NASA Spaceplace Partners' Article, August 2015

Solar Wind Creates—and Whips—a Magnetic Tail Around Earth

By Ethan Siegel

As Earth spins on its axis, our planet's interior spins as well. Deep inside our world, Earth's metal-rich core produces a magnetic field that spans the entire globe, with the magnetic poles offset only slightly from our rotational axis. If you fly up to great distances, well above Earth's surface, you'll find that this magnetic web, called the magnetosphere, is no longer spherical. It not only bends away from the direction of the sun at high altitudes, but it exhibits some very strange features, all thanks to the effects of our parent star.

The sun isn't just the primary source of light and heat for our world; it also emits an intense stream of charged particles, the solar wind, and has its own intense magnetic field that extends much farther into space than our own planet's does. The solar wind travels fast, making the 150 million km (93 million mile) journey to our world in around three days, and is greatly affected by Earth. Under normal circumstances, our world's magnetic field acts like a shield for these particles, bending them out of the way of our planet and protecting plant and animal life from this harmful radiation.

But for every action, there's an equal and opposite reaction: as our magnetosphere bends the solar wind's ions, these particles also distort our magnetosphere, creating a long magnetotail that not only flattens and narrows, but whips back-and-forth in the onrushing solar wind. The particles are so diffuse that collisions between them practically never occur, but the electromagnetic interactions create waves in Earth's magnetosphere, which grow in magnitude and then transfer energy to other particles. The charged particles travel within the magnetic field toward both poles, and when they hit the ionosphere region of Earth’s upper atmosphere, they collide with ions of oxygen and nitrogen causing aurora. Missions such as the European Space Agency and NASA Cluster mission have just led to the first accurate model and understanding of equatorial magnetosonic waves, one such example of the interactions that cause Earth's magnetotail to whip around in the wind like so.

The shape of Earth's magnetic field not only affects aurorae, but can also impact satellite electronics. Understanding its shape and how the magnetosphere interacts with the solar wind can also lead to more accurate predictions of energetic electrons in near-Earth space that can disrupt our technological infrastructure. As our knowledge increases, we may someday be able to reach one of the holy grails of connecting heliophysics to Earth: forecasting and accurately predicting space weather and its effects. Thanks to the Cluster Inner Magnetosphere Campaign, Van Allen Probes, Mars Odyssey Thermal Emission Imaging System, Magnetospheric Multiscale, and Heliophysics System Observatory missions, we're closer to this than ever before.

Kids can learn about how solar wind defines the edges of our solar system at NASA Space Place. http://spaceplace.nasa.gov/interstellar

Image credit: ESA / C. T. Russell (L), of Earth's magnetic tail and its cause: the solar wind; Southwest Research Institute / IBEX Science Team (R), of the first image of the plasma sheet and plasmasphere created around Earth by the solar wind.

Sky Object of the Month – July 2015

Xi (ξ) Scorpii (Σ1998) – Double Star in Scorpius
by Glenn Chaple

Our cosmic wanderings take us 93 light years away to the triple star xi (ξ) Scorpii (Σ1998), located in the Scorpion’s northwest corner. A 60mm refractor magnifying 60X will reveal two stars (xi Scorpii A and C), of magnitudes 4.9 and 7.3 and separated by 7.0”. If the seeing is extremely steady, check out the brighter star with a larger scope (minimum aperture of 4 inches) and magnification of 150X or more.

You should capture a magnitude 5.2 companion (xi Scorpii B) just 1.1” away. Xi Scorpii A and B are a binary pair with an orbital period of 46 years. As the diagram shows, they are currently near greatest separation.

When I first viewed xi Scorpii with a 3-inch reflecting telescope in the summer of 1971, I was surprised to see a faint double star in the same field. I had “discovered” Σ1999 (magnitudes 7.5 and 8.1; separation 11.8”. Although nearly 5 minutes of arc separate Σ1999 from xi Scorpii, the two have the same common proper motion and are likely gravitationally bound.

