Observing Archives

February 6, 2017February 6, 2017 by David Dickinson

Ancient Annular: Dating Joshua’s Eclipse

Annular Eclipse — The May 2012 annular eclipse low to the horizon. Image credit and copyright: Jared Bowens.

Astronomy turns up in fascinating junctures in history. Besides just the romantic angle, we can actually pin down contextual events in ancient history if we can tie them in with a spectacle witnessed in the heavens. A recent look at the story of ‘Joshua’s eclipse’ is one such possible tale.

Lunar and solar eclipses are especially dramatic events, something that would have really made the ancients stop and take notice. A recent study published in an edition of the Beit Mikra Journal (in Hebrew) by researchers from Ben Gurion University may have pinpointed a keypoint in biblical history: the date of the Battle of Gibeon.

This study first came to our attention via the Yahoo! SEML eclipse message board and a recent Times of Israel article. The article makes mention of NASA eclipse data, which is free for anyone to peruse looking over the five millennium canon of solar and lunar eclipses… hey, it’s what we do for fun.

We did obtain a look at a translation of the abstract from the paper, which ends with the following:

“In the period between 1500-1000 BCE which is the relevant time for the biblical story, there were only three eclipses seen from Jerusalem, one total eclipse and two annular eclipses. We show that the most appropriate one is the annular solar eclipse that occurred on October 30 in 1206 BCE at sunset, an appropriate date for the time of conquest and the early settlement period, at the time of Marneptah’ rule in Egypt.”

The path of the eclipse of October 30th, 1206 BC. Credit: NASA/GSFC/Espenak/Meeus.

Joshua 10:12 reads: “Sun, stand still upon Gibeon; and you, Moon, in the valley of Ayalon.”

According to tradition, Joshua commanded the Sun to stand still long enough to defeat the Canaanite kings. Of course, the Sun and the Moon still move during an eclipse be it lunar or solar, though its mostly our planet that’s doing the moving. Still, the actual biblical term “-dom” is open to interpretation, and the researchers chose the Hebrew “to become dark” instead of the King James translation of “to stand still,” or “stationary”.

If this Bible verse sounds familiar, that’s because it turns up in astronomical history again in medieval Europe, when Church proponents used it as supposed proof of geocentricism.

Mid eclipse — Mid-eclipse over central Israel at sunset on October 30th, 1206 BC. Credit: Stellarium.

It’s tough to predict eclipses in distant time. The rotation of the Earth is not entirely smooth, and the minute change in the length of the day (known as Delta T) accumulates to the point that a leap second must be inserted on occasion to keep observed time in sync with reckoned terrestrial time. Braking action by the Sun and Moon, tectonic activity, and even global warming all cause small changes in the Earth’s rotation that slowly build up over time. This means that it’s tough to predict eclipses more than a few thousand years out, where at best we can only judge which continent they might have or will fall on.

“Not everyone likes the idea of using physics to prove things from the Bible,” said researcher Hezi Yitzhak to the Israeli news site Haaretz. “We do not claim that everything written in the Bible is true or took place… but there is also a grain of historical truth that has archaeological evidence behind it.”

The eclipse in question occurred on October 30^th, 1206 BC. This was an annular eclipse, crossing the Atlantic and the Mediterranean and ending over Israel and Jordan at sunset. Researchers pegged this suspect eclipse because of its fit for historical context and visibility. Annularity for the eclipse was 86% obscuration and started at an altitude of nine degrees above the western horizon, and would have still been in progress during its final phases at sunset.

The end of the eclipse path over modern day Israel and Jordan. Credit: NASA/GSFC data.

Lots of eclipses turn up in history. A partial lunar eclipse preceded the fall of Constantinople in 1453, seeming to fulfill prophecy. Solar and lunar eclipses made a showing at lots of battles, including the Second Battle of Syracuse on August 28^th, 412 BC and during the Zulu War on January 22^nd, 1879. A solar eclipse on June 15th, 762 BC mentioned in Assyrian texts pinpoints a crucial time in ancient history, giving us a benchmark for later dates. It’s worth noting that prior to modern times, it seems that battles were the only thing worth writing down…

Still, it’s interesting to imagine the scene as ancient armies clash, only to stop and gaze at the wondrous sight on the horizon: a pair of glowing horns, hanging low in the pre-dusk sky. We caught the 1994 annular eclipse from the Sandusky, Ohio on the shores of Lake Erie and can attest that even a 98% eclipsed Sun is still pretty bright, giving even a clear day a deep steely blue tint. Lower to the horizon though, an annular eclipse is more readily visible to the unaided eye.

You have to be careful when attempting to read ancient texts as astronomical guide books. Great minds, including Kepler and Newton, expended lots of mental juice on attempting to link biblical accounts such as Ezekiel’s Wheel and the Star of Bethlehem with actual astronomical events. We’ll probably never know for sure if a coincidental conjunction graced the sky over the manger in Bethlehem, or if Ezekiel saw the breakup of a brilliant comet, but it’s always fun to imagine and wonder. Then, there’s the inevitable embellishment that accompanies stories that may have been first sparked by meteor showers or sundogs, centuries ago. We don’t, for example, see flaming swords or banners emblazoned with Latin inscriptions across the sky today, though if you can believe medieval accounts, they seemed common back in the day.

And don’t forget: we’ve got our very own history making eclipse (hopefully sans battlefields) this coming August 21^st, 2017 crossing the United States from coast-to-coast.

Though far from conclusive, the results of the study concerning Joshua’s eclipse and the battle of Gideon are interesting to consider. Most likely we’ll never truly know what happened that ancient afternoon, unless, of course, we perfect time travel. What other events remain hidden and lost to time, ready for some historical astro-sleuth to uncover them?

-Can’t get enough of eclipses, historical or otherwise? Check out our original eclipse-fueled sci-fi tales Exeligmos, Peak Season and Class Field Trip.

February 2, 2017February 3, 2017 by David Dickinson

Superbowl Smackdown: Watch the Moon Occult Aldebaran on Sunday

Daytime Aldebaran — Can you see it? Dave Walker accidentally (!) caught Aldebaran near the daytime Moon on October 19th, 2016. Image credit and copyright: Dave Walker

Author’s note: This Superbowl Sunday event and 101 more like it are featured in our latest free e-book, 101 Astronomical Events for 2017, out now from Universe Today.

Sure, this Superbowl Sunday brings with it the promise of sacks, fumbles and tackles… but have you ever seen the Moon run down a star in the end zone? Just such an event, referred to as an occultation, happens this weekend for folks living around the Mediterranean and — just maybe for some sharp-eyed, telescope-owning observers based around the Caribbean region — this coming weekend.

Update: be sure to watch this Sunday’s occultation of Aldebaran by the Moon courtesy of Gianluca Masi and the Virtual Telescope Project live starting at 22:00 UT/5:00 PM EST:

Live starting at 22:00 UT. Credit: The Virtual Telescope Project

We’re talking about Sunday’s occultation of the bright star Aldebaran by the 64% illuminated waxing gibbous Moon. This is the 2^nd occultation of Aldebaran by the Moon for 2017 and the 28th of the current ongoing cycle of 49 spanning from January 29^th, 2015 to September 3^rd, 2018. The Moon actually occults Aldebaran and Regulus once for every lunation in 2017. We won’t have another year featuring the occultations of two +1^st magnitude stars (Spica and Antares) again until 2024.

Occultation footprint — The footprint for the February 5th occultation of Aldebaran by the Moon. The broken lines show where the occultation occurs during daytime, and the solid lines denote where the occultation occurs under dark skies. Image credit: occult 4.2.

The event occurs under dark skies for observers based around the Mediterranean and under daytime afternoon skies for folks in central America, the Caribbean, northern South America and the Florida peninsula, including Astroguyz HQ based in Spring Hill, just north of the Tampa Bay area. We’ve managed to spy Aldebaran near the daytime Moon while the Sun was still above the horizon using binocs, and can attest that the +1st magnitude star is indeed visible, if you know exactly where to look for it.

Note that, like solar eclipses belonging to the same saros cycle, occultations of Aldebaran in the ongoing cycle drift north and westward from one to the next, to the tune of about 120 degrees longitude. Though most of North America sits this one out, we do get a front row seat for next lunation’s occultation of Aldebaran on the evening of March 4/5th. The next one is the best bright star occultation of Aldebaran by the Moon for North America in 2017. And be sure to check out the Moon this Sunday evening after the big game, and note Aldebaran hanging just off of its bright limb.

Moon motion — No, the wind is not shaking the ‘scope… Sharin Ahmad chronicled the motion of the Moon past Aldebaran from Kuala Lumpur, Malaysia last month. Image credit and copyright: Shahrin Ahmad (@shahgazer)

The ref will have a close call to make for this one. The northern grazeline in Florida might make this an especially interesting event to watch, though it’ll be challenge, as the occultation occurs in the afternoon under daylight skies. This crosses right along near the cities of Jacksonville and Gainsville. Clear, deep blue high contrast skies are key, and we’ll be watching from Astroguyz HQ north of Tampa Bay during this event.

The northern grazeline across the Florida peninsula for Sunday’s ‘big game’. Credit: Dave Dickinson.

Here are some key times from the occultation zone (noted in Universal Time):

Tampa, Florida

Ingress: 20:08 UT/Moon altitude: 23 degrees

Egress: 20:34 UT/Moon altitude: 29 degrees

Bogota, Columbia

Ingress: 19:34 UT/ Moon Altitude: 49 degrees

Egress: 20:29 UT/ Moon altitude: 31 degrees

The view from Jimena de la Frontera Spain just before the occultation. Credit: Stellarium.

Rome, Italy

Ingress: 20:21 UT/Moon altitude: 37 degrees

Egress: 23:12 UT/ Moon altitude: 28 degrees

Tel Aviv, Israel

Ingress: 22:39 UT/Moon altitude: 16 degrees

Egress: 23:29 UT/Moon altitude: 5 degrees

Casablanca, Morocco

Ingress: 21:49 UT/ Moon altitude: 61 degrees

Egress: 23:07 UT/ Moon altitude: 45 degrees

Note that this occultation spans five continents, a truly worldwide event. The International Occultation Timing Association (IOTA) maintains a page with an extensive list of times for cities worldwide. Note that when the Moon tackles Aldebaran, its also crossing the scrimmage line of the Hyades open cluster, so expect numerous occultations of fainter stars worldwide as well.

Aldebaran is the brightest star along the Moon’s path in our current epoch, along with runner-ups Spica, Regulus and Antares. Though Aldebaran is 1.5 times the mass of our Sun, it’s also 65 light years away, and only appears 20 milliarcseconds (mas) in size, about the equivalent of a 40 meter diameter crater from the distance of the Moon. Still, you might just notice a brief pause as Aldebaran fades then winks out on the dark limb of the Moon, a tiny hitch betraying its diminutive angular size.

And the clockwork gears of that biggest game of all, the Universe, grind on. Don’t miss this first big ticket astronomical event for February 2017, coming to a sky above you. Next up, we’ll watching out for another bright star occultation, two eclipses, and the close passage of a comet near the Earth.

Stay tuned!

January 31, 2017February 15, 2017 by Evan Gough

Vortex Coronagraph A Game Changer For Seeing Close In Exoplanets

The vortex coronagraph at the Keck Observatory captured this image of the protoplanetary disk surrounding the young star HD 141569. which is about 380 light years from Earth. Image: NASA/JPL-Caltech — The vortex coronagraph at the Keck Observatory captured this image of the protoplanetary disk surrounding the young star HD 141569, which is about 380 light years from Earth. Image: NASA/JPL-Caltech

The study of exoplanets has advanced a great deal in recent years, thanks in large part to the Kepler mission. But that mission has its limitations. It’s difficult for Kepler, and for other technologies, to image regions close to their stars. Now a new instrument called a vortex coronagraph, installed at Hawaii’s Keck Observatory, allows astronomers to look at protoplanetary disks that are in very close proximity to the stars they orbit.

The problem with viewing disks of dust, and even planets, close to their stars is that stars are so much brighter than objects that orbit them. Stars can be billions of times brighter than the planets near them, making it almost impossible to see them in the glare. “The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet,” said Gene Serabyn of NASA’s Jet Propulsion Laboratory (JPL). “The vortex coronagraph may be key to taking the first images of a pale blue dot like our own.”

“The power of the vortex lies in its ability to image planets very close to their star, something that we can’t do for Earth-like planets yet.” – Gene Serabyn, JPL.

“The vortex coronagraph allows us to peer into the regions around stars where giant planets like Jupiter and Saturn supposedly form,” said Dmitri Mawet, research scientist at NASA’s Jet Propulsion Laboratory and Caltech, both in Pasadena. “Before now, we were only able to image gas giants that are born much farther out. With the vortex, we will be able to see planets orbiting as close to their stars as Jupiter is to our sun, or about two to three times closer than what was possible before.”

Rather than masking the light of stars, like other methods of viewing exoplanets, the vortex coronagraph redirects light away from the detectors by combining light waves and cancelling them out. Because there is no occulting mask, the vortex coronagraph can capture images of regions much closer to stars than other coronagraphs can. Dmitri Mawet, research scientist who invented the new coronagraph, compares it to the eye of a storm.

The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the "vortex" microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University — The vortex mask shown at left is made out of synthetic diamond. When viewed with a scanning electron microscope, right, the “vortex” microstructure of the mask is revealed. Image credit: University of Liège/Uppsala University

“The instrument is called a vortex coronagraph because the starlight is centered on an optical singularity, which creates a dark hole at the location of the image of the star,” said Mawet. “Hurricanes have a singularity at their centers where the wind speeds drop to zero — the eye of the storm. Our vortex coronagraph is basically the eye of an optical storm where we send the starlight.”

The results from the vortex coronagraph are presented in two papers (here and here) published in the January 2017 Astronomical Journal. One of the studies was led by Gene Serabyn of JPL, who is also head of the Keck vortex project. That study presented the first direct image of HIP79124 B, a brown dwarf that is 23 AU from its star, in the star-forming region called Scorpius-Centaurus.

The vortex coronagraph captured this image of the brown dwarf PIA21417. Image: NASA/JPL-Caltech

“The ability to see very close to stars also allows us to search for planets around more distant stars, where the planets and stars would appear closer together. Having the ability to survey distant stars for planets is important for catching planets still forming,” said Serabyn.

“Having the ability to survey distant stars for planets is important for catching planets still forming.” – Gene Serabyn, JPL.

The second of the two vortex studies presented images of a protoplanetary disk around the young star HD141569A. That star actually has three disks around it, and the coronagraph was able to capture an image of the innermost ring. Combining the vortex data with data from the Spitzer, WISE, and Herschel missions showed that the planet-forming material in the disk is made up pebble-size grains of olivine. Olivine is one of the most abundant silicates in Earth’s mantle.

“The three rings around this young star are nested like Russian dolls and undergoing dramatic changes reminiscent of planetary formation,” said Mawet. “We have shown that silicate grains have agglomerated into pebbles, which are the building blocks of planet embryos.”

These images and studies are just the beginning for the vortex coronagraph. It will be used to look at many more young planetary systems. In particular, it will look at planets near so-called ‘frost lines’ in other solar systems. The is the region around star systems where it’s cold enough for molecules like water, methane, and carbon dioxide to condense into solid, icy grains. Current thinking says that the frost line is the dividing line between where rocky planets and gas planets are formed. Astronomers hope that the coronagraph can answer questions about hot Jupiters and hot Neptunes.

Hot Jupiters and Neptunes are large gaseous planets that are found very close to their stars. Astronomers want to know if these planets formed close to the frost line then migrated inward towards their stars, because it’s impossible for them to form so close to their stars. The question is, what forces caused them to migrate inward? “With a bit of luck, we might catch planets in the process of migrating through the planet-forming disk, by looking at these very young objects,” Mawet said.

January 26, 2017 by David Dickinson

A Farewell to Plutoshine

Sometimes, its not the eye candy aspect of the image, but what it represents. A recent image of Pluto’s large moon Charon courtesy of New Horizons depicting what could only be termed ‘Plutoshine’ caught our eye. Looking like something from the grainy era of the early Space Age, we see a crescent Charon, hanging against a starry background…

So what, you say? Sure, the historic July 14^th, 2015 flyby of New Horizons past Pluto and friends delivered images with much more pop and aesthetic appeal. But look closely, and you’ll see something both alien and familiar, something that no human eye has ever witnessed, yet you can see next week.

We’re talking about the reflected ‘Plutoshine‘ on the dark limb of Charon. This over-exposed image was snapped from over 160,000 kilometers distant by New Horizons’ Ralph/Multispectral imager looking back at Charon, post flyby. For context, that’s just shy of half the distance between the Earth and the Moon. “Bigger than Texas” (Cue Armageddon), Charon is about 1200 kilometers in diameter and 1/8^th the mass of Pluto. Together, both form the only true binary (dwarf) planetary pair in the solar system, with the 1/80^th Earth-Moon pair coming in at a very distant second.

Earthshine on the Moon. Credit: Dave Dickinson

We see reflected sunlight coming off of a gibbous Pluto which is just out of frame, light that left the Sun 4 hours ago and took less than a second to make the final Pluto-Charon-New Horizons bounce. You can see a similar phenomenon next week, as Earthshine or Ashen Light illuminates the otherwise dark nighttime side of the Earth’s Moon, fresh off of passing New phase this weekend. Snow and cloud cover turned Moonward can have an effect on how bright Earthshine appears. One ongoing study based out of the Big Bear Solar observatory in California named Project Earthshine seeks to characterize long-term climate variations looking at this very phenomenon.

The view on the evening of January 28th looking west at dusk. Credit: Stellarium.

Standing on Pluto, you’d see a 3.5 degree wide Charon, 7 times larger than our own Full Moon. Of course, you’d need to be standing in the right hemisphere, as Pluto and Charon are tidally locked, and keep the same face turned towards each other. It would be a dim view, as the Sun shines at -20 magnitude at 30 AU distant, much brighter than a Full Moon, but still over 600 times fainter than sunny Earth. Dim Plutoshine on the nightside of Charon would, however, be easily visible to the naked eye.

A small 6 cm instrument, Ralph images in the visual to near-infrared range. Ralph compliments New Horizons larger LORRI instrument, which has a diameter and very similar optical configuration to an amateur 8-inch Schmidt-Cassegrain telescope.

Charon as seen from Pluto. Credit: Starry Night.

Don’t look for Pluto now; it just passed solar conjunction on the far side of the Sun on January 7^th, 2017. Pluto reaches opposition and favorable viewing for 2017 on July 10^th, one of the 101 Astronomical Events for 2017 that you’ll find in our free e-book, out from Universe Today.

And for an encore, New Horizons will visit the 45 kilometer in diameter Kuiper Belt Object 2014 MU69 on New Year’s Day 2019. From there, New Horizons will most likely chronicle the environs of the the distant solar system, as it joins Pioneer 10 and 11 and Voyagers 1 and 2 as human built artifacts cast adrift along the galactic plane.

A pretty pair: Pluto and Charon. Credit: NASA/JPL/New Horizons

And to think, it has taken New Horizons about 18 months for all of its flyby data to trickle back to the Earth. Enjoy, as it’ll be a long time before we visit Pluto and friends again.

January 21, 2017January 24, 2017 by Bob King

How to See the Space Station Fly in Front of the Moon

A beautiful ISS transit on June 19 2015 recorded at Biscarrosse, France. Credit: David Duarte

What strange creature is this flitting across the Moon? Several members of the European Space Agency’s Astronomy Center captured these views of the International Space Station near Madrid, Spain on January 14 as it flew or transited in front of the full moon. Credit: Michel Breitfellner, Manuel Castillo, Abel de Burgos and Miguel Perez Ayucar / ESA

One-one thou… That’s how long it takes for the International Space Station, traveling at over 17,000 mph (27,300 kph), to cross the face of the Full Moon. Only about a half second! To see it with your own eyes, you need to know exactly when and where to look. Full Moon is best, since it’s the biggest the moon can appear, but anything from a half-moon up and up will do.

The photo above was made by superimposing 13 separate images of the ISS passing in front of the Moon into one. Once the team knew when the pass would happen, they used a digital camera to fire a burst of exposures, capturing multiple moments of the silhouetted spacecraft.

The ISS transits the Full Moon in May 2016

The ISS is the largest structure in orbit, spanning the size of a football field, but at 250 miles (400 km) altitude, it only appears as big as a modest lunar crater. While taking a photo sequence demands careful planning, seeing a pass is bit easier. As you’d suspect, the chances of the space station lining up exactly with a small target like the Moon from any particular location is small. But the ISS Transit Finder makes the job simple.

This is a screen grab from the homepage of Bartosz Wojczy?ski’s most useful ISS Transit Finder. Credit: Bartosz Wojczy?ski

Click on the link and fill in your local latitude, longitude and altitude or select from the Google maps link shown. You can always find your precise latitude and longitude at NASA’s Latitude/Longitude Finder and altitude at Google Maps Find Altitude. Next, set the time span of your Moon transit search (up to one month from the current date) and then how far you’re willing to drive to see the ISS fly in front of the Moon.

When you click Calculate, you’ll get a list of events with little diagrams showing where the ISS will pass in relation to the Moon and sun (yes, the calculator also does solar disk crossings!) from your location. Notice that most of the passes will be near misses. However, if you click on the Show on Map link, you’ll get a ground track of exactly where you will need to travel to see it squarely cross Moon or Sun. Times shown are your local time, not Universal or UT.

A beautiful ISS transit on June 19 2015 recorded at Biscarrosse, France. The photographer used CalSky, another excellent satellite site, to prepare a week in advance of the event. This composite image was made with a Canon EOS 60D. Notice how bright the space station appears against the moon due to the lower-angled lighting across the lunar landscape at crescent phase compared to full, when the ISS appears in silhouette. Credit: David Duarte

The map also includes Recalculate for this location link. Clicking that will show you a sketch of the ISS’ predicted path across the Moon from the centerline location along with other details. I checked my city, and while there are no lunar transits for the next month, there’s a very nice solar one visible just a few miles from my home on Feb. 8. Remember to use a safe solar filter if you plan on viewing one of these!

The ISS transits the Sun on May 3, 2016. Click for details on how the photo was taken. Credit: Szabolcs Nagy

While you might attempt to see a transit of the ISS in binoculars, your best bet is with a telescope. Nothing fancy required, just about any size will do so long as it magnifies at least 30x to 40x. Timing is crucial. Like an occultation, when the moon hides a background star in an instant, you want to be on time and 100% present.

Make sure you’re set up and focused on the moon or sun (with filter) at least 5 minutes beforehand. Keep your cellphone handy. I’ve found the time displayed at least on my phone to be accurate. One minute before the anticipated transit, glue your eye to the eyepiece, relax and wait for the flyby. Expect something like a bird in silhouette to make a swift dash across the moon’s face. The video above will help you anticipate what to expect.

The next lunar transit nearest my home is an hour and a half away in the small town of Biwabik, Minn. according to the ISS Transit Finder. On Jan. 30 at 8:00:08 p.m local time, the ISS will cross the crescent moon from there. Once you know the time of the prediction and the exact latitude and longitude of the location (all information shown in the info box on the map using the ISS Transit Finder), you can turn on the satellites feature in the free Stellarium program (stellarium.org), select the ISS and create a simulated, detailed path. Created with Stellarium

Even if you never go to the trouble of identifying a “direct hit”, you can still use the transit finder to compile a list of cool lunar close approaches that would make for great photos with just a camera and tripod.

The Transit Finder isn’t the only way to predict ISS flybys. Some observers also use the excellent satellite site, CalSky. Once you tell it your location, select the Lunar/Solar Disk Crossings and Occultations link for lots of information including times, diagrams of crossings, ground tracks and more.

I use Stellarium (above) to make nifty simulated paths and show me where the Moon will be in the sky at the time of the transit. When you’ve downloaded the free program, get the latest satellite orbital elements this way:

* Move you cursor to the lower left of the window and select the Configuration box
* Click the Plugins tab and scroll down to Satellites and click Configure and then Update
* Hover the cursor at the bottom of the screen for a visual menu. Slide over to the satellite icon and click it once for Satellite hints. The ISS will now be active.
* Set the clock and location (lower left again) for the precise time and location, then do a search for the Moon, and you’ll see the ISS path.

There you have it — lots of options. Or you can simply use the Transit Finder and call it a day! I hope you’ll soon be in the right place at the right time to see the space station pass in front of the Moon. Checking my usual haunts, I see that the space station will be returning next weekend (Jan. 27) to begin an approximately 3-week run of easily viewable evening passes.

January 11, 2017 by David Dickinson

Venus Rules the Dusk Skies at Greatest Elongation

Venus at dusk — Venus, Mars, and the waxing crescent moon at dusk from the evening of January 3rd, 2017. Image credit and copyright: Alan Dyer.

“What’s that bright light in the sky?” The planet Venus never fails to impress, and indeed makes even seasoned observers look twice at its unexpected brilliance. The third brightest natural object in the sky, Venus now rules the dusk, a fine sight for wintertime evening commuters. Venus reaches greatest elongation tomorrow, a excellent time to admire this dazzling but shrouded world of mystery.

