Sky & Telescope news
Friday, October 9
• Now that we're well into October, Deneb is replacing brighter Vega as the zenith star after dark (for skywatchers at mid-northern latitudes). Accordingly, Capricornus has replaced Sagittarius as the most notable constellation down in the south.
• In early dawn on Saturday morning the 10th, look east for the waning crescent Moon below the Venus-Jupiter-Mars collection, as shown here.
Saturday, October 10
• A dawn challenge for Sunday morning the 11th: About 30 or 40 minutes before sunrise, scan low with binoculars almost due east for the tiny point of Mercury (magnitude +0.6) with the thin crescent Moon, as shown in the second panel. They're far below and perhaps a bit left of bright Venus and Jupiter.
Despite appearances, Mercury and the Moon are fairly similar places — except that Mercury is 40% larger and has twice as much surface gravity, and it's hotter and brighter in the daytime.
Sunday, October 11
• The little constellation Delphinus, about a fist at arm's length upper left of Altair early these evenings, is a familiar group to scan with binoculars. But did you know about its twin orange variable stars for binoculars? See Gary Seronik's Binocular Highlight column and chart in the October Sky & Telescope, page 43. Also discover some deep telescopic targets in Delphinus in Ken Hewitt-White's Going Deep, page 57.
Monday, October 12
• Look low in the southeast in late twilight for Fomalhaut coming up. It stands highest in the south about 10 or 11 p.m.
• The eclipsing variable star Algol should be at its minimum light, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 11 p.m. Eastern Daylight Time, according to its recently revised timetable.
• New Moon (exact at 8:06 p.m. EDT).
Tuesday, October 13
• The Great Square of Pegasus balances on its corner high in the east at nightfall. Seen from your location, when it is exactly balanced? That is, when is the Square's bottom corner exactly below its bottom corner? It'll be sometime soon after the end of twilight, depending on both your latitude and longitude.
Wednesday, October 14
• Vega is the brightest star very high in the west at nightfall. Arcturus, equally bright, is getting low in the west-northwest. The brightest star in the vast expanse between them, about a third of the way from Arcturus back up toward Vega, is Alphecca, magnitude 2.2 — the crown jewel of Corona Borealis. Alphecca is a 17-day eclipsing binary, but its brightness dips are too slight for the eye to see reliably.
Thursday, October 15
• Look for the crescent Moon, Saturn, and Antares lined up in the southwest in late twilight, as shown here.
Friday, October 16
• The Moon hangs over Saturn and Antares in the southwest at dusk, as shown here.
• This is the time of year when, after nightfall, W-shaped Cassiopeia stands on end halfway up the northeastern sky — and when, off to its left, the dim Little Dipper extends leftward from Polaris in the north.
Saturday, October 17
• After dark, spot the W pattern of Cassiopeia standing on end high in northeast. The third segment of the W, counting from the top, points almost straight down. Extend it twice as far down and you're at the Double Cluster in Perseus. This pair of star-swarms is dimly apparent to the unaided eye in a dark sky, and visible in binoculars or a small, wide-field telescope from almost anywhere.
Want to become a better astronomer? Learn your way around the constellations. They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.
This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.
Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and once you know your way around, the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.
You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.
Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). As Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."This Week's Planet Roundup
Mercury is having a fine dawn apparition. Look for it about 45 to 30 minutes before sunrise low in the east, well below and perhaps a bit left of brilliant Venus and Jupiter. Mercury brightens from magnitude +1.0 to +0.2 this week.
Venus, Mars, and Jupiter hang together in the east (in Leo) before and during dawn. Venus, on top, is the brightest at magnitude –4.6. Jupiter is –1.8, and Mars, much closer to Jupiter, is much fainter at +1.8.
Jupiter and Mars pass through conjunction on October 17th and 18th just 0.4° apart. Jupiter and Venus are also approaching each other. Look too for Regulus (magnitude +1.4) above Venus.
