Astronomy Archives

January 15, 2015December 23, 2015 by Ramin Skibba

Like a BOSS: How Astronomers are Getting Precise Measurements of the Universe’s Expansion Rate

Distribution of galaxies and quasars in a slice of BOSS out to a redshift of 3, or 11 billion years in the past. Credit: SDSS-III

Astrophysicists studying the expansion of the Universe with the largest galaxy catalogs ever assembled are ushering in an exciting era of precision cosmology. Last week, the Sloan Digital Sky Survey (SDSS) issued its final public data release, and scientists working in its largest program, the Baryon Oscillation Spectroscopic Survey (BOSS) also presented their final results at the American Astronomical Society meeting in Seattle, Washington.

By mapping over 10,000 square degrees — 25% of the sky — BOSS is “measuring our universe’s accelerated expansion with the world’s largest extragalactic redshift survey,” according to SDSS-III Director Daniel Eisenstein of the Harvard-Smithsonian Center for Astrophysics. The BOSS results include new and precise measurements of the universe’s expansion rate (called the “Hubble constant”) and matter density, which includes dark matter, stars, gas, and dust.

BOSS conducted its observations at 2.5-meter Sloan Foundation Telescope at Apache Point Observatory in New Mexico, producing spectra and spatial positions for 1.5 million galaxies and 300,000 quasars in a volume equivalent to a cube with length 8.5 billion light-years on a side (see image above). Astronomers used this rich dataset to map the objects’ distributions and to detect the characteristic scale imprinted by baryon acoustic oscillations in the early universe. Sound waves propagate outward with time, like ripples spreading in a pond, and are indicated by a large-scale clustering signal in the positions of galaxies relative to each other (see illustration below). By analyzing this signal at different times, it is possible to study the behavior of the mysterious “dark energy” causing the accelerating expansion of the universe.

An illustration of the concept of baryon acoustic oscillations, imprinted in the early universe and seen today in galaxy surveys. (courtesy: Chris Blake and Sam Moorfield)

In BOSS’s final results, hundreds of scientists in the international collaboration measured this scale with unprecedented precision. In particular, Ashley Ross from Ohio State University presented results that demonstrated the power of combining an analysis of the transverse and line-of-sight distributions of galaxies. In a paper by Eric Aubourg and collaborators, BOSS astronomers measured the cosmic distance scale of galaxies in the “local” universe and of quasars in the distance universe with impressively small systematic errors—at less than the 1% level—when combined with cosmic microwave background constraints. Their cosmological analysis yields a measurement of the Hubble constant and of the matter density of the universe consistent with a “flat” cold dark matter cosmology with a cosmological constant (see below). Cosmological models including curvature, evolving dark energy, or massive neutrinos are not completely ruled out but are less supported by the data than before. Other results from the collaboration will be submitted for publication in the coming months.

Cosmological constraints on the Hubble parameter h, matter density Ωm, and curvature parameter Ωk from BOSS's baryon acoustic oscillations (BAO) combined with supernovae (SN) and Planck results. (Courtesy: Aubourg et al. 2014) — Cosmological constraints on the Hubble parameter h, matter density Ω_m, and curvature parameter Ω_k from BOSS’s baryon acoustic oscillations (BAO) combined with supernovae (SN) and Planck results. (Courtesy: Aubourg et al. 2014)

The BOSS dataset “represents the gold standard in mapping out the network of galaxies that comprises the large-scale structure of the Universe…The data enables us to trace, with greater precision than ever before, the presence of dark energy, the behaviour of gravity on cosmic scales, and the effect of massive neutrinos,” says Chris Blake of Swinburne University, not affiliated with the collaboration.

Where will the BOSS team go from here? The collaboration has begun work on SDSS-IV, whose six-year mission includes an ambitious extended BOSS (eBOSS) survey. According to eBOSS Targeting Coordinator Jeremy Tinker of New York University, eBOSS observations of over 700,000 quasars will precisely measure the distance scale “at a much higher redshift regime that is not covered by current large-scale surveys.”

You can read more about BOSS and updates about the three other componenets of the SDSS in our previous article here.
SDSS website

(Full disclosure: Ramin Skibba had been a member of the BOSS collaboration during 2010-2012.)

January 15, 2015December 23, 2015 by Elizabeth Howell

What Is The Gibbous Moon?

Astrophoto: The Moon by Logan Mancuso — The Moon. Credit: Logan Mancuso

What does it mean when you hear the term “gibbous moon”? It’s when the Moon is more than half full, but not quite fully illuminated, when you look at it from the perspective of Earth. The reason the light changes has to do with how the Moon orbits the Earth.

