Watch a Bright Star Disappear Behind the Moon Monday Night

Ever dabbled in the occult? You’ll have your chance Monday night March 10 when the waxing gibbous moon glides in front of the star Lambda Geminorum for much of North America, occulting it from view for an hour or more. Occultations of stars by the moon happens regularly but most go unnoticed by casual skywatchers. Lambda is an exception because it’s one of the brighter stars that happens to lie along the moon’s path. Shining at magnitude +3.6, any small telescope and even a pair of 10×50 or larger binoculars will show it disappear along the dark edge of the moon. 

Map showing where the occulation of Lambda Gem will be visible. Credit: International Occultation Timing Assn. (IOTA)
Map showing where the disappearance (right half of tube-like figure) and reappearance of Lambda Gem will be visible. Credit: International Occultation Timing Assn. (IOTA)

With a telescope you can comfortably watch the star creep up to the moon’s edge and better anticipate the moment of its disappearance. The fun starts a few minutes before the impending black out when the moon, speeding along its orbit at some 2,280 mph (3,700 km/hr),  draws very close to the star. During the final minute, Lambda may seem to hover forever at the moon’s invisible dark limb, and then – PFFFT – it’s gone! Whether you’re looking through telescope or binoculars, the star will blink out with surprising suddenness because the moon lacks an atmosphere.

Disappearance and reappearance seen from Minneapolis, Minn. Monday night. I've lightened the moon so you can see the dark limb. You'll likely not see this edge in a telescope because of glare. Stellarium
Disappearance and reappearance seen from Minneapolis, Minn. Monday night. I’ve lightened the moon so you can see the dark limb. You’ll likely not see this edge in a telescope because of glare. Stellarium

If there was air up there, Lambda would gradually dim and disappear. Even without special instruments, early astronomers could be certain the moon had little if anything to protect it from the vacuum of space by observing occultations.

As the moon moves approximately its own diameter in an hour, you can watch Lambda re-emerge along the bright limb roughly an hour later, though its return will lack the drama and contrast of a dark limb disappearance. While occultations allow us to see how swiftly the moon moves in real time as well as provide information on its atmosphere or lack thereof, real science can be done, too.


Planets also are occasionally occulted by the moon. Time lapse of Venus’ disappearance on May 16, 2010

Observers along the occultation boundary in the southern U.S. can watch the star pop in and out of view as it’s alternately covered and uncovered by lunar peaks jutting from the moon’s limb. Before spacecraft thoroughly mapped the moon, careful timings made during these “grazing occultations” helped astronomers refine the profile of the moon’s limb as well as determine elevations of peaks and crater walls in polar regions. They can still be useful for refining a star’s position and motion in the sky.

The moon’s limb can also be used much like a doctor’s scalpel  to split unsuspected  double stars that otherwise can’t be resolved by direct observations. Take Lambda Gem for instance. We’ve known for a long time that it totes around a magnitude +10.7 companion star 10 arc seconds to its north-northeast,  but previous occultations of the star have revealed an additional companion only a few hundredths of an arc second away orbiting the bright Lambda primary. The star plays a game of hide-and-seek, visible during some occultations but not others. Estimated by some as one magnitude fainter than Lambda, keep an eye out for it Monday night in the instant after Lambda goes into hiding.


Lunar occultation and reappearance of Antares Oct. 21, 2009

I watched just such a  “two-step” disappearance of Antares and it fainter companion some years back. With brilliant Antares briefly out of view behind the moon’s limb, I easily spotted its magnitude +5.4 companion just 2.5 arc seconds away – an otherwise very difficult feat at my northern latitude.

Want to know more about things that disappear (and reappear) in the night? Make a visit to the International Occultation Timing Association’s website where you’ll find lists of upcoming events, software and how to contribute your observations. If you’re game for Monday night’s occultation, click HERE for a list of cities and times. Remember that the time show is Universal or Greenwich Time. Subtract 4 hours for Eastern Daylight, 5 for Central, 6 for Mountain and 7 for Pacific.  Wishing you clear skies as always!

How to Not Die While Stargazing in the Cold

Bitter cold lies ahead for many skywatchers in the U.S. and Canada in the coming week as the polar vortex swoops down from Santa’s village for round two this season. Will that stop you from going out to enjoy the winter wonders of Jupiter, the M82 supernova and Orion? It needn’t if you take the proper precautions.