Saturn (magnitude +0.6, just off the head of Scorpius) sinks away in the southwest in twilight. Don't confuse it with orange Antares twinkling 10° to its left. Binoculars help.
Uranus (magnitude +5.7, in Pisces) and Neptune (magnitude +7.8, in Aquarius) are well up in the east and southeast, respectively, by 8 or 9 p.m. Finder charts for Uranus and Neptune.
All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.
Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.
“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”
— Neil deGrasse Tyson
Watch for any slow, unusual meteors starting at nightfall tonight and tomorrow.
Some meteor showers are as regular as the seasons, but the Draconid meteors of early October are wildly variable. Most years nothing happens. But in 1933 and 1946 the Draconids produced two of the great meteor storms of the last century. Certain other years have produced lesser displays, with rates ranging from 20 to more than 500 meteors visible per hour by an ideally placed observer.
But don't expect any cosmic fireworks this year. Even though the Moon is out of the picture (a waning crescent that doesn't rise until about 4 a.m.), the meteor pros predict that this year's Draconids might come at a zenithal hourly rate, or ZHR, at the low end. You might see one every 5 minutes or so from a dark location.
The good news is that the shower's radiant lies near the head of Draco, a constellation that winds around Polaris and the Little Dipper. The radiant is highest in the evening, rather than in the morning hours as for most showers, so start watching at nightfall. The Draconids appear exceptionally slow-moving as meteors go; they are catching up to Earth from behind, so encounter velocities are only 20 km (12 miles) per second.
The Draconids are shed by Comet 21P/Giacobini-Zinner, a short-period comet in the Jupiter family that currently rounds the Sun about every 6.6 years. Most outbursts of Draconid meteors have happened in years close to the comet's perihelion, which it last reached in February 2012. That would suggest not much will happen in 2015, but with such a short-period comet you never know.
Nor is the timing of any possible shower very predictable. Activity in the recent past suggests that if we see anything this year, its brief peak could happen anytime from 21h Universal Time on the 8th (Thursday afternoon in the North American time zones) to 14h UT on the 9th (midday Friday in North America).
In 2011, bright moonlight and the shower's reputation for nonperformance resulted on only spotty amateur data. Too bad; the few counts that the International Meteor Organization received suggests that the ZHR that year hit 300. Researcher Josep Maria Trigo (Institute of Space Sciences, Spanish National Research Council) concludes that Earth passed in rapid succession through three dense streams of particles. Two of these streams were predicted to exist; the third was a surprise. A Draconid fireball over Spain rivaled the brightness of the waxing gibbous Moon in the same sky. Then in 2012 came a swarm of unusually faint Draconids, detected mostly by radar.
So even though mo such outburst is predicted this year, you never know. So take some time to enjoy the great outdoors tonight — and maybe catch a few flecks shed by a passing comet.
To learn more about meteors and especially the famous Perseid meteor shower, which dazzles skywatchers every August, download our free "shooting stars" eBook.
Keep watch on your northern sky after dark tonight (Wednesday October 7th). The aurora borealis could sweep down into our view from its usual far northern latitudes.
For the last 24 hours a geomagnetic storm has been building. It reached a geomagnetic K-index of 7, meaning strong, by 4 p.m. Eastern Standard Time (19h UT). According to an alert from NOAA's Space Weather Prediction Center, "aurora may be seen as low as Pennsylvania to Iowa to Oregon."
Maybe. Aurorae have a quite the habit of outwitting space-weather predictors. But occasionally they come even farther south than predicted.
The alert also warns of possible power-system voltage irregularities, intermittent problems with GPS reception, and loss of shortwave radio communication.
It doesn't take a solar flare or even a coronal mass ejection to disturb Earth's magnetic field and allow extra solar electrons to stream into the uppermost atmosphere. A coronal hole in the Sun's outer atmosphere is pointing our way, sending us extra-high-speed solar wind. In the transition zone between normal and fast solar wind, notes Tony Phillips of SpaceWeather.com, "solar-wind plasma piles up, producing density gradients and shock waves that do a good job of sparking auroras."
