Posted on by Bob King

How to Find and Make the Most of Comet Lovejoy

This photo map shows Comet Lovejoy's nightly position among the winter stars through January 19th as it travels across the constellation Taurus not far from Aldebaran and the Pleiades star cluster. Click to enlarge. Credit: Bob King

Comet Q2 Lovejoy passed closest to Earth on January 7th and has been putting on a great show this past week. Glowing at magnitude +4 with a bluish coma nearly as big as the Full Moon, the comet’s easy to see with the naked eye from the right location if you know exactly where to look. I wish I could say just tilt your head back and look up and bam! there it would be, but it’ll take a little more effort than that. But just a little, I promise. 

Comet Lovejoy and its spectacular "lively" ion tail photographed on January 8th by Nick Howes at Tzec Muan Network at Siding Spring Australia
Comet Lovejoy and its spectacular “lively” ion tail photographed on January 8th by Nick Howes at Tzec Muan Network at Siding Spring Australia

Last night, under a dark rural sky, once I spotted the comet and noticed its position in relation to nearby bright stars, I could look up and see it anytime. Finding anything other than the Moon or a bright planet in the night sky often requires a good map. I normally create a star-chart style map but thought, why not make a photographic version? So last night I snapped a few guided images of Lovejoy as it glimmered in the wilds of southern Taurus and then cloned the comet’s nightly position through onto the image. Maybe you’ll find this useful, maybe not. If not, the regular map is also included.

Comet Lovejoy position is shown for each night tonight through January 23rd. The comet should remain in the 4-5 magnitude range throughout. Click for a larger map you can print out and use outdoors. Click to enlarge and print for use outdoors. Source: Chris Marriott’s SkyMap software
Comet Lovejoy’s position is shown for each night tonight through January 23rd. The comet should remain in the 4-5 magnitude range throughout. Lovejoy is currently high in the southeastern sky at nightfall and crosses the meridian due south around 9 o’clock local time. Click for a larger map you can print out and use outdoors. Source: Chris Marriott’s SkyMap software

To see Comet Lovejoy with the naked eye you’ll need reasonably dark skies. It should be faintly visible from outer ring suburbs, but country skies will guarantee a sighting. I’ve been using bright stars in Orion and Taurus to guide binoculars – and then my eye – to the comet. Pick a couple bright stars like Aldebaran and Betelgeuse and extend a line from each to form a triangle with Lovejoy at one of the corners. If you then point binoculars at that spot in the sky, the comet should pop out. If you don’t find it immediately, sweep around the position a bit.  After you find it, lower the binoculars and try to spot it with the naked eye.

Comet Lovejoy last night January 9th around 8 p.m. (CST) shows a bright coma and faint ~1.5-degree-long
Comet Lovejoy last night January 9th around 8 p.m. (CST) shows a bright coma and faint ~1.5-degree-long tail. This photo, made with a 200mm lens, gives a good idea of what the comet looks like in 50mm binoculars. Details: f/2.8, ISO 800, 2-minute exposure. Credit: Bob King

This week, as Lovejoy continues trekking north, you can use bright orangey Aldebaran in Taurus and the Pleiades, also called the Seven Sisters star cluster, to “triangulate” your way to the comet. Look for a glowing fuzzball. In 10×50 and 8×40 binoculars, it’s obviously different from a star — all puffed up with a brighter center. The 50mm glass even shows a hint of the coma’s blue color caused by carbon molecules fluorescing in ultraviolet sunlight and a faint, streak-like tail extending to the northeast. With the naked eye, at first you might think it’s just a dim star; closer scrutiny reveals the star has a hazy appearance, pegging it as a comet.