In all honesty, you’ll probably still get cold if you attempt to observe on windy, subzero nights, but if you follow these helpful hints, you won’t get as cold. That said, there are two key ingredients to a successful and happy night under the winter sky: dressing well and planning in advance what you want to see.

I know it looks like an alien an abduction with only clothes left behind, but consider this an illustration of good nighttime winterwear. Credit: Bob King
I know it looks like an alien abduction with only the clothes left behind, but consider this an illustration of good nighttime winterwear. Credit: Bob King

Dressing well means having to accept the fact that even though you still feel warm walking out the door, 10 minutes later you won’t be. Always layer to the hilt. Insulated pack boots like those made by Sorrel or LaCrosse will keep your feet toasty for at least an hour of standing in place at the telescope.

I still wear blue jeans during winter, but when out getting a winter star tan, I pull on a pair of insulated snow pants.  To keep heat from escaping the rest of the body, a flannel shirt, thick sweater and some kind of down or insulated coat will provide protection right up to your neck. Some folks like the all-in-one approach and don a snowmobile suit. Add a scarf, a bomber cap with furry ear flaps for the head region and lined mittens or gloves for your digits, and you’re almost ready to do battle. Assuming you still have energy left after building a fortress around your person.

Chemical heating packets are VERY helpful tucked inside your gloves or boots if your feet have a tendency to get cold. Open them up 10 minutes beforehand and be sure enough air circulates around them. It makes them more effective. Credit: Bob King
Tuck chemical hand warmer packets inside your gloves or boots. Credit: Bob King

About gloves. I use lined deerskin gloves with chemical hand-warmers nestled in each palm. It’s so nice to have something warm to push your fingers into when they get chilled. Others prefer the wiser dual-glove approach – wearing a pair of thin gloves inside mittens that Velcro open across the palm. That way you use your fingers to adjust focus or check a chart and then safely tuck your hands back into the mittens.

On super-cold nights I’ll set the telescope up right outside the house so I can bail when necessary, but on exceptional nights when it might be well below zero but not windy, I’ll make the drive to the country for darker skies and set up on the proverbial road in the middle of nowhere.

I limit my observing to two hours maximum. Not because I have any control over time; that’s as much as this body can take when it’s -20 F. One little trick I’ve employed over the years to survive astronomical cold is to keep moving. I check charts constantly, set eyepieces down in the trunk of the car, then return to pick up a different eyepiece, take a short walk and even run in place. Hey, only the wolves are watching, so who cares? All this to keep the body moving to generate heat.

On very cold nights it's a good idea to make a concise observing plan to efficiently use your time at the telescope. I grab a few charts and often take brief notes outside using a red flashlight. Credit: Bob King
On very cold nights it’s a good idea to make a concise observing plan to efficiently use your time at the telescope. I grab a few charts and often take brief notes outside using a red flashlight. Credit: Bob King

If I do freeze, the car provides some solace. A typical drive home will find me steering with my inner arms, my crabbed hands straining to absorb every molecules of hot air blasting from the vents

The second key ingredient to a successful, soulful, subzero night is planning. If you prepare a short list either on paper or mentally of winter sky gems before you walk out the door, you’ll spend your stellar minutes more efficiently and return indoors a happy camper.

I keep it simple. If there’s a bright planet out, that’s always on my list. With Jupiter shining so enticingly these nights, how can you not go out to see what the weather’s doing on the solar system’s biggest planet? Relish the thought that the cloud tops you’re seeing are cold enough at -230 F (-145 C) to snow ammonia flakes. Makes 20 below almost seem like shirtsleeve weather.

The well-dressed stargazer does not fear the winter night. Credit: Bob King
A well-dressed stargazer relishes a night under the winter stars. Credit: Bob King

Add in a few variable stars, a supernova, maybe a comet and two or three deep sky objects and I feel a sense of connection and accomplishment by the time I return inside to what now feels like a Hawaiian vacation in my living room. Total time elapsed: maybe an hour. Too much? 15 minutes for a pretty double star and a current planet will do. Astronomy photos, articles and book are great, but we all need the real thing from time to time; there’s no substitute for a direct connection to the cosmic wilderness.