No promises. . . but don't wake up tomorrow to news of the sight you missed!
Unexplained ripples have been found racing outward in a dusty disk around a star.
Nearby debris disks — the dusty, sometimes rocky planes circling young stars — have only recently become the hunting grounds of astronomers, who search for the telltale signs of forming planets: gaps, clumps or warped features in these disks. But thus far, very few disks have revealed planets hidden inside. The majority remain a mystery waiting to be unfolded.
SPHERE, an instrument mounted on the Very Large Telescope in Chile, is designed to directly image debris disks and reveal their secrets. Its coronagraph blocks the light of the host star, while the instrument’s adaptive optics reveals details around the star to a resolution of 0.5 arcseconds, rivaling the Hubble Space Telescope’s imaging prowess.
In 2014, Anthony Boccaletti (Paris Observatory) and his colleagues pointed SPHERE at a test target known as AU Microscopii, a young star 32 light-years away in the southern constellation Microscopium. But what they found was something utterly unexpected: wave-like arches on one side of the disk. Were they real? The team turned to data gathered by the Hubble Space Telescope in 2010 and 2011, and sure enough, the features were there too.
What’s more, the arching waves had moved at a breakneck pace through the disk, moving away from the central star at 4 to 10 kilometers per second (between 9,000 and 22,000 mph).
“This is a fascinating result,” says Richard Nelson (Queen Mary University of London), who was not involved in the study. “But interpreting the observations is a real puzzle.” Not only have astronomers never seen anything like it, they really can’t find a viable explanation.
The five bright smears in AU Mic’s disk lie within 10 and 60 times the Earth-Sun distance of the star, and are probably clumps or clouds of dust shining in near-infrared light. The Hubble photos allowed the team to track the ripples over a 4-year baseline, revealing their immense speed. The outer waves moved much faster than the inner ones, and at least three of the features are moving so fast that they could easily slip beyond the star’s gravitational pull.No Good Explanation
Such high speeds rule out any classic scenarios caused by orbiting planets. A warp carved in the disk by a nearby planet, for example, would move at speeds too lethargic compared to the observed ripples. Boccaletti and his colleagues searched high and low for a planet with no luck. “If there was a planet in there and it was larger than 6 Jupiter masses, we'd be able to find it,” says co-author Dean Hines (Space Telescope Science Institute). “If there's something in there stirring up the pot, which there almost certainly is, it's going to be smaller than that.”
So maybe, the authors propose, two smaller as-yet unseen planets collided within the disk. After all, most astronomers expect that all forming planetary systems are extremely violent. Our solar system, for example, is still scarred by the collisions of its youth, which should have been readily visible to an extraterrestrial observer.
“If you grind up chalk, put it in a bag and pop it, the chalk dust goes everywhere,” Hines says. “It’s really hard if you're in the back of the room to see that piece of chalk, but once you explode it, it has a huge surface area and it's easy to see.” Although a collision might explain the asymmetries in brightness from one side of the disk to the other, it couldn’t cause material to move so fast.
The most promising scenario requires an even more violent interaction. Young stars, while promising abodes for life, are wildly active. They emit giant flares — huge eruptions of charged particles — that can wreak havoc on a circling planetary disk. If a flare hits a forming planet, it could easily strip material away from the planet and propagate it outward at rapid speeds. Nelson, however, doubts whether even these speeds would be fast enough to match those found within AU Microscopii’s disk.
The team plans to continue to observe the system with SPHERE and other facilities. “It's not often that you see something changing on human timescales,” says Hines, who is excited to see further changes that will allow them to narrow down the range of possibilities.
"We wish we knew what it was,” says co-author John Debes (Space Telescope Science Institute). “But sometimes you just have to throw up you hands and say 'We don't know what it is yet and we'll keep looking and keep thinking to try to come up with the answer.'”
