The Gloucester Area Astronomy Club

NGC 7331– Spiral Galaxy in Pegasus
by Glenn Chaple

What would the Andromeda Galaxy look like were it 20 times more distant? To find the answer, we need look no further than the spiral galaxy NGC 7331 in Pegasus. In size (a 130,000 LY diameter) and mass (300 billion suns), NGC 7331 is essentially a twin of the Andromeda Galaxy. Place the Andromeda Galaxy beside NGC 7331 and it, too, would be a magnitude 9.5 “faint fuzzy” with 10.5 by 3.5 arcminute dimensions.

I first viewed NGC 7331 in the fall of 1977, using a 3-inch reflector and a magnifying power of 60X. To me it appeared as “a faint small object that seemed slightly elliptical.” A recent observation with a 4.5-inch reflector yielded a similar result. In both instances, I was seeing the galaxy’s nucleus. Would a larger scope reveal the spiral arms?

A 10-inch reflector did, but barely. In my logbook, I wrote, “Some hint of extensions – like a small, faint M31.”

The accompanying finder chart shows the location of NGC 7331 – a 4 ½ degree star-hop north and slightly west of eta (() Pegasi. Just ½ degree SSW of NGC 7331 is Stephan’s Quintet. This clump of galaxies, ranging in magnitudes from 12.7 to 13.1) is a favorite target of owners of large-aperture telescopes.

Finder chart www.astrosurf.com;  7°45' x 7°45'. North is up. Photo by Mario Motta M.D.

October will mark the tenth anniversary of the Gloucester Area Astronomy Club! To celebrate we're having a special "10 years of GAAC" program at our Friday, October 11 meeting, followed by observing (weather permitting), right there on the lawn at the Lanesville Community Center.

The evening will begin at 8:00 pm, and will feature 10 minute talks by a parade of speakers, including young Clark Thakuria, Jim Koerth, Barry Yomtov, Alan Winter, Dr. Bill Waller, and a couple of surprise guests to boot.

There will be the usual good conversation, extra good things to eat and drink, and an appropriately festive air. And we hear there will be cake! Don't miss this one!

GAAC meets at the Lanesville Community Center at 8:00 on the second Friday of every month. There are no dues or fees, and the public is warmly welcomed. See our Contact page for  a map and driving directions.

Sagittarius and Saturn are setting earlier and earlier now, and old friends like Orion and Jupiter won't be back for a couple of months, but the fall sky is hardly a wasteland: some of the best astronomy of the year is upon us! Cooler, dryer weather (we hope), fewer insects and earlier nightfall allow eager astronomers to start sessions sooner, view in better comfort, and stay out longer. So, what is there to look at?

At the September 13 GAAC meeting, our own Alan Winter will take us on a tour of the wonders now appearing in our evening sky. We won't just look at pretty pictures; we'll also learn about how far back in time we're viewing, how big these objects really are, and what makes them tick.

On the September agenda: sparkling open clusters and asterisms like Little Dagger in the Heart, Kemble's Cascade, Muscleman and the Circus Bear, and the Dragonfly Cluster; a parade of odd little planetaries like the Saturn and Little Dumbbell Nebulae, as well as some giant favorites, like the Veil and North American Nebulae, now at optimum zenith visibility; and bigger-than-life views of our closest galactic neighbor, the Andromeda Galaxy, with its own little galactic orbiters.

We all look forward to seeing you there!

Size Does Matter, But So Does Dark Energy

By Dr. Ethan Siegel

Here in our own galactic backyard, the Milky Way contains some 200-400 billion stars, and that's not even the biggest galaxy in our own local group. Andromeda (M31) is even bigger and more massive than we are, made up of around a trillion stars! When you throw in the Triangulum Galaxy (M33), the Large and Small Magellanic Clouds, and the dozens of dwarf galaxies and hundreds of globular clusters gravitationally bound to us and our nearest neighbors, our local group sure does seem impressive.

Yet that's just chicken feed compared to the largest structures in the universe. Giant clusters and superclusters of galaxies, containing thousands of times the mass of our entire local group, can be found omnidirectionally with telescope surveys. Perhaps the two most famous examples are the nearby Virgo Cluster and the somewhat more distant Coma Supercluster, the latter containing more than 3,000 galaxies. There are millions of giant clusters like this in our observable universe, and the gravitational forces at play are absolutely tremendous: there are literally quadrillions of times the mass of our Sun in these systems.

The largest superclusters line up along filaments, forming a great cosmic web of structure with huge intergalactic voids in between the galaxy-rich regions. These galaxy filaments span anywhere from hundreds of millions of light-years all the way up to more than a billion light years in length. The CfA2 Great Wall, the Sloan Great Wall, and most recently, the Huge-LQG (Large Quasar Group) are the largest known ones, with the Huge-LQG -- a group of at least 73 quasars – apparently stretching nearly 4 billion light years in its longest direction: more than 5% of the observable universe! With more mass than a million Milky Way galaxies in there, this structure is a puzzle for cosmology.