One crucial tip on doing astronomy in winter. Make sure your telescope is COLD. A spare meat locker for storage would be ideal. Barring that, place the scope outside and let it cool down before you begin your observing session. If it comes directly from the house, 45 minutes to an hour should be enough, depending on the temperature and aperture size. If you store it in a garage or shed, 20 minutes should do the trick.

A brilliant moonlit night in January with the Big Dipper rising in the northeastern sky. Credit: Bob King
A brilliant moonlit night in January with the Big Dipper rising in the northeastern sky. Credit: Bob King

Ready to zip up? Go for it! I ran into a woman a couple weeks back who told me she loved winter because the cold made her feel alive. Man, she hit it right on the head. I’ll leave you with a quote from one of my favorite old-time authors, Joseph Elgie, an English amateur astronomer who wrote about the pleasures of the sky no matter the season in a book titled The Night Skies of a Year. This entry is from February about the year 1907:

“Shortly after nine o’clock Procyon could be seen through the openings in the flying clouds, not far from the meridian. The sky resembled a vast snow-field in swift motion – a snow field showing fleeting patches of blue, which were studded with sparklets of silver, and Procyon was one of those sparklets. In the sou’west too, I could discern a coppery gleam on the pale blue background of the sky. It was Betelgeuse. What pictures of tender loveliness were these!”

Dark Sky Regulations Bring Zodiacal Light to Rhode Island Observatory

The result of sunlight reflected off fine particles of dust aligned along the plane of the Solar System, zodiacal light appears as a diffuse, hazy band of light stretching upwards from the horizon after sunset or before sunrise. Most people have never seen zodiacal light because it’s very dim, and thus an extremely dark sky is required. But thanks to recent dark sky regulations that were passed in the coastal Rhode Island town of Charlestown, this elusive astronomical phenomenon has become visible — to the particular delight of one local observatory.


Frosty Drew Observatory is a small, privately-run observatory featuring a Meade Schmidt Cassegrain LX200 16″ telescope mounted on an alt-azimuth pier inside a dome that stands among the sports fields, parking areas, and nature trails of Ninigret Park and Wildlife Refuge in southern Rhode Island. Being a good distance from urban centers and developed areas, the skies there are some of the darkest in the state. But situated along the eastern seaboard of the United States, even Charlestown’s coast lies beneath a perpetual haze of light pollution.

A new town ordinance, passed in 2012, helped to darken the skies a notch. And while watching comet ISON one evening, astronomer Scott MacNeill became aware of the results.

The following is an excerpt from a Jan. 7 article by Cynthia Drummond of The Westerly Sun, reprinted with permission:

Scott MacNeill was in Ninigret Park, his telescope trained on the comet “Ison,” when he saw something he had never seen before: a celestial phenomenon called “zodiacal light.” After several decades of being obscured by light pollution, the feature was visible again, thanks to the town’s “dark sky” ordinance.

At first, MacNeill, an astronomer and the assistant director of the Frosty Drew observatory, didn’t believe what he was seeing. The cone of light, which he initially thought was light pollution, turned out to be a faint, white glow that astronomers at the observatory hadn’t glimpsed in recent memory.

A line of visitors is cast in silhouette against the evening sky as they wait to go into the Frosty Drew Observatory. (Susannah Snowden / The Westerly Sun)
A line of visitors is cast in silhouette against the evening sky as they wait to go into the Frosty Drew Observatory. (Susannah Snowden / The Westerly Sun)

“To see it in New England, period, is amazing, Zodiacal light is a common marker for the quality of a dark sky location.”

– Scott MacNeill, Astronomer, Frosty Drew Observatory

“I was sitting back for a minute, just looking at the sky, and I said ‘wait a minute. This is the southeast, and to the southeast is the ocean. What is coming up in the southeast?’ And then I noticed the cone. And I’m like ‘no way. That can’t be zodiacal light.’ I’ve heard so many stories about the days of old at Frosty Drew when you used to see zodiacal light here,” he said.

MacNeill credits Charlestown’s dark sky ordinance with reducing light pollution to the point where zodiacal light can be seen again. The ordinance, adopted in October 2012, regulates commercial outdoor lighting in order to improve the town’s dark sky for star-gazers, and to protect residents, wildlife and light-sensitive plants from the effects of light pollution.

One of the provisions of the ordinance requires that new lighting fixtures be designed to focus downward so light does not radiate up into the sky. Lighting installed before the ordinance was passed is exempt from the new regulations.