Anthony Boccaletti et al. “Fast-Moving Structures in the Debris Disk Around AU Microscopii.” Nature. October 8, 2015.
Like people doing good imitations, novae often mimic planetary nebulae. Read on to learn how to watch the evolution of these tricksters using a common nebula filter.
Three novae highlight the October sky within reach of small to medium telescopes — V339 Delphini, V5668 Sagittarii, and a brand new discovery, V5669 Sagittarii. Japanese amateur astronomer Koichi Itagaki found the last while patrolling the sky with a 9-inch telescope and CCD camera on September 27, 2015. Itagaki pegged it at magnitude +9.8 at discovery; since then it's risen to about magnitude +9.0 and is easily visible in a small telescope at the end of evening twilight.
Whether it will rocket to new heights or plunge quickly back into the depths of obscurity is anyone's guess, but it's worth keeping an eye on. That's the fun of novae watching — you never know what to expect.
You'll find charts and links for this and the other featured novae in this article below, so you'll have the tools to follow their ups and downs.
Novae occur in close binary star systems where a normal, Sun-like star is paired with a planet-sized, supremely dense white dwarf. Gases captured from the companion by the dwarf accumulate on its surface, where they're compressed and heated through gravity until they reach a flash point. Boom! A powerful thermonuclear explosion lifts the star from obscurity to celebrity.
A system that once slumbered away at 15th magnitude or fainter suddenly becomes a "new star" 50,000-100,000 times more luminous than the Sun and easily visible with a small telescope or even the naked eye. Some of the energy from the nova explosion gets absorbed by hydrogen gas surrounding the star and re-radiated as hydrogen-alpha light that gives novae a crimson hue in their early stages.
Try to picture the cataclysm. The dwarf survives but remains hidden by the expanding fireball of debris hurtling into space at thousands of miles a second — a miniature supernova. Novae often radiate prominently. Early on, the fiery gases are thick and radiate light across the spectrum from infrared to ultraviolet and beyond. But as the fireball expands and cools, the material thins and soon emits the classic "forbidden lines" characteristic of highly rarefied gas ... and planetary nebulae.
One of the strongest emissions in both planetary nebulae and evolving novae is that of doubly-ionized oxygen or O III. Back in the 1860s, when early spectroscopes were focused on planetary nebulae, astronomers detected lines they'd never seen before and attributed them to a new element they named nebulium. Later, it was found to be none other than oxygen,emitting a greenish-turquoise light at 500.7 and 495.9 nanometers under highly rarefied conditions uncommon on Earth — hence the "forbidden" line designation.
Oxygen-III and similar high contrast filters that isolate this prominent emission line can be found in the eyepiece cases of many amateur astronomers. They not only reveal subtle details in nebulae otherwise lost to natural and human-made light pollution, but are extremely useful when tracking down faint, stellar planetary nebulae via a method known as "blinking".
In the blink method, you identify a likely suspect nebula, then slide the O III filter between eye and eyepiece. The filter darkens the field and attenuates the stars, but the planetary pops right into view because the filter allows blue-green O III to pass through to your eye. With a filter, a stellar planetary can appear 1-1.5 magnitudes brighter than it would without. The difference can be dramatic, making it easy to pick out the nebula even in a busy star field.
Guess what? Novae blink, too. Not right after their explosive phase, but several months later as the gas thins and begins emitting like a planetary. Both V339 Del (former Nova Delphini 2013) and V5668 Sgr (former Nova Sagittarii 2015 #2), discovered in March this year, are blinkers.
I've been blinking V339 Del since the early winter of 2013; V5668 Sgr only began its "optically thin" phase late this summer. I discovered it by accident during a star party when a rise in the nova's light to magnitude +9.0 after a long spell at 12th magnitude prompted me to use the filter.
