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Friday, 30 September 2011

Astronomy Update

Trusty Comet Garradd
September 1, 2011
by Alan MacRobert and Tony Flanders
Comet Elenin has been getting a lot of press in recent months — and now it seems almost certain to be a total bust.

Meanwhile, people in the know have been following a comet that has never been hyped much, but seems almost certain to be a fine, though not spectacular performer for many months to come.

Comet Garradd and M71
Comet Garradd passed M71 in Sagitta on the evening of August 26th.
Nick Howes
We're talking about Comet Garradd (C/2009 P1). In early September it was already a fine sight through telescopes of all sizes, shining high in the evening sky at 7th magnitude. It has a bright head, a sharp starlike nucleus, and a tail that's stubby but well defined. And it's forecast to shine near its 6th-magnitude best all the way from October to mid-March. Not since Hale-Bopp has any comet remained so bright for so long.

Comet Garradd passes through the Coathanger asterism on the evening of Friday, September 2nd, then crosses the northwest corner of Sagitta, and soon enters Hercules, where it will remain until February. That means it's high in the west after nightfall in October, lower but still in good view in November, and near the west-northwest horizon at the end of twilight around Christmas. But by then it's already up higher in the east before the first light of dawn; the best viewing tips from evening to morning on December 16th.

Path of Comet Garradd Oct 2011 - Jan 2012
Comet Garradd crosses Vulpecula and Sagitta in early September, then remains in Hercules for the next six months. Click above for a full-page, printable finder chart.
S&T Diagram
As the comet climbs high in the early-morning sky of January and February, it will pass the Keystone of Hercules, skim ½° by the globular cluster M92 on the morning of February 3rd (mark your calendar), then sail northward past the head of Draco. It should stay bright all the way into spring as it returns to the evening sky.

Click here for a full-page, printable finder chart for Comet Garradd from September through early February, 2012.

Why is it changing so slowly? Comet Garradd is unusually large and distant as 6th-magnitude comets go. It never comes closer to the Sun than Mars's average distance; at perihelion on December 23rd it's 1.55 astronomical units from the Sun. Nor does the comet ever come near Earth; it's about 2 a.u. from us all through October and November, and when closest next March 5th it will still be 1.27 a.u. away. Too bad! Garradd might have qualified for "Great Comet" status if had been on a trajectory to pass close to the Sun and if Earth weren't on the wrong side of its orbit at the time.

Astronomer Gordon J. Garradd discovered the comet at 17th magnitude on August 13, 2009, at Australia's Siding Spring Observatory while hunting for — ironically — near-Earth objects.


OBSERVING BLOG by Kelly Beatty

M101's Supernova Shines On

Update: Supernova 2001fe was gradually fading as of September 26th, down to about magnitude 10.5 from its peak of 9.9 in mid-September. See an up-to-date light curve. Catch it while it's still this bright, and before it moves lower in the northwest after dusk.

In 1987, when an exploding star erupted to eyeball visibility in the far-southern constellation of Dorado, northern skygazers could only wistfully imagine how it must have looked.
Supernova in M101
Observing from Puerto Rico with a 12-inch telescope, Efrain Morales Rivera captured the supernova in M101 on August 29th, when the outburst was roughly 11th magnitude. Rivera submitted this image to our online Image Gallery; click here for a larger view.
Efrain Morales Rivera
Now they've gained some measure of redemption, thanks to a remarkable and relatively bright stellar detonation in M101, sometimes called the Pinwheel Galaxy, poised near the Big Dipper's handle. Although only 17th magnitude when discovered on August 24th, Supernova 2011fe was just beginning its performance.

Right now it's fading slowly from a peak brightness of 9.9, where it remained for nearly a week. But the stellar outburst is still 10th magnitude, and, with intrusive moonlight gone from the early-evening sky, the next few nights offer your best chance to spot it.

In a light-polluted sky the star is much easier to see than M101 itself. The face-on spiral galaxy is large but dim and is easily wiped out by skyglow. If you've got a dark enough sky, M101 makes a nearly equilateral triangle in a finderscope with Alkaid and Mizar, the final two stars in the Big Dipper's handle.
How to find spiral galaxy M101
The face-on spiral galaxy Messier 101 (M101) sits above the Big Dipper's handle, forming an equilateral triangle with the stars Alkaid and Mizar.
To identify which tiny speck is the supernova, use the comparison-star charts that you can generate courtesy of the American Association of Variable Star Observers. Enter the star name SN 2011fe, and choose the "predefined chart scales" A, B, and C. Print out all three. The two brightest stars on the "A" chart are the last two in the the Big Dipper's handle.