Building and Zoning Official Joe Warner explained that after the ordinance passed, two major sources of light pollution near the observatory were modified so they would be less polluting.

“At Ninigret Wildlife Refuge, some of the pole lights were changed to dark sky compliant lighting. The Charlestown Ambulance barn also replaced their lights with dark sky compliant lights,” he said.

Charlestown has been recognized as one of the only dark spots on the New England coast — a rare treat for people who enjoy looking at the night sky.

(Read the full article on The Westerly Sun’s website here.)

_________________

It’s fantastic to see results like this both occurring and being publicized, as dark skies have become quite rare in many populated areas of the world. People who live in or near major metropolitan areas — even in the surrounding sprawling suburbs — often never truly get a dark sky, not such that the dimmer stars, the Milky Way, meteor showers — and yes, the zodiacal light — can be readily seen on an otherwise clear night. The view of a star-filled night sky that has been a part of the human existence for millennia has steadily been doused by the murky glow of artificial lighting. Luckily groups like the International Dark Sky Association are actively trying to change that, but change isn’t always welcome — or quick.

At least, in one Rhode Island town anyway, a small victory has been won for the night.

(HT to Brown University’s Ladd Observatory in Providence for the heads-up on this story.)

Super-sensitive Camera Captures a Direct Image of an Exoplanet

The world’s newest and most powerful exoplanet imaging instrument, the recently-installed Gemini Planet Imager (GPI) on the 8-meter Gemini South telescope, has captured its first-light infrared image of an exoplanet: Beta Pictoris b, which orbits the star Beta Pictoris, the second-brightest star in the southern constellation Pictor. The planet is pretty obvious in the image above as a bright clump of pixels just to the lower right of the star in the middle (which is physically covered by a small opaque disk to block glare.) But that cluster of pixels is really a distant planet 63 light-years away and several times more massive — as well as 60% larger — than Jupiter!

And this is only the beginning.

GPI installed on the Gemini South 8m telescope. GPI is the boxed suite mounted under the platform. (Gemini Observatory)
GPI installed on the Gemini South 8m telescope. GPI is the boxed suite mounted beneath the platform. (Gemini Observatory)

While many exoplanets have been discovered and confirmed over the past couple of decades using various techniques, very few have actually been directly imaged. It’s extremely difficult to resolve the faint glow of a planet’s reflected light from within the brilliant glare of its star — but GPI was designed to do just that.

“Most planets that we know about to date are only known because of indirect methods that tell us a planet is there, a bit about its orbit and mass, but not much else,” said Bruce Macintosh of the Lawrence Livermore National Laboratory, who led the team that built the instrument. “With GPI we directly image planets around stars – it’s a bit like being able to dissect the system and really dive into the planet’s atmospheric makeup and characteristics.”

And GPI doesn’t just image distant Jupiter-sized exoplanets; it images them quickly.

“Even these early first-light images are almost a factor of ten better than the previous generation of instruments,” said Macintosh. ” In one minute, we were seeing planets that used to take us an hour to detect.”

Despite its large size, Beta Pictoris b is a very young planet — estimated to be less than 10 million years old (the star itself is only about 12 million.) Its presence is a testament to the ability of large planets to form rapidly and soon around newly-formed stars.

Read more: Exoplanet Confirms Gas Giants Can Form Quickly

“Seeing a planet close to a star after just one minute, was a thrill, and we saw this on only the first week after the instrument was put on the telescope!” added Fredrik Rantakyro a Gemini staff scientist working on the instrument. “Imagine what it will be able to do once we tweak and completely tune its performance.”

Another of GPI’s first-light images captured light scattered by a ring of dust that surrounds the young star HR4796A , about 237 light-years away:

GPI first-light images of HR4796A. (Processing by Marshall Perrin, Space Telescope Science Institute.)
GPI first-light images of HR4796A. (Processing by Marshall Perrin, Space Telescope Science Institute.)

The left image shows shows normal light, including both the dust ring and the residual light from the central star scattered by turbulence in Earth’s atmosphere. The right image shows only polarized light. Leftover starlight is unpolarized and hence removed. The light from the back edge of the disk (to the right of the star) is strongly polarized as it reflects towards Earth, and thus it appears brighter than the forward-facing edge.