The average distance between the Earth and the Moon is about 382,500 km (237,675 miles). As the Moon orbits our planet, the illumination of the Sun changes on its surface. The Moon takes about 29.5 days to go from a new moon to a full moon and then back again. This is called a “synodic period” or sometimes, a “synodic month.”

It’s slightly longer than the “sidereal period” or “sidereal month” (27.3 days) for the Moon to return to the same position relative to the stars. That’s because the Earth is moving at the same time along its orbit of the Sun, requiring the Moon to “catch up” to reach the same illumination, according to NASA.

How the phases of the Moon work. Credit: NASA/Bill Dunford

So as the Moon orbits the Earth, the illumination of the Sun changes. When the Moon is in between the Earth and the Sun — with the three objects perfectly aligned — the angle between the Moon and the Sun is 0 degrees. This produces a “new moon”, which is when the Moon is not illuminated or barely illuminated at all.

The first quarter occurs when the Moon is at a 90-degree angle with the Sun, as seen from Earth. Once the Moon’s angle exceeds 90 degrees, that’s when it enters the waxing gibbous phase. At 180 degrees from the Sun, the Moon is fully illuminated (a full moon). Then after it reaches 180 degrees, when the Moon and the Sun are on the opposite sides of the Earth, it becomes a waning gibbous moon.

At 270 degrees, the Moon finishes its gibbous phase, enters the third quarter of its synodic period and becomes a waning crescent, until it reaches the new moon phase and starts the cycle anew. And actually, the Moon’s position around the Earth plays a role in solar and lunar eclipses.

Total solar eclipse in 1999. The alignment of the nearby Moon and massive Sun, the weightiest body in the Solar System by far, didn't cause anyone to float off the ground. To my knowledge. Credit: Luc Viatour — Total solar eclipse in 1999. Credit: Luc Viatour

A solar eclipse can only happen when the Moon is in its “new phase”. This is, again, because of geometry — because the Moon is in between the Sun and the Earth. From time to time, the position of the Moon lines up with the position of the Sun in Earth’s sky. Coincidentally, the Sun and the Moon appear to be about the same size from Earth’s surface, which makes it possible for the Moon to completely (or almost completely) block the Sun. This creates a solar eclipse. The full eclipse phase can last anywhere from seconds to minutes.

By contrast, a lunar eclipse happens when the Moon is in its “full phase.” At this time, the Earth is in between the Moon and the Sun. When the Moon enters the Earth’s shadow, the shadow can completely or partially fall across the Moon’s surface. A total lunar eclipse phase tends to last anywhere from minutes to over an hour. It creates a ruddy (red or brown) glow due to the effect of sunsets and sunrises all around the Earth shining on the Moon at the same time, according to Bad Astronomy’s Phil Plait.

You’ll notice that as the Moon goes through its various phases, it keeps the same side of itself turned towards Earth. This is due to an effect called tidal locking. After the Moon was formed (likely through a near-cataclysmic collision with Earth), its rotation period didn’t align with that of Earth’s. But over millions of years, the tug of the Earth’s gravity produced a bulge in the Moon’s interior on the side closest to Earth.

Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit the Earth (left side). If the Moon didn't spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Credit: Wikipedia — Tidal locking results in the Moon rotating about its axis in about the same time it takes to orbit the Earth (left side). If the Moon didn’t spin at all, then it would alternately show its near and far sides to the Earth while moving around our planet in orbit, as shown in the figure on the right. Credit: Wikipedia

As Discovery News explains, over time that bulge was pulled back and forth as the Moon orbited Earth. If the rotation is much slower than the orbit, the bulge “lags behind” while the smaller body orbits. Eventually, this causes one side to always face the larger body.

Tidal locking, by the way, is a fairly common phenomenon in our Solar System — particularly at Jupiter and Saturn, which are massive gas giants that (compared to their immense size) have nat-sized moons orbiting close by. Tidal locking also likely takes place with exoplanets that are orbiting close in to their parent stars.

We have done many stories on Universe Today about the Moon. Here’s one about the phases of the Moon. Want to know when the next full moon is going to be? Here’s a handy guide from NASA that covers the phases of the Moon for 6000 years. And here’s a good explainer on the phases of the Moon. We also discussed the formation of the Moon on Astronomy Cast, Episode 17: Where Did the Moon Come From?

January 14, 2015December 23, 2015 by Tim Reyes

Did a House-Sized Meteorite Create This Mysterious Circle in Antarctica?