If you can see the galaxy itself, the supernova is located 4.4 arcminutes south (and a bit west) of M101's center, at right ascension 14
hh 3m 5.8s, declination +54° 16′ 25″.

The supernova is easy to spot in a 4- or 6-inch telescope. Although it looks like any ordinary star, it's thousands of times more distant than any other that's visible in amateur telescopes from northern latitudes. (M101 is about 23 million light-years away.) In fact, you might even pick it up through big, mounted binoculars. "I was able to clearly see SN 2011fe in M101 using mounted 16×60 Pentax binoculars on September 3rd," reports Colorado amateur Mike Prochoda.
Light curve of Supernova 2011fe
More than 1,400 observations from members of the American Association of Variable Star Observers show that the dramatic rise in brightness of Supernova 2011fe peaked about September 10th.
According to Matthew Templeton, science director for the American Association of Variable Star Observers, SN 2011fe has been a huge hit with its worldwide team of observers: 1,432 observations to date by 117 observers. (One especially prolific member in Spain has submitted more than 500 CCD observations!). "Our main science plan is simply to make sure the light curve is as well-covered and accurate as possible," Templeton explains, "so that the data will be available and useful to the science community."

Meanwhile, SN 2011fe's early detection and its relative nearness have drawn plenty of interest from professional astronomers. Being a Type Ia supernova (the complete thermonuclear explosion of a white-dwarf star in a binary system), this one is getting special research attention — because Type Ia blasts tend to have the same intrinsic brightness and thus serve as uniform "standard candles" for telling distances all across the far universe.

Only rarely, once every couple of decades, do we get one to study in close detail right in our cosmic backyard. "A bright supernova lets you use instruments that don't ordinarily get enough photons," notes Robert Kirshner (Harvard-Smithsonian Center for Astrophysics). "Polarimetry and high-dispersion spectra (to look for gas in the vicinity, along the line of sight in the host galaxy, and in the high-latitude zones of the Milky Way) are good possibilities."

Kirshner adds, "We're especially keen to get good series of infrared spectra, because Type Ia supernovae are better standard candles in the infrared."

Caltech astronomer Richard Ellis says that the Hubble Space Telescope has been tracking the development of SN 2011fe. "We have a regular 'Target of Opportunity' program for nearby Type Ia supernovae," he explains. "We are gathering ultraviolet spectra in a sequence starting from a couple of days after explosion through maximum light and beyond."

Interestingly, no one has been able to identify the star that blew up.
Careful searching of archived HST images by Weidong Li (University of California, Berkeley) and others — nor was an X-ray signature evident in before-the-blast observations from the Swift and Chandra spacecraft. So astronomers will have to dig deeper if they hope to determine whether the companion of the now-obliterated white dwarf was a red-giant star, a main-sequence star, or another white dwarf.

OBSERVING BLOG by Kelly Beatty
Jupiter: Big, Bright, and Beautiful
What's your favorite planet?

If it's Mars, you certainly have lots of company. The fascination with the Red Planet as a possible abode of life goes back well over a century. But Mars is almost always tiny in a telescope, and in 2011 it's not placed well for viewing. Or perhaps you're fondest of Saturn. Nothing compares to those wonderful rings.
Jupiter through a 12½-inch telescope
S&T imaging editor Sean Walker used a 12½-inch reflector to capture Jupiter on August 17, 2011, from Masil Observatory East in New Hampshire. Note the Great Red Spot, which overlaps the dark South Equatorial Belt below center.
Sean Walker
For me, however, it's Jupiter. What makes Jupiter such a treat is that it offers more to see in a telescope than any other planet. It's the only one that shows distinct features in even a fairly small scope. And it's got four large moons that hover nearby like bright fireflies, forever shuttling back and forth around Jupiter's glaring globe.

Jupiter was king of the gods in Roman mythology, and in late 2011 it rules unchallenged as the brightest "star" shining in the evening sky. You'll find it low in the east after sunset in October, and it climbs higher up week by week through year's end. By next April, Jupiter's early evening position will have shifted far to the west.

Before you track down this planet with your telescope, grab your binoculars and find a tree or wall to brace against while pointing them toward Jupiter. If your binoculars are good quality and magnify at least seven times (they'll be marked 7×35 or 7×50, for example), you'll see Jupiter as a tiny white disk.

Look closely to either side of Jupiter's disk — do you see a line of three or four tiny stars? Each of these is a satellite of Jupiter roughly the size of our own Moon. They only look tiny and faint because they're about 2,000 times farther away.