V339 Del shines faintly at magnitude +13.1 but watch it pop with the O III filter. V5668 Sgr is much brighter — magnitude +8.8 — and appears even brighter when compared to nearby field stars of similar magnitude with a filter in place. Give it a try. It's a delightful way to observe the evolution of a stellar explosion right from home.
Over thousands of years, the material in a nova outburst thins, fades, and seeds its environment with gas and dust grains that may one day be gathered up to form a new star. And the dwarf? It returns to its thieving ways, only to erupt again in a thousand or ten thousand years.
Sky Atlas 2000.0 can help you get there.
The post Mosaic North America and Pelican nebula in narrowband appeared first on Sky & Telescope.
Comet 67P’s nucleus was born when two became one.
Comet nuclei often look weird. They can be oblong or misshapen potatoes, marred with craters and sinkholes. But when ESA’s Rosetta spacecraft first sent back images of the nucleus of Comet 67P/Churyumov-Gerasimenko, team scientists were a bit baffled by the “rubber ducky” they saw. The dirty iceball has two, kilometer-scale lobes, one about twice as wide as the other, connected by a thick “neck.”
Since these first images came in, astronomers have debate why Comet 67P looks this way. They have two ideas: either the current nucleus is the product of two separate ones that gently collided in the outer solar system and stuck together, or so much material eroded away from the neck region that it narrowed into a column.
The Rosetta team now says they have the answer, and it’s that the comet was born when two nuclei became one.
Matteo Massironi (University of Padova, Italy) and colleagues used images from the narrow-angle and wide-angle cameras of Rosetta’s Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) to investigate the nucleus’s origin. Some of these images reveal features down to 0.1 meter (0.3 foot) across, showing a nucleus akin to frozen putty, covered with terraces, pits, and cliffs.
It’s these features that the team took advantage of. With OSIRIS, the scientists peered down into pits and along terraces and found strata, layers of material like those you would see in rock on Earth, built up as the rock formed one layer at a time. Many of Comet 67P’s layers extend 150 meters or deeper, in some places reaching 650 meters down. You can think of them like the layers in an onion, the team explains September 28th in Nature.
The layers are too flat to be material rained down on the irregular surface after its formation, so like terrestrial strata, they were probably deposited during the nucleus’s formation.
If so, then these onion layers should form concentric rings around their parent body’s center of mass. If the nucleus began as one object, then the strata will encircle one center; if it began as two, then the strata in the duck's head and body will be oriented around different centers of mass, each in their respective lobes.
The team traced out the strata’s surfaces and extrapolated where the onion center was. They found that the layers do encircle two different centers, one in each lobe. Thus, Comet 67P’s nucleus formed in a low-speed collision of two nuclei. But the result also shows that the two objects — which we could now call Churyumov and Gerasimenko — formed in a similar way, accreting layers over time. Layering observed in other comet nuclei during flybys hints that Churyumov and Gerasimenko aren’t the only ones to have formed this way, study coauthor Björn Davidsson (Uppsala University, Sweden) says in the ESA press release.
Reference: M Massironi et al. “Two independent and primitive envelopes of the bilobate nucleus of comet 67P.” Nature. Published online September 28, 2015.
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AstroSat launched into orbit on September 28, 2015, and will soon start returning visible, ultraviolet, and X-ray images of the universe.
Indian astrophysics got a boost recently when an Indian Space Research Organization (ISRO) PSLV rocket launched from Satish Dhawan Space Center on September 28th, placing Astrosat in a low-Earth orbit inclined 6° to the equator. The multi-purpose observatory is equipped to observe the Universe across the X-ray spectrum, accompanied by simultaneous visible and ultraviolet light observations.
Previously, India has lofted X-ray detectors aboard high-altitude balloons and sub-orbital sounding rockets, but this is India’s first astronomical satellite. Data from AstroSat will be available to the Indian astronomy community via proposals for observations.
