The Gloucester Area Astronomy Club

A Two-Toned Wonder from the Saturnian Outskirts

By Dr. Ethan Siegel

Although Saturn has been known as long as humans have been watching the night sky, it's only since the invention of the telescope that we've learned about the rings and moons of this giant, gaseous world. You might know that the largest of Saturn's moons is Titan, the second largest moon in the entire Solar System, discovered by Christiaan Huygens in 1655. It was just 16 years later, in 1671, that Giovanni Cassini (for whom the famed division in Saturn's rings—and the NASA mission now in orbit there—is named) discovered the second of Saturn's moons: Iapetus. Unlike Titan, Iapetus could only be seen when it was on the west side of Saturn, leading Cassini to correctly conclude that not only was Iapetus tidally locked to Saturn, but that its trailing hemisphere was intrinsically brighter than its darker, leading hemisphere. This has very much been confirmed in modern times!

In fact, the darkness of the leading side is comparable to coal, while the rest of Iapetus is as white as thick sea ice. Iapetus is the most distant of all of Saturn's large moons, with an average orbital distance of 3.5 million km, but the culprit of the mysterious dark side is four times as distant: Saturn's remote, captured moon, the dark, heavily cratered Phoebe!

Orbiting Saturn in retrograde, or the opposite direction to Saturn's rotation and most of its other Moons, Phoebe most probably originated in the Kuiper Belt, migrating inwards and eventually succumbing to gravitational capture. Due to its orbit, Phoebe is constantly bombarded by micrometeoroid-sized (and larger) objects, responsible for not only its dented and cavity-riddled surface, but also for a huge, diffuse ring of dust grains spanning quadrillions of cubic kilometers! The presence of the "Phoebe Ring" was only discovered in 2009, by NASA's infrared-sensitive Spitzer Space Telescope. As the Phoebe Ring's dust grains absorb and re-emit solar radiation, they spiral inwards towards Saturn, where they smash into Iapetus—orbiting in the opposite direction—like bugs on a highway windshield. Was the dark, leading edge of Iapetus due to it being plastered with material from Phoebe? Did those impacts erode the bright surface layer away, revealing a darker substrate?

In reality, the dark particles picked up by Iapetus aren't enough to explain the incredible brightness differences alone, but they absorb and retain just enough extra heat from the Sun during Iapetus' day to sublimate the ice around it, which resolidifies preferentially on the trailing side, lightening it even further. So it's not just a thin, dark layer from an alien moon that turns Iapetus dark; it's the fact that surface ice sublimates and can no longer reform atop the leading side that darkens it so severely over time. And that story—only confirmed by observations in the last few years—is the reason for the one-of-a-kind appearance of Saturn's incredible two-toned moon, Iapetus!

Learn more about Iapetus here: http://saturn.jpl.nasa.gov/science/moons/iapetus.

Kids can learn more about Saturn’s rings at NASA’s Space Place: http://spaceplace.nasa.gov/saturn-rings.

Images credit: Saturn & the Phoebe Ring (middle) - NASA / JPL-Caltech / Keck; Iapetus (top left) - NASA / JPL / Space Science Institute / Cassini Imaging Team; Phoebe (bottom right) - NASA / ESA / JPL / Space Science Institute / Cassini Imaging Team.

Kemble’s Cascade/NGC 1502 – Asterism and Open Cluster in Camelopardis
by Glenn Chaple

In 1980, while scanning a rather vacant area of the constellation Camelopardis with 7 X 35 binoculars, Canadian amateur astronomer Fr. Lucian J. Kemble came across “a beautiful cascade of faint stars tumbling from the northwest down to the open cluster NGC 1502.” He reported his finding to Sky and Telescope “Deep Sky Wonders” columnist Walter Scott Houston, who featured the remarkable asterism in the December, 1980, issue. Houston appropriately christened it “Kemble’s Cascade.”

This 2½ degree-long chain is comprised of some two dozen magnitude 7 to 9 stars with a 5th magnitude star at its midpoint. NGC 1502 is visible as a fuzzy patch of light at the southeastern end of the Cascade. This dazzling 8 arcminute-wide open star cluster is comprised of several dozen stars, magnitudes 10 to 11. At its center is the pretty double star Struve 485 ((485), a pair of 7th magnitude stars separated by 18 arcseconds.