It’s thought that the reflective ring could be from a belt of asteroids or comets orbiting HR4796A, and possibly shaped (or “shepherded,” like the rings of Saturn) by as-yet unseen planets. GPI’s advanced capabilities allowed for the full circumference of the ring to be imaged.

The GPI integration team celebrates after obtaining first light images (Gemini Observatory)
The GPI integration team celebrating after obtaining first light images (Gemini Observatory)

GPI’s success in imaging previously-known systems like Beta Pictoris and HR4796A can only indicate many more exciting exoplanet discoveries to come.

“The entire exoplanet community is excited for GPI to usher in a whole new era of planet finding,” says physicist and exoplanet expert Sara Seager of the Massachusetts Institute of Technology. “Each exoplanet detection technique has its heyday. First it was the radial velocity technique (ground-based planet searches that started the whole field). Second it was the transit technique (namely Kepler). Now, it is the ‘direct imaging’ planet-finding technique’s turn to make waves.”

This year the GPI team will begin a large-scale survey, looking at 600 young stars to see what giant planets may be orbiting them.

“Some day, there will be an instrument that will look a lot like GPI, on a telescope in space. And the images and spectra that will come out of that instrument will show a little blue dot that is another Earth.”

– Bruce Macintosh, GPI team leader

The observations above were conducted last November during an “extremely trouble-free debut.” The Gemini South telescope is located near the summit of Cerro Pachon in central Chile, at an altitude of 2,722 meters.

Source: Gemini Observatory press release

See the Youngest Moon of Your Life Tonight

The new year starts out with a bang, offering the chance to spy an exceptionally thin crescent moon shortly after sunset. Here’s how to find it. 

The moon’s age is determined by how many hours or days have passed since new moon phase. New moon occurs once a month when the moon lies in nearly the same direction as the sun in the sky. No one can see a new moon because it stays very close to the sun and lost in the glare of daylight.

To attempt your personal youngest moon yet, find a flat horizon to the southwest and start looking about 10 minutes after sunset. This panel shows the sky from four different locations. The times shown are 20 minute after local sunset and the moon's elevation at those times is also noted. Created with Stellarium
To attempt your personal youngest moon yet, find a flat horizon to the southwest and start looking about 10 minutes after sunset. This panel shows the sky from four different locations. The times and moon’s elevation are shown for 20 minutes after local sunset. The moon’s orientation is approximate. Created with Stellarium

Under favorable circumstances it isn’t too difficult to spot a 1-day-old moon, referred to as a young moon because it’s the first or youngest bit of moon we see after new moon. Young moons are delicate and tucked far down in the twilight glow shortly after sunset. Spotting one fewer than 24 hours old requires planning. You need a flat horizon, haze-free skies and a pair of binoculars. Being on time’s important, too. Be sure to arrive at your observing spot shortly before sundown. Knowing the point on the horizon where the sun sets will guide you to the crescent’s location.

An 18-hour-old crescent moon photographed in a 12-inch telescope on April 22, 2012. Credit and copyright: John Chumack and Maurice Massey
An 18-hour-old crescent moon photographed in a 12-inch telescope on April 22, 2012. Credit and copyright: John Chumack and Maurice Massey

Ready to rock and roll? New moon occurred at 5:14 a.m. (CST) today. For the U.S. Midwest that makes the moon approximately 12 hours old at sunset this evening. Since the moon moves to the east or away from the sun at the rate of one moon-diameter per hour, skywatchers in the western U.S. will have it somewhat easier shot at seeing it. In Denver, the moon will be 13 hours old, while in San Francisco it will have aged to 14 hours. Hawaii residents will have their shot at a 16-hour-old moon, still very young but farther yet from the sun and easier to see. To know exactly when the sun and moon set for your city, click HERE.

Luckily you’ll have more than just the sunset point to help know in which direction to look; Venus, itself a very thin crescent moon at the moment, hovers 7-8 degrees to the upper left of the moon. You should have no problem seeing a crescent Venus in binoculars.

The record for youngest moon spotted with the naked eye goes to writer and amateur astronomer Steven James O’Meara, who nabbed a 15 hour 32 minute crescent in May 1990. The skinniest moon ever seen with optical aid goes to Mohsen G. Mirsaeed of Tehran on September 7, 2002 at just 11 hours 40 minutes past new.