“Expectations naturally depend on the aspirations of the astronomer,” says payload manager Arikkala Raghurama Rao (Tata Institute of Fundamental Research). “Personally, I expect Astrosat to break new ground in understanding the jet emission from black holes (stellar-mass as well as supermassive black holes), the beaming geometry of pulsars, and extending the observations of short gamma-ray bursts to higher redshifts.”
With the capability of observing from visible wavelengths all the way through high-energy X-rays, Astrosat will also be capable of studying everything from nearby white dwarfs, pulsars, and supernova remnants to faraway galaxy clusters.From Visible Light to X-rays
Astrosat carries five astronomical instruments that observe the sky in five different wavelength ranges, from visible through near- and far-ultraviolet, to low-energy and high-energy X-rays.
- The Ultraviolet Imaging Telescope (UVIT) is a twin optical system, each primary mirror 37.5 centimeters in diameter and in a Ritchey-Chrétien configuration. Think of the UVIT payload as a set of binoculars in space, with each ocular about twice the size of a backyard 8-inch diameter Schmidt-Cassegrain telescope. The primary purpose of this instrument is to accompany X-ray observations with simultaneous visible, near-, and far-ultraviolet images, covering 130 to 530 nanometers.
- The Soft X-ray Telescope (SXT) focuses “soft” X-rays (that is, low-energy X-rays between 300 and 8,000 electron Volts) into images from which low-resolution spectra can also be extracted. Its design is similar to the Swift’s X-ray Telescope.
- The Large Area Xenon Proportional Counters (LAXPC) are three block-shaped detectors that collect X-rays with higher energies, between 3,000 and 80,000 eV. Unlike the SXT, this instrument doesn’t focus X-rays into images, but it does provide incredibly precise arrival times for each photon. Astronomers can also reconstruct low-resolution spectra from the data LAXPC collects.
- The Cadmium-Zinc-Telluride Imager (CZTI) collects X-ray photons with even higher energies, up to 150,000 eV. While it also doesn’t focus X-rays, this instrument can carry out polarization measurements, a capability lacking on most other X-ray telescopes.
- The Scanning Sky Monitor (SSM), a detector with a huge 10° by 90° field of view, which will scan the sky for transient X-ray sources. Its design is much like the decommissioned Rossi X-ray Timing Explorer (RXTE).
Another auxiliary payload aboard Astrosat is a Charged Particle Monitor (CPM), which counts charged particles to protect the satellite’s instruments, particularly when the spacecraft passes through the South Atlantic Anomaly region, an area of high electron and proton flux.New Capabilities
Astrosat joins several other X-ray observatories already in orbit: Chandra makes out fine details in low-energy X-ray images, NuSTAR brings high-energy X-rays into sharp focus, Swift monitors the sky for distant explosions bright in X-rays and gamma rays, and the European Space Agency’s (ESA) XMM-Newton is a light bucket that can measure X-ray spectra of faint sources. So what does Astrosat bring to the table?
Kulinder Pal Singh (Tata Institute for Fundamental Research) compares Astrosat to a combination of the Swift satellite and the now-retired Rossi X-ray Timing Explorer satellite (RXTE). Like Swift, Astrosat will hunt for X-ray transients and observe these sources across the visible-to-X-ray spectrum. And like RXTE, LAXPC’s triplet of detectors will measure the arrival time of each photon. LAXPC has the largest collecting area of any X-ray instrument ever built, and it’s currently the only one capable of studying X-ray fluctuations over millisecond timescales.
The satellite is now undergoing systems checks: the CPM and CZTI are now operational, and Singh says we can expect to see Astrosat’s first images about 6 to 8 weeks post-launch. The satellite has an expected lifetime of at least five years.
By the way, NORAD cataloged Astrosat as ID 2015-052A/40930 shortly after launch, but unfortunately for northern satellite spotters, Astrosat’s low-inclination orbit makes it visible only from Earth’s equatorial regions due to its low inclination orbit.