Kemble’s Cascade can be found by sweeping your binoculars from beta (() through epsilon (() Cassiopeiae and continuing in a straight line an equal distance beyond. A dark-sky location on a moonless night will help you pick up the fainter Cascade members. Should you decide to view Kemble’s Cascade via telescope, work with a rich-field instrument and an eyepiece that magnifies 15 – 20 times and captures a 3 degree field. NGC 1502 and its embedded double star are best viewed with a boost to 30X or more.

     

Finder chart for Kemble's Cascade and NGC 1502 generated with Sky Tools 2 by Capella Soft; Sketch by Kiminori Ikebe (www.asod.info/?p=1272)

Surprising Young Stars in the Oldest Places in the Universe

By Dr. Ethan Siegel

Littered among the stars in our night sky are the famed deep-sky objects. These range from extended spiral and elliptical galaxies millions or even billions of light years away to the star clusters, nebulae, and stellar remnants strewn throughout our own galaxy. But there's an intermediate class of objects, too: the globular star clusters, self-contained clusters of stars found in spherically-distributed halos around each galaxy.

Back before there were any stars or galaxies in the universe, it was an expanding, cooling sea of matter and radiation containing regions where the matter was slightly more dense in some places than others. While gravity worked to pull more and more matter into these places, the pressure from radiation pushed back, preventing the gravitational collapse of gas clouds below a certain mass. In the young universe, this meant no clouds smaller than around a few hundred thousand times the mass of our Sun could collapse. This coincides with a globular cluster's typical mass, and their stars are some of the oldest in the universe!

These compact, spherical collections of stars are all less than 100 light-years in radius, but typically have around 100,000 stars inside them, making them nearly 100 times denser than our neighborhood of the Milky Way! The vast majority of globular clusters have extremely few heavy elements (heavier than helium), as little as 1% of what we find in our Sun. There's a good reason for this: our Sun is only 4.5 billion years old and has seen many generations of stars live-and-die, while globular clusters (and the stars inside of them) are often over 13 billion years old, or more than 90% the age of the universe! When you look inside one of these cosmic collections, you're looking at some of the oldest stellar swarms in the known universe.

Yet when you look at a high-resolution image of these relics from the early universe, you'll find a sprinkling of hot, massive, apparently young blue stars! Is there a stellar fountain of youth inside? Kind of! These massive stellar swarms are so dense -- especially towards the center -- that mergers, mass siphoning and collisions between stars are quite common. When two long-lived, low-mass stars interact in these ways, they produce a hotter, bluer star that will be much shorter lived, known as a blue straggler star. First discovered by Allan Sandage in 1953, these young-looking stars arise thanks to stellar cannibalism. So enjoy the brightest and bluest stars in these globular clusters, found right alongside the oldest known stars in the universe!

Learn about a recent globular cluster discovery here

Kids can learn more about how stars work by listening to The Space Place’s own Dr. Marc: http://spaceplace.nasa.gov/podcasts/en/#stars.

Photo: Globular Cluster NGC 6397. Credit: ESA & Francesco Ferraro (Bologna Astronomical Observatory) / NASA, Hubble Space Telescope, WFPC2.

The Big Picture: GOES-R and the Advanced Baseline Imager

By Kieran Mulvaney

The ability to watch the development of storm systems – ideally in real time, or as close as possible – has been an invaluable benefit of the Geostationary Operational Environmental Satellites (GOES) system, now entering its fortieth year in service. But it has sometimes come with a trade-off: when the equipment on the satellite is focused on such storms, it isn’t always able to monitor weather elsewhere.

“Right now, we have this kind of conflict,” explains Tim Schmit of NOAA’s National Environmental Satellite, Data, and Information Service (NESDIS). “Should we look at the broad scale, or look at the storm scale?” That should change with the upcoming launch of the first of the latest generation of GOES satellites, dubbed the GOES-R series, which will carry aloft a piece of equipment called the Advanced Baseline Imager (ABI).