Venus, seen here several years back to the lower right of the moon along with Jupiter, will not only help with focus tonight but will guide toward the thin crescent. Credit: Bob King
Venus, seen here several years back to the lower right of the moon along with Jupiter, will not only help with focusing tonight but will guide skywatchers toward the thin crescent. Credit: Bob King

Based on these facts, it’s likely few will see the faint arc of moon with the naked eye especially in the eastern U.S. where the crescent will be only 11 hours old. Binoculars and telescopes will be required for most of us.  To meet tonight’s challenge, make sure your binoculars are focused at infinity before you start. Again, Venus comes to our aid. Carefully focus the planet until you see its crescent as sharply as possible. You can also focus on any clouds that might be present. Lacking that, aim for the most distant object in the landscape. Focus is critical. If you’re off, the thin moon will soften, spread out and appear even fainter.

I couldn't resist adding this pic of the waning moon taken by one of the International Space Station astronauts as it rose over the limb of the Earth. Credit: NASA
I couldn’t resist adding this fine photo of the waning moon taken by one of the International Space Station astronauts as it rose over the limb of the Earth. Credit: NASA

Start looking for the moon about 10 minutes after sundown in nearly the same direction as the sunset point within a strip of sky as wide as a typical binocular field of view or about 5 degrees. Slowly scan up and down and back and forth over the next 25 minutes looking for a wispy sliver of light against the deepening blue sky. Should you find the moon, you might be surprised at the broken appearance of the arc. These seeming breaks are caused by oblique lighting on crater walls and mountain peaks creating shadows long enough to bite into and hide portions of the moon’s sunlit edge.

I wish you the best in your search tonight for what could be one of the rarest astronomical sightings of your life. It won’t be easy. Whether you succeed or not, please drop us a comment and share your story.

Watch This Asteroid Not Hit Earth

Earlier today the near-Earth asteroid 2013 NJ sailed by, coming as close as 2.5 lunar distances — about 960,000 km/596,500 miles. That’s a relatively close call, in astronomical terms, but still decidedly a miss (if you hadn’t already noticed.) Which is a good thing since 2013 NJ is estimated to be anywhere from 120–260 meters wide (400-850 feet) and would have caused no small amount of damage had its path intersected ours more intimately.

Luckily that wasn’t the case, and instead we get watch 2013 NJ as it harmlessly passes by in the video above, made from images captured by “shadow chaser” Jonathan Bradshaw from his observatory in Queensland, Australia. Nice work, Jonathan!

Keep tabs on known near-Earth objects on the JPL close pass page here.

Guide to Safely Viewing Comet ISON on Perihelion Day, November 28

The day of truth is fast approaching. Will Comet ISON’s sungrazing ways spark it to brilliance or break it to bits? How bright will the comet become? Studying the latest images from NASA’s STEREO Ahead sun-watching spacecraft, it’s obvious that ISON remains healthy and intact. The most recent pictures taken from the ground confirm that no major breakup has occurred. Assuming that ISON doesn’t crumble apart on Nov. 28, when it passes just 730,000 miles (1.2 million km) from the sun, it could brighten to -4 magnitude or better in the hours leading up to and after the moment of perihelion at 12:24:57 p.m. CST (18:24:57 UT).

This beautiful photo of Comet ISON was taken from a mountaintop observatory with a 300mm lens by Juan Carlos Casado of Spain on Nov. 24, 2013. Casado “stacked” or composited four photos to enhance the brightness of the comet against twilight. Click to enlarge.
This beautiful photo of Comet ISON was taken from a mountaintop observatory with a 300mm lens by Juan Carlos Casado of Spain on Nov. 24, 2013. Casado “stacked” or composited four photos to enhance the brightness of the comet against twilight. Click to enlarge.

For comparison, the planet Venus hovers around -4 magnitude and is routinely visible visible with the naked eye in broad daylight if you know exactly where to look. For the sake of establishing a baseline, let’s imagine that ISON will match Venus in magnitude during its crack-the-whip fling around the sun. Naturally, this would put the comet within range of naked eye visibility smack in the middle of the day. Well, maybe. ISON presents us with a little problem. While it may grow bright enough to view in daylight, it will be very close to the sun on perihelion day. Not only will it be difficult to tease from the solar glare, but with the sun only a degree or two away, there’s a real danger you could damage your eyes if you stray too close.