You see, with the normal matter, dark matter, and dark energy in our universe, there's an upper limit to the size of gravitationally bound filaments that should form. The Huge-LQG, if real, is more than double the size of that largest predicted structure, and this could cast doubts on the core principle of cosmology: that on the largest scales, the universe is roughly uniform everywhere. But this might not pose a problem at all, thanks to an unlikely culprit: dark energy. Just as the local group is part of the Virgo Supercluster but recedes from it, and the Leo Cluster -- a large member of the Coma Supercluster -- is accelerating away from Coma, it's conceivable that the Huge-LQG isn't a single, bound structure at all, but will eventually be driven apart by dark energy. Either way, we're just a tiny drop in the vast cosmic ocean, on the outskirts of its rich, yet barely fathomable depths.

Learn about the many ways in which NASA strives to uncover the mysteries of the universe: http://science.nasa.gov/astrophysics/. Kids can make their own clusters of galaxies by checking out The Space Place’s fun galactic mobile activity: http://spaceplace.nasa.gov/galactic-mobile/

Image Caption:
Digital mosaic of infrared light (courtesy of Spitzer) and visible light (SDSS) of the Coma Cluster, the largest member of the Coma Supercluster. Image credit: NASA / JPL-Caltech / Goddard Space Flight Center / Sloan Digital Sky Survey.

NGC 6826 “the Blinking Planetary” – Planetary Nebula in Cygnus

by Glenn Chaple

Backyard astronomers are familiar with the tactic of using averted vision to capture faint detail in deep-sky objects. A sideward glance allows photons to fall on the light-sensitive region of the retina, rendering the invisible visible. The effect of averted vision is particularly dramatic when the telescopic target is NGC 6826.

This 9th magnitude, 25 arcsecond-wide planetary nebula is dominated by a magnitude 10.6 central star. Gaze directly at NGC 6826, and all you see is the central star. Look to the side, however, and a bluish shell surrounding the star pops into view. Return your gaze to the central star, and the nebula disappears. Here is a deep sky object that does something!

This remarkable planetary nebula was discovered by William Herschel in 1783. The first documented description of the blinking effect seems to have come from James Mullaney, who described the phenomenon in the August, 1963, issue of Sky and Telescope and coined the nick-name “Blinking Planetary.”

Although NGC 6826 is visible in a modest 2.4-inch refractor, the blink effect is best-seen with medium-aperture scopes. Last September, I viewed NGC 6826 with 4-inch and 10-inch reflectors and noted: “Located near a pretty double star (16 Cyg). Unable to detect "blinking” illusion with the 4-inch. With a 10-inch Dob and 6mm eyepiece (208X), blinking effect obvious but not immediate unless I stared at the nebula for several seconds. When I did, the nebulosity faded until just the central star was visible. A quick sideward glance and "voila," the nebula reappeared."

16 Cygni, located just one-half degree west of NGC 6826, is a striking twin system consisting of magnitude 6.0 and 6.1 G-type stars separated by 39 arcseconds. Double star and planetary nebula can be captured together in a low-power field. Don’t go too low, however. With magnifications of 25X or less, NGC 6826 appears starlike and may elude detection.

As telescope size increases, the blinking affect lessens because a large-aperture instrument begins to reveal nebulosity even when NGC 6826 is viewed head-on. If your scope is too big to make NGC 6826 blink, try your luck with its FLIERs. In her book Deep-sky Wonders, author Sue French invites users of medium- to large-aperture telescopes to look for a tiny bright patch at each end of the planetary’s long axis. Each is a so-called FLIER (Fast Low-Ionization Emission Region) – an enigmatic feature possibly caused by the interaction of material being ejected by the central star with gases already in the shell.

Inventing Astrophotography: Capturing Light Over Time

By Dr. Ethan Siegel

We know that it’s a vast Universe out there, with our Milky Way representing just one drop in a cosmic ocean filled with hundreds of billions of galaxies. Yet if you’ve ever looked through a telescope with your own eyes, unless that telescope was many feet in diameter, you’ve probably never seen a galaxy’s spiral structure for yourself. In fact, the very closest large galaxy to us, Andromeda, M31, wasn’t discovered to be a spiral until 1888, despite being clearly visible to the naked eye! This crucial discovery wasn’t made at one of the world’s great observatories, with a world-class telescope, or even by a professional astronomer; it was made by a humble amateur to whom we all owe a great scientific debt.

Beginning in 1845, with the unveiling of Lord Rosse’s 6-foot (1.8 m) aperture telescope, several of the nebulae catalogued by Messier, Herschel and others were discovered to contain an internal spiral structure. The extreme light-gathering power afforded by this new telescope allowed us, for the first time, to see these hitherto undiscovered cosmic constructions. But there was another possible path to such a discovery: rather than collecting vast amounts of light through a giant aperture, you could collect it over time, through the newly developed technology of photography. During the latter half of the 19th Century, the application of photography to astronomy allowed us to better understand the Sun’s corona, the spectra of stars, and to discover stellar and nebulous features too faint to be seen with the human eye.