The Indian Space Research Organization has proven itself a force to be reckoned with thanks to recent success stories, including the Chandrayaan-1 lunar orbiter and the Mars Orbiter Mission, which successfully entered orbit around the Red Planet on September 24, 2014. (It’s worth noting that India is the only nation that was successful in fielding a mission to Mars on its first try!)
Now we can add Astrosat to India’s list of space success stories, one that holds a promise of some exciting astrophysics discoveries to come.
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SkyandTelescope.com's New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors statements. For further information contact the manufacturer or distributor. Announcements should be sent to nps@SkyandTelescope.com. Not all announcements will be listed.
Learn to see more detail on Jupiter by drawing at the eyepiece.
By Michael Rosolina in the Sky & Telescope January 2014 issue
Jupiter is consistently one of the most exciting subjects to observe in the solar system. Its large apparent size makes it a prime target for observers with almost any size telescope. But besides the two dusky equatorial bands that are usually visible, the planet’s cloud tops are relatively low contrast, making it a challenge to glean the most out of the view.
One way to improve your chances of detecting small-scale features and subtle color variations is to train your eye to see better with lots of practice. The best method to do that is by sketching the planet while observing.
Sketching forces you to carefully examine a feature and then record it on paper. The longer you focus on an area, the easier it becomes to distinguish delicate contrasts between features, or detect small storms in the planet’s many belts and zones. This month Jupiter is at its best for the year, so it’s a great time to try your hand to become a better observer through sketching.Preparation: The Key to Success
Before starting, you’ll need some drawing supplies. Planetary sketchers often use a pre-printed template that has the planet’s oblate shape already in place, as well as lines to record important details of the observation, such as the date, time, conditions, and instrument used. You can download these from planetary observing groups’ websites, including those of the Association of Lunar and Planetary Observers (www.alpo-astronomy.org), the British Astronomy Association (http://britastro.org/baa), and even some internet forums such as Cloudy Nights (www.cloudynights.com). Using a template enables you to concentrate on your target region of the planet without having to fuss with getting the shape of the planet correct. A template also provides a standardized form that is accepted by each of these observing groups, allowing you to contribute your observations to historical records when complete.
You’ll also need some pencils or other form of drawing tool. Graphite pencils come in different degrees of hardness; your standard No. 2 pencil will work fine. Multiple grades of pencil hardness are available through art supply stores. Additionally, you should have an eraser besides the one attached to your pencil. I use a kneaded eraser, which is a type of soft eraser that enables you to mold it quickly into any shape to erase very small areas.
You’ll also need a clipboard or a table and a comfortable observing chair: it’s easiest to concentrate on your view if you can be seated while observing. Finally, a battery-operated light of some kind is a must. Because Jupiter is so bright, you don’t have to preserve your night vision, so a white light is best (it’s a requirement if you are drawing in color at the telescope).
This year, the best part of Jupiter’s apparition occurs in the winter for Northern Hemisphere observers, so you’ll need to dress warmly. I can’t draw with gloves on, so I keep a couple of chemical hand warmers in my pockets. Fingerless gloves or pull-back mittens are also good options to keep your hands warm while drawing.Getting Down to Business
Now that you have everything ready, spend a few minutes soaking in the view before starting your sketch. This gives your eyes time to get used to the subtle contrasts and pastel hues of the planet’s belts and zones. There is so much to see on Jupiter that trying to draw the entire planet can be difficult, if not impossible, under excellent seeing. Jupiter’s rapid rotation of 9.9 hours to complete a single “day” causes features to move position in just a few minutes, so you’ll have to sketch quickly to capture the most detail. A guide to observing Jupiter appears on page 50.
One feature often overlooked on most planets is the slight darkening of the planet’s limb. When the planet is near quadrature, one limb will have more pronounced limb darkening than the other.
Because of the relatively low contrast of Jupiter’s cloud tops, it’s usually best to resist the temptation to employ high magnification. Depending on seeing conditions, I find a magnification range of roughly 200 to 260× gives the best balance between scale and sharpness in most cases. In poor seeing I rarely go higher than 160×, because above that the image becomes too soft.