Comet ISON swings rapidly around the sun on perihelion day Nov. 28. Times shown are CST with north up and west to the right. Created with Chris Marriott's SkyMap software
Comet ISON swings rapidly around the sun on perihelion day Nov. 28.  Positions are shown hourly with north up and west to the right. Created with Chris Marriott’s SkyMap software

During the early morning hours of the 28th, ISON will lie approximately 2.5 degrees from the sun’s limb or edge. At the time of perihelion that separation narrows to less than 1/2 degree or one solar diameter.  This is likely when the comet will shine brightest, but with the sun so close, it will be next to impossible to spot it with naked eye or binoculars at that time. Matter of fact, don’t even try – it’s not worth the risk of damaging your retinas. An expert observer with a carefully-aimed telescope might pick it up, but must use extreme caution that sunlight not enter the field of view. Come sunset, the distance widens again to a somewhat more comfortable 2.5 degrees.

Once, when following Venus as a crescent through inferior conjunction, I dared track it within 2.5 degrees of the sun. THAT was almost too close for comfort. I had to avert my vision from a brilliant wedge of internally reflected sunlight along one side of the view and wear sunglasses to temper the brilliance of the “safe zone” where Venus appeared.. Red and polarizing filters can help reduce glare and increase contrast for near-sun viewing of comets and planets.

Comet McNaught on Jan. 13, 2007 photographed with a 500mm lens. "Comet was easily visible by naked eye," said photographer Mark Vornhusen of Gais, Switzerland. Click to enlarge
Comet McNaught on Jan. 13, 2007 photographed with a 500mm lens. “Comet was easily visible by naked eye,” said photographer Mark Vornhusen of Gais, Switzerland. Will ISON give us a similar show? Click to enlarge. Credit: Mark Vornhusen / Wikipedia

In mid-January 2007, Comet C/2006 P1 McNaught had a similar close brush with the sun and peaked around magnitude -5. For several days around perihelion on Jan. 12 it was plainly visible with the naked eye in broad daylight. I spotted it 5.6 degrees from the sun at magnitude  -3.5 (twice as faint as Venus) at 10 a.m. on Jan. 13 and 5 degrees from the sun the following day when I estimated its magnitude at -4.5. While close, 5 degrees is a much more comfortable distance for comet and inner planet viewing.

Example using a rooftop to block the sun so you can search near it for any sign of the comet. If using binoculars, BE SURE you focus them at infinity before daytime comet hunting otherwise there's no way to know if the comet will be in focus. I use clouds (the best) or a distant treeline. Credit: Bob King
Example using a rooftop to block the sun. When using binoculars for daytime comet hunting, BE SURE you focus them first at infinity otherwise there’s no way to know if the comet will be in focus. I use clouds (the best) or a distant treeline. Credit: Bob King

Whether naked eye, binocular or telescope, the favorite method for finding Comet McNaught in 2007 remains the best for Comet ISON in 2013. Block out the sun by placing something with a crisp edge in its way. Power poles, street lights (finally a good use for them), buildings, roof gables, church steeples and even clouds make ideal sun filters. They effectively remove the sun and allow you to look as close as is safe. Safety is critical here – never look directly at the sun. The damage to your retina will be swift and painless. No comet is worth losing your precious sense of sight.

As Earth rotates, the sun slowly moves across the sky. When using binoculars, if you start to see a bright reflection from approaching sunlight in the field of view, shift your position and re-cover the sun. I’ve been asked if  you can simply hold an appropriate solar filter over your eye to dim the sun. Yes you can, but the filter will also completely block your view of the much, much fainter comet. Use the filter instead to dim the sun so you can hunt nearby for the comet.

Use these little pictures to help you know in what direction from the sun to look for Comet ISON every 2 hours from 8 a.m. to 2 p.m. CST Thursday Nov. 28. Stellarium
Use these little pictures to help you know what direction from the sun to look for Comet ISON between 8 a.m. and 2 p.m. CST Thursday Nov. 28. Add one hour for Eastern time; subtract 1 hour for Mountain and 2 hours for Pacific. Be sure to face the direction shown when using the diagrams and completely block the sun from view.  Stellarium
Our final view shows the comet shortly before sunset in the southwestern sky when it lie about 2.5 degrees directly above the sun.
Our final view shows the comet shortly before sunset in the southwestern sky when it lie about 2-2.5 degrees directly above the sun. Time is 4 p.m. CST

 

Since ISON will be 2.5 degrees from the sun in the early morning and again just before sunset, those might be the best times to find it. Compared to the hour or two around perihelion, the glare will be less though ISON will likely be a little fainter.  You can use the diagram above, suitable for mid-northern latitudes, to know in what direction from the sun to look for the comet. If ISON becomes at least as bright as Venus and your sky is deep blue and haze-free, you might just see it on Thursday before sitting down to that Thanksgiving turkey dinner. But of course much depends upon the comet.