Working initially with a 7-inch refractor that was later upgraded to a 20-inch reflector, amateur astronomer Isaac Roberts pioneered a number of astrophotography techniques in the early 1880s, including “piggybacking,” where his camera/lens system was attached to a larger, equatorially-mounted guide scope, allowing for longer exposure times than ever before. By mounting photographic plates directly at the reflector’s prime focus, he was able to completely avoid the light-loss inherent with secondary mirrors. His first photographs were displayed in 1886, showing vast extensions to the known reaches of nebulosity in the Pleiades star cluster and the Orion Nebula.

But his greatest achievement was this 1888 photograph of the Great Nebula in Andromeda, which we now know to be the first-ever photograph of another galaxy, and the first spiral ever discovered that was oriented closer to edge-on (as opposed to face-on) with respect to us. Over a century later, Andromeda looks practically identical, a testament to the tremendous scales involved when considering galaxies. If you can photograph it, you’ll see for yourself!

Astrophotography has come a long way, as apparent in the Space Place collection of NASA stars and galaxies posters at http://spaceplace.nasa.gov/posters /#stars.

Image caption:
Great Nebula in Andromeda, the first-ever photograph of another galaxy. Image credit: Isaac Roberts, taken December 29, 1888, published in A Selection of Photographs of Stars, Star-clusters and Nebulae, Volume II, The Universal Press, London, 1899.

July 12 will be upon us soon -- mark your calendars for our next GAAC meeting, featuring old friend and NASA Solar System Ambassador Ted Blank, with a presentation on the Mars Curiosity rover. Ted will give us a colorful and in-depth look at the news and photos "just in from Mars"! 

The meeting will begin at 8:00 at the Lanesville Community Center.

The Curiosity rover and the Mars Science Laboratory it carries are the most expensive, most complex instruments ever sent to the surface of another planet. In addition to great pictures, Curiosity is now returning cutting-edge science data for the first time, including, for just one example, checking out the martian radiation environment in advance of human visitors!

This is exciting stuff. Ted is one of our most popular speakers, so come early and bring your questions.

High-energy Spy

By Dr. Martin C. Weisskopf

The idea for the Chandra X-Ray Observatory was born only one year after Riccardo Giacconi discovered the first celestial X-ray source other than the Sun. In 1962, he used a sounding rocket to place the experiment above the atmosphere for a few minutes. The sounding rocket was necessary because the atmosphere blocks X-rays. If you want to look at X-ray emissions from objects like stars, galaxies, and clusters of galaxies, your instrument must get above the atmosphere. 

Giacconi’s idea was to launch a large diameter (about 1 meter) telescope to bring X-rays to a focus. He wanted to investigate the hazy glow of X-rays that could be seen from all directions throughout the sounding rocket flight.  He wanted to find out whether this glow was, in fact, made up of many point-like objects. That is, was the glow actually from millions of X-ray sources in the Universe. Except for the brightest sources from nearby neighbors, the rocket instrument could not distinguish objects within the glow.

Giacconi’s vision and the promise and importance of X-ray astronomy was borne out by many sounding rocket flights and, later satellite experiments, all of which provided years-, as opposed to minutes-, worth of data.

By 1980, we knew that X-ray sources exist within all classes of astronomical objects. In many cases, this discovery was completely unexpected. For example, that first source turned out to be a very small star in a binary system with a more normal star. The vast amount of energy needed to produce the X-rays was provided by gravity, which, because of the small star’s mass (about equal to the Sun’s) and compactness (about 10 km in diameter) would accelerate particles transferred from the normal star to X-ray emitting energies. In 1962, who knew such compact stars (in this case a neutron star) even existed, much less this energy transfer mechanism?

X-ray astronomy grew in importance to the fields of astronomy and astrophysics. The National Academy of Sciences, as part of its “Decadal Survey” released in 1981, recommended as its number one priority for large missions an X-ray observatory along the lines that Giacconi outlined in 1963. This observatory  was eventually realized as the Chandra X-Ray Observatory, which launched in 1999.

The Chandra Project is built around a high-resolution X-ray telescope capable of sharply focusing X-rays onto two different X-ray-sensitive cameras. The focusing ability is of the caliber such that one could resolve an X-ray emitting dime at a distance of about 5 kilometers! 

The building of this major scientific observatory has many stories.

Learn more about Chandra at www.science.nasa.gov/missions/chandra .  Take kids on a “Trip to the Land of the Magic Windows” and see the universe in X-rays and other invisible wavelengths of light at spaceplace.nasa.gov/magic-windows.

Dr. Weisskopf is project scientist for NASA's Chandra X-ray Observatory. This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

Image Caption: Composite image of DEM L50, a so-called superbubble found in the Large Magellanic Cloud. X-ray data from Chandra is pink, while optical data is red, green, and blue. Superbubbles are created by winds from massive stars and the shock waves produced when the stars explode as supernovas.