Comet Lovejoy sketches from last night made using a 15-inch telescope. The coma is big - almost a half-degree across. The drawing shows the bright nuclear region and tiny "false nucleus". At right, a suspected plume extends to the southwest of the false nucleus. Color is how the comet really looks in the telescope. Credit: Bob King
Comet Lovejoy sketches from last night made using a 15-inch telescope. The coma is big – almost a half-degree across. The drawing shows the bright nuclear region and tiny “false nucleus”. At right, a suspected plume extends to the southwest of the false nucleus. Color is how the comet really looks in the telescope. South is up. Credit: Bob King

Through a telescope the coma is a HUGE pale blue tiki lamp of a thing with a small, much brighter nuclear region. The rays of the ion tail, so beautifully shown in photographs, are indistinct but visible with patience and a moderate-sized telescope under dark skies. At low magnification, the nucleus – the false nucleus actually, since the real comet nucleus is hidden by a shroud of dust and gas – looks like a misty star of about magnitude +9. On close inspection at high magnification (250x and up), you penetrate more deeply into the nuclear zone and the star-like center shrinks and dims to around magnitude +13.

Fascinating plumes of dust recorded by Gianluca Masi on January 6th. South is up, west to the left. Credit: Gianluca Masi
Fascinating plumes of dust recorded by Gianluca Masi on January 6th. South is up, west to the left. Credit: Gianluca Masi

If the seeing is good and comet active, high magnification will often reveal jets or fans of dust in the sunward direction, in this case west of nucleus. I’ve been studying the comet the past couple nights and am almost convinced I can see a short, very low contrast plume poking to the south of center. Generally, plumes and jets are subtle, low-contrast features. Challenging? Yes, but with Lovejoy as close as it’s going to get, now’s the time to seek them.

In this photo taken January 8th, the comet's tail is caught in the act of separated from the head or coma. Magnetic fields embedded in the stream of particles from the Sun occasionally reconnect on the rear side of a comet and pinch off its tail. Credit: Rolando Ligustri
In this photo taken January 8th, the comet’s tail is caught in the act of separated from the head or coma. Magnetic fields embedded in the stream of particles from the Sun occasionally reconnect on the rear side of a comet and pinch off its tail. A new one quickly grows to replace the old. Credit: Rolando Ligustri

Just before Christmas, fluctuations in the solar wind snapped off Comet Lovejoy’s tail. Guess what? It happened again on January 8th as recorded in dramatic fashion by astrophotographer Rolando Ligustri. An ion or gas tail like the one in the photo forms when cometary gases, primarily carbon monoxide, are ionized by solar radiation and lose an electron to become positively charged. Once “electrified”, they can be twisted, kinked and even snapped off by magnetic fields embedded in the Sun’s particle wind.

Of course, the comet didn’t miss a breath but grew another tail immediately. Look closely at the photo and you see another faint streak of light pointing beyond the coma below and left of the bright nuclear region. This may be Lovejoy’s dust tail. Most comets sport both types of tails – gas and dust – since they release both materials as the Sun heats and vaporizes their ices.

Lovejoy’s been a thrill to watch because it’s doing all the cool stuff that makes them so fun to follow. Gianluca Masi, an Italian astrophysicist and lover of all things cometary, will offer a live feed of the comet on Monday January 12th starting at 1 p.m. CST (7 p.m. UT). May your skies be clear tonight!

Posted on by Bob King

New Mosaic Reveals Jets Blasting from Rosetta’s Comet

Two jets of gas and dust blast from Comet 67P/C-G in this reassembled and enhanced mosaic made from four photos taken by Rosetta's navigation camera on September 2, Credit: ESA/Rosetta/ Navcam/Bob King

Hidden among the four new images of Comet 67P/Churyumov-Gerasimenko released by ESA this week are a pair of dusty jets shooting from the nucleus of Comet Churyumov-Gerasimenko. The photos were taken September 2, 2014 and posted as a mosaic of four separate images. I re-assembled the four, albeit imperfectly, and added some additional contrast to better show the dual geyser of ice crystals mixed with dust venting from the nucleus. 