A discovery photo of the ringed formation, 2km (1.24 miles) that AWI researchers are proposing is a meteorite impact site. (Credit:Tobias Binder, AWI)

Endless blinding white ice as far as the eye can see. This is the common scene from the window of planes delivering researchers to Antarctica. However, this is not always the case. While there are mountain ranges and valleys, for a recent research expedition, a large ringed structure came into view on the King Baudouin ice shelf as they were beginning aerial surveys.

Geophysicist Christian Mueller with the Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Germany, was looking out the window of an instrument laden plane when the previously unknown ringed formation, 2000 meters (1.24 miles) in diameter, came into view. Looking into research publications, he found evidence that this may be a meteorite impact event from 2004.

Research team members from Alfred Wegener Institute in Germany embark from a landing site at Princess Elisabeth, Antarctica. They discovered something totally unexpected - a large ringed formation on a nearby ice shelf. (Credit: AWI) — Research team members from Alfred Wegener Institute in Germany embark from a landing site at Princess Elisabeth, Antarctica. They discovered something totally unexpected – a large ringed formation on a nearby ice shelf. (Credit: AWI)

The discovery occurred on December 20th from the AWI Polar 6 aircraft as they were flying over the Princess Ragnhild Coast. The formation is located on the King Baudouin Ice Shelf not far from their landing site at Princess Elizabeth station.

Two studies were found in the literature by the researchers which pointed to a possible impact event over east Antarctica in 2004. Triangulation of infrasound monitoring data pointed to the area where the ringed formation is located. The infrasound monitoring sites are located worldwide and primarily used to detect nuclear testing events. On February 15, 2013, the same type of data was used to better understand the asteroid explosion over Chelyabinsk, Russia.

Location of the ring formation on the ice shelf off the Antarctic continent. The site is on the King Baudouin Ice Shelf. (Map Credits: Google Maps, NOAA)

The second study involved local observations. A separate set of researchers, located at Davis Station, an Australian base off the coast of east Antarctica, reported seeing a dust trail in the upper atmosphere during the same time.

Researcher Mueller stated in the AWI provided video, “I looked out of the window, and I saw an unusual structure on the surface of the ice. There was some broken ice looking like icebergs, which is very unusual on a normally flat ice shelf, surrounded by a large, wing-shaped, circular structure.” Altogether, the AWI researchers said that they make the claim “without any confidence.” They intend to request funding to make followup studies to determine its origin.

Cheryl Santa Maria, of the Digital Reporter, also reported that there are survey images showing this structure that date back 25 years. Furthermore, a story by LiveScience quoted Dr. Peter Brown of Centre of Planetary Science and Exploration at the University of Western Ontario as stating that the size of a meteorite is roughly 5 to 10% of the impact crater’s diameter. This would indicate an impactor about 100 meters in size and much larger than the estimated size of the event as estimated by infrasound data from 2004.

The infrasound data estimated that the asteroid was probably the size of a house, about 10 meters (33 feet) across. In contrast, the asteroid that exploded over Chelyabinsk, Russia, had an estimated size of 20 meters. Dr. Brown was quoted as expressing doubt that the formation is an impact site. The effects of a 100 meter object would have been much more distinctive and likely more readily detected by researchers located in eastern Antarctica. Thus, reporting of the ring formation by the AWI researchers is bringing to light additional information and comments from experts that raises doubts. Follow up studies will be necessary to determine the true origins of the ringed structured.

January 14, 2015December 23, 2015 by David Dickinson

Challenge Yourself! See an Astronomical Event that Only Happens Once Every 26 Years

This artist’s impression shows an eclipsing binary star system. Credit: ESO/L. Calçada.

Update: It’s off. This past weekend, the AAVSO issued Special Notice #395 calling off the campaign to observe Alpha Comae Berenices this month due to “position measurements published a century ago (which) contained errors that affected the predictions for the time of eclipse…”

And the mystery of Alpha Comae Berenices continues. Oh well. Such is the wiles and whims of the universe, and the exciting field of variable star observing!

A truly fascinating event may be in the offing this month.

Picture two distant burning embers (candles, light bulbs, LEDs, what have you) circling each other in the distance. From our far-flung vantage point, the two points of light are too faint to resolve individually, but as they pass in front of each other, a telltale dip in combined brightness occurs as one blocks out the other.

Welcome to the fascinating world of eclipsing binary stars. This week, we’d like to turn our attention towards a special star in the constellation of Coma Berenices which may — or may not — put on such a dimming act later this month.