According to Schmit, who has been working on its development since 1999, the ABI will provide images more frequently, at greater resolution and across more spectral bands (16, compared to five on existing GOES satellites). Perhaps most excitingly, it will also allow simultaneous scanning of both the broader view and not one but two concurrent storm systems or other small-scale patterns, such as wildfires, over areas of 1000km x 1000km.

Although the spatial resolution will not be any greater in the smaller areas than in the wider field of view, the significantly greater temporal resolution on the smaller scale (providing one image a minute) will allow meteorologists to see weather events unfold almost as if they were watching a movie.

So, for example, the ABI could be pointed at an area of Oklahoma where conditions seem primed for the formation of tornadoes.  “And now you start getting one-minute data, so you can see small-scale clouds form, the convergence and growth,” says Schmit.

In August, Schmit and colleagues enjoyed a brief taste of how that might look when they turned on the GOES-14 satellite, which serves as an orbiting backup for the existing generation of satellites.

“We were allowed to do some experimental imaging with this one-minute imagery,” Schmit explains. “So we were able to simulate the temporal component of what we will get with ABI when it’s launched.”

The result was some imagery of cloud formation that, while not of the same resolution as the upcoming ABI images, unfolded on the same time scale. You can compare the difference between it and the existing GOES-13 imagery here

Learn more about the GOES-R series of satellites here

Kids should be sure to check out a new online game that’s all about ABI! It’s as exciting as it is educational. Check it out at http://scijinks.gov/abi

[Photo: The Advanced Baseline Imager. Credit: NOAA/NASA.]

Gamma () Ceti– Double Star in Cetus
by Glenn Chaple

We open the New Year with a double star that’s as easy to split as it is to pronounce its Arabic name, Kaffaljidhma. We’ll simply refer to it by the Bayer designation, gamma () Ceti. Discovered by the German-Russian astronomer F. G. W. Struve in 1825 (it bears the Struve Catalog identity 299), gamma Ceti is the southernmost member of a circlet of stars that forms the head of the celestial Whale.

Gamma Ceti’s component stars are separated by 2.3 arcseconds, putting them at the resolution limit of a 2-inch scope. However, the primary is 9 times brighter than its partner (magnitudes 3.6 and 6.2), making them a challenge for telescopes with twice the aperture, even under ideal seeing conditions. My first split of gamma Ceti was accomplished with a 5-inch f/12 Maksutov-Cassegrain and a magnifying power of 250X. The companion appeared as a bump on the primary diffraction ring of the main star.

There’s an interesting twist to the colors observers report when viewing gamma Ceti. Most note colors of yellowish and blue – the opposite of what you’d expect for a pair whose spectral classes are A3 and F3. These impressions are likely illusory - a result of a contrast effect between a bright primary and fainter companion.
As they say in the TV ads, “But wait, There’s more!” A 10th magnitude K-type dwarf situated 14 arcminutes to the northwest shares the same proper motion as the main pair. All three lie about 80 light years away.
Gamma Ceti is just 3 degrees north of the M77. If you happen to be visiting this galaxy and the seeing conditions are favorable, don’t depart without giving Kaffal-whatchamacallit a try.

[Chart from IAU and Sky and Telescope. Sketch by P. J. Anway (doublestarobserver.com). Both are oriented with North at the top and West to the right.]

NGC 891– Spiral Galaxy in Andromeda
by Glenn Chaple

Last month, we turned our attention to the spiral galaxy NGC 7331 to get an idea what the Andromeda Galaxy (which is similar in size and structure) might look like were it 20 times more distant. From its new location, this naked eye object would now be a 9th magnitude “faint fuzzy,” visible only with the aid of telescope or large binocular.

How might our Milky Way Galaxy appear to eyes gazing our way from an extragalactic perspective? From a distance of 30 million light years and angled edge-on to the observer’s line of sight, it would appear very much like NGC 891 in Andromeda. Discovered by William Herschel’s sister Caroline in 1784 and located 3 ½ degrees east of the colorful double star Almach (gamma [(] Andromedae), NGC 891 is essentially a twin to the Milky Way.

A 10th magnitude sliver 13 arcminutes long and 3 arc-minutes wide, NGC 891 is an elusive   target. A dark dust lane that runs its length greatly diminishes its overall brightness. Just to glimpse NGC 891 with small aperture telescope is a challenging task. The dust lane doesn’t really come into view until an 8 to 10 inch scope is used.