Four image montage of comet 67P/C-G, using images taken on 2 September. Credits: ESA/Rosetta/NAVCAM
Original four image montage of comet 67P/C-G, using images taken on September 2. The dark spot at center is imaging artifact. Credits: ESA/Rosetta/NAVCAM

An earlier Rosetta photo taken of Comet 67P/ Churyumov-Gerasimenko from a great distance and deliberately overexposed showed jets of dust-laden vapor shooting from the comet, but this is the first image I’m aware of that shows both the comet’s surface and its much fainter exhalations.

Jets or sprays of vaporizing ice are what gives a comet its lively appearance. Dust released with water vapor is ultimately pushed back by the pressure of sunlight to grow 67P/C-G’s dust tail. Ultraviolet light from the sun causes volatiles within the vapor to fluoresce a pale blue, creating a second ion or gas tail. The coma or comet atmosphere is a mix of both.

Rosetta took a long-exposure image with its wide-angle camera on August 2, 2014, to observe jets of dust escaping from the comet. The photo was taken from a distance of 550 kilometers. ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA
On August 2, 2014 at distance of 342 miles (550 km), Rosetta took this wide-angle view of the comet and jets of dust and vapor shooting into space.
ESA / Rosetta / MPS for OSIRIS Team MPS / UPD / LAM / IAA / SSO / INTA / UPM / DASP / IDA

We can expect the jets to grow stronger and hopefully more numerous as 67P/C-G approaches perihelion in August 2015. Because the spacecraft is maneuvering into orbit between the comet and sun, we don’t get the best view of jetting activity. The comet nucleus, illuminated by sunlight, drowns out the fainter jets. Rosetta will make an excursion to the nightside on September 24. Assuming the jets remain active, we might see them backlit by the sun as bright beams extending from the darkened nucleus into space.

Posted on by Jason Major

Subaru Telescope Captures the Fine Details of Comet Lovejoy’s Tail

Comet C/2011 W3 (Lovejoy) imaged by the Subaru Telescope on Dec. 3. Image credit: NAOJ with data processing by Masafumi Yagi (NAOJ)

Comet ISON may be no more than just a cloud of icy debris these days but there’s another comet that’s showing off in the morning sky: C/2013 R1 (Lovejoy), which was discovered in September and is steadily nearing its Christmas Day perihelion. In the early hours of Dec. 3, astronomers using the 8.2-meter Subaru Telescope atop Mauna Kea in Hawaii captured this amazing image of Lovejoy, revealing the intricate flows of ion streamers in its tail. (Click the image above for extra awesomeness.)

According to a news story on the NAOJ website:

At the time of this observation, at around 5:30 am on December 3, 2013 (Hawaii Standard Time), Comet Lovejoy was 50 million miles (80 million km) distant from Earth and 80 million miles (130 million km) away from the Sun.

The entire image of comet Lovejoy was made with the Subaru Telescope’s Suprime-Cam, which uses a mosaic of ten 2048 x 4096 CCDs covering a 34′ x 27′ field of view and a pixel scale of 0.2”.

Where to find comet Lovejoy in the morning sky, Dec. 7 (via spaceweather.com)
Where to find comet Lovejoy in the morning sky, Dec. 7 (via spaceweather.com)

“Subaru Telescope offers a rare combination of large telescope aperture and a wide-field camera,” said a member of the observation team, which included astronomers from Stony Brook University in New York, Universidad Complutense in Madrid,  Johns Hopkins University, and the National Astronomical Observatory of Japan. “This enabled us to capture a detailed look at the nucleus while also photogenically framing inner portions of Comet Lovejoy’s impressive ion tail.”

Comet Lovejoy is currently visible in the early morning sky as a naked-eye object in the northern hemisphere.

Read more about Lovejoy’s journey through the inner solar system in this article by Bob King here.

Image of comet Lovejoy on Dec. 5 by Flickr user "Willo2173".
Image of comet Lovejoy on Dec. 5 by Flickr user Willo2173.

Do you have photos of comet Lovejoy or any other astronomical objects to share? Upload them to the Universe Today Flickr group!