Hide-and-Seek Moons

Now put a low-power eyepiece in your telescope and center Jupiter. Focus carefully so that the planet's edge is as sharp as possible, let any vibrations settle down, and then take a good long look.

Jupiter and its satellites
Jupiter and three of its four Galilean satellites, as they would appear in a small telescope.
Sky & Telescope illustration
Depending on the size of your scope and the quality of the night's seeing, you'll see something like the view here. Now the moons are much more obvious. You'll probably see all four — but possibly only three depending on when you look. The count often changes from night to night (or if you're patient, even from hour to hour). That's because while orbiting Jupiter they sometimes glide in front of the planet, behind it, or through its shadow.

These hide-and-seek movements confounded Galileo Galilei when he first spied these "stars" in 1610. But he soon realized they were actually circling around Jupiter, forming a miniature solar system of sorts. We see their orbits almost exactly edge on.

Sketch showing Jovian belts and zones
Almost any kind of Jupiter observation requires familiarity with the correct names for the various belts and zones. This diagram replicates the view in an inverting telescope such as a Newtonian reflector, or a refractor, Schmidt-Cassegrain, or Maksutov used without a star diagonal. Telescopes used with a star diagonal will have north up but east and west reversed. The planet's rotation causes features to move from east (following) to west (preceding). Click on the image for a larger view.
Sky & Telescope illustration; art: Don Davis
The four are named Io, Europa, Ganymede, and Callisto — or, collectively, the Galilean satellites — and it's hard to tell which is which just by looking. Callisto is usually (but not always) farthest from Jupiter, and Ganymede is a little brighter than the others. Sulfur-coated Io has a pale yellow-orange cast. Still not sure? The answers are just a mouse clicks away, thanks to's handy guide to identifying the Galilean satellites at any time and date.

Earning Your Stripes

Now turn your attention to Jupiter itself. Center its round disk in the middle of your telescope's view, then carefully switch to a higher-power eyepiece and refocus. Study the disk closely, and two things should be noticeable. First, the disk is not perfectly round. Jupiter spins so fast (once every 10 hours) that its equatorial midsection bulges out a bit. It's 7% wider across the equator than from pole to pole.

Jupiter is a gas-giant planet — it consists almost entirely of hydrogen and helium, nearly all the way down. The "surface" you see is actually the top layers of cloud decks floating near the top of an immensely deep atmosphere.
Jupiter's appearance in 2009 and 2010
In 2010 observers were surprised to find that Jupiter's South Equatorial Belt had completely disappeared over a 10-month span — leaving the Great Red Spot quite easy to glimpse. But since then the SEB has returned.
Anthony Wesley
Look for at least two tawny-colored stripes running parallel to the equator. These darkish cloud bands are called belts, and the brighter cloud areas between them are called zones. The North and South Equatorial Belts, usually the most prominent, straddle the bright Equatorial Zone like a cream-filled cookie sandwich. If you're using at least a 6-inch telescope, you may be able to pick out a few belts and zones closer to Jupiter's poles.

The single most famous cloud feature on Jupiter is the Great Red Spot, an enormous, oval-shaped storm about twice the size of Earth. Astronomers have observed the Red Spot for at least 150 years, but there's still no agreement on what chemical compounds create its distinctive color. Like any big storm, the spot changes appearance over time. The intensity of its color has sometimes been brick red (very rarely), pale orange tan (more often), pinkish tan, or an almost invisible creamy yellowish. Changes usually happen over a year or two.

When the spot is so pale as to be invisible, you may be able to identify it indirectly by noting the indentation it makes in the south edge of the South Equatorial Belt: a feature dubbed the "Red Spot Hollow."

Be forewarned that seeing the Great Red Spot is a challenge in a small telescope. Your best prospects will be when the spot appears near the middle of Jupiter's disk —'s
online calculator helps you know when to look. The planet's rapid rotation means that these windows of opportunity last only a couple hours, so be prepared to search for the spot over several consecutive nights.

No matter how you look at it, Jupiter is so easy to see that it makes an irresistible telescopic target anytime it's visible in the night sky — and that's why it's my favorite planet.
Good Clear Skies
Colin James Watling
Various Voluntary work-Litter Picking for Parish Council (Daytime) and also a friend of Kessingland Beach (Watchman)
Real Astronomer and head of the Comet section for LYRA (Lowestoft and Great Yarmouth Regional Astronomers) also head of K.A.G (Kessingland Astronomy Group) and Navigator (Astrogator) of the Stars (Fieldwork)
Information -- More Info -- And More Info

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