Comet ISON will be under constant view Nov. 27-30 in the SOHO coronagraph, an instrument that blocks the sun so scientists can study the near-solar environment. Click to see images. Credit: NASA/ESA
Comet ISON will be under constant view Nov. 27-30 in the SOHO coronagraph, an instrument that blocks the sun so scientists can study the near-solar environment. Click to see images. Credit: NASA/ESA

Don’t fret if it’s cloudy. Head over to the Solar and Heliospheric (SOHO) website. There you’ll have a ringside seat Nov. 27-30 as Comet ISON makes its death-defying turn around the sun. Thereafter it will appear risk-free in the morning sky with what we hope will be a beautiful tail.

Why Is Comet ISON Green?

Undoubtedly, you’ve been seeing the recent images of Comet ISON now that it is approaching its close encounter with the Sun on November 28. ISON is currently visible to space telescopes like the Hubble and amateur astronomers with larger telescopes. But you might be wondering why many images show the comet with a green-ish “teal” or blue-green color.

Amateur Astronomer Chris Schur has put together this great graphic which provides information on the spectra of what elements are present in the comet’s coma.

For the conspiracy theorists out there, the green color is actually a good omen, and lots of comets display this color. The green color is a sign the comet is getting more active as gets closer to the Sun – meaning it is now putting on a good show for astronomers, and if it can continue to hold itself together, it might become one of the brightest comets in the past several years.

“ISON’s green color comes from the gases surrounding its icy nucleus,” says SpaceWeather.com’s Tony Phillips. “Jets spewing from the comet’s core probably contain cyanogen (CN: a poisonous gas found in many comets) and diatomic carbon (C2). Both substances glow green when illuminated by sunlight in the near-vacuum of space.”

Comet ISON on October 4, 2013 as seen over Arizona, viewed with a 12.5" telescope, over an hour exposure time. Credit and copyright: Chris Schur.
Comet ISON on October 4, 2013 as seen over Arizona, viewed with a 12.5″ telescope, over an hour exposure time. Credit and copyright: Chris Schur.

Both are normally colorless gases that fluoresce a green color when excited by energetic ultraviolet light in sunlight.

And if those poisonous gasses sound dangerous, don’t worry. They are spread out in space much too thinly to touch us here on Earth. So don’t fall prey to fear mongers who are out to bilk the masses – like people did in 1910 when Comet Halley made a return to the skies and swindlers pitched their ‘gas masks’ and special ‘comet pills’ for protection. And of course, nothing happened.

But back to the color. Chris Schur provided this info along with his graphic:

Your readers may appreciate knowing why comets can appear this color. The background image is the shot I took with my 12.5″ and an ST10xme CCD camera for 20 minutes in mid-October. A pale coloration of the front of the coma is seen. To the lower left is a shot with the same instrument but with a 100 lpmm (line pair per millimeter) diffraction grating in front of the CCD chip to break out the spectra of the objects in the entire field.

Here ISON is faintly seen to the left of center, and the first order spectra a band to its right. But the real answer comes when we use the software called Rspec to analyze this band of light. The result is on the lower right. Normally reflected sunlight is rather flat and bland, and mostly that is what ISON is right now, reflected from dust. But labeled are two humps in the blue and green parts of the spectrum labeled “C2” for a carbon molecule. This blue/green emission pair is what gives ISON the color.

Chris notes that as the comet nears the Sun, astronomers and astrophotographers will be able to resolve more spectral details in the comet. “It will be exciting to watch the changes as more molecules pop out,” Chris said via email, “and possibly when it is closest to the Sun, we just may see some metal lines like iron or magnesium from MELTED vaporized rock. How exciting!”

And for those who insist there is something nefarious about Comet ISON, take a look at this FAQ from our friend Stuart Atkinson, who hosts the great site Waiting for ISON. He addresses the many conspiracy theories that are out there regarding this comet.

ISON FAQ Sept 9 jpg