Friday, May 27, 2011

From 2MASS To You... The Most Complete 3-D Map of Local Universe

Written by Tammy Plotner

Isn't this era of astronomy incredible? There are times when I thumb through my old astronomy books with their outdated information and simply marvel over today's capabilities. Who would have believed just 50 years ago that we'd be peering into the far reaches of our Universe - let alone mapping them? Thanks to an endeavor that took more than 10 years to complete, the 2MASS Redshift Survey (2MRS) has provided us with 3-D map which cuts through the dust and pushes the envelope of the Galactic Plane out to 380 million light-years.

With our current understanding of expansion, we accept a distant galaxy's light is stretched into longer wavelengths - or redshifted. By default, this means the further a galaxy is away, the greater the redshift will be. This then becomes a critical factor in producing a three-dimensional point in mapping. To cut through the layers of obscuring dust, the original Two-Micron All-SkySurvey (2MASS) visualized the entire visible sky in three near-infrared wavelength bands. While it gave us an incredible look at what's out there, it lacked a critical factor... distance. Fortunately, some of the galaxies logged by 2MASS had known redshifts, and thus began the intense "homework" of measurements in the late 1990s using mainly two telescopes: one at the Fred Lawrence Whipple Observatory on Mt. Hopkins, AZ, and one at the Cerro Tololo Inter-American Observatory in Chile.

"Our understanding of the origin and evolution of the Universe has been fundamentally transformed with seminal redshift, distant supernovae and cosmic microwave background surveys. The focus has shifted to the distribution and nature of dark matter and dark energy that drive the dynamics of the expanding cosmos." says team member, Thomas Jarrett. "The study of the local Universe, including its peculiar motions and its clustering on scales exceeding 100 Mpc, is an essential ingredient in the connection between the origin of structure in the early Universe and the subsequent formation of galaxies and their evolution to the state we observe today. Key issues include the location and velocity distribution of galaxies, leading to the mass-to-light relationship between what is observed and what is influencing the mass density field."

What makes this work so impressive? The 2MRS has logged what's been previously hidden behind our Milky Way - allowing us to comprehend the impact they have on our motion. From the time astronomers first measured our movement relative to the rest of the Universe and realized it couldn't be explained by the gravitational attraction from any visible matter, it became a huge jigsaw puzzle just waiting to have the pieces match up. Now massive local structures, like the Hydra-Centaurus region (the "Great Attractor") which were previously hidden almost behind the Milky Way are shown in great detail by 2MRS. The Galactic "zone of avoidance" (ZoA) is still, however, a formidable barrier due to the sheer number of stars that produce a foreground (confusion) "noise". Near the center of the Milky Way the confusion noise is extreme, blocking nearly 100% of the background light; whereas far from the Galactic center the confusion noise is minimal and the veil of the Milky Way is lifted at near-infrared wavelengths

"The 2MASS catalog has proven to be quite versatile to the astronomical community: supporting observation and future mission planning, seeding studies of star formation and morphology in nearby galaxies, penetrating the zone of avoidance, providing the base catalog of redshift and Tully-Fisher HI surveys, and so on. But perhaps its most important function is to provide the "big picture" context for analysis and interpretation of data concerning galaxy clusters, large scale structure and the density of matter in the Universe." says Jarrett. "And so the primary motivation of this work, with the construction of qualitative "road" maps to the local Universe, is to provide a broad framework for studying the physical connection between the local Universe (Milky Way, Local Group, Local Supercluster, "Great Wall", etc) and the distant Universe where galaxies and the cosmic web first formed. The best is yet to come."

Image Credit: T.H. Jarrett (IPAC/SSC)

Wednesday, May 18, 2011

Aurora Alert!

Written by Tammy Plotner

Thanks to some very "hot" activity on the Sun, high latitude observers could be treated to some magnificent apparition of the Aurora Borealis. But don't count yourself out if you live a bit south of the pole... Sometimes the Northern Lights can surprise you!

According to Space Weather: "A magnetic filament exploded away from the sun on May 17th and propelled a cloud of plasma into space. The cloud (a CME) was not aimed directly at Earth, but it could deliver a glancing blow to our planet's magnetic field during the late hours of May 19th." And it wasn't just then either... the Sun has been delivering some outstanding activity now for several days. Just check out this shot...

While the probability figures show as fairly low, don't let that discourage you from looking. According to the latest information, the auroral oval is dipping low across the northern tier of the United States - leaving SkyWatchers from Canada through Kentucky an opportunity to spot a little skyglow. Why so optimistic? It's the time of year...