The real grandeur of NGC 891 begins to unfold under the scrutiny of large Dobsonian-mounted reflectors.  Whatever telescope you use, your quest for NGC 891 should be made from a dark-sky location with a magnification in excess of 100X. Its dim appearance is a sobering reminder that our mighty Milky Way isn’t so mighty in the cosmic scheme of things.

Chart credit: astrosurf.com / NGC891: Mario Motta

The most volcanically active place is out-of-this-world!

By Dr. Ethan Siegel

Volcanoes are some of the most powerful and destructive natural phenomena, yet they're a vital part of shaping the planetary landscape of worlds small and large. Here on Earth, the largest of the rocky bodies in our Solar System, there's a tremendous source of heat coming from our planet's interior, from a mix of gravitational contraction and heavy, radioactive elements decaying. Our planet consistently outputs a tremendous amount of energy from this process, nearly three times the global power production from all sources of fuel. Because the surface-area-to-mass ratio of our planet (like all large rocky worlds) is small, that energy has a hard time escaping, building-up and releasing sporadically in catastrophic events: volcanoes and earthquakes!

Yet volcanoes occur on worlds that you might never expect, like the tiny moon Io, orbiting Jupiter. With just 1.5% the mass of Earth despite being more than one quarter of the Earth's diameter, Io seems like an unlikely candidate for volcanoes, as 4.5 billion years is more than enough time for it to have cooled and become stable. Yet Io is anything but stable, as an abundance of volcanic eruptions were predicted before we ever got a chance to view it up close. When the Voyager 1 spacecraft visited, it found no impact craters on Io, but instead hundreds of volcanic calderas, including actual eruptions with plumes 300 kilometers high! Subsequently, Voyager 2, Galileo, and a myriad of telescope observations found that these eruptions change rapidly on Io's surface.

Where does the energy for all this come from? From the combined tidal forces exerted by Jupiter and the outer Jovian moons. On Earth, the gravity from the Sun and Moon causes the ocean tides to raise-and-lower by one-to-two meters, on average, far too small to cause any heating. Io has no oceans, yet the tidal forces acting on it cause the world itself to stretch and bend by an astonishing 100 meters at a time! This causes not only cracking and fissures, but also heats up the interior of the planet, the same way that rapidly bending a piece of metal back-and-forth causes it to heat up internally. When a path to the surface opens up, that internal heat escapes through quiescent lava flows and catastrophic volcanic eruptions! The hottest spots on Io's surface reach 1,200 °C (2,000 °F); compared to the average surface temperature of 110 Kelvin (-163 °C / -261 °F), Io is home to the most extreme temperature differences from location-to-location outside of the Sun.

Just by orbiting where it does, Io gets distorted, heats up, and erupts, making it the most volcanically active world in the entire Solar System! Other moons around gas giants have spectacular eruptions, too (like Enceladus around Saturn), but no world has its surface shaped by volcanic activity quite like Jupiter's innermost moon, Io!

Io image credit: NASA / JPL-Caltech, via the Galileo spacecraft.

Learn more about Galileo’s mission to Jupiter: http://solarsystem.nasa.gov/galileo/

Kids can explore the many volcanoes of our solar system using the Space Place’s Space Volcano Explorer: http://spaceplace.nasa.gov/volcanoes.

At the Friday November 8 GAAC meeting we are thrilled to host a presentation by our very own Astronomy Ph.D. Bill Waller, speaking on the state of our galaxy.

Bill's talk, "Navigating the Milky Way Galaxy," will highlight the Milky Way as it appears in our sky and as it could possibly look if viewed from afar.  Along the way he will highlight a host of spectacular nebulae, star clusters, and other galactic objects that continue to fascinate both professional astronomers and the curious public.

This sounds like a really great night and the public is warmly invited. GAAC meets on Friday night, 11/8, at 8:00pm at the Lanesville Community Center, 8 Vulcan street in Lanesville.

No astronomy experience or telescope is needed to enjoy your evening, and there are never any dues or fees. Maps and directions can be found on our contact page.