miami. It’s worth noting that 2013 is one of the very few years where the primary weekend falls on or before our shift one hour forward to Daylight Saving time, occurring this year on March 10^th for North America.

Students of the Messier catalog will also know of the several controversies that exist within the list. For example, one wide double star in Ursa Major made its way into the catalog as Messier 40. There’s also been debate over the years as to the true identity of Messier 102, and most marathoners accept the galaxy NGC 5866 in its stead. Optics of the day weren’t the most stellar (bad pun intended) and this is evident in the inclusion of some objects but the omission of others. For example, it’s hard to imagine a would-be comet hunter mistaking the Pleiades (M45) for an icy interloper, but curiously, Messier omits the brilliant Double Cluster in Perseus.

M42, the Orion Nebula. (Photo by Author, taken back in the days of ye ole film!)

It’s vital for Messier marathoners to run through objects in proper sequence. Most visual observers run these in groups, although Alex McConahay suggests in a recent April 2013 Sky & Telescope article that folks running a photographic marathon (see below) beware of wasting precious time crossing the celestial meridian (a maneuver which requires a telescope equipped with a German Equatorial mount to “flip” sides) hunting down objects. The unspoken “code of the skies” for visual Messier marathoners is that “Go-To” equipped scopes are forbidden. Part of the intended purpose of the exercise is to acquaint you with the night sky via star hopping to the target.

Most observers complete Messier objects in groups. You’ll want to nab M77 and M74 immediately after local dusk, or the marathon will be over before it starts. You’ll then want to move over to the Andromeda Galaxy and the collection of objects in its vicinity before scouring Orion and environs. From that point out, you can begin to slow down a bit and pace yourself through the galaxy groups in Coma Berenices and the Bowl of Virgo asterism. Another cluster of objects stretch out in the sky past midnight along the plane of our Milky Way Galaxy from Sagittarius to Cygnus, and the final (and often most troublesome) targets to bag are the Messier objects in Aquarius and M30 in Capricornus just before dawn. Remember, dark skies, warm clothes, and hot coffee are your friends in this endeavor!

There have been alternate rules or versions of Messier marathons over the years. Some imagers complete one-night photographic messier marathons. There are even abbreviated or expanded versions of the feat. It is also possible to nab most of the Messier catalog with a good pair of binoculars under clear skies. Probably the most challenging version we’ve heard of is sketching all 110 Messier objects in one evening… you might be forgiven for using a Go-To enabled telescope to accomplish this!

Finally, just like running marathons, the question we often get is why. Some may eschew transforming the art of dark sky observing into a task of visual gymnastics. We feel that to run through this most famous of catalogs in an evening is a great way to learn the sky and practice the fast-disappearing art of star hopping. And hey, no one’s saying you can’t take a year or three to finish the Messier catalog… its a big universe, and the New General Catalog (NGC) and Index Catalog (IC) containing thousands of objects will still be waiting. Have YOU seen all 110?

– A perpetual listing of Messier marathon visibility by latitude by Tom Polakis.

– An All Sky Map of the Messier catalog.

– A handy priority list for a Messier marathon compiled by Don Machholz.

February 27, 2013December 23, 2015 by Nancy Atkinson

Losing the Night: New Video Highlights Problems of Light Pollution

Air glow (along with a lightning sprite) is visible in this image from the International Space Station. Credit: NASA

Light pollution is a two-way murky street. Not only have millions of people never seen the glow of our Milky Way in the night sky because of light pollution, but also when astronauts in the International Space Station look down at Earth, they see lights almost everywhere and a faint green or yellow air-glow — caused mostly by light pollution — hovers over the planet in a majority of the images they send back from space.

“Light pollution threatens the health of every living thing on Earth,” says a new planetarium-like video from the International Dark-Sky Association in collaboration with Loch Ness Productions, a U.S.-based full-dome planetarium show production company.

“Losing the Dark” illustrates problems caused by light pollution, with particular emphasis on how it affects night-sky visibility. But the video also offers simple solutions for mitigating light pollution, and reminds everyone it is not too late to save the starry sky.

Bob Parks, IDA Executive Director said, “Everyone who views ‘Losing the Dark’ can see how easy it is to make wise choices about outdoor lighting, and that together we can work to restore the night sky to its former glory.”

The video is narrated by astronomer Carolyn Collins Petersen, (whose voice you may recognize from past 365 Days of Astronomy podcasts), and the show is also available in full-dome versions for planetariums and science centers as a public service announcement.

“Planetariums champion the night sky already,” Collins Petersen said. “They tap into public awareness, so their audiences are a prime demographic for this message. The show gives planetarium professionals another tool to help educate the public about this critical issue. The HD version extends the message to more people through presentations by educators and dark-sky advocates.”

For more information about the video, see the International Dark Skies Association website.

February 25, 2013April 26, 2016 by David Dickinson

Light-travel-time Effect Finds New Astronomical Applications

Io and Jupiter as seen by New Horizons during its 2008 flyby. (Credit: NASA/Johns Hopkins University APL/SWRI).

Sometimes the tried and true methods are still the best, even in observational astronomy. Researchers at the University of Prague demonstrated this recently in a study of the eclipsing binary system V994 Herculis (V994 Her).

Researchers P. Zasche and R. Uhla used a method known as the Light-travel-time Effect to verify that V994 Her is actually a double binary. If that method sounds familiar to any astronomy historians out there, that’s because it was first used by 17^th century astronomers to gauge the speed of light.

V994 Her is a rarity in the skies. While many eclipsing binaries are known, V994 Her is one of only six quadruple eclipsing binary stars discovered. An eclipsing binary star is a system where the two stars pass one in front of the other from our line of sight. Although too close to be split visually, eclipsing binaries rise and fall in brightness periodically. One famous example is the star Algol (Beta Persei) in the constellation Perseus. Algol means the “Demon Star” in Arabic, which suggests that its curious nature was known to Arab astronomers in pre-telescopic times.

Continue reading “Light-travel-time Effect Finds New Astronomical Applications”

February 22, 2013April 26, 2016 by David Dickinson

Comet PANSTARRS: How to See it in March 2013

Comet 2011 L4 PanSTARRS imaged from Argentina by Luis Argerich on February 13th, 2013. (Credit: Luis Argerich - Nightscape photography. Used with Permission).

Great ready. After much anticipation, we could have the first naked eye comet of 2013 for northern hemisphere observers in early March. As discussed earlier this week on Universe Today, 2013 may well be the Year of the Comet, with two bright comets currently putting on a show in the southern hemisphere and comet C/2012 S1 ISON set to perform the closing cometary act of 2013. But while comet C/2012 F6 Lemmon won’t be visible for northern hemisphere residents until April, Comet C/2011 L4 PanSTARRS (which we’ll refer to simply as “Comet PanSTARRS” from here on out) may well become a fine early evening object in the first two weeks of March.

That is, if it performs. Comets are often like cats. Though we love posting pictures of them on the Internet, they often stubbornly refuse to perform up to our expectations. Some comets have been solid performers, like Hale-Bopp in 1997. Others are often promoted to great fanfare like Comet Kohoutek in 1973-74, only to fizzle and fade into notoriety.
Continue reading “Comet PANSTARRS: How to See it in March 2013”

February 20, 2013April 26, 2016 by David Dickinson

In Search of Darkness: the Battle Against Light Pollution

Where the dark skies are (and aren't). NASA image in the Public Domain courtesy of Marc Imhoff, Craig Mayhem & Robert Simon (NASA/GSFC) Christopher Elvidge(NOAA).

A good majority of modern Americans have never seen truly dark skies. I was fortunate to grow up in northern Maine in the 1970s with skies dark enough to see the summer Milky Way right from my doorstep. For most of the Eastern Seaboard of the United States, this is no longer the case. During the blackout brought on by Hurricane Sandy over the tri-state area in 2012 and after Hurricane Andrew hit Miami in 1992, many urbanites got to see an unfamiliar sight first hand; a dark night sky. There were even calls to 9/11 reporting fires on the horizon, which were in fact the Milky Way!

Do your skies look like this? (Photo by Author). — Do your skies look like this?
(Photo by Author).

In just over two weeks time on March 10^th, most of North America will “spring forward” once again to daylight savings time; three weeks afterwards on March 31^st, the European Union will follow suit.

For astronomers, this means waiting until the later evening hours for total darkness and late start times for star parties. If it seems like we spend more of the year on daylight savings time, we in fact do; the Energy Policy Act of 2005 mandates that daylight savings for most of the U.S. (a majority of Arizona is a staunch hold out) now starts on the second Sunday of March and runs until the first Sunday of November, or about 65% of the year. But discussions of DST’s utility or anachronism aside, it puts just one more hurdle between astronomers and what they love: dark skies.

Does your observatories' night sky look like this? (Photo by Author). — Observatory versus light pollution. (Photo by Author).

You can’t even see your hand in front of your face under truly dark skies. Such darkness is measured on what’s known as the Bortle Scale, with 1 being dark enough to notice air glow and phenomena like the Gegenschein, while 9 is a washed out inner-city night sky, with perhaps only the Moon and the brightest planets punching through the haze.

We once did a Bortle scale estimation while waiting for an airport shuttle on the Las Vegas strip; Vegas is arguably the most light-polluted locale on the planet. Jupiter, the Moon and the brightest stars of Orion could only be seen if you knew exactly where to look for them. In contrast, we’ve heard many service members remark about how splendid the sky looks from such deployed locations as Afghanistan.

A vanishing treasure; true dark skies. (Photo by Author).

The encroachment of civilization on wilderness areas also means that most school star parties and downtown observatories are restricted to bright targets, and serious deep sky observers must now drive several hours for a reasonably dark sky. Living just outside the Tampa/Saint Petersburg area in Florida, I can actually tell if it’s cloudy or clear at night just by how bright our bedroom appears with lights out. A cloudy sky reflects all the city lights back down, creating a “false dawn” that fills the room.

Dark sky sites are like secret fishing holes for backyard astronomers. Everyone knows of a few, some of which are even carefully hidden and discussed in hushed tones for fear of the light generating hordes which will descend upon them.

For dark skies in the Tampa Bay area, most observers head north to Chiefland along the Nature Coast about a two hour drive north. If you’ve got boat access, a truly dark sky locale can be had in the Dry Tortugas off of the Florida Keys to the south.

Dark Skies at Dunham Farms, Georgia (Photo by Author).

We recently visited such a hidden “dark sky island” in northern Georgia. Dunham Farms is a great old farmhouse Bed & Breakfast in Liberty County near Hinesville, Georgia. Despite how close as it is to Savanna, Dunham Farms sits in a “triangle of darkness,” a rarity along the Atlantic coast. We estimated the sky at a Bortle Scale of 2-3 while we were there doing nighttime astrophotography. Astronomy clubs in nearby Savanna also find dark sky requiem at nearby Tybee Pier, and further north, clubs such as the Midlands Astronomers based out of Melton Observatory in Columbia, South Carolina head to nearby Congaree Swamp.

And so it is along much of the U.S. East Coast, as observers must make to pilgrimage ever further inland in search of dark skies. Truth is, much of nighttime lighting is simply wasted energy headed skyward to illuminate the undersides of clouds and aircraft. Not only does this destroy our pristine night sky, but it’s also a threat to nocturnal wildlife and humans as well. Nigh-time lighting confuses migrating birds, often casuing them to fly into buildings. In 2009 the American Medical Association joined the fight against light pollution, citing it as a health risk. Light pollution effects our natural circadian rhythms, and studies show it may be linked to increased cancer rates as well. Turns out, our bodies need darkness.

But there is light (bad pun intended) at the end of the tunnel. Light pollution ordinances are now on the books in many municipalities. In 2001, the International Dark Sky Association recognized Flagstaff, Arizona as the first dark sky certified city. Increasingly, observatories around cities in Arizona such as Tucson and Flagstaff are being recognized as national scientific assets to be safeguarded.

Of course, legislation on the books is only as good as its enforcement. There are no “light pollution police” on the beat, and ordinances against “light trespass” are only put into practice when someone complains about it. We’ve found that frequently, inviting the neighbors over for a “backyard star party” can avoid having them install a World War II surplus anti-aircraft spotlight in their back yard to begin with… hey, that’s what your security light looks like to us!

And there’s nothing stopping hardware outlets from selling light fixtures that are illegal to install. A good fixture directs light downward where it’s needed. Lowes has recently launched its line of dark sky compliant outdoor lighting, and hey, if enough customers “vote with their wallets” more may follow suit. Its money saved in these cash strapped times, and a night sky gained!

February 15, 2013April 26, 2016 by David Dickinson

Jupiter and the Moon Have a Close Encounter in the Sky February 18, 2013

The January 2013 occultation of Jupiter by the Moon as seen from South America. (Image courtesy of Luis Argerich & Nightscape Photography; used with permission.

The movement of the Moon makes a fascinating study of celestial mechanics. Despite the light pollution it brings to the nighttime sky, we’re fortunate as a species to have a large solitary satellite to give us lessons in “Celestial Mechanics 101″

This weekend, we’ll get to follow that motion as the Moon crosses into the constellation Taurus for a near-pass of the planet Jupiter, and for a very few citizens of our fair world, occults it.

The Moon versus Jupiter during the previous occultation of the planet last month. (Image courtesy of Luis Argerich at Nightscape Photography; used with permission).

In astronomy, the term “occultation” simply means that one astronomical body passes in front of another. The term has its hoary roots in astronomy’s ancient past; just like the modern day science of chemistry sprung from the pseudo-science of alchemy, astronomy was once intertwined with the arcane practice of astrology, although the two have long since parted ways. When I use the term “occultation” around my non-space geek friends, (I do have a few!) I never fail to get a funny look, as if I just confirmed every wacky suspicion that they ever had about us backyard astronomers…

But those of us who follow lunar occultations never miss a chance to observe one. You’ll actually get to see the motion of the Moon as it moves against the background planet or star, covering it up abruptly. The Moon actually moves about 12° degrees across the sky per 24 hour period.

The position of the Moon & Jupiter as seen from Tampa (Feb 18th, 7PM EST), Perth, (Feb 18th 11:30UT) & London (Feb 18th at 19UT). Created by the author using Stellarium.

On the evening of Monday, February 18th, the 56% illuminated waxing gibbous Moon will occult Jupiter for Tasmania and southern Australia around 12:00 Universal Time (UT). Folks along the same longitude as Australia (i.e., eastern Asia) will see a close pass of the pair. For North America, we’ll see the Moon approach Jupiter and Aldebaran of February 17^th (the night of the Virtual Star Party) and the Moon appear past the pair after dusk on the 18^th.

Orientation of Jupiter, the Moon & Vesta on the evening of February 18th for North America. (Created by the author in Starry Night).

But fret not; you may still be able to spot Jupiter near the Moon on the 18th… in the daytime. Daytime planet-spotting is a fun feat of visual athletics, and the daytime Moon always serves as a fine guide. Jupiter is juuuuuust bright enough to see near the Moon with the unaided eye if you know exactly where to look;

Jupiter captured during a close 2012 pass in the daytime! (Photo by author).

To see a planet in the daytime, you’ll need a clear, blue sky. One trick we’ve used is to take an empty paper towel tube and employ it as a “1x finder” to help find our target… binoculars may also help! To date, we’ve seen Venus, Jupiter, Sirius & Mars near favorable opposition all in the daylight… Mercury and Vega should also be possible under rare and favorable conditions.

This week’s occultation of Jupiter is the 3^rd and final in a series that started in December of last year. The Moon won’t occult a planet again until an occultation of Venus on September 8^th later this year, and won’t occult Jupiter again until July 9^th, 2016. We’re also in the midst of a long series of occultations of the bright star Spica (Alpha Virginis) in 2013, as the Moon occults it once every lunation from somewhere in the world. Four major stars brighter than +1^st magnitude lie along the Moon’s path near the ecliptic; Spica, Aldebaran, Regulus, and Antares which we caught an occultation of in 2009;

Also of note: we’re approaching a “plane-crossing” of the Jovian moons next year. This means that we’ll start seeing Callisto casting shadows on the Jovian cloud tops this summer on July 20^th, and it will continue until July 21^st, 2016. The orbits of the Jovian moons appear edge-on to us about every five years, and never really deviate a large amount. Callisto is the only moon that can “miss” casting a shadow on the disk of Jupiter in its passage. The actual plane crossing as seen from the Earth occurs in November 2014. Jupiter reaches solar conjunction this year on June 19th and doesn’t come back into opposition until early next year on January 5th. 2013 is an “opposition-less” year for Jupiter, which occurs on average once per every 11-12 years. (One Jovian orbit equals 11.8 Earth years).

The Moon plus Jupiter during last month's close conjunction. (Photo by author). — The Moon plus Jupiter during last month’s close conjunction. (Photo by author).

But wait, there’s more… the Moon will also occult +7.7th magnitude 4 Vesta on February 18^th at~21:00 UT. This occultation occurs across South America and the southern Atlantic Ocean. It would be fun to catch its ingress behind the dark limb of the Moon, and we bet that a precisely timed video might just show evidence for Vesta’s tiny angular diameter as it winks out. For North American observers, Vesta will sit just off the northern limb of the Moon… if you have never seen it, now is a great time to try!

Finally, we realized that also in the field with 4 Vesta is an explorer that just departed its environs, NASA’s Dawn spacecraft. Although unobservable from Earth, we thought that it would be an interesting exercise to see if it gets occulted by the Moon as well this week, and in fact it does, for a very tiny slice of the planet;

The occultation of the Dawn spacecraft as seen from Earth. Created by the author using Occult 4.0.

Hey, calculating astronomical oddities is what we do for fun… be sure to post those pics of Jupiter, the Moon and more up to our Universe Today Flickr page & enjoy the celestial show worldwide!

See more of Luis Argerich’s astrophotography at Nightscape Photography.

Graphics created by author using Stellarium, Starry Night and Occult 4.0 software.

February 11, 2013December 23, 2015 by David Dickinson

Asteroid 2012 DA14: Observing Prospects and How to See It

Mark your calendars: this Friday, February 15, 2013, is the close flyby of Near Earth Asteroid 2012 DA14, passing just 27,630 kilometers (17,168 miles) from the surface of the Earth. About 50 meters (164 feet) in size, 2012 DA14 and its close shave marks the the first time there has been passage of an asteroid this close that we’ve known a year beforehand. Yes, it passes within the ring of geosynchronous satellites girdling the Earth. No, there’s no danger, either to said satellites or the Earth, so Bruce Willis can stay home for this one. But right behind those inquiries, the question we most frequently get is… how can I see it?

The orbital path of asteroid 2012 DA14 as seen face on (top) & near edge on (bottom). (Credit: JPL Small Body Database Browser).

The great news is that an advanced observer can indeed catch 2012 DA14 on its close pass the night of February 15^th… with a little skill and luck. Now for the bad news; the asteroid won’t be visible without binoculars or a telescope, and North America will largely miss out.

2012 DA14 will be really moving across the sky on closest approach, covering 0.8° per minute, or the diameter of a Full Moon every 45 seconds! With its passage closer to the Earth than the ring of geosynchronous satellites, it’s worth treating the passage of the asteroid as a satellite and hunting it down accordingly. Catching and watching such a pass can be an unforgettable experience; not many objects in the sky show such swift motion in real time. In fact, 2012 DA₁₄ will span the celestial sphere from declination -60° to +60° in just 4 hours! Needless to say, its passage through the Earth’s gravity well will alter its orbit considerably; most planetarium software programs do not account for this and thus will introduce a large error for a heliocentric object. Compounding the dilemma is the large amount of parallactic shift of such a nearby object. As viewed from the span of the Earth, 2012 DA14 will have a parallax of ~20° at greatest approach!

The path of asteroid 2012 DA14 through the celestial sphere on February 15th. (Created by Author).

But two sites on the web can help you with the search. One is Heavens-Above, which currently has a link on its main page to custom generate sky charts for specific locations for 2012 DA14 (make sure you’re logged in as a registered user and your observing location is set correctly). Another option is to generate an ephemeris customized for your location from the JPL Solar System Dynamics Horizons Web-Interface.

Asteroid 2012 DA14 is approaching the planet Earth from “down under,” and moving almost exactly parallel to the 12 hour line in right ascension. In fact, it’ll cross very near the equinoctial point in Virgo (one of the two points where the celestial equator and the ecliptic cross) shortly after its closest approach on Friday, February 15^th at 19:25UT. The asteroid will be at the local zenith (straight overhead) for observers in the pre-dawn hours located in western Indonesia at closest approach. Australia and eastern Asia will have a shot at seeing the asteroid as it whizzes through the sky in the early morning hours of February 16^th local. Observers in western Asia, Africa and Europe will see the asteroid lower to the east on the night of the 15^th. Note that 2012 DA14 juuuuuust misses Earth’s shadow (see strip chart) at closest approach. The shadow of our fair planet is ~20° across at the distance of the geosynchronous satellites; had it passed about a month later, we would have seen an “asteroid eclipse!” In fact, “eclipse season” for geosynchronous satellites occurs right around the equinoxes and is only a month away.

The “banana strip chart” shows the path of 2012 DA14 from the time it reaches a magnitude brighter than +10 at 17:40UT until it dips back down below it at 22:10UT on the same night. It also shows the width of uncertainty for its position due to the aforementioned 20° of parallax, and the points that it enters and departs the distance sphere of the geosynchronous satellites. Keep in mind, these satellites still orbit roughly hundred times higher than the International Space Station!

A good search strategy to catch 2012 DA14 is to actually to treat it like you’re hunting for a faint satellite. Find the time that it’s crossing a set declination and begin scanning with binoculars in right ascension back and forth until you “ambush” your astronomical prey moving slowly against the starry background. If using a telescope, use the lowest power and widest field of view that the instrument will allow. We’ve used this technique in the past to sweep up Near Earth Asteroids 2005 YU55 and 99942 Apophis and routinely use it to hunt for satellites fainter than naked eye visibility. At closest approach, asteroid 2012 DA14 will shine at around +8^th magnitude as it crosses the Bowl of Virgo northward past Denebola in the constellation Leo.

Recent measurements early this month conducted by astronomers at the Las Campanas observatory in Chile refined the orbit of 2012 DA14, placing its February 15^th passage just 45 kilometres closer to Earth than previously calculated but still well outside the threat zone. Campaigns are underway to refine measurements of its orbit even further on this pass. We won’t get another close pass of 2012 DA14 until February 16^th, 2046 when the asteroid misses us at about twice the distance of the Moon. An impact has been ruled out for this century. Predictions get less certain the further you project them into time, and 2012 DA14 will definitely be a space rock worth keeping tabs on!

February 6, 2013April 26, 2016 by David Dickinson

Mercury’s False Moon: The Mercury/Mars Planetary Conjunction this Weekend

Mercury and Mars on February 8, 2013. See how close they'll be? Image credit: Stellarium.

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The history of astronomy is littered with astronomical objects in the solar system that have fallen to the wayside. These include fleeting sightings of Venusian moons, inter-mercurial planets, and even secondary moons of the Earth.

While none of these observations ever amounted to true discoveries, this weekend gives observers and astrophotographers a unique chance to “mimic” a spurious discovery that has dotted astronomical lore: a visual “pseudo-moon” for the planet Mercury. This “moon illusion” will occur on February 8, 2013 during the closest conjunction of two naked eye planets in 2013. February offers a chance to see the fleeting Mercury in the sky, and this conjunction with Mars will provide the opportunity to see how Mercury would look in the night sky if it had a moon!

Mercury has been suspected of having moons before. On March 29^th 1974, the Mariner 10 spacecraft became the first mission to image the innermost world up close. Mariner 10 mapped 40-45% of Mercury on 3 successive passes, revealing a pock-marked world not that different than our own Moon. But Mariner 10 also detected something more: brief anomalies in the ultra-violet spectrum suggestive of a moon with a 3 day period. For a very brief time, Mercury was thought to have a moon of its own, and NASA nearly made a press release to this effect. The spectroscopic binary 31 Crateris is now suspect in the anomalous readings. Still, the Mariner 10 observation made researchers realize the observations in the extreme UV were possible over interstellar distances.

The planet Mercury as seen by NASA's Messenger spacecraft (Credit: NASA/JPL). — The planet Mercury as seen by NASA's MESSENGER spacecraft (Credit: NASA/JHUAPL).

Today, NASA has a permanent emissary orbiting Mercury with its MESSENGER spacecraft. MESSENGER first entered orbit around Mercury on March 18^th, 2011 after a series of trajectory changing flybys. MESSENGER has filled in the map of the remainder of Mercury’s surface, with no signs of the anomalous “moon.” Interestingly, MESSENGER was also on the lookout for “Vulcanoids” (tiny asteroids interior to Mercury’s orbit; sorry, Mr. Spock) while enroute to its final orbital insertion. NASA even released an April Fool’s Day prank of a fake “discovery” of a Mercurial moon dubbed Caduceus in 2012.

But MESSENGER has made some fascinating true to life discoveries, such as sampling Mercury’s tenuous exosphere & the possibility of ice at its permanently shadowed poles. Lots of new features have been mapped and named on Mercury, following the convention of naming features after famous deceased artists, musicians and authors set forth by the International Astronomical Union. It’s amazing to think that we had no detailed views at the entire surface of Mercury until the 1970’s, although some ground-based professional observatories and even skilled amateurs are now doing just that.

Fast forward to this weekend. Mercury is just beginning its first apparition of six in 2013 this week and is currently visible low in the dusk sky after sunset to the west. Mercury reaches greatest eastern elongation on February 16th at 18.1° from the Sun. Interestingly, that’s very close to the shortest elongation that can occur. Mercury’s orbit is eccentric enough that greatest elongation as seen from the Earth can vary from 17.9° to 27.8°. This month’s elongation happens within only 5 hours of Mercury reaching perihelion at 46 million kilometers from the Sun. This means that Mercury won’t peak above the dusk horizon for mid-northern latitude observers quite as high as it will during the next evening apparition of the planet in June.

Mercury Mars — caption =”Looking west 30 minutes after sunset on Feb. 8th from latitude 30° north.

This appearance of Mercury does, however, have some things going for it. First off, the ecliptic sits at a favorable viewing angle, roughly perpendicular to the western horizon at dusk for mid- to high northern latitude observers. This gives Mercury a bit of a “boost” out of the weeds. Secondly, Mercury is a full magnitude (2.512 times) brighter when it reaches maximum elongation near perihelion than aphelion, such as its next appearance in the dawn sky on March 31^st of this year. Mercury will reach magnitude -0.5, versus +0.5 in late March.

To see Mercury, find a site with a western horizon free of ground clutter and start sweeping the horizon with binoculars about 15 minutes after local sunset. See a reddish dot just above Mercury? That’s the planet Mars, shining about 7 times fainter than -1.0 magnitude Mercury at magnitude +1.2. Mercury is fast approaching a conjunction with Mars; the two will be only 15’ apart (half the average width of a Full Moon) on the evening of February 8^th at 17:00 Universal Time!

If you ever wondered how Mercury would appear with a moon, now is a good time to take a look! Again, binoculars are the best optical tool for the job. Can you see both with the naked eye? Can you place both in the same low power field of view with a telescope? You’ll only have a 15-30 minute window (depending on latitude) to snare the pairing before they follow the setting Sun below the horizon. Photographing the pair will be tricky, though not impossible, as they present a very low contrast against the bright background twilight sky.

Cass_Obs_13_Feb_5_6 — caption =”Mercury (lower center) & Mars (upper center) imaged by Mike Weasner on February 5th.

Don’t expect to see detail on Mercury or Mars telescopically; Mercury only appears 5.8” across on the 8^th, while Mars is 4” in apparent size. Mars disappears from view later this month to reach solar conjunction on April 18^th 2013. The waxing crescent Moon just 1 day after New joins the pair on the evenings of February 10^th and 11^th.

Now for the “Wow” factor of what you’re seeing. The conjunction of Mars and Mercury only appears close; in reality, they are over 180 million kilometers apart. Mercury is 1.15 Astronomical Units (A.U.s)/178 million kilometers from us on February 8^th, while Mars is nearly at its farthest from us at 2.31 A.U.s/358 million kilometers distant. It’s splendid to think that with Curiosity and friends operating on Mars and Messenger orbiting Mercury, we now have permanent robotic “eyes” on and around both!

Credits: Simulation created by the author using Starry Night.

Mercury & Mars courtesy of Mike Weasner and the Cassiopeia Observatory. Used with permission.