The Gloucester Area Astronomy Club

Under Pressure...

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!

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.

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

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.

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 a number of different 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!

The Hottest Planet in the Solar System

By Dr. Ethan Siegel

When you think about the four rocky planets in our Solar System—Mercury, Venus, Earth and Mars—you probably think about them in that exact order: sorted by their distance from the Sun. It wouldn't surprise you all that much to learn that the surface of Mercury reaches daytime temperatures of up to 800 °F (430 °C), while the surface of Mars never gets hotter than 70 °F (20 °C) during summer at the equator. On both of these worlds, however, temperatures plummet rapidly during the night; Mercury reaches lows of -280 °F (-173 °C) while Mars, despite having a day comparable to Earth's in length, will have a summer's night at the equator freeze to temperatures of -100 °F (-73 °C).

Those temperature extremes from day-to-night don't happen so severely here on Earth, thanks to our atmosphere that's some 140 times thicker than that of Mars. Our average surface temperature is 57 °F (14 °C), and day-to-night temperature swings are only tens of degrees. But if our world were completely airless, like Mercury, we'd have day-to-night temperature swings that were hundreds of degrees. Additionally, our average surface temperature would be significantly colder, at around 0 °F (-18 °C), as our atmosphere functions like a blanket: trapping a portion of the heat radiated by our planet and making the entire atmosphere more uniform in temperature.

But it's the second planet from the Sun -- Venus -- that puts the rest of the rocky planets' atmospheres to shame. With an atmosphere 93 times as thick as Earth's, made up almost entirely of carbon dioxide, Venus is the ultimate planetary greenhouse, letting sunlight in but hanging onto that heat with incredible effectiveness. Despite being nearly twice as far away from the Sun as Mercury, and hence only receiving 29% the sunlight-per-unit-area, the surface of Venus is a toasty 864 °F (462 °C), with no difference between day-and-night temperatures! Even though Venus takes hundreds of Earth days to rotate, its winds circumnavigate the entire planet every four days (with speeds of 220 mph / 360 kph), making day-and-night temperature differences irrelevant.

Catch the hottest planet in our Solar System all spring-and-summer long in the pre-dawn skies, as it waxes towards its full phase, moving away from the Earth and towards the opposite side of the Sun, which it will finally slip behind in November. A little atmospheric greenhouse effect seems to be exactly what we need here on Earth, but as much as Venus? No thanks!

Check out these “10 Need-to-Know Things About Venus”:
http://solarsystem.nasa.gov/planets/profile.cfm?Object=Venus.  

Kids can learn more about the crazy weather on Venus and other places in the Solar System at NASA’s Space Place: http://spaceplace.nasa.gov/planet-weather. 

Image credit: NASA's Pioneer Venus Orbiter image of Venus's upper-atmosphere clouds as seen in the ultraviolet, 1979.

The annual GAAC "Welcome to Amateur Astronomy Night" meeting is coming up on Friday, May 9, from 8:00 to 9:30 at the Lanesville Community Center. In addition to the usual good things to eat and drink and great conversation, this month we're focused on everyone who may have an interest in amateur astronomy but doesn't know what to do about it.

We'll have all kinds of telescopes and equipment set up inside for you to look at, and we'll explain everything you ever wanted to know about amateur astronomy and about the dark Cape Ann sky over your head.

It'll be an exciting evening, featuring a series of speakers with ten-minute presentations on everything from "Why are we doing this" to "Yes, we're made of stardust," from "How different kinds of telescopes work" to "How to aim your telescope," and much more.

There are no dues or fees: it doesn't cost anything to come to a GAAC meeting. If you've ever wondered about astronomy, or even about what’s up there in our dark Cape Ann skies, this is for you. Last year this was one of our most popular meetings, so get there early!

The Gloucester Area Astronomy Club meets at 8:00 pm on the second Friday of every month at the Lanesville Community Center, 8 Vulcan Street in Lanesville. You can get directions on our Contact page.

The Power of the Sun's Engines

By Dr. Ethan Siegel

Here on Earth, the sun provides us with the vast majority of our energy, striking the top of the atmosphere with up to 1,000 Watts of power per square meter, albeit highly dependent on the sunlight's angle-of-incidence. But remember that the sun is a whopping 150 million kilometers away, and sends an equal amount of radiation in all directions; the Earth-facing direction is nothing special. Even considering sunspots, solar flares, and long-and-short term variations in solar irradiance, the sun's energy output is always constant to about one-part-in-1,000. All told, our parent star consistently outputs an estimated 4 × 1026 Watts of power; one second of the sun's emissions could power all the world's energy needs for over 700,000 years.

That's a literally astronomical amount of energy, and it comes about thanks to the hugeness of the sun. With a radius of 700,000 kilometers, it would take 109 Earths, lined up from end-to-end, just to go across the diameter of the sun once. Unlike our Earth, however, the sun is made up of around 70% hydrogen by mass, and it's the individual protons — or the nuclei of hydrogen atoms — that fuse together, eventually becoming helium-4 and releasing a tremendous amount of energy. All told, for every four protons that wind up becoming helium-4, a tiny bit of mass — just 0.7% of the original amount — gets converted into energy by E=mc2, and that's where the sun's power originates.

You'd be correct in thinking that fusing ~4 × 1038 protons-per-second gives off a tremendous amount of energy, but remember that nuclear fusion occurs in a huge region of the sun: about the innermost quarter (in radius) is where 99% of it is actively taking place. So there might be 4 × 1026 Watts of power put out, but that's spread out over 2.2 × 1025 cubic meters, meaning the sun's energy output per-unit-volume is just 18 W / m3. Compare this to the average human being, whose basal metabolic rate is equivalent to around 100 Watts, yet takes up just 0.06 cubic meters of space. In other words, you emit 100 times as much energy-per-unit-volume as the sun! It's only because the sun is so large and massive that its power is so great.

It's this slow process, releasing huge amounts of energy per reaction over an incredibly large volume, that has powered life on our world throughout its entire history. It may not appear so impressive if you look at just a tiny region, but — at least for our sun — that huge size really adds up!

Check out these “10 Need-to-Know Things About the Sun”: http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun. 

Kids can learn more about an intriguing solar mystery at NASA’s Space Place: http://spaceplace.nasa.gov/sun-corona.

Image credit: composite of 25 images of the sun, showing solar outburst/activity over a 365 day period; NASA / Solar Dynamics Observatory / Atmospheric Imaging Assembly / S. Wiessinger; post-processing by E. Siegel.

Old Tool, New Use: GPS and the Terrestrial Reference Frame

By Alex H. Kasprak

Flying over 1300 kilometers above Earth, the Jason 2 satellite knows its distance from the ocean down to a matter of centimeters, allowing for the creation of detailed maps of the ocean’s surface. This information is invaluable to oceanographers and climate scientists. By understanding the ocean’s complex topography—its barely perceptible hills and troughs—these scientists can monitor the pace of sea level rise, unravel the intricacies of ocean currents, and project the effects of future climate change.

But these measurements would be useless if there were not some frame of reference to put them in context. A terrestrial reference frame, ratified by an international group of scientists, serves that purpose.  “It’s a lot like air,” says JPL scientist Jan Weiss. “It’s all around us and is vitally important, but people don’t really think about it.” Creating such a frame of reference is more of a challenge than you might think, though. No point on the surface of Earth is truly fixed.

To create a terrestrial reference frame, you need to know the distance between as many points as possible. Two methods help achieve that goal. Very-long baseline interferometry uses multiple radio antennas to monitor the signal from something very far away in space, like a quasar. The distance between the antennas can be calculated based on tiny changes in the time it takes the signal to reach them. Satellite laser ranging, the second method, bounces lasers off of satellites and measures the two-way travel time to calculate distance between ground stations.

Weiss and his colleagues would like to add a third method into the mix—GPS. At the moment, GPS measurements are used only to tie together the points created by very long baseline interferometry and satellite laser ranging together, not to directly calculate a terrestrial reference frame.

“There hasn’t been a whole lot of serious effort to include GPS directly,” says Weiss. His goal is to show that GPS can be used to create a terrestrial reference frame on its own. “The thing about GPS that’s different from very-long baseline interferometry and satellite laser ranging is that you don’t need complex and expensive infrastructure and can deploy many stations all around the world.”

Feeding GPS data directly into the calculation of a terrestrial reference frame could lead to an even more accurate and cost effective way to reference points geospatially. This could be good news for missions like Jason 2. Slight errors in the terrestrial reference frame can create significant errors where precise measurements are required. GPS stations could prove to be a vital and untapped resource in the quest to create the most accurate terrestrial reference frame possible. “The thing about GPS,” says Weiss, “is that you are just so data rich when compared to these other techniques.”

You can learn more about NASA’s efforts to create an accurate terrestrial reference frame here: http://space-geodesy.nasa.gov/.

Kids can learn all about GPS by visiting http://spaceplace.nasa.gov/gps and watching a fun animation about finding pizza here: http://spaceplace.nasa.gov/gps-pizza.

Picture Caption: Artist’s interpretation of the Jason 2 satellite. To do its job properly, satellites like Jason 2 require as accurate a terrestrial reference frame as possible. Image courtesy: NASA/JPL-Caltech.

Plan ahead; March 14 is movie night at GAAC! We have found a terrific film on discoveries made by a giant, little-known observatory, tucked away in Pennsylvania of all places, that has revolutionized our understanding of the universe all around us.

The film features Dr. Neil DeGrasse Tyson of the American Museum of Natural History, and Dr. Tom Crouch of the Smithsonian, and is guaranteed to entertain and astonish, in true GAAC fashion. Come and explore the heavens with your friends and neighbors. This is great stuff, and you don't want to miss it.

GAAC movie nights feature all the great goodies and conversation that we always have at every meeting, but with popcorn and junior mints and soda. It's a free night at the movies, so come early and grab a good seat!

M46 and NGC 2438 – Open Cluster and Planetary Nebula in Puppis
by Glenn Chaple

There’s a saying that goes, “You can’t see the forest for the trees.” In the case of the planetary nebula NGC 2438, “you can’t see the nebula for the stars.” NGC 2438 lies within the northern portion of the open cluster Messier 46 and is often overshadowed by the surrounding stars.

M46 and NGC 2438 are located in a rather star-poor region in the northwest corner of Puppis. To find them, trace an imaginary line from beta () Canis Majoris through Sirius and extend it about 14 degrees eastward. Here, binoculars and finderscopes will reveal a pair of clusters just 1 ½ degrees apart. The brighter, splashier one is M47 (we’ll look at that one another time). The fainter, more concentrated one to its east is M46.

M46 was discovered by Charles Messier in 1771. Shining at 6th magnitude, it spans an area about 20 arc-minutes across and contains some 180-plus stars brighter than 13th magnitude. My first encounter with M46 came in 1978 when I viewed it with a 3-inch reflector and magnifying power of 30X. My logbook entry reads, “much fainter than 388 (note: my 1966 edition of Norton’s Star Atlas plotted M47 using its Herschel designation of 388); individual stars hinted at with averted vision.” In 2010, I revisited M46, using a 4.5-inch reflector and the same 30X magnification. The cluster was more readily resolved, and I noted “numerous mag 10-11 members.” On both occasions, NGC 2438 went unobserved. I had failed to see “the nebula for the stars.”

That changed last winter when I made a purposeful search for NGC 2438. Using a 10-inch reflector and a magnification of 80X, I easily spotted the 11th magnitude “puff-ball,” which is about an arc-minute across. Knowing where to look, I switched to the 4.5-inch reflector – this time with 75X. Sure enough, I could make out a faint, averted vision glow in the correct spot. By the way, Messier also failed to see “the nebula for the stars.” NGC 2438 was discovered by William Herschel 15 years after Messier found M46.

finder chart: freestarcharts.com       ngc2438 photo by Mario Motta, MD