An Alpha Comae Berenices (Diadem) finder chart, with comparison stars and magnitudes, decimals omitted. Credit: Starry Night Education Software.

The brightest star in the constellation Coma Berenices, Alpha (sometimes referred to as Diadem, or the ‘crown’ of Queen Berenice) shines at an apparent magnitude of +4.3. Located 63 light years distant, the system consists of two +5^th magnitude F-type stars each about 3 times more luminous than our Sun locked in a 26 year orbital embrace. The physical separation of the pair is about 10 astronomical units: place Alpha Comae Berenices in our solar system, and the pair would fit nicely between the Sun and Saturn.

The orbital plane of the pair is inclined nearly along our line of sight as seen from the Earth, and it’s long been thought that catching a grazing or central eclipse of the pair might just be possible. No eclipse was recorded last time ‘round back in February 1989, but times have changed lots in observational astronomy. Today, there are enough backyard observers armed with dedicated observatories and rigs that’d be the envy of a small university that documenting such an eclipse might just be possible. In fact, a central eclipse might just dim the star by 0.8 magnitudes, and should be noticeable to the naked eye.

The binary nature of Alpha Comae Berenices was first noted by F. G. W. Struve in 1827, and the split is a challenging one during the best of years with a maximum angular separation of just 0.7 arc seconds. The pair also has a third faint +10th magnitude companion located about 89 arc seconds away.

Simplified — A simplified diagram depicting an eclipsing binary event along our line of sight. Created by the author.

The American Association of Variable Star Observers (AAVSO) has an Alert Notice calling for sky watchers worldwide to monitor the star. We also understand the orbit of Alpha Comae Berenices much better in 2015 than back in 1989, and the suspected eclipse should occur somewhere between January 22^nd and January 28^th and may last anywhere from 28 to 45 hours. This lingering ambiguity means that having a dedicated team of observers worldwide may well be key to nabbing this eclipse.

Bootes-Labeled — Alpha Comae Berenices rising. Photo by the author.

The Navy Precision Optical Interferometer (NPOI) has already begun refining measurements of the brightness of the star last month, and professional facilities, to include the Fairborn Observatory atop Mt Hopkins in Arizona and the CHARA (the Center for High Angular Resolution Astronomy) Array at Mount Wilson Observatory in southern California will also be monitoring the event.

Sky and Telescope magazine also has an excellent article in their January 2015 issue on the prospects for catching this eclipse.

Looking eastward past local midnight. Credit: Stellarium.

In late January, the constellation of Coma Berenices rises high to the northeast just after local midnight. It’s worth noting that, if the eclipsing binary nature of Alpha Comae Berenices is confirmed, it would be the longest period known, beating out 14.6 year Gamma Persei discovered in 1990 by more than a decade. A system with as wide a separation as Alpha Comae Berenices would have about a 1 in 1,200 chance in eclipsing along our line of sight due to random chance.

Note: Epsilon Aurigae does have a comparable 27 year period involving a debris disk surrounding its host star. Thanks to sharp-eyed reader Dr. John Barentine for pointing this out!

Of course, the universe does provide us with lots of near misses, allowing for an ‘occasional Diadem’ to indeed occur. Most famous eclipsing variables, such as Algol or Beta Lyrae have periods measured over the span of days or hours. Incidentally, these also make great ‘practice stars’ to test your skills as a visual athlete leading up to the big event next week. A skilled visual observer can note a change as slight as a 0.1 of a magnitude, and it’s a good idea to begin familiarizing yourself with the environs of the star now. The Coma Cluster of galaxies, the globular cluster M53, and the galactic plane crossing intruder Arcturus all lie nearby.

The Coma Cluster as seen by Spitzer Space Telescope and the Sloan Digital Sky Survey. Credit: NASA/Spitzer.

Why study eclipsing binaries? Well, said fleeting mutual events when coupled with spectroscopic measurements and determinations of parallax can tell us a good deal about the astrophysical nature of the stars involved. Eclipsing binary stars have even been used to back up standard candle measurements over extragalactic distances. And of course, orbiting observatories such as Kepler and TESS (to be launched in 2017) look for transiting exoplanets using virtually the same method.

Credit: Brad Timerson. — Have a scope+DSLR? Then you can make refined measurements of eclipsing variable stars. Credit: Brad Timerson/IOTA.

But beyond its practical application, we just think that it’s plain cool that you can actually see something out beyond our solar system changing in the span of just a few days or hours.

Observers also still carry out visual observations of variable stars, just like those pipe-smoking, pocket watