This illustration shows Earth surrounded by filaments of dark matter called “hairs. A hair is created when a stream of dark matter particles goes through the planet. A new study proposes that Earth and the other planets are filled with “hair”. Credit: NASA/JPL-Caltech
I’m losing mine, but the Solar System may be way hairier than we ever thought, with thick crops of filamentary dark matter streaming through Earth’s core and back out again even as you read this.
Estimated distribution of matter and energy in the universe. Credit: NASA
A new study publishing this week in the Astrophysical Journal by Gary Prézeau of NASA’s Jet Propulsion Laboratory proposes the existence of long filaments of dark matter, or “hairs.” Dark matter is a hypothetical form of matter that emits no light, thereby resisting our attempts to see and photograph it, but based on many observations of its gravitational pull on ordinary matter, astronomers have measured the amount of dark matter to an accuracy of 1%.
Massive amounts of it formed a tangled web of filaments after the Big Bang and ensuing epoch of cosmic inflation that served as sites for the “condensation” of bright matter galaxies. We likely owe our existence to this stuff, whatever it is, which has yet to be directly detected. Along with dark energy, it remains one of the greatest mysteries of our age.
This Hubble image shows the distribution of dark matter in the center of the giant galaxy cluster Abell 1689, containing about 1,000 galaxies and trillions of stars. Researchers used the observed positions of 135 lensed images of 42 background galaxies to calculate the location and amount of dark matter in the cluster. They superimposed a map of these inferred dark matter concentrations, tinted blue, on an image of the cluster. The greastest concentration of dark matter is in the cluster’s center. Credit: NASA, ESA, D. Coe, N. Benitez , T. Broadhurst
As if that weren’t enough, dark matter comprises 85% of all the known matter reserves in the universe and 27% of the entire matter-energy cosmic budget. Ordinary stuff like stars, baseball bats and sushi constitute just 4.9% of the the total. The leading theory is that dark matter is “cold,” meaning it moves slowly compared to the speed of light, and it’s “dark” because it doesn’t produce or interact with light. The axion, a hypothetical elementary particle, appears to be good candidate for dark matter as do WIMPs or weakly interacting massive particles, but again, these exist only on paper.
According to calculations done in the 1990s and simulations performed in the last decade, dark matter forms “fine-grained streams” of particles that move at the same velocity and orbit galaxies such as ours. Streams can be much larger than our Solar System and criss-cross the galaxy. Prézeau compares the formation of fine-grained streams of dark matter to mixing chocolate and vanilla ice cream. Swirl a scoop of each together a few times and you get a mixed pattern, but you can still see the individual colors.
“When gravity interacts with the cold dark matter gas during galaxy formation, all particles within a stream continue traveling at the same velocity,” Prézeau said.
This illustration zooms in to show what dark matter hairs would look like around Earth. The hairs in this illustration are not to scale. Simulations show that the roots of such hairs can be 600,000 miles (1 million km) from Earth. Credit: NASA /JPL-Caltech
But a different scenario unfolds when a stream passes by an obstacle like the Earth or a moon. Prézeau used computer simulations to discover that when dark matter stream passes through a planet — dark matter passes right through us unlike ordinary matter — it’s focused into an ultra-dense filament or hair. Not a solo strand but a luxuriant crop bushy as a brewer’s beard.
According to Prézeau, hairs emerging from planets have both “roots,” the densest concentration of dark matter particles in the hair, and “tips,” where the hair ends. When particles of a dark matter stream pass through Earth’s core, they focus at the “root” of a hair, where the density of the particles is about a billion times more than average. The root of such a hair should be around 600,000 miles (1 million km) away from the surface, or a little more than twice as far as the moon. The stream particles that graze Earth’s surface will form the tip of the hair, about twice as far from Earth as the hair’s root.
The root of a dark matter hair produced from particles going through Jupiter’s core would be about 1 trillion times denser than average. Credit: NASA/JPL-Caltech
A stream passing through more massive Jupiter would have roots a trillion times denser than the original stream. Naturally, these dense concentrations would make ideal places to send a probe to study dark matter right here in the neighborhood.
The computer simulations reveal that changes in Earth’s density from inner core to outer core to mantle and crust are reflected in the shape of the hairs, showing up as “kinks” that correspond to transitions from one zone to the next. If it were possible to get our hands on this kind of information, we could use it to map to better map Earth’s interior and even the depth of oceans inside Jupiter’s moon Europa and Saturn’s Enceladus.
Earth getting its roots done. What’ll they think of next?
Each new probe we launch into space follows a finely-tuned, predetermined trajectory that opens up a new avenue of understanding into our solar system and our universe. The results from each probe shapes the objectives of the next. Each probe is built with maximum science in mind, and is designed to answer crucial questions and build our understanding of astronomy, cosmology, astrophysics, and planetary studies.
The Juno probe is no different. When it arrives at Jupiter in July 2016, it will begin working on a checklist of scientific questions about Jupiter.
But there’s a problem.
Jupiter’s structure and composition. (Image Credit: Kelvinsong CC by S.A. 3.0)
Jupiter is enormous. And at it’s heart is a chunk of ice and rock, or so we think. Surrounding that is an enormous region of liquid metallic hydrogen. This core is 10 to 20 times as massive as Earth’s, and it’s rotating. As it rotates, it generates a powerful magnetic field that draws in particles from the sun, then whips them into a near-light-speed frenzy. This whirlwind of radiation devastates anything that gets too close.
Enter the tiny Juno spacecraft, about the size of a bus. Juno has to get close to Jupiter to do its work—within 5,000km (3,100 miles) above the cloud tops—and though it’s designed to weave its way carefully past Jupiter’s most dangerous radiation fields, its orbits will still expose it to the paper-shredder effect of those fields. There’s no way around it.
Juno Project Scientist Steve Levin, and Dave Stevenson from Caltech explain Juno’s orbiting pattern in this short video:
The most vulnerable part of Juno is the sensitive electronics that are the heart and brains of the spacecraft. Jupiter’s extreme radiation would quickly destroy Juno’s sensitive systems, and the Juno designers had to come up with a way to protect those components while Juno does its work. The solution? The titanium vault.
All kinds of materials and methods have been employed to protect spacecraft electronics, but this is the first time that titanium has been tried. Titanium is renowned for its light weight and its strength. It’s used in all kinds of demanding manufacturing applications here on Earth.
The titanium vault won’t protect Juno’s heart forever. In fact, some of the components are not expected to last the length of the mission. The radiation will slowly degrade the titanium, as high velocity particles punch microscopic holes in it. Bit by bit, radiation will perforate the vault, and the electronics within will be exposed. And as the electronic systems stop functioning, one by one, Juno will slowly become brain-dead, before plunging purposefully into Jupiter.
But Juno won’t die in vain. It will answer important questions about Jupiter’s core, atmospheric composition, planetary evolution, magnetosphere, polar auroras, gravitational field, and more. The spacecraft’s onboard camera, the Junocam, also promises to capture stunning images of Jupiter. But beyond all that, Juno—and its titanium vault—will show us how good we are at protecting spacecraft from extreme radiation.
Juno is still over 160 million km (100 million miles) from Jupiter and is fully functional. Once it arrives, it will insert itself into orbit and begin to do its job. How well it can do its job, and for how long, will depend on how effectively the titanium vault shields Juno’s heart.
The conjunction of Venus (brightest), Jupiter (above Venus) and Mars (dimmer below Venus & Jupiter) looking east in the morning twilight on October 25, 2015, as seen from the west shore of Lake Annette, in Jasper National Park, Alberta. The mountain is the Watchtower. Morning mist covers the lake waters. Haze in the sky adds the natural glows around the planets — no filters were used. Credit and copyright: Alan Dyer.
Have you seen the views in the morning skies this week, with three planets huddling together at dawn? Just one degree separated planets Jupiter and Venus, with Mars sneaking in nearby. Astrophotographers were out in full force to capture the scene!
Above, the very talented photographer Alan Dyer from Canada captured a stunning image of the planetary trio over Lake Annette, in Jasper National Park, Alberta, Canada. He took several gorgeous shots, and so we’ve added one more of his below, plus dozens of other wonderful shots from our astrophotographer friends around the world. Each of these images are from Universe Today’s Flickr pool, so you can click on each picture to get a larger view on Flickr.
Enjoy these great views, as there won’t be a more compact arrangement of three planets again until January 10, 2021.
A panorama of roughly 120° showing a star- and planet-filled sky in the dawn twilight over Lake Annette in Jasper National Park, Alberta, on the morning of October 25, 2015. At left, to the east, are the two bright planets, Venus (brightest) and Jupiter in a close conjunction 1° apart (and here almost merging into one glow), plus reddish Mars below them, all in Leo, with the bright star Regulus above them. Right of centre, to the south, is Orion and Canis Major, with the bright star Sirius low in the south. At upper right are the stars of Taurus, including Aldebaran and the Hyades star cluster. Venus was near greatest elongation on this morning. Credit and copyright: Alan Dyer.Taken from Coral Towers Observatory in Queensland, Australia on October 28, 2014. Venus is to the right of and slightly below Jupiter and Mars is to the right of and below Venus. The pre-dawn landscape is illuminated by moonlight. Credit and copyright: Joseph Brimacombe.Jupiter, Venus, and Mars rise behind the 14,155 foot peak of Mount Democrat in Colorado. Credit and copyright: Patrick Cullis.Spooky Selfie, Three Planets and a Dead Satellite. The planetary conjunction of Jupiter, Venus and Mars on October 26, 2015, along with the ADEOS II satellite, which died in orbit in 2003 after the solar panels failed. Credit and copyright: Tom Wildoner.Planetary conjunction of Jupiter, Venus and Mars as seen from Search Results Map of Le Puy Saint-Bonnet, 49300 Cholet, France Le Puy Saint-Bonnet, 49300 Cholet, France Le Puy-Saint-Bonnet in France on October 26, 2015. Credit and copyright: David de Cueves.Venus, Jupiter and Mars grace the morning skies in France on October 26, 2015. Credit and copyright: Frank Tyrlik.
Here’s a timelapse from Damien Weatherley of his planet imaging session from the morning of October 25, 2015:
Venus, Jupiter & Mars create a close triangle in the eastern sky at dawn! John Chumack captured this image above his backyard Observatory in Dayton, Ohio on 10-26-2015. Credit and copyright: John Chumack.A zoomed out view of the planetary trio from John Chumack’s observatory in Dayton, Ohio on October 25, 2015. Credit and copyright: John Chumack.Conjunction of Venus, Jupiter & Mars on the morning of Monday Oct. 26, 2015. Credit and copyright: Holly Roberts.Jupiter and Venus conjunction on October 25, 2015. They were approximately with a degree and a half of each other. Jupiter’s moons are visible. Credit and copyright: Chris Lyons. Venus and the almost invisible Jupiter struggled to shine through the haze on the morning of October 25, 2015, as seen in Malaysia. Credit and copyright:Shahrin Ahmad.Venus, Jupiter and Mars in the hazy, cloudy morning skies over the UK on October 25, 2015. Credit and copyright: Sarah and Simon Fisher.
And here’s just a reminder that this planetary conjunction has been setting up for a while. Here’s a shot from October 10 of the planets as they started moving closer together:
A spooky planetary conjunction of Venus, Jupiter and Mars on October 10, 2015 on the Isle of Mull, Scotland. Credit and copyright: Shaun Reynold.
Eclipse tetrads of doom. Mars, now bigger than the Full Moon each August. The killer asteroid of the month that isn’t. Amazing Moons of all stripes, Super, Blood, Black and Blue…
Venus, Mars, Jupiter and the Moon from October 9th. Image credit and copyright: @TaviGreiner
The internet never lets reality get in the way of a good meme, that’s for sure. Here’s another one we’ve caught in the wild this past summer, one that now appears to be looking for a tenuous referent to grab onto again next week.
You can’t miss Jupiter homing in on Venus this month, for a close 61.5’ pass on the morning on Oct 25th. -1.4 magnitude Jupiter shows a 33” disk on Sunday’s pass, versus -4 magnitude Venus’ 24” disk.
Looking east on the morning of October 26th. Credit: Stellarium
We also had a close pass on July 1st, which prompted calls of ‘the closest passage of Venus and Jupiter for the century/millennia/ever!’ (spoiler alert: it wasn’t) Many also extended this to ‘A Star of Bethlehem convergence’ which, again, set the web a-twittering.
Will the two brightest planets in the sky soon converge every October, in the minds of Internet hopefuls?
This idea seems to come around every close pass of Jupiter and Venus as of late, and may culminate next year, when an extra close 4’ pass occurs on August 27th, 2016. But the truth is, close passes of Venus and Jupiter are fairly common, occurring 1-2 times a year. Venus never strays more than 47 degrees from the Sun, and Jupiter moves roughly one astronomical constellation eastward every Earth year.
Much of the discussion in astrological circles stems from the grouping of Jupiter, Venus and the bright star Regulus this month. Yes, this bears a resemblance to a grouping of the same seen in dawn skies on August 12th, 2 BCE. This was part of a series of Jupiter-Venus conjunctions that also occurred on May 24th, 3 BCE and June 17th, 1 BCE. The 2 BCE event was located in the constellation Leo the Lion, and Regulus rules the sign of kings in the minds of many…
Looking eastward on the morning of August 12th, 2 BCE. Credit: Stellarium
But even triple groupings are far from uncommon over long time scales. Pairings of Jupiter, Venus in any given zodiac constellation come back around every 11-12 years. Many great astronomical minds over the centuries have gone broke trying to link ‘The Star’ seen by the Magi to the latest astronomical object in vogue, from conjunctions, to comets, to supernovae and more. If there’s any astronomical basis to the allegorical tale, we’ll probably never truly know.
The October 25th pass of Venus vs Jupiter. Created using Starry Night Education software.
“The 3/2 BCE conjunctions don’t fit the time of Jesus’ birth. There is also no evidence that these sorts of conjunctions were considered all that good; I even found evidence that they were bad news for a king, especially if Jupiter was circling around Regulus. And of course, none of this even comes close to doing the things the Star of Bethlehem was claimed to have done.
So, we have a not terribly rare situation in the sky that conforms to something that doesn’t really fit the Gospel story in a time frame that doesn’t fit the Jesus chronology which doesn’t really have anything all that auspicious about that to ancient observers.”
The dance of the planets also gives us a brief opening teaser on Saturday morning, as Mars passes just 0.38 degrees NNE of Jupiter on Oct 17th looking like a fifth pseudo-moon.
Finally, the crescent Moon joins the scene once again on November 7th, passing 1.9 degrees SSW of Jupiter and 1.2 SSW of Venus, a great time to attempt to spy both in the daytime using the crescent Moon as a guide. And keep an eye on Venus, as the next passage of the crescent Moon on December 7th features a close grouping with binocular Comet C/2013 US10 Catalina as well.
How close can the two planets get?
Stick around ‘til November 22nd 2065, and you can watch Venus actually transit the face of Jupiter:
Though rare, such an occlusion involving the two brightest planets happens every other century or so… we ran a brief simulation, and uncovered 11 such events over the next three millennia:
Credit: Dave Dickinson
Bruce McCurdy of the Royal Canadian Astronomical Society posed a further challenge: how often does Venus fully occult Jupiter? We ran a simulation covering 9000 BC to 9000 AD, and found no such occurrence, though the July 14th, 4517 AD meeting of Jupiter and Venus is close.
Let’s see, I’ll be on my 3rd cyborg body, in the post- Robot Apocalypse by then…
This sort of total occlusion of Jupiter by Venus turns out to be rarer than any biblical conjunction. Why?
Well, for one thing, Venus is generally smaller in apparent size than Jupiter. When Jupiter is near Venus, it’s also near the Sun and in the 30-35” size range. Venus only breaks 30” in size for about 20% of its 584 synodic period. But we suspect a larger cycle may be in play, keeping the occurrence of a large Venus meeting and covering a shrunken Jove in our current epoch.
A Moon, a star, three planets and… a space station? A close pass of Tiangong-1 (arrowed) near this month’s grouping. Image credit: Dave Dickinson
Astronomy makes us ponder the weirdness of our skies gracing our backyard over stupendously long time scales. Whatever your take on the tale and the modern hype, be sure to get out and enjoy the real show on Sunday morning October 25th, as the brightest of planets make for a brilliant pairing.
This new image from the largest planet in the Solar System, Jupiter, was made during the Outer Planet Atmospheres Legacy (OPAL) programme. The images from this programme make it possible to determine the speeds of Jupiter’s winds, to identify different phenomena in its atmosphere and to track changes in its most famous features.
The map shown was observed on 19 January 2015, from 2:00 UT to 12:30 UT.
Credit:
NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), and G. Orton (JPL-Caltech)
Jupiter global map created from still images from the Hubble Space Telescope
It’s been widely reported, including at Universe Today, that the apple of Jupiter’s eye, the iconic Great Red Spot (GRS), has been shrinking for decades. Even the rate of shrinkage has been steadily increasing.
Back in the late 1800s you could squeeze three Earths inside the GRS. Those were the days. Last May it measured just 10,250 miles (16,496 km) across, big enough for only 1.3 of us.
And while new photos from the Hubble Space Telescope show that Jupiter’s swollen red eye has shrunk an additional 150 miles (240 km) since 2014, the good news is that the rate of shrinkage appears to be well, shrinking. The contraction of the GRS has been studied closely since the 1930s; even as recently as 1979, the Voyager spacecraft measured it at 14,500 miles (23,335 km) across. But the alarm sounded in 2012, when amateur astronomers discovered sudden increase in the rate of 580 miles (933 km) a year along with a shift in shape from oval to roughly circular.
For the moment, it appears that the GRS is holding steady, making for an even more interesting Jupiter observing season than usual. Already, the big planet dominates the eastern sky along with Venus on October mornings. Consider looking for changes in the Spot yourself in the coming months. A 6-inch or larger scope and determination are all you need.
Hubble photos of the Great Red Spot taken on a first rotation (left frames) and 10 hours later (right frames) show the counterclockwise rotation of the newly-discovered filament or wisp inside the GRS. Credit: NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), and G. Orton (JPL-Caltech)
New imagery from the Hubble OPAL program also shows a curious wisp at the center of the Great Red Spot spanning almost the entire width of the hurricane-like vortex. This filamentary streamer rotates and twists throughout the 10-hour span of the Great Red Spot image sequence, drawn out by winds that are blowing at 335 mph (540 km/hr). Color-wise, the GRS remains orange, not red. Currently, the reddest features on the planet are the North Equatorial Belt and the occasional dark, oval “barges” (cyclonic storms) in the northern hemisphere.
The newly-found waves in Jupiter’s atmosphere are located in regions where cyclones and anticyclones are common. They look like dark eyelashes. A cyclone is a storm or system of winds that rotates around an area of low pressure. Anticyclones spin around areas of high pressure. Credit: NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), and G. Orton (JPL-Caltech)
That’s not all. The photos uncovered a rare wave structure just north of Jupiter’s equator that’s only been seen once before and with difficulty by the Voyager 2 spacecraft in 1979. The scientists, whose findings are described in this just-published Astrophysical Journal paper, say it resembles an earthly atmospheric feature called a baroclinic wave,a large-scale meandering of the jet stream associated with developing storms.
Hubble view of Jupiter’s baroclinic waves on January 19, 2015 (top) and our only other view of them photographed by Voyager 2 in 1979. Credit: NASA, ESA, A. Simon (GSFC), M. Wong (UC Berkeley), and G. Orton (JPL-Caltech)
Jupiter’s “current wave” riffles across a region rich with cyclonic and anticyclonic storms. The wave may originate in a clear layer beneath Jupiter’s clouds, only becoming visible when it propagates up into the cloud deck, according to the researchers. While it’s thought to be connected to storm formation in the Jovian atmosphere, it’s a mystery why the wave hasn’t been observed more often.
The OPAL program focuses on long-term observation of the atmospheres of Jupiter, Uranus and Neptune until the end of the Saturn Cassini Mission and all four planets afterwords. We have to keep watch from Earth as no missions to Saturn and beyond are expected for quite some time. To date, Neptune and Uranus have already been observed with photos to appear (hopefully) soon in a public archive.
The sky sparkles with the Moon (top, overexposed), Regulus, Venus, Mars, and Jupiter at dawn this morning October 7, 2015.
Tomorrow morning might be a good time to call for extra celestial traffic control. A slip of a crescent Moon will join a passel of planets in the dawn sky for the first of several exciting conjunctions over the next few days.
The scene facing east about 1 1/2 hours before sunrise Thursday morning Oct. 8. Let your eyes delight in the tumble of Moon and planets. Source: Stellarium
In the space of three mornings beginning tomorrow, four planets, the Moon and the star Regulus will participate in six separate conjunctions. Here’s how it’ll play out. Time are shown in UT / Greenwich Mean Time and Central Daylight and 1° equals two full moon diameters:
October 8: Venus 2.5° south of Regulus at 18 UT (1 p.m. CDT)
October 8: Regulus 3.1° north of the moon at 19 UT (2 p.m. CDT)
October 8: Venus 0.6° north of the moon at 20 UT (3 p.m. CDT)
October 9: Mars 3.2° north of the moon at 14 UT (9 a.m. CDT)
October 9: Jupiter 2.5° north of the moon at 21 UT (4 p.m.)
October 11: Mercury 0.8° north of the moon 11 UT (6 a.m. CDT)
The crescent Moon will be near Venus all day Thursday for the Americas until it sets in late afternoon. What a great opportunity to catch sight of the planet in the middle of the day. This binocular view depicts their arrangement around noon CDT Oct. 8, when the planet lies less than 2° from the Moon. Source:: Stellarium
Since several of the events occur in the middle of the afternoon for skywatchers in the Americas, here’s an expanded viewing guide:
* Thursday, October 8: Skywatchers will see Venus pass 2.5° south of Leo’s brightest star Regulus with a cool crescent moon a little more than 3° to the west of the brilliant planet. If you live in Japan and the Far East, you’ll see a splendidly close conjunction of the moon and Venus at dawn on October 9, when the pair will be separated by a hair more than one moon diameter (0.6°). At nearly the same time, the moon will be in conjunction with Regulus.
Observers in Australia and New Zealand will see the Moon occult Venus in a dark sky sky before dawn (or in daylight, depending on exact location) on the 9th. Click HERE for information, times and a map for the event.
Ready to set the alarm again? The following morning, October 9, the moon makes a neat triangle with Jupiter and Mars. Source: Stellarium
* Friday, October 9: An even thinner moon passes about 3° north of Mars in the Americas at dawn and approximately 4° from Jupiter. Watch for the three luminaries to sketch a nifty triangle in the eastern sky 90 minutes to an hour before sunrise. Venus will gaze down at the planetary conclave 10° further west.
There’s not much of the Moon left by Saturday morning the 11th. The knife-edge crescent will hang less than a degree below the planet Mercury 40 minutes before sunrise. Make sure you find a spot with a good eastern horizon. Source: Stellarium
* Sunday, October 11: Mercury, which has quietly taken up residence again in the dawn sky, hovers 0.8° above a hair-thin moon this morning at 6 a.m. CDT. Best views will be about 45 minutes before sunrise, when the pair rises high enough to clear distant trees. Bring binoculars to help you spot the planet.
After a short break, Mars and Jupiter will cozy up 0.4 degree apart just before the start of dawn on October 17 CDT. Venus won’t be far away. Source: Stellarium
You’re thinking, why does this all have to happen in the morning? Thankfully, sunrise occurs around 7 a.m. for many locations, so you can see all these cool happenings in twilight around 6 a.m. — not terribly unreasonable. And now that the The Martian has finally hit the movie theaters, what better time to see the planet in the flesh? By pure coincidence, the location of stranded astronaut Mark Watney in the fictional account — Acidalia Planitia (Mare Acidalium) — will be facing dawn risers across the Americas and Hawaii this week.
October wraps up with a tight trio of three planets before dawn. It will be the closest gathering of three planets since May 27, 2013. The next won’t happen till January 10, 2021. Source: Stellarium
Dare I say this string of continuous conjunctions is only a warm-up for more to come? Earth’s revolution around the Sun quickly brings Jupiter higher in the eastern sky, while Mars races eastward as if on a collision course. The following Saturday on October 17, the two will meet in conjunction less than 1/2 degree (one Full Moon width) apart. Very nice!
But it gets even better. On Tuesday morning, October 27, you’ll see all three planets huddle at dawn. One degree will separate Jupiter and Venus with Mars bringing up the rear several degrees further east. Feast on the view because there won’t be a more compact arrangement of three planets again until January 10, 2021.
Mars and Regulus are already close. This photo was taken this morning (Sept. 21) about an hour 10 minutes before sunrise. Credit: Bob King
I was up before dawn today hoping to find the returning comet 205P/Giacobini and a faint new supernova in the galaxy IC 1776 in Pisces. I was fortunate to see them both. But the morning held a pleasant surprise I hadn’t anticipated. Venus rose brilliantly in the east followed by the much dimmer planet Mars some 10° to its lower left. And there, not more than a couple degrees below Mars, shone Leo’s brightest star, Regulus. At first glance both appeared about equally bright, but looking closer, it was clear that Regulus, at magnitude +1.3, bested Mars by nearly half a magnitude. What was especially appealing was the color contrast between the two with Mars’ dusty, rusty surface so different from the pure white radiance of Regulus.
On Friday morning September 25, Mars and Regulus will be just 0.8 degrees apart in the eastern sky below brilliant Venus at dawn. They’ll be nearly as close Thursday morning. Source: Stellarium
While star and planet are both close enough to catch the eye, they’re headed for an excellent conjunction Thursday and Friday mornings, September 24 and 25. The actual time of closest approach, when star and planet will be separated by just 0.8°, occurs around 11 p.m. CDT — before Mars rises for skywatchers in the Americas and Canada, but about perfect for European and African observers.
Just the same, everyone around the planet will see them less than a degree apart low in the eastern sky about 90 minutes to an hour before sunrise on those dates. Joining the scene will be Venus, now spectacularly bright against the deep blue, early dawn, and Jupiter, bringing up the rear further lower down in Leo’s tail.
Regulus is a main sequence star like the Sun but hotter. It spins so fast that it’s stretched into an oblate spheroid 4.3 times the diameter of the Sun.
Regulus, Latin for “little king”, may have received that name because it’s the brightest star in the Leo the Lion, king of the beasts. The ancient Greeks knew it by the same name, Basiliscos, as did the Babylonians before them who called it Lugal (king). Regulus is the only 1st magnitude star to sit almost directly on the ecliptic, the path followed by the Moon, Sun and planets through the sky. That means it gets regular visitors. Mars this week; Venus and the crescent Moon both on October 8. Few bright stars are as welcoming of unannounced guests.
I encourage beginning and advanced astrophotographers alike to capture the Regulus-Mars conjunction using a tripod-mounted camera. Just find an attractive setting and make a series of exposures at ISO 800 with a standard 35mm lens. Click here to find out when the Sun rises, so you’ll know what time to back up from to see the event. Now that fall brings much later sunrises, it’s not so hard anymore to catch dawn sky offerings.
It’s also a delight to see the Red Planet again, which will come to a close opposition in the constellation Scorpius next May. Let the fun begin!
The Moon, just a couple days before new phase and the upcoming partial solar eclipse, joins Venus and Mars in the dawn sky on Thursday Sept. 10. Well below the triplet, look for returning Jupiter. Source: Stellarium
The dawn sky’s where it’s happening. With Saturn swiftly sinking westward at dusk, bright planets have become scarce in the evening hours. But if you get up early and look east, you’ll discover where the party is. Venus, Mars and now Jupiter have the dance floor.
Tale of two crescents. A montage of the thick crescent Moon and crescent Venus photographed earlier this month. Credit: Tom Ruen
What’s more, the sky gods have seen fit to roll a thin crescent Moon alongside Venus Thursday morning (Sept. 10). This lovely twinning of crescents is best seen about 75 minutes to an hour before sunrise. All you need is a pair of 10x binoculars to see the peewee Venusian version. Its waning crescent phase closely mimics the Moon’s.
From the U.S., the separation between the two will vary from 3° for the East Coast to 4.5° for the West. European and African skywatchers will witness the actual conjunction with the Moon gliding 2.5° north of the planet.
Venus is very bright, making it easy to see in the daytime if you know where to look. Try using the thin Moon soon after sunrise (7:30 a.m. local time shown here) to spot Venus. Aim and focus your binoculars on the Moon, then glide up and to the right to find Venus. If you succeed, lower the binoculars and see if you can spot it without optical aid. Source: Stellarium
Much fainter Mars, checking in at magnitude +1.8, lies 6° to the left or east of the Moon. It thrills me to see Mars begin a new apparition with its return to the morning sky. Next year, the Red Planet reaches opposition on May 22 in the constellation Scorpius, when it will be brighter than Sirius and more than 18 arc seconds across, its biggest and closest since 2005.
Remember Jupiter? We lost it in the solar glare more than a month ago, but if you can find a location with a nice, open eastern horizon, you can welcome the ever-jovial planet back Thursday. Bring binoculars just in case! Jove’s only a few degrees high in moderately-bright twilight.
The bright sunlit crescent contrasts with the darker lighting of twice-reflected light contributed by own planet. Credit: Bob King
When you look at the Moon Thursday, most of it will be illuminated not by sunlight but by Earth-light called earthshine. This smoky, dark glow results from sunlight bouncing off the globe into space to softly light the otherwise shadowed portion of the Moon. The effect is most pleasing to the eye and remarkable in binoculars, which reveal lunar seas and even larger craters shrouded in blue-dark. Don’t miss it!
Ever since the invention of the telescope four hundred years ago, astronomers have been fascinated by the gas giant known as Jupiter. Between its constant, swirling clouds, its many, many moons, and its Giant Red Spot, there are many things about this planet that are both delightful and fascinating.
But perhaps the most impressive feature about Jupiter is its sheer size. In terms of mass, volume, and surface area, Jupiter is the biggest planet in our Solar System by a wide margin. And since people have been aware of its existence for thousands of years, it has played an active role in the cosmological systems many cultures. But just what makes Jupiter so massive, and what else do we know about it?
Size, Mass and Orbit:
Jupiter’s mass, volume, surface area and mean circumference are 1.8981 x 1027 kg, 1.43128 x 1015 km3, 6.1419 x 1010 km2, and 4.39264 x 105 km respectively. To put that in perspective, Jupiter diameter is roughly 11 times that of Earth, and 2.5 the mass of all the other planets in the Solar System combined.
But, being a gas giant, it has a relatively low density – 1.326 g/cm3 – which is less than one quarter of Earth’s. This means that while Jupiter’s volume is equivalent to about 1,321 Earths, it is only 318 times as massive. The low density is one way scientists are able to determine that it is made mostly of gases, though the debate still rages on what exists at its core (see below).
Jupiter orbits the Sun at an average distance (semi-major axis) of 778,299,000 km (5.2 AU), ranging from 740,550,000 km (4.95 AU) at perihelion and 816,040,000 km (5.455 AU) at aphelion. At this distance, Jupiter takes 11.8618 Earth years to complete a single orbit of the Sun. In other words, a single Jovian year lasts the equivalent of 4,332.59 Earth days.
However, Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours (9 hours, 55 minutes and 30 seconds to be exact. Therefore, a single Jovian year lasts 10,475.8 Jovian solar days. This orbital period is two-fifths that of Saturn, which means that the two largest planets in our Solar System form a 5:2 orbital resonance.
Structure and Composition:
Jupiter is composed primarily of gaseous and liquid matter. It is the largest of the gas giants, and like them, is divided between a gaseous outer atmosphere and an interior that is made up of denser materials. It’s upper atmosphere is composed of about 88–92% hydrogen and 8–12% helium by percent volume of gas molecules, and approx. 75% hydrogen and 24% helium by mass, with the remaining one percent consisting of other elements.
This cut-away illustrates a model of the interior of Jupiter, with a rocky core overlaid by a deep layer of liquid metallic hydrogen. Credit: Kelvinsong/Wikimedia Commons
The atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds as well as trace amounts of benzene and other hydrocarbons. There are also traces of carbon, ethane, hydrogen sulfide, neon, oxygen, phosphine, and sulfur. Crystals of frozen ammonia have also been observed in the outermost layer of the atmosphere.
The interior contains denser materials, such that the distribution is roughly 71% hydrogen, 24% helium and 5% other elements by mass. It is believed that Jupiter’s core is a dense mix of elements – a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. The core has also been described as rocky, but this remains unknown as well.
In 1997, the existence of the core was suggested by gravitational measurements, indicating a mass of from 12 to 45 times the Earth’s mass, or roughly 4%–14% of the total mass of Jupiter. The presence of a core is also supported by models of planetary formation that indicate how a rocky or icy core would have been necessary at some point in the planet’s history in order to collect all of its hydrogen and helium from the protosolar nebula.
However, it is possible that this core has since shrunk due to convection currents of hot, liquid, metallic hydrogen mixing with the molten core. This core may even be absent now, but a detailed analysis is needed before this can be confirmed. The Juno mission, which launched in August 2011 (see below), is expected to provide some insight into these questions, and thereby make progress on the problem of the core.
The temperature and pressure inside Jupiter increase steadily toward the core. At the “surface”, the pressure and temperature are believed to be 10 bars and 340 K (67 °C, 152 °F). At the “phase transition” region, where hydrogen becomes metallic, it is believed the temperature is 10,000 K (9,700 °C; 17,500 °F) and the pressure is 200 GPa. The temperature at the core boundary is estimated to be 36,000 K (35,700 °C; 64,300 °F) and the interior pressure at roughly 3,000–4,500 GPa.
Jupiter’s Moons:
The Jovian system currently includes 67 known moons. The four largest are known as the Galilean Moons, which are named after their discoverer, Galileo Galilei. They include: Io, the most volcanically active body in our Solar System; Europa, which is suspected of having a massive subsurface ocean; Ganymede, the largest moon in our Solar System; and Callisto, which is also thought to have a subsurface ocean and features some of the oldest surface material in the Solar System.
Then there’s the Inner Group (or Amalthea group), which is made up of four small moons that have diameters of less than 200 km, orbit at radii less than 200,000 km, and have orbital inclinations of less than half a degree. This groups includes the moons of Metis, Adrastea, Amalthea, and Thebe. Along with a number of as-yet-unseen inner moonlets, these moons replenish and maintain Jupiter’s faint ring system.
Jupiter also has an array of Irregular Satellites, which are substantially smaller and have more distant and eccentric orbits than the others. These moons are broken down into families that have similarities in orbit and composition, and are believed to be largely the result of collisions from large objects that were captured by Jupiter’s gravity.
Illustration of Jupiter and the Galilean satellites. Credit: NASA
Atmosphere and Storms:
Much like Earth, Jupiter experiences auroras near its northern and southern poles. But on Jupiter, the auroral activity is much more intense and rarely ever stops. The intense radiation, Jupiter’s magnetic field, and the abundance of material from Io’s volcanoes that react with Jupiter’s ionosphere create a light show that is truly spectacular.
Jupiter also experiences violent weather patterns. Wind speeds of 100 m/s (360 km/h) are common in zonal jets, and can reach as high as 620 kph (385 mph). Storms form within hours and can become thousands of km in diameter overnight. One storm, the Great Red Spot, has been raging since at least the late 1600s. The storm has been shrinking and expanding throughout its history; but in 2012, it was suggested that the Giant Red Spot might eventually disappear.
Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. These clouds are located in the tropopause and are arranged into bands of different latitudes, known as “tropical regions”. The cloud layer is only about 50 km (31 mi) deep, and consists of at least two decks of clouds: a thick lower deck and a thin clearer region.
There may also be a thin layer of water clouds underlying the ammonia layer, as evidenced by flashes of lightning detected in the atmosphere of Jupiter, which would be caused by the water’s polarity creating the charge separation needed for lightning. Observations of these electrical discharges indicate that they can be up to a thousand times as powerful as those observed here on the Earth.
A color composite image of the June 3rd Jupiter impact flash. Credit: Anthony Wesley
Historical Observations of the Planet:
As a planet that can be observed with the naked eye, humans have known about the existence of Jupiter for thousands of years. It has therefore played a vital role in the mythological and astrological systems of many cultures. The first recorded mentions of it date back to the Babylon Empire of the 7th and 8th centuries BCE.
In the 2nd century, the Greco-Egyptian astronomer Ptolemy constructed his famous geocentric planetary model that contained deferents and epicycles to explain the orbit of Jupiter relative to the Earth (i.e. retrograde motion). In his work, the Almagest, he ascribed an orbital period of 4332.38 days to Jupiter (11.86 years).
In 499, Aryabhata – a mathematician-astronomer from the classical age of India – also used a geocentric model to estimate Jupiter’s period as 4332.2722 days, or 11.86 years. It has also been ventured that the Chinese astronomer Gan De discovered Jupiter’s moons in 362 BCE without the use of instruments. If true, it would mean that Galileo was not the first to discovery the Jovian moons two millennia later.
In 1610, Galileo Galilei was the first astronomer to use a telescope to observe the planets. In the course of his examinations of the outer Solar System, he discovered the four largest moons of Jupiter (now known as the Galilean Moons). The discovery of moons other than Earth’s was a major point in favor of Copernicus’heliocentric theory of the motions of the planets.
Galileo shows of the sky in Saint Mark’s square in Venice. Note the lack of adaptive optics. Credit: Public Domain
During the 1660s, Cassini used a new telescope to discover Jupiter’s spots and colorful bands and observed that the planet appeared to be an oblate spheroid. By 1690, he was also able to estimate the rotation period of the planet and noticed that the atmosphere undergoes differential rotation. In 1831, German astronomer Heinrich Schwabe produced the earliest known drawing to show details of the Great Red Spot.
In 1892, E. E. Barnard observed a fifth satellite of Jupiter using the refractor telescope at the Lick Observatory in California. This relatively small object was later named Amalthea, and would be the last planetary moon to be discovered directly by visual observation.
In 1932, Rupert Wildt identified absorption bands of ammonia and methane in the spectra of Jupiter; and by 1938, three long-lived anticyclonic features termed “white ovals” were observed. For several decades, they remained as separate features in the atmosphere, sometimes approaching each other but never merging. Finally, two of the ovals merged in 1998, then absorbed the third in 2000, becoming Oval BA.
Beginning in the 1950s, radiotelescopic research of Jupiter began. This was due to astronomers Bernard Burke and Kenneth Franklin’s detection of radio signals coming from Jupiter in 1955. These bursts of radio waves, which corresponded to the rotation of the planet, allowed Burke and Franklin to refine estimates of the planet’s rotation rate.
Infrared image of Jupiter from SOFIA’s First Light flight composed of individual images at wavelengths made by Cornell University’s FORCAST camera. Credit: Anthony Wesley/Cornell University
Over time, scientists discovered that there were three forms of radio signals transmitted from Jupiter – decametric radio bursts, decimetric radio emissions, and thermal radiation. Decametric bursts vary with the rotation of Jupiter, and are influenced by the interaction of Io with Jupiter’s magnetic field.
Decimetric radio emissions – which originate from a torus-shaped belt around Jupiter’s equator – are caused by cyclotronic radiation from electrons that are accelerated in Jupiter’s magnetic field. Meanwhile, thermal radiation is produced by heat in the atmosphere of Jupiter. Visualizations of Jupiter using radiotelescopes have allowed astronomers to learn much about its atmosphere, thermal properties and behavior.
Exploration:
Since 1973, a number of automated spacecraft have been sent to the Jovian system and performed planetary flybys that brought them within range of the planet. The most notable of these was Pioneer 10, the first spacecraft to get close enough to send back photographs of Jupiter and its moons. Between this mission and Pioneer 11, astronomers learned a great deal about the properties and phenomena of this gas giant.
Artist impression of Pioneer 10 at Jupiter. Image credit: NASA/JPL
For example, they discovered that the radiation fields near the planet were much stronger than expected. The trajectories of these spacecraft were also used to refine the mass estimates of the Jovian system, and radio occultations by the planet resulted in better measurements of Jupiter’s diameter and the amount of polar flattening.
Six years later, the Voyager missions began, which vastly improved the understanding of the Galilean moons and discovered Jupiter’s rings. They also confirmed that the Great Red Spot was anticyclonic, that its hue had changed sine the Pioneer missions – turning from orange to dark brown – and spotted lightning on its dark side. Observations were also made of Io, which showed a torus of ionized atoms along its orbital path and volcanoes on its surface.
On December 7th, 1995, the Galileo orbiter became the first probe to establish orbit around Jupiter, where it would remain for seven years. During its mission, it conducted multiple flybys of all the Galilean moons and Amalthea and deployed an probe into the atmosphere. It was also in the perfect position to witness the impact of Comet Shoemaker–Levy 9 as it approached Jupiter in 1994.
On September 21st, 2003, Galileo was deliberately steered into the planet and crashed in its atmosphere at a speed of 50 km/s, mainly to avoid crashing and causing any possible contamination to Europa – a moon which is believed to harbor life.
Artist impression of New Horizons with Jupiter. Image credit: NASA/JPL/JHUAPL
Data gathered by both the probe and orbiter revealed that hydrogen composes up to 90% of Jupiter’s atmosphere. The temperatures data recorded was more than 300 °C (570 °F) and the wind speed measured more than 644 kmph (400 mph) before the probe vaporized.
In 2000, the Cassini probe (while en route to Saturn) flew by Jupiter and provided some of the highest-resolution images ever taken of the planet. While en route to Pluto, the New Horizons space probe flew by Jupiter and measured the plasma output from Io’s volcanoes, studied all four Galileo moons in detail, and also conducting long-distance observations of Himalia and Elara.
NASA’s Juno mission, which launched in August 2011, achieved orbit around the Jovian planet on July 4th, 2016. The purpose of this mission to study Jupiter’s interior, its atmosphere, its magnetosphere and gravitational field, ultimately for the purpose of determining the history of the planet’s formation (which will shed light on the formation of the Solar System).
As the probe entered its polar elliptical orbit on July 4th after completing a 35-minute-long firing of the main engine, known as Jupiter Orbital Insertion (or JOI). As the probe approached Jupiter from above its north pole, it was afforded a view of the Jovian system, which it took a final picture of before commencing JOI.
Illustration of NASA’s Juno spacecraft firing its main engine to slow down and go into orbit around Jupiter. Credit: NASA/Lockheed Martin
On July 10th, the Juno probe transmitted its first imagery from orbit after powering back up its suite of scientific instruments. The images were taken when the spacecraft was 4.3 million km (2.7 million mi) from Jupiter and on the outbound leg of its initial 53.5-day capture orbit. The color image shows atmospheric features on Jupiter, including the famous Great Red Spot, and three of the massive planet’s four largest moons – Io, Europa and Ganymede, from left to right in the image.
The next planned mission to the Jovian system will be performed by the European Space Agency’s Jupiter Icy Moon Explorer (JUICE), due to launch in 2022, followed by NASA’s Europa Clipper mission in 2025.
Exoplanets:
The discovery of exoplanets has revealed that planets can get even bigger than Jupiter. In fact, the number of “Super Jupiters” observed by the Kepler space probe (as well as ground-based telescopes) in the past few years has been staggering. In fact, as of 2015, more than 300 such planets have been identified.
Notable examples include PSR B1620-26 b (Methuselah), which was the first super-Jupiter to be observed (in 2003). At 12.7 billion years of age, it is also the third oldest known planet in the universe. There’s also HD 80606 b (Niobe), which has the most eccentric orbit of any known planet, and 2M1207b (Lerna), which orbits the brown dwarf Fomalhaut b (Illion).
Here’s an interesting fact. Scientist theorize that a gas gain could get 15 times the size of Jupiter before it began deuterium fusion, making it a brown dwarf star. Good thing too, since the last thing the Solar System needs is for Jupiter to go nova!
Jupiter was appropriately named by the ancient Romans, who chose to name after the king of the Gods (also known as Jove). The more we have come to know and understand about this most-massive of Solar planets, the more deserving of this name it appears.
Like splitting double stars, hunting for the faint lesser known moons of the solar system offers a supreme challenge for the visual observer.
Sure, you’ve seen the Jovian moons do their dance, and Titan is old friend for many a star party patron as they check out the rings of Saturn… but have you ever spotted Triton or Amalthea?
Welcome to the challenging world of moon-spotting. Discovering these moons for yourself can be an unforgettable thrill.
One of the key challenges in spotting many of the fainter moons is the fact that they lie so close inside the glare of their respective host planet. For example, +11th magnitude Phobos wouldn’t be all that tough on its own, were it not for the fact that it always lies close to dazzling Mars. 10 magnitudes equals a 10,000-fold change in brightness, and the fact that most of these moons are swapped out is what makes them so tough to see. This is also why many of them weren’t discovered until later on.
But don’t despair. One thing you can use that’s relatively easy to construct is an occulting bar eyepiece. This will allow you to hide the dazzle of the planet behind the bar while scanning the suspect area to the side for the faint moon. Large aperture, steady skies, and well collimated optics are a must as well, and don’t be afraid to crank up the magnification in your quest. We mentioned using such a technique previously as a method to tease out the white dwarf star Sirius b in the years to come.
A homemade occulting bar eyepiece with the barrel removed. One bar is a strip of foil, and the other is a E-string from a guitar. Image credit: Dave Dickinson
What follows is a comprehensive list of the well known ‘easy ones,’ along with some challenges.
We included a handy drill down of magnitudes, orbital periods and maximum separations for the moons of each planet right around opposition. For the more difficult moons, we also noted the circumstances of their discovery, just to give the reader some idea what it takes to see these fleeting worlds. Remember though, many of those old scopes used speculum metal mirrors which were vastly inferior to commercial optics available today. You may have a large Dobsonian scope available that rivals these scopes of yore!
The orbits of the Martian moons. Image credit: Starry Night Education Software
Mars- The two tiny moons of Mars are a challenge, as it’s only possible to nab them visually near opposition, which occurs about once every 26 months. Mars next reaches opposition on May 22nd, 2016.
Phobos:
Magnitude: +11.3
Orbital period: 7 hours 39 minutes
Maximum separation: 16”
Deimos:
Magnitude: +12.3
Orbital period: 1 day 6 hours and 20 minutes
Maximum separation: 54”
The moons of Mars were discovered by American astronomer Asaph Hall during the favorable 1877 opposition of Mars using the 26-inch refracting telescope at the U.S. Naval Observatory.
Jupiter- Though the largest planet in our solar system also has the largest number of moons at 67, only the four bright Galilean moons are easily observable, although owners of large light buckets might just be able to tease out another two. Jupiter next reaches opposition March 8th, 2016.
Ganymede:
Magnitude: +4.6
Orbital period: 7.2 days
Maximum separation: 5’
Callisto
Magnitude: +5.7
Orbital period: 16.7 days
Maximum separation: 9’
Io
Magnitude: +5.0
Orbital period: 1.8 days
Maximum separation: 1’ 50”
Europa
Magnitude: +5.3
Orbital period: 3.6 days
Maximum separation: 3’
Amalthea
Magnitude: +14.3
Orbital period: 11 hours 57 minutes
Maximum separation: 33”
Himalia
Magnitude: +15
Orbital period: 250.2 days
Maximum separation: 52’
Note that Amalthea was the first of Jupiter’s moons discovered after the four Galilean moons. Amalthea was first spotted in 1892 by E. E. Barnard using the 36” refractor at the Lick Observatory. Himalia was also discovered at Lick by Charles Dillon Perrine in 1904.
Titan and Rhea imaged via Iphone and a Celestron NexStar 8SE telescope. Image credit: Andrew Symes (@failedprotostar)
Saturn- With a total number of moons at 62, six moons of Saturn are easily observable with a backyard telescope, though keen-eyed observers might just be able to tease out another two:
(Note: the listed separation from the moons of Saturn is from the limb of the disk, not the rings).
Titan
Magnitude: +8.5
Orbital period: 16 days
Maximum separation: 3’
Rhea
Magnitude: +10.0
Orbital period: 4.5 days
Maximum separation: 1’ 12”
Iapetus
Magnitude: (variable) +10.2 to +11.9
Orbital period: 79 days
Maximum separation: 9’
Enceladus
Magnitude: +12
Orbital period: 1.4 days
Maximum separation: 27″
Dione
Magnitude: +10.4
Orbital period: 2.7 days
Maximum separation: 46”
Tethys
Magnitude: +10.2
Orbital period: 1.9 days
Maximum separation: 35”
Mimas
Magnitude: +12.9
Orbital period: 0.9 days
Maximum separation: 18”
Hyperion
Magnitude: +14.1
Orbital period: 21.3 days
Maximum separation: 3’ 30”
Phoebe
Magnitude: +16.6
Orbital period: 541 days
Maximum separation: 27’
Hyperion was discovered by William Bond using the Harvard observatory’s 15” refractor in 1848, and Phoebe was the first moon discovered photographically by William Pickering in 1899.
Uranus- All of the moons of the ice giants are tough. Though Uranus has a total of 27 moons, only five of them might be spied using a backyard scope. Uranus next reaches opposition on October 12th, 2015.
Titania
Magnitude: +13.9
Orbital period:
Maximum separation: 28”
Oberon
Magnitude: +14.1
Orbital period: 8.7 days
Maximum separation: 40”
Umbriel
Magnitude: +15
Orbital period: 4.1 days
Maximum separation: 15”
Ariel
Magnitude: +14.3
Orbital period: 2.5 days
Maximum separation: 13”
Miranda
Magnitude: +16.5
Orbital period: 1.4 days
Maximum separation: 9”
The first two moons of Uranus, Titania and Oberon, were discovered by William Herschel in 1787 using his 49.5” telescope, the largest of its day.
Triton in orbit around Neptune near opposition in 2011. Image credit: Efrain Morales
Neptune- With a total number of moons numbering 14, two are within reach of the skilled amateur observer. Opposition for Neptune is coming right up on September 1st, 2015.
Triton
Magnitude: +13.5
Orbital period: 5.9 days
Maximum separation: 15”
Nereid
Magnitude: +18.7
Orbital period: 0.3 days
Maximum separation: 6’40”
Triton was discovered by William Lassell using a 24” reflector in 1846, just 17 days after the discovery of Neptune itself. Nereid wasn’t found until 1949 by Gerard Kuiper.
Pluto-Yes… it is possible to spy Charon from Earth… as amateur astronomers proved in 2008.
Charon
Magnitude: +16
Orbital period: 6.4 days
Maximum separation: 0.8”
Pluto! Click here for a (possible) capture of Charon as well. Image credit: Wendy Clark
In order to cross off some of the more difficult targets on the list, you’ll need to know exactly when these moons are at their greatest elongation. Sky and Telescope has some great apps in the case of Jupiter and Saturn… the PDS Rings node can also generate corkscrew charts of lesser known moons, and Starry Night has ‘em as well. In addition, we tend to publish cork screw charts for moons right around respective oppositions, and our ephemeris for Charon elongations though July 2015 is still active.
Good luck in crossing off some of these faint moons from your astronomical life list!