Posted on by Bob King

Comet ISON Goes Green

Comet ISON, photographed with a 3-inch (80mm) telescope on this morning Sept. 28 shows a circular green coma and short dust tail pointing northwest. Click to enlarge. Credit: Michael Jaeger

As NASA and the European Space Agency prepare  their remote photojournalists – Mars Express, Mars Reconnaissance Orbiter and the Curiosity and Opportunity rovers – to capture photos of Comet ISON’s flyby of Mars early next week, amateur astronomers continue to monitor and photograph the comet from backyard observatories across the blue Earth. Several recent color photos show ISON’s bright head or nucleus at the center of  a puffy, green coma. Green’s a good omen – a sign the comet’s getting more active as it enters the realm of the inner solar system and sun’s embrace.

Another photo of a "greening" Comet ISON taken on Sept. 24 with a 17-inch (43-cm) telescope. Click to enlarge. Credit: Damian Peach
Another great photo of the “greening” of Comet ISON taken on Sept. 24 with a 17-inch (43-cm) telescope. Click to enlarge. Credit: Damian Peach

Sunlight beating down on the comet’s nucleus (core) vaporizes dust-impregnated ice to form a cloud or coma, a temporary atmosphere of water vapor, dust, carbon dioxide, ammonia and other gases. Once liberated , the tenuous haze of comet stuff rapidly expands into a huge spherical cloud centered on the nucleus. Comas are typically hundreds of thousands of miles across but are so rarified you could wave your hand through one and not feel a thing. The Great Comet of 1811 sported one some 864,000 miles (1.4 million km) across, nearly the same diameter as the sun!

Among the materials released by solar heating are cyanogen and diatomic carbon. Both are colorless gases that fluoresce a delicious candy-apple green when excited by energetic ultraviolet light in sunlight.

Sounds like a plan. Newspaper clipping from 1910.
Sounds like a plan. Newspaper clipping from 1910.

Cyanogen smells pleasantly of almonds, but it’s a poisonous gas composed of one atom each of carbon and nitrogen. Diatomic carbon or C2 is equally unpleasant. It’s a strong, corrosive acid found not only in comets but also created as a vapor in high-energy electric arcs. But nature has a way of taking the most unlikely things and fashioning them into something beautiful. If you’re concerned about the effects of cometary gas and dust on people, rest easy. They’re spread too thinly to touch us here on Earth. That didn’t stop swindlers from selling “comet pills” and gas masks to protect the public from poisoning during the 1910 return of Halley’s Comet. Earth passed through the tail for six hours on May 19 that year. Amazingly, those who took the pills survived … as did everyone else.

Comet ISON's location and approximate appearance on October 1 seen from the Curiosity Rover. ISON will pass only 6.7 million miles (10.8 million km) from Mars on Tuesday Oct. 1. Stellarium
Comet ISON’s location and approximate appearance on October 1 seen from the Curiosity Rover. ISON will pass only 6.7 million miles (10.8 million km) from Mars on Tuesday Oct. 1. Stellarium

While Comet ISON is still too faint for visual observers to discern its Caribbean glow, that will change as it beelines for the sun and brightens. If you could somehow wish yourself to Mars in the next few days, I suspect you’d easily see the green coma through a telescope. The comet – a naked eye object at magnitude 2.5-3 – glows low in the northern sky from the Curiosity rover’s vantage point 4.5 degrees south of the Martian equator.

Comet Hale-Bopp shows off its whitish dust tail and fainter, blue ion tail in early 1997. Credit: Bob King
Comet Hale-Bopp shows off its bright dust tail and fainter, blue ion tail in early spring 1997. Credit: Bob King

I’ve noticed that when a comet reaches about 7th magnitude, the green coloration becomes apparent in 8-inch (20 cm) and larger telescopes. Bright naked eye comets often display multiple subtle colors that change chameleon-like over time. Dust tails, formed when sunlight pushes dust particles downwind from the coma, glow pale yellow. Gusty solar winds sweep back molecules from the coma into a second “ion” tail that glows pale blue from jazzed up carbon monoxide ions fluorescing in solar UV.

The highlight of seeing the comet through the telescope was its brilliant, pea-like false nucleus glowing yellow from sunlit dust. The real comet nucleus – the actual comet – lies within the false nucleus and shrouded by dust. Drawing: Bob King
One of the highlights of seeing Comet L4 PANSTARRS through a small telescope was its brilliant, pea-like false nucleus glowing yellow from sunlit dust. The real comet nucleus – the actual comet – lies within the false nucleus and hidden by dust. Drawing: Bob King

During close encounters with the sun, millions of pounds of  dust per day boil off a comet’s nucleus, forming a small, intensely bright, yellow-orange disk in the center of the coma called a false nucleus. Earlier this year, when Comet C/2011 L4 PANSTARRS emerged into the evening sky after perihelion, not only was its yellow tail apparent to binocular users but the brilliant false nucleus glowed a lovely shade of lemon in small telescopes.

With ISON diving much closer to the sun than L4 PANSTARRS, expect a full color palette in the coming weeks. While it may not be easy being green for Sesame Street’s Kermit the Frog, comets do it with aplomb.

Posted on by Jerry Coffey

What Are Comets Made Of?

Artists concept of the stardust spacecraft flying throug the gas and dust from comet Wild 2. Credit: NASA/JPL

[/caption]What are comets made of? Good question! Comet nuclei are loose collections of ice, dust and small rocky particles, ranging from a few kilometers to tens of kilometers across. As a comet approaches the inner solar system, solar radiation causes the volatile materials within the comet to vaporize and stream out of the nucleus, carrying dust away with them. The streams of dust and gas form a huge, extremely tenuous atmosphere around the comet called the coma, and the force exerted on the coma by the radiation pressure of the Sun and solar wind cause a tail to form. The tail always points away from the sun.

In order to understand what are comets made of, we need to break down the three main parts of the comet: the nucleus, coma, and tail. Comet nuclei are known to range from about 100 meters to more than 40 kilometers across. They are composed of rock, dust, ice and frozen gases such as carbon monoxide, carbon dioxide, methane, and ammonia. Sometimes called dirty snowballs, recent studies have shown that the ice of a comet is covered by a crust. Comets also contain a variety of organic compounds as well as the gases already mentioned. Some of these are methanol, hydrogen cyanide, formaldehyde, ethanol, and ethane. More complex molecules such as long-chain hydrocarbons and amino acids may also be in comets. Because of their low mass, comets cannot become spherical under their own gravity, and will thus have irregular shapes.

The coma is the the nebulous envelope around the nucleus of a comet. It is formed when the comet passes close to the Sun on a highly elliptical orbit. As the comet warms, parts of it turn from solid to gas(sublimate). Larger charged dust particles are left along the comet’s orbital path while smaller charged particles are pushed away from the Sun into the comet’s tail by solar wind. This helps astronomers distinguish comets from stars because it creates a fuzzy appearance.

The tail is illuminated by the Sun and may become visible from Earth when a comet passes through the inner solar system, the dust reflecting sunlight directly and the gases glowing from ionization. The streams of dust and gas each form their own distinct tail, pointing in slightly different directions. The tail of dust is left behind in the comet’s orbit in such a manner that it often forms a curved tail called the antitail. At the same time, the ion tail, made of gases, always points directly away from the Sun, as this gas is more strongly affected by the solar wind than is dust, following magnetic field lines rather than an orbital trajectory. Paralax viewing from the Earth may sometimes mean the tails appear to point in opposite direction.

Understanding the three parts of the comet is essential to know what are comets made of. Here is an article with a little more detail. Here on Universe Today there is a great article on a comet/asteroid hybrid. Astronomy Cast has another outstanding episode about solar dust.

Source: NASA