Right now Earth’s magnetosphere and magnetopause (the point of contact) are positioned correctly to interact with the Sun’s influencing interplanetary magnetic field (IMF), and the plasma stream that flows past us as the solar wind. During the time around equinox - and even later - this leaves the door wide open for one of the most awesome signs of Spring... aurora! Visit the Geophysical Institute to sign up for aurora alerts, and use their tools to help locate the position of Earth’s auroral oval.

Spotting aurora isn't hard, it simply just takes patience and reasonably dark skies. From experience you may see what looks like a distant search light - or it may appear as a red glow. At times the aurora can take on the appearance of a glowing green cloud that may or may not obscure the stars behind it. It shimmers and moves. How do you distinguish it from a cloud? Sometimes that can be difficult, but aurora will seem to "evaporate" rather than move with the wind. Having a few clouds won't diminish the view and even moderate light pollution won't stop it if the activity is strong enough. The most important factor is to give your eyes plenty of time to adjust to low light conditions and allow plenty of time for activity to happen.

Good luck... and may the aurora be with you!

Many thanks to John Chumack of Galactic Images for sharing his recent solar photo and Aurora shots with us!

Friday, May 13, 2011

Weekend Observing Challenges - May 13-15, 2011

Written by Tammy Plotner

Greetings, fellow SkyWatchers!

If you've got a telescope, then we've got some projects for you. While it's definitely going to be a "moon light" weekend, that doesn't mean that you can't have fun! Let's take a look at what the night has to offer...

On Friday and Saturday evening, the most prominent lunar feature will be the ancient and graceful Gassendi. Its bright ring stands on the north shore of Mare Humorum – an area about the size of the state of Arkansas. Around 113 km in diameter and 2012 meters deep, you will see a triple mountain peak in its center and the south wall eroded by lava flows. Gassendi offers a wealth of details to telescopic observers on its ridge and rille covered floor.

When you have finished with your lunar observations, let’s travel on to a fascinating double star. A little less than a handspan south of the last star in the handle of the “Big Dipper”, you will see a fairly bright star that is on the edge of unaided eye detection thanks to tonight’s gibbous Moon. Aim your telescopes or steady binoculars there for a real treat! Alpha Canum is more commonly known as Cor Caroli – or the “heart of Charles” – and is a true jewel easily split by the most modest of instruments. Although some observers may not be able to distinguish a color difference between the magnitude 2.8 and 5.6 companions, it has been my experience that most will see a faded blue primary (a magnetic spectrum variable) and pale orange secondary on this 120 light year distant pair. If you are equatorially aligned, turn off the drive and wait for 150 seconds. Widely separated Struve 1702 will be coming into view…

On Sunday night your lunar challenge will be a challenging one – worthy of the larger scope. Start by identifying and studying craters, Hansteen and Billy. Due west of Hansteen you will find a small crater near the terminator known as Sirsalis. It will appear as a small, dark ellipse with a bright west wall with its twin, Sirsalis B on the edge. The feature you will be looking for is the Sirsalis Rille – the longest presently known. Stretching northeast of Sirsalis and extending for 459 kilometers south to the bright rays of Byrgius, this major “crack” in the lunar surface will show several branches – like a long dry river bed.

Tonight let’s go from one navigational extreme to another as viewers in the northern hemisphere try their hand at Polaris. As guide star for north, Polaris is also a wonderful double with an easily resolved, faint blue companion for the mid-sized telescope. But what about the south? Viewers in the southern hemisphere can never see Polaris – is there a matching star for the south? The answer is yes – Sigma Octantis – but at magnitude 5, it doesn’t make a very good unaided eye guide. Ancient navigators found better success with the constellation of Crux, better known as the “Southern Cross”. While Crux has many wonderful double stars, if southern hemispere viewers would like to see a star very similar to Polaris, then try your luck with Lambda Centauris. The magnitude difference between components and separation are about the same!

Many thanks to Damien Peach for his exquisite lunar photos!

Wednesday, May 4, 2011

The Early Morning Show... Eta Aquarid Meteor Shower Peaks During Planetary Alignment

Written by Tammy Plotner

Are you ready for the Eta Aquarid Meteor Shower? While the peak activity will be on the night of May 5/6, the offspring of Comet Halley are already beginning to make their appearance known. No matter where you live or what time zone you observe from, the best time to look for "shooting stars" is over the next week or so during the hours just before dawn.