Venus at greatest elongation

Only the two planets interior to Earth’s orbit – Mercury and Venus – can reach a point known as greatest elongation from the Sun. As the name suggests, this is simply the point at which either planet appears to be at its maximum angular distance from the Sun. Think of a big right triangle in space, with Venus or Mercury at the right angle vertex, and the Sun and Earth at the other two corners. High school geometry can come in handy!

Venus elongation — Venus at greatest elongation (planets and orbits not to scale). Credit: Dave Dickinson

This Thursday on January 12^th Venus reaches a maximum of 47 degrees elongation from the Sun at 11:00 Universal Time (UT) / 6:00 AM Eastern Standard Time, shining at magnitude -4.4. The maximum/minimum elongation for Venus that can occur is 47.3 to 45.4 degrees respectively, and this week’s is the widest until 2025.

Here’s some key dates to watch out for:

Jan 12^th: Venus passes less than a degree from Neptune.

Jan 14^th: Venus reaches theoretical dichotomy?

Jan 14^th: Venus passes 3′ from +3.7 the magnitude star Lambda Aquarii.

Jan 17^th: Venus crosses the ecliptic plane northward.

Venus and Mars reach ‘quasi-conjunction’ in late January.

January 30^th: Venus crosses the celestial equator northward.

January 31^st: The Moon passes 4 degrees south of Venus, and the two also form a nice equilateral triangle with Mars on the same date.

Looking west on the evening of January 31st, 2017. Image credit: Stellarium.

February 17^th: Venus reaches a maximum brilliancy of magnitude -4.6.

March 26^th: Solar conjunction for Venus occurs eight degrees north of the Sun … it is possible to spy Venus at solar conjunction from high northern latitudes, just be sure to block out the Sun.

Through the telescope, Venus displays a tiny 24.4” size half phase right around greatest elongation. You could stack 74 Venuses across the diameter of tomorrow’s Full Moon. When does Venus look to reach an exact half phase to you? This point, known as theoretical dichotomy, is often off by just a few days. This is a curious observed phenomenon, first noted by German amateur astronomer Johann Schröter in 1793. The effect now bears his name. A result of atmospheric refraction along the day/terminator on Venus, or an optical illusion?

Gibbous Venus — Almost there… a waning gibbous Venus from the evening of January 5th, 2017. Image credit and copyright: Shahrin Ahmad (@Shahgazer)

And hey, amateurs are now using ultraviolet filters to get actual detail on the cloud-tops of Venus… we like to use a variable polarizing filter to cut down the dazzling glare of Venus a bit at the eyepiece.

Also, keep an eye out for another strange phenomenon, known as the Ashen Light of Venus. Now,ashen light or Earthshine is readily apparent on dark side of the Moon, owing to the presence of a large sunlight reflector nearby, namely the Earth. Venus has no such large partner, though astronomers in the early age of telescopic astronomy claimed to have spied a moon of Venus, and even went as far as naming it Neith. An optical illusion? Or real evidence of Venusian sky glow on its nighttime side? After tomorrow, Venus will begin heading between the Earth and the Sun, becoming a slender crescent in the process. Solar conjunction occurs on March 25^th, 2017. Venus sits just eight degrees north of the Sun on this date, and viewers in high Arctic latitudes might just be able to spy Venus above the horizon before sunrise on the day of solar conjunction. We performed a similar feat of visual athletics on the morning of January 16^th, 1998 observing from North Pole, Alaska.

Venus as seen from Fairbanks, Alaska on the morning of solar conjunction, 2017. Image credit: Starry Night.

From there, Venus heads towards a fine dawn elongation on June 3^rd, 2017. All of these events and more are detailed in our free e-book: 101 Astronomical Events for 2017.

Spying Venus in the Daytime

Did you know: you can actually see Venus in the daytime, if you know exactly where to look for it? A deep blue, high contrast sky is the key, and a nearby crescent Moon is handy in your daytime quest. Strange but true fact: Venus is actually brighter than the Moon per square arc second, with a shiny albedo of 70% versus the Moon’s paltry 12%. But Venus is tiny, and hard to spot against the blue daytime sky… until you catch sight of it.

The Moon passing Venus on January 31st, 2017 in the daytime sky. Image credit: Stellarium.

There’s another reason to brave the January cold for northern hemisphere residents: Venus can indeed cast a shadow if you look carefully for it. You’ll need to be away from any other light sources (including the Moon, which passes Full tomorrow as well with the first Full Moon of 2017, known as a Full Wolf Moon). And a high contrast surface such as freshly fallen snow can help… a short time exposure shot can even bring the shadow cast by Venus into focus.

If you follow Venus long enough, you’ll notice a pattern, as it visits very nearly the the same sky environs every eight years and traces out approximately the same path in the dawn and dusk sky. There’s a reason for this: 8 Earth years (8x 365.25 = 2922 days) very nearly equals 5 the synodic periods for Venus (2922/5=584 days, the number of days it takes Venus to return to roughly the same point with respect to the starry background, separate from its true orbit around the Sun of 225 days). For example, Venus last crossed the Pleiades star cluster in 2012, and will do so again in – you guessed it — in 2020. Unfortunately, this pattern isn’t precise, and Venus won’t also transit the Sun again in 2020 like it did in 2012. You’ll have to wait until one century from this year on December 10-11^th, 2117 to see that celestial spectacle again….

Hopefully, we’ll have perfected that whole Futurama head-in-a-jar thing by then.

January 1, 2017 by Bob King

Start the Year With Spark: See the Quadrantid Meteor Shower

The Quadrantid meteor shower, named for the obsolete constellation Quadran Muralis, will appear to stream from a point in the sky called the radiant (yellow star), located below the end of the Big Dipper’s handle and across from the bright, orange-red star Arcturus. The map shows the sky around 4 a.m. local time Tuesday, Jan. 3. The shower will be best between 4 a.m. and 6 a.m., the start of dawn. Map: Bob King, Source: Stellarium

If one of your New Year’s resolutions is to spend more time under the stars in 2017, you’ll have motivation to do so as soon as Tuesday. That morning, the Quadrantid (kwah-DRAN-tid) meteor shower will peak between 4 to about 6 a.m. local time just before the start of dawn. This annual shower can be a rich one with up to 120 meteors flying by an hour — under perfect conditions.

Those include no moon, a light-pollution free sky and most importantly, for the time of maximum meteor activity to coincide with the time the radiant is highest in the pre-dawn sky. Timing is everything with the “Quads” because the shower is so brief. Meteor showers occur when Earth passes through either a stream of dusty debris left by a comet or asteroid. With the Quads, asteroid 2003 EH1 provides the raw material — bits of crumbled rock flaked off the 2-mile-wide (~3-4 km) object during its 5.5 year orbit around the sun.

A Quadrantid fireball flares to the left of the Hyades star cluster and Jupiter in 2013. As Earth travels across the debris stream, bits and pieces of asteroid 2003 EH1 strike the atmosphere at nearly 100,000 mph (43 km/second) and vaporize while creating a glowing dash of light called a meteor. Credit: Jimmy Westlake via NASA

Only thing is, the debris path is narrow and Earth tears through it perpendicularly, so we’re in and out in a hurry. Just a few hours, tops. This year’s peak happens around 14 hours UT or 8 a.m. Central time (9 a.m. Eastern, 7 a.m. Mountain and 6 a.m. Pacific), not bad for the U.S. and Canada. The timing is rather good for West Coast skywatchers and ideal if you live in Alaska. Alaska gets an additional boost because the radiant, located in the northeastern sky, is considerably higher up and better placed than it is from the southern U.S. states.

Another Quadrantid fireball. Credit: NASA

The Quads will appear to radiate from a point in the sky below the Big Dipper’s handle, which stands high in the northeastern sky at the time. This area was once home to the now defunct constellation Quadrans Muralis (mural quadrant), the origin of the shower’s name. As with all meteor showers, you’ll see meteors all over the sky, but all will appear to point back to the radiant. Meteors that point back to other directions don’t belong to the Quads are called sporadic or random meteors.

The long-obsolete constellation Quadrans Muralis represents the wall quadrant, a instrument once used to measure star positions. It was created by French astronomer Jerome Lalande in 1795. Credit: Johann Bode atlas

Off-peak observers can expect at least a decent shower with up to 25 meteors an hour visible from a reasonably dark sky. Peak observers could see at least 60 per hour. Tropical latitude skywatchers will miss most of the the show because the radiant is located at or below the horizon, but they should be on the lookout for Earthgrazers, meteors that climb up from below the horizon and make long trails as they skirt through the upper atmosphere.

Set your clock for 4 or 5 a.m. Tuesday, put on a few layers of clothing, tuck hand warmers in your boots and gloves, face east and have at it! The Quads are known for their fireballs, brilliant meteors famous for taking one’s breath away. Each time you see one chalk its way across the sky, you’re witnessing the fiery end of an asteroid shard. As the crumble burns out, you might be fulfilling another resolution: burning away those calories while huddling outside to see the show.

December 31, 2016January 5, 2017 by Fraser Cain

Our Free Book: 101 Astronomical Events in 2017

Let’s forget all about 2016, and instead look forward to the amazing 2017 we all know we’re going to have. And to help you celebrate this amazing year in space, we’re pleased to publish an entire book on what you can observe in the upcoming year: 101 Astronomical Events in 2017.

This totally free ebook was written by our own David Dickinson and contains all the predictable events coming up: the occultations, the eclipses, the meteor showers, the equinoxes, the super-moons and mini-moons. Every significant event coming up in 2017.

In addition, a few amateur astronomers like Cory Schmitz from PhotographingSpace and the Upside Down Astronomer Paul Stewart provided some of the beautiful photographs to inspire you to get outside.

Once again, this book is totally free. There’s no cost to purchase it, there are no advertisements in it. All we ask is that you get out there, enjoy the night sky with your friends and family, and take amazing pictures to share with us and the rest of astronomy community.

Well, it would also really help if you shared the book with your friends, family, astronomy club, and forums.

This is an experiment. Will you download and actually use it? If so, then expect us to release a new edition every year. If not, then, we’ll go back to the regular blog post version.

Thanks again to David for putting in an enormous amount of work 6 months ago to think through an entire year of observing, and to the readers and photographers who helped doublecheck the math to make sure it’s accurate.

Click here to download a copy in PDF format, or click here to download a copy in EPUB format.

Also, here’s a great Google Calendar link to all 101 events courtesy of Christopher Becke (@BeckePhysics)… thanks Chris!

Fraser Cain
Publisher, Universe Today

December 25, 2016December 25, 2016 by Bob King

See a Christmas-Time Binocular Comet: 45P/Honda-Mrkos-Pajdusakova

45P/H-M-P displays a colorful coma and long ion tail on Dec. 22, 2016. Credit: Gerald Rhemann

Comet 45P/Honda-Mrkos-Pajdusakova captured in its glory on Dec. 22, 2016. It displays a bright, well-condensed blue-green coma and long ion tail pointing east. Credit: Gerald Rhemann — Comet 45P/Honda-Mrkos-Pajdusakova captured in its glory on Dec. 22, 2016. It displays a bright, well-condensed blue-green coma and long ion or gas tail pointing east. Comet observers take note: a Swan Band filter shows a larger coma and increases the comet’s contrast. Credit: **Gerald Rhemann**

Merry Christmas and Happy Holidays all! I hope the day finds you in the company of family or friends and feeling at peace. While we’ve been shopping for gifts the past few weeks, a returning comet has been brightening up in the evening sky. Named 45P/Honda-Mrkos-Pajdusakova, it returns to the hood every 5.25 years after vacationing beyond the planet Jupiter. It’s tempting to blow by the name and see only a jumble of letters, but let’s try to pronounce it: HON-da — MUR-Koz — PIE-doo-sha-ko-vah. Not too hard, right?

Tonight, the comet will appear about 12. 5 degrees to the west of Venus in central Capricornus. You can spot it near the end of evening twilight. Use larger binoculars or a telescope. Stellarium

Comet 45P is a short period comet — one with an orbital period of fewer than 200 years — discovered on December 3, 1948 by Minoru Honda along with co-discoverers Antonin Mrkos and Ludmila Pajdusakova. Three names are the maximum a comet can have even if 15 people simultaneously discover it. 45P has a history of brightening rapidly as it approaches the sun, and this go-round is proof. A faint nothing a few weeks back, the comet’s now magnitude +7.5 and visible in 50mm or larger binoculars from low light pollution locations.

You can catch it right around the end of dusk this week and next as it arcs across central Capricornus not far behind the brilliant planet Venus. 45P will look like a dim, fuzzy star in binoculars, but if you can get a telescope on it, you’ll see a fluffy, round coma, a bright, star-like center and perhaps even a faint spike of a tail sticking out to the east. Time exposure photos reveal a tail at least 3° long and a gorgeous, aqua-tinted coma. I saw the color straight off when observing the comet several nights ago in my 15-inch reflector at low power (64x).

Use this map to help you follow the comet night to night. Tick marks start this evening (Dec. 25) and show its nightly position through Jan. 8. Venus, at upper left, is shown through the 28th. Created with Chris Marriott's SkyMap software — Use this map to help you follow the comet night to night. Tick marks start this evening (Dec. 25) and show its nightly position through Jan. 8 around 6 p.m. local time or about an hour and 15 minutes after sunset. Venus, at upper left, is shown through the 28th with stars to magnitude +7. Click the chart for a larger version you can save and print out for use at your telescope. Created with Chris Marriott’s SkyMap software

Right now, and for the remainder of its evening apparition, 45P will never appear very high in the southwestern sky. Look for it a little before the end of evening twilight, when the sky is reasonably dark and the comet is as high as it gets — about a fist above the horizon as seen from mid-northern latitudes. That’s pretty low, so make the best of your time. I recommend you being around 1 hour 15 minutes after sunset.

The further south you live, the higher 45P will appear. To a point. It hovers low at nightfall this month and next. That will change in February when the comet pulls away from the sun and makes a very close approach to the Earth while sailing across the morning sky.

How about a helping hand? On New Year's Eve, the 2-day-old crescent Moon will be just a few degrees from 45P. This simulation shows the view through 50mm or larger binoculars with an ~6 degree field of view. Map: Bob King, Source: Stellarium — How about a helping hand? On New Year’s Eve, the 2-day-old crescent Moon will be just a few degrees from 45P. This simulation shows the view through 50mm or larger binoculars with an ~6 degree field of view for the Central time zone. Map: Bob King, Source: Stellarium

45P reaches perihelion or closest distance to the sun on Dec. 31 and will remain visible through about Jan. 15 at dusk. An approximately 2-week hiatus follows, when it’s lost in the twilight glow. Then in early February, the comet reappears at dawn and races across Aquila and Hercules, zipping closest to Earth on Feb. 11 at a distance of only 7.7 million miles. During that time, we may even be able to see this little fuzzball with the naked eye; its predicted magnitude of +6 at maximum is right at the naked eye limit. Even in suburban skies, it will make an easy catch in binoculars then.

I’ll update with new charts as we approach that time, plus you can check out this earlier post by fellow Universe Today writer David Dickinson. For now, enjoy the prospect of ‘opening up’ this cometary gift as the last glow of dusk subsides into night.

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!