When viewing xi Scorpii and Σ1999, pay close attention to the colors of their component stars. Xi Scorpii A and B are F-type stars, while C is a cooler G8 dwarf. Both Σ1999 stars have K spectral classes. What colors do you see?

 

GAAC Program note for July 10 2015

Our Friday July 10 meeting, 8:00 at the Lanesville Community Center, will feature astrophotographer extraordinaire Phil Orbanes with "Springtime for Galaxies," an expansive, colorful look at the island universes all around us, unspeakably large and far away but connected directly and materially to us by the light they radiate. Galaxies, in their number and distance from us, test the limits of our understanding, but there they are nonetheless.

Phil's presentation features a spectacular, lavishly illustrated look at 36 galaxies, alone, and in pairs and groups, culled from the areas between the Big Dipper and Virgo. Each galaxy, like our own, shines with the light of hundreds of billions of stars.

Phil will also be giving away, to one lucky GAACster, a new copy of James Geach's wonderful book "Galaxy," and there will be a consolation drawing as well. We're not going to tell you the prize; you'll have to come in and take your chances. There's big fun here folks, goodies to eat, great conversation, and an enlightening presentation on a stunning subject.

GAAC meets on the second Friday of the month at 8:00 pm at the Lanesville Community Center, 8 Vulcan Street in the Lanesville neighborhood of Gloucester, MA. GAAC is always free, no dues, fees or costs. Plenty of free parking.

GAAC Program note for June 12 2015

Save the date! Friday June 12 @8:00 is our annual Welcome to Amateur Astronomy Night.

We'll have telescopes of every size and description set up inside the Lanesville Community Center for you to inspect and ask their owners about.  What are the benefits of that particular scope? What can you see? How much did it cost? Get lots of answers while munching a brownie. And that's not all:

You'll enjoy six quick, colorful ten-minute presentations on different Astronomy topics, featuring GAAC faves Mario Motta, Glenn Chaple, Elaine Kolaczkowski, Jim Koerth, Alan Winter, and John Hobbs.

Our program:

  • What you need to know to get started in astronomy
  • How to buy your first scope, and what you need to do before you buy
  • The upcoming 2017 solar eclipse, how and where to view it
  • All the best astronomy gadgets, from the gadget meister
  • The how's and why's of binocular astronomy -- seeing more with less
  • How to do astrophotography without a telescope (with examples!)

Of course we'll have the usual goodies and wonderful conversation you've come to enjoy from GAAC.

We meet at the Lanesville Community Center, 8 Vulcan Street in Gloucester, MA, at 8:00 on the second Friday of every month. Everything we do is free; there are no dues or fees, ever.

Don't miss this annual overview of everything you need to know to begin exploring the cosmos in the company of very nice people.

Sky Object of the Month – June 2015

Messier 3 (NGC 5272) – Globular Cluster in Canes Venatici
by Glenn Chaple

As May gives way to June, backyard astronomers begin to anticipate the arrival of summer’s globular clusters, and with good reason. The globular-laden constellations Ophiuchus, Scorpius, and Sagittarius are beginning to show up in the early evening sky. We needn’t wait for this globular onslaught. Already well-placed for after-sunset viewing is Messier 13 in Hercules - grandest of all the northern sky globulars. Also available is Messier 3 in Canes Venatici. Compared to M13, it’s slightly fainter (magnitude 6.2 to M13’s 5.8) and smaller (18 arcminutes to 20 arcminutes). Looks can be deceiving, as M3 is about half again as distant as M13 (33,000 LY to 26,000 LY) and is intrinsically the larger of the two.

M13 is my globular cluster of choice at public star parties. Conveniently placed between zeta (ζ) Herculis and eta (η) Herculis in the “Keystone” of Hercules, it’s quick and easy to locate – something I consider when a line of people is waiting by my telescope.