Somewhere in the outer reaches of our solar system beyond the orbit of Jupiter, Comet Halley continues on its track - far away from its 1986 debris trail. However, now isn't the only time we encounter this famous comet's leftovers. Three times a year the Earth cruises through the dusty trail causing the Eta Aquarids, the Beta Aquarids (both in May) and the Orionids (during October). When a piece of this debris enters our atmosphere, it is traveling about 66 kilometers per second and can shine as brightly as the stars (3rd magnitude) in the constellation from which it appears to originate. Encountering a dense paticle stream material which may spark activity of up to 70 meteors per hour for lucky observers in the southern hemisphere. But don’t count yourself out if you live in the north! Because the constellation of Aquarius is relatively low for northern observers, this means we have at least better chance of spotting those breathtaking Earth grazers!

Staring aound 4:00 a.m. (local time) the constellation of Aquarius is beginning to rise low to the southeast for the northern hemisphere and fall rates could be as marked as an average of one meteor every three or four minutes. Although meteors can appear from any point in the sky, your best northern skies bet will be to face generally southeast, gaze roughly halfway up the sky and get as comfortable as possible. A reclining lawn chair makes a wonderful meteor watching companion! Getting as far away as possible from city lights will also increase the amount of meteors you see.

Don’t be discouraged if you’re clouded out or unable to view at the peak time. The most wonderful part about the Eta Aquarids are the fact that the stream is very broad and activity is extended from April 21 until May 12. And there's an added treat - the ongoing planetary alignment rising in the East...

Don’t let anyone deter you from watching the Eta Aquarids if you have an opportunity. While it isn’t one of the most prolific showers of the year for the north, it is very well established and having dark skies will help tremendously. There is nothing finer than cradling a cup of hot coffee and waiting on the dawn. I am sure that you'll come away feeling very happy indeed that you took the time to look for Comet Halley’s children racing by!

Comet Halley image courtesy of Halley/Giotto Team, ESO/NASA, Skymap courtesy of NASA and conjunction image of May 1 courtesy of Dave Rencke.

Sunday, May 1, 2011

Catch T Pyxidis Now!

Written by Tammy Plotner

Are you ready to observe a nova event which can be caught in simple binoculars? Then open your eyes wide and locate T Pyxidis! Right now it’s showing up as just slightly fainter than magnitude 7, which means it is going to appear as an “extra star” in an otherwise rather starless portion of the constellation of Pyxis. Are you ready? Then let’s dance…

T Pyxidis is actually a binary star – one much like our own Sun with a white dwarf companion. Thanks to its diminuative, heavy-weight companion, matter from the primary star is always being drawn toward the secondary causing periodic thermonuclear explosions. Since there hasn’t been any real activity in about 45 years, astronomers believed T Pyx could possibly have began evolving into an entirely new system and activity wouldn’t occur perhaps for centuries. But they were wrong…

With a normal magnitude of 15.5, T Pyxidis would only be visible to some of the largest of amateur telescopes, but right now it can easily be spotted with average binoculars. The first finder chart seen on this page will get you in the right area and the one below will get you spot on (RA 09h 04m 41.50s Dec -32° 22′ 47.5″).

The fun part about observing T Pxidis is that it’s an object well suited for both hemispheres – one where the south is a bit more favored than the north – and all the “buzz” that goes with it. According to many sources, the white dwarf may be nearing its Chandrasekhar limit and become a Type 1a supernova when it collapses under its own weight. Says Edward Sion (et al); “The recurrent nova T Pyxidis has had 5 recorded thermonuclear explosions, more than any other recurrent nova, with an average time between nova outbursts of 19 years. However, it has been 44 years since its last nova outburst in 1966, making it long overdue for the next nova (supernova?). ”

However, don’t worry about this 3,300 light year distant stellar explosion happening any time soon. It’s estimated that kind of action may take as long as another couple of million years. “A key fact about T Pyx is that its accretion rate has been secularly declining since before the 1890 eruption, with the current rate being only 3% of its earlier rate. The decline in the observed accretion rate shows that the supersoft source is not self-sustaining, and we calculate that the accretion in T Pyx will effectively stop in upcoming decades.” say Bradley E. Schaefer (et al). “With this, T Pyx will enter a state of hibernation, lasting for an estimated 2,600,000 years, before gravitational radiation brings the system into contact again. Thus, T Pyx has an evolutionary cycle going from an ordinary CV state, to its current RN state, to a future hibernation state, and then repeating this cycle.”

But don’t you wait that long to observe it... It might be the only chance in your lifetime. For the next week or so, the Moon won’t interfere with your early evening chance to see this very cool cosmic customer!