In addition to looking at cloud-top features, check for one or more of the Galilean moons or their shadows transiting the face of the Jovian disk. All of the moons can be seen as they ingress and egress the Jovian limb. An article on observing Galilean moon transits appears on page 54.
After you’ve taken time to study Jupiter, it’s time to begin your sketch. It’s important to work fast because of Jupiter’s high rotation rate — 15 to 20 minutes is about all you have before features have moved significantly.
Begin by noting your start time in Universal Time (UT), and then start lightly drawing in the two main equatorial belts with your pencil to anchor your sketch. Add as many of the narrower belts and zones to the north and south as are visible in order to rough out the entire disk. Once this initial sketch is complete, go back to the main belts and shade in darkness along their north and south edges. The kneaded eraser comes in very handy to quickly carve out rifts within the belts, as well as to refine irregularities along their edges. Use your pencil with harder pressure to shade in any dark knots, barges, or other concentrations, and less pressure to lightly shade in any wispy festoons. Do the same thing with the narrower belts and zones, which have their own variations of shading and brightness. Use your kneaded eraser shaped to a point to render any bright ovals you see. There is often less detail near the limbs due to foreshortening and limb shading, so concentrate your efforts on features seen well away from these areas.
You’ll have an additional challenge if the Great Red Spot (GRS) is visible during your observing session. Portraying it accurately can be a little tricky. Just like the belts and zones, the longer you look, the more you’ll see. There are often subtle gradients within the famous elliptical storm. In addition, the GRS is sometimes surrounded by a white or light-colored “cavity” in the south edge of the South Equatorial Belt (SEB) known as the Red Spot Hollow.
To finish up the sketch, double check the positions and proportions of the various features you have recorded. Use your eraser to remove or lighten features where needed. For more control, you can press or roll the kneaded eraser instead of rubbing on the places you want to lighten. There are mostly no hard edges in the cloud tops of Jupiter, so you may need to soften the boundaries between the belts and zones by lightly blending. You can use your finger to blend adjacent light and dark areas, or use a tightly rolled stick of paper called a blending stump. Blending is also an easy way to depict limb darkening. Note the time you finish the drawing, and you are done.Strip Sketching
An innovative technique that you can employ to sidestep the difficulties of Jupiter’s rapid rotation is known as a strip sketch. With the strip sketch, you use a blank sheet of drawing paper instead of the oblate disk template. Start this drawing as close to the preceding limb as you can, and continue from there toward the planet’s central meridian (CM). Once you’ve reached the CM, you can simply add features as they cross the CM successively. Using this method, you let Jupiter’s rotation work for you,and you can continue working on the drawing for as long as you observe the planet that evening. Be sure to note the start and end time so you can figure out how many degrees of longitude you have recorded.
I often try to include some additional information, such as my observing conditions, unusual colored areas, or interesting occurrences during the session. Additionally, I indicate the direction of south or north in the drawing, the direction of the planet’s rotation, and the magnification used. I always include the System I and System II longitudes in order to track the positions of features I recorded. Depending on your personal preference, you can also add the planet’s altitude and diameter at the time of the observation.
The final step with your drawing, whether it is an extended strip sketch or a full disk sketch, is to preserve and share it. Drawings are usually preserved using spray fixative to keep the media from smudging or rubbing off (hair spray is an alternative). Many sketchers like to scan their work and use image-processing software to adjust the contrast, add color, mirror-reverse, or replace their handwritten notes with clean type. The sketch is then ready to share in online forums or the planetary observers’ associations mentioned earlier.
You now have a visual record of your observation and, more importantly, you have taken a huge step in training your eye to bring your observing talents up to a higher level. Good luck with your Jupiter sketch in this and future apparitions!
Michael Rosolina observes Jupiter with a Celestron C14 from the dark skies of Greenbrier County, West Virginia.
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