When time constraints aren’t an issue, I like to place M3 on the observing menu. It isn’t really all that hard to find, being bright enough to be easily spotted in binoculars and finderscopes (it’s even been seen without optical aid by keen-eyed observers in dark-sky locations). To capture M3, point your telescope midway between alpha (α) Canum Venaticorum (Cor Caroli) and alpha (α) Bootis (Arcturus), but slightly closer to the latter (refer to the accompanying finder chart). A low-power sweep should pick up a roundish smudge of light. Switch to higher magnitudes, and you’re in business!

While most globular clusters require apertures of 6 inches and above to resolve their individual stars, M3 can be partially resolved in small-aperture scopes. The accompanying sketch shows its appearance as seen through a 4.5-inch reflector. Visible is the core and a smattering of stars near its outer edge. Large telescopes bring the outermost reaches of M3 into view – a spectacular sight, as an image taken by Amateur Telescope Makers of Boston President Neil Fleming shows. Rotate the Fleming photo about 30 degrees clockwise, and scale and orientation of both fields will be identical.

Think of this as you gaze at M3. You’re looking at a half million stars packed into a sphere just 190 light years across!

 

 

 


NASA Space Place Column, April 2015

Is the Most Massive Star Still Alive?

By Ethan Siegel

The brilliant specks of light twinkling in the night sky, with more and more visible under darker skies and with larger telescope apertures, each have their own story to tell. In general, a star's color correlates very well with its mass and its total lifetime, with the bluest stars representing the hottest, most massive and shortest-lived stars in the universe. Even though they contain the most fuel overall, their cores achieve incredibly high temperatures, meaning they burn through their fuel the fastest, in only a few million years instead of roughly ten billion like our sun.

Because of this, it's only the youngest of all star clusters that contain the hottest, bluest stars, and so if we want to find the most massive stars in the universe, we have to look to the largest regions of space that are actively forming them right now. In our local group of galaxies, that region doesn't belong to the giants, the Milky Way or Andromeda, but to the Large Magellanic Cloud (LMC), a small, satellite galaxy (and fourth-largest in the local group) located 170,000 light years distant.

Despite containing only one percent of the mass of our galaxy, the LMC contains the Tarantula Nebula (30 Doradus), a star-forming nebula approximately 1,000 light years in size, or roughly seven percent of the galaxy itself. You'll have to be south of the Tropic of Cancer to observe it, but if you can locate it, its center contains the super star cluster NGC 2070, holding more than 500,000 unique stars, including many hundreds of spectacular, bright blue ones. With a maximum age of two million years, the stars in this cluster are some of the youngest and most massive ever found.

At the center of NGC 2070 is a very compact concentration of stars known as R136, which is responsible for most of the light illuminating the entire Tarantula Nebula. Consisting of no less than 72 O-class and Wolf-Rayet stars within just 20 arc seconds of one another, the most massive is R136a1, with 260 times the sun's mass and a luminosity that outshines us by a factor of seven million. Since the light has to travel 170,000 light years to reach us, it's quite possible that this star has already died in a spectacular supernova, and might not even exist any longer! The next time you get a good glimpse of the southern skies, look for the most massive star in the universe, and ponder that it might not even still be alive.


Images credit: ESO/IDA/Danish 1.5 m/R. Gendler, C. C. Thöne, C. Féron, and J.-E. Ovaldsen (L), of the giant star-forming Tarantula Nebula in the Large Magellanic Cloud; NASA, ESA, and E. Sabbi (ESA/STScI), with acknowledgment to R. O'Connell (University of Virginia) and the Wide Field Camera 3 Science Oversight Committee (R), of the central merging star cluster NGC 2070, containing the enormous R136a1 at the center.

NASA Space Place Column, March 2015

The Cold Never Bothered Me Anyway

By Ethan Siegel

For those of us in the northern hemisphere, winter brings long, cold nights, which are often excellent for sky watchers (so long as there's a way to keep warm!) But there's often an added bonus that comes along when conditions are just right: the polar lights, or the Aurora Borealis around the North Pole. Here on our world, a brilliant green light often appears for observers at high northern latitudes, with occasional, dimmer reds and even blues lighting up a clear night.

We had always assumed that there was some connection between particles emitted from the Sun and the aurorae, as particularly intense displays were observed around three days after a solar storm occurred in the direction of Earth. Presumably, particles originating from the Sun—ionized electrons and atomic nuclei like protons and alpha particles—make up the vast majority of the solar wind and get funneled by the Earth's magnetic field into a circle around its magnetic poles. They're energetic enough to knock electrons off atoms and molecules at various layers in the upper atmosphere—particles like molecular nitrogen, oxygen and atomic hydrogen. And when the electrons fall back either onto the atoms or to lower energy levels, they emit light of varying but particular wavelengths—oxygen producing the most common green signature, with less common states of oxygen and hydrogen producing red and the occasional blue from nitrogen.

But it wasn't until the 2000s that this picture was directly confirmed! NASA's Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) satellite (which ceased operations in December 2005) was able to find out how the magnetosphere responded to solar wind changes, how the plasmas were energized, transported and (in some cases) lost, and many more properties of our magnetosphere. Planets without significant magnetic fields such as Venus and Mars have much smaller, weaker aurorae than we do, and gas giant planets like Saturn have aurorae that primarily shine in the ultraviolet rather than the visible. Nevertheless, the aurorae are a spectacular sight in the evening, particularly for observers in Alaska, Canada and the Scandinavian countries. But when a solar storm comes our way, keep your eyes towards the north at night; the views will be well worth braving the cold!

Image: Auroral overlays from the IMAGE spacecraft. Image credit: NASA Earth Observatory (Goddard Space Flight Center) / Blue Marble team.

Friday March 13 GAAC Meeting: Cassini and the Moons of Saturn

This month GAAC is fortunate to host Robert Naeye, former Editor in Chief of Sky & Telescope, the world’s most respected and influential popular astronomy magazine. Robert will be speaking to us Friday, March 13, on the Cassini mission to Saturn and its moons.

In July 2004, NASA’s Cassini spacecraft fired its braking rocket and entered orbit around Saturn. Since then, Cassini has orbited the Ring Planet hundreds of times, and returned hundreds of thousands of images, many of which we will see on the 13th, along with a flood of data about Saturn’s magnetic field, particle environment, and ring composition. This enormous dataset has revolutionized science’s understanding of the Saturnian system.

Besides studying Saturn and its rings, Cassini has unveiled its mysterious moons, showing the planet and moons to be a mini-solar system unto itself. In 2005, Cassini deployed the European-built Huygens probe, which parachuted and landed on the surface of Saturn’s largest moon, Titan, arguably the most Earth-like world in the solar system other than Earth itself. Cassini and Huygens have revealed Titan to be a world of complex meteorology and geology, with lakes and rivers fed by methane rainfall.

Perhaps most exciting of all, Cassini has also found jets of water-ice particles laced with organics shooting away from the moon Enceladus, making this small world a potential abode for life. And Cassini images of Iapetus have helped explain how this bizarre moon got its yin-yang appearance, with one side darker than coal and the other as bright as freshly fallen snow.

Robert Naeye earned a master’s degree in science journalism from Boston University in 1992, and later worked on the editorial staffs of Discover and Astronomy magazine. He served as Editor in Chief of Mercury magazine (published by the Astronomical Society of the Pacific) from 2000 to 2003. He worked as a Senior Editor at Sky & Telescope from 2003 to 2007, before moving to NASA’s Goddard Space Flight Center to work as a Senior Science Writer for the Astrophysics Science Division. He returned to Sky & Telescope in June 2008 to serve as Editor in Chief.

Robert is the author of two books: Through the Eyes of Hubble: The Birth, Life, and Violent Death of Stars (Kalmbach, 1997) and Signals from Space: The Chandra X-ray Observatory (Turnstone, 2000). He has contributed to two other books, and has won several awards for his writing and outreach activities.