Sky Object of the Month – September 2014

Messier 22  – Globular Cluster in Sagittarius
by Glenn Chaple

On early evenings in September, the constellation Sagittarius arches above the southern horizon, its rich deep-sky treasures accessible to those of us who inhabit mid-northern latitudes. One of the more spectacular of these cosmic splendors is the globular cluster M22 Its discovery is attributed to the German astronomer Abraham Ihle, who came across it on August 26, 1665 while observing Saturn.

Among globular clusters, M22 is exceeded in brightness and apparent size only by omega Centauri and 47 Tucanae. Much of its grandeur results from its nearness to the earth. At a distance of 10,500 light years, it’s over two times closer than the much-heralded M13. In reality, M13 is half again as large and contains several hundred thousand stars, compared to M22’s estimated 70.000.

I’ve always been a proponent of small telescopes for backyard astronomy, but had to admit that large aperture scopes are the way to go should you want to resolve the stars in a globular cluster. M22 is an exception. I’ve resolved it quite nicely with a 4-inch f/4 RFT (an Edmund Astroscan) and a magnifying power of just 74X.

Naturally, to view M22 in all its glory you’ll want to use a large instrument and 2 or 3 times that magnification.M22 is relatively easy to locate, if you use the “Teapot” of Sagittarius as a guide. In binoculars and finderscopes, it appears as a 5th magnitude smudge just 2 ½ degrees northeast of Kaus Borealis (Lambda [] Sagittarii) - a 3rd magnitude star that forms the top of the Teapot’s lid. Next time you’re visiting M13, drop southward and give M22 a look-see. Which do you prefer?

Chart credit: freestarcharts.com photo by Mario Motta, MD

NASA Spaceplace Partners' Article, August 2014

Droughts, Floods and the Earth's Gravity, by the GRACE of NASA
By Dr. Ethan Siegel

When you think about gravitation here on Earth, you very likely think about how constant it is, at 9.8 m/s2 (32 ft/s2). Only, that's not quite right. Depending on how thick the Earth's crust is, whether you're slightly closer to or farther from the Earth's center, or what the density of the material beneath you is, you'll experience slight variations in Earth's gravity as large as 0.2%, something you'd need to account for if you were a pendulum-clock-maker.

But surprisingly, the amount of water content stored on land in the Earth actually changes the gravity field of where you are by a significant, measurable amount. Over land, water is stored in lakes, rivers, aquifers, soil moisture, snow and glaciers. Even a change of just a few centimeters in the water table of an area can be clearly discerned by our best space-borne mission: NASA's twin Gravity Recovery and Climate Experiment (GRACE) satellites.

Since its 2002 launch, GRACE has seen the water-table-equivalent of the United States (and the rest of the world) change significantly over that time. Groundwater supplies are vital for agriculture and provide half of the world's drinking water. Yet GRACE has seen California's central valley and the southern high plains rapidly deplete their groundwater reserves, endangering a significant portion of the nation's food supply. Meanwhile, the upper Missouri River Basin—recently home to severe flooding—continues to see its water table rise.

NASA's GRACE satellites are the only pieces of equipment currently capable of making these global, precision measurements, providing our best knowledge for mitigating these terrestrial changes. Thanks to GRACE, we've been able to quantify the water loss of the Colorado River Basin (65 cubic kilometers), add months to the lead-time water managers have for flood prediction, and better predict the impacts of droughts worldwide. As NASA scientist Matthew Rodell says, "[W]ithout GRACE we would have no routine, global measurements of changes in groundwater availability. Other satellites can’t do it, and ground-based monitoring is inadequate." Even though the GRACE satellites are nearing the end of their lives, the GRACE Follow-On satellites will be launched in 2017, providing us with this valuable data far into the future. Although the climate is surely changing, it's water availability, not sea level rise, that's the largest near-term danger, and the most important aspect we can work to understand!

Learn more about NASA’s GRACE mission here: http://www.nasa.gov/mission_pages/Grace/

Kids can learn al about launching objects into Earth’s orbit by shooting a (digital) cannonball on NASA’s Space Place website. Check it out at: http://spaceplace.nasa.gov/how-orbits-work/

Image credit: NASA Earth Observatory image by Jesse Allen, using GRACE data provide courtesy of Jay Famigleitti, University of California Irvine and Matthew Rodell, NASA Goddard Space Flight Center. Caption by Holli Riebeek.

NASA Spaceplace Partners' Article, July 2014

The Invisible Shield of our Sun

By Dr. Ethan Siegel

Whether you look at the planets within our solar system, the stars within our galaxy or the galaxies spread throughout the universe, it's striking how empty outer space truly is. Even though the largest concentrations of mass are separated by huge distances, interstellar space isn't empty: it's filled with dilute amounts of gas, dust, radiation and ionized plasma. Although we've long been able to detect these components remotely, it's only since 2012 that a manmade spacecraft -- Voyager 1 -- successfully entered and gave our first direct measurements of the interstellar medium (ISM).

What we found was an amazing confirmation of the idea that our Sun creates a humongous "shield" around our solar system, the heliosphere, where the outward flux of the solar wind crashes against the ISM. Over 100 AU in radius, the heliosphere prevents the ionized plasma from the ISM from nearing the planets, asteroids and Kuiper belt objects contained within it. How? In addition to various wavelengths of light, the Sun is also a tremendous source of fast-moving, charged particles (mostly protons) that move between 300 and 800 km/s, or nearly 0.3% the speed of light. To achieve these speeds, these particles originate from the Sun's superheated corona, with temperatures in excess of 1,000,000 Kelvin!

When Voyager 1 finally left the heliosphere, it found a 40-fold increase in the density of ionized plasma particles. In addition, traveling beyond the heliopause showed a tremendous rise in the flux of intermediate-to-high energy cosmic ray protons, proving that our Sun shields our solar system quite effectively. Finally, it showed that the outer edges of the heliosheath consist of two zones, where the solar wind slows and then stagnates, and disappears altogether when you pass beyond the heliopause.

Unprotected passage through interstellar space would be life-threatening, as young stars, nebulae, and other intense energy sources pass perilously close to our solar system on ten-to-hundred-million-year timescales. Yet those objects pose no major danger to terrestrial life, as our Sun's invisible shield protects us from all but the rarer, highest energy cosmic particles. Even if we pass through a region like the Orion Nebula, our heliosphere keeps the vast majority of those dangerous ionized particles from impacting us, shielding even the solar system's outer worlds quite effectively. NASA spacecraft like the Voyagers, IBEX and SOHO continue to teach us more about our great cosmic shield and the ISM's irregularities. We're not helpless as we hurtle through it; the heliosphere gives us all the protection we need!

Want to learn more about Voyager 1’s trip into interstellar space? Check this out: http://www.jpl.nasa.gov/news/news.php?release=2013-278.

Kids can test their knowledge about the Sun at NASA’s Space place: http://spaceplace.nasa.gov/solar-tricktionary/

Image credit: Hubble Heritage Team (AURA / STScI), C. R. O'Dell (Vanderbilt), and NASA, of the star LL Orionis and its heliosphere interacting with interstellar gas and plasma near the edge of the Orion Nebula (M42). Unlike our star, LL Orionis displays a bow shock, something our Sun will regain when the ISM next collides with us at a sufficiently large relative velocity.

GAAC July Meeting, "Astrophotography, From Beginner to Expert"

The 8:00 pm Friday July 11 meeting of the Gloucester Area Astronomy Club is a free astrophoto festival, filled with outstanding photos of planets, and immense, distant, colorful galaxies, nebulae, and star clusters, shown on GAAC's 100 inch screen! The meeting will feature in-person presentations by four outstanding photographers, showing off their best work, and an introduction by our own Steve K, who will demonstrate how simple astrophotography can be for beginners.

Photographers Mario Motta, Phil Orbanes, John Hobbs and Barry Yomtov will each present their ten favorite pictures, and will talk briefly about what the objects are, how far away they are, how big, and a little about why and how each person got that shot.

This will be a spectacular, colorful night, with great presenters, and we'll have a wonderful time getting a rare, entertaining and accessible look into the world of astrophotography. Many of the photographs can be previewed in the Gallery section of this website.

The club meets on the second Friday of every month at the Lanesville Community Center, 8 Vulcan Street Lanesville, from 8:00 to 9:30 pm. Parking is free. The public is warmly welcomed and there is no cost. More information is available through the website, or on Facebook at http://www.facebook.com/gaacpage or in the club twitter feed, @gaactweet.

It’s Star Party Season!

GAAC summer star party information:

Sun Day, Sunday June 22, 5:00-9:00pm at the fisherman statue, Gloucester Boulevard

Halibut Point State Park, Friday June 27, dusk to 10:00, cloud date Saturday June 28

Halibut Point State Park, Friday July 18, dusk to 10:00, cloud date Saturday July 19

Halibut Point State Park, Friday Sept 5, dusk to 10:00, cloud date Saturday Sept 6

And the Acadia Night Sky Festival is on September 25-29; more info at  http://www.acadianightskyfestival.com/

NEFAF, at UNH, happens on October 17-18, with Carolyn Porco, lead for the Cassini mission! More info is here: http://www.physics.unh.edu/observatory/NEFAF

Sunday June 22 is International Sun Day!

Sunday June 22nd is International Sun Day, and, weather permitting, the Gloucester Area Astronomy Club  will be celebrating  in downtown Gloucester, by the Fisherman statue, from 5:00 pm until 9:00. There will be safe solar observing glasses for the public, handouts and activities for the kids, and specially filtered solar telescopes to take some good long looks at our nearest star.

How is our sun like a pot of boiling spaghetti? What is space weather and why should we care?  We'll find out! We'll see giant solar prominences live, as they happen, and sunspots big enough to swallow the earth as they make their way around the sun's surface.   When it starts to get dark we'll take a look at the planet Saturn, giant Jupiter and beautiful star clusters and nebulae.

Come join us on the Boulevard for International Sun Day Sunday as we explore the universe around us, both near and far!

NASA Spaceplace Partners' Article, June 2014

A Glorious Gravitational Lens

By Dr. Ethan Siegel

As we look at the universe on larger and larger scales, from stars to galaxies to groups to the largest galaxy clusters, we become able to perceive objects that are significantly farther away. But as we consider these larger classes of objects, they don't merely emit increased amounts of light, but they also contain increased amounts of mass. Under the best of circumstances, these gravitational clumps can open up a window to the distant universe well beyond what any astronomer could hope to see otherwise.

The oldest style of telescope is the refractor, where light from an arbitrarily distant source is passed through a converging lens. The incoming light rays—initially spread over a large area—are brought together at a point on the opposite side of the lens, with light rays from significantly closer sources bent in characteristic ways as well. While the universe doesn't consist of large optical lenses, mass itself is capable of bending light in accord with Einstein's theory of General Relativity, and acts as a gravitational lens!

The first prediction that real-life galaxy clusters would behave as such lenses came from Fritz Zwicky in 1937. These foreground masses would lead to multiple images and distorted arcs of the same lensed background object, all of which would be magnified as well. It wasn't until 1979, however, that this process was confirmed with the observation of the Twin Quasar: QSO 0957+561. Gravitational lensing requires a serendipitous alignment of a massive foreground galaxy cluster with a background galaxy (or cluster) in the right location to be seen by an observer at our location, but the universe is kind enough to provide us with many such examples of this good fortune, including one accessible to astrophotographers with 11" scopes and larger: Abell 2218.

Located in the Constellation of Draco at position (J2000): R.A. 16h 35m 54s, Dec. +66° 13' 00" (about 2° North of the star 18 Draconis), Abell 2218 is an extremely massive cluster of about 10,000 galaxies located 2 billion light years away, but it's also located quite close to the zenith for northern hemisphere observers, making it a great target for deep-sky astrophotography. Multiple images and sweeping arcs abound between magnitudes 17 and 20, and include galaxies at a variety of redshifts ranging from z=0.7 all the way up to z=2.5, with farther ones at even fainter magnitudes unveiled by Hubble. For those looking for an astronomical challenge this summer, take a shot at Abell 2218, a cluster responsible for perhaps the most glorious gravitational lens visible from Earth!

Learn about current efforts to study gravitational lensing using NASA facilities: http://www.nasa.gov/press/2014/january/nasas-fermi-makes-first-gamma-ray-study-of-a-gravitational-lens/

Kids can learn about gravity at NASA’s Space Place: http://spaceplace.nasa.gov/what-is-gravity/

Image: Abel 2218. Image credit: NASA, ESA, and Johan Richard (Caltech). Acknowledgement: Davide de Martin & James Long (ESA/Hubble).

NASA Spaceplace: What's It Like Inside Jupiter?

Under Pressure...

Cassini image of Jupiter.

If you have ever spent any time at the bottom of the deep end of a pool, you probably noticed that everything around you seemed heavier. Your ears might have hurt a bit and you might have felt your goggles press harder against your face. This is because the deeper you go, the more water there is on top of you. All that water presses against you and you experience more pressure.

If you notice this effect in a relatively shallow swimming pool, imagine how much pressure you would feel at the bottom of the deepest part of the ocean. At the bottom of the Pacific Ocean, you would feel as if there were over 16,000 pounds of force pressing on every square inch of your body! That’s like having the weight of three cars pressing against every square inch of your body. Obviously no human could survive under such conditions—that’s why we’ve had to build incredibly strong submarines to go that deep.

But that kind of pressure is nothing compared to what would be found at the center of the Earth. Think of everything that would be on top of you—oceans, mountains, millions of tons of molten material, an iron core... In theory, you would experience about 53 million pounds (or around 10,000 cars) of pressure on every square inch of your body at that depth.

But as powerful as that may sound, the pressure at the center of Earth is child’s play compared to the pressure at the center of Jupiter. How much weight would each square inch of your body experience there? Potentially over 650 million pounds! That’s nearly 130,000 cars! If you were to stack up all those cars they would rise up 117 miles above Earth—and if you can imagine it, there would be one stack like that for each square inch of your body!

animation of cars stacked on top of each other

Remember: We are talking about a whole stack of cars, like those shown above, for every square inch of your body!

What Happens Under That Much Pressure?

It turns out some pretty crazy things happen under that kind of immense pressure. Jupiter is made up almost entirely of hydrogen. When you think of hydrogen, you probably think of a common, colorless, odorless gas. But under the millions of pounds of pressure found inside Jupiter, the hydrogen gas is compressed so much that it actually changes into a liquid! Even deeper, the pressure is so great that the liquid hydrogen acts like a metal. Scientists call it liquid metallic hydrogen.

 

diagram of Jupiter's interior.
Here's what we think it looks like inside of Jupiter. Earth is shown for scale.

At least we are pretty sure that’s what is going on inside Jupiter. The conditions on Jupiter are so extreme that they can’t really be recreated here on Earth. Scientists have been trying for years to create liquid metallic hydrogen. But it is nearly impossible to mimic the interior of Jupiter on Earth for more than a couple millionths of a second.

The Largest Ocean in the Solar System

animation of cars stacked on top of each other Jupiter's Great Red Spot. The spot is a hurricane-like storm that has been raging on the planet's gaseous exterior for hundreds of years. But what's happening inside may just be even crazier than that!

Despite how hard it is to create these conditions here on Earth, Jupiter is so extremely massive that it probably has an entire ocean of liquid metallic hydrogen deep underneath its cloudy exterior. Incredibly, if scientists are right, it would be the largest ocean in our solar system.

An entire ocean of something we can barely produce here on Earth! Turns out pretty crazy things happen when something is surrounded by the weight of 130,000 cars in every direction!

 

Jupiter. Credit: NASA/JPL/Univ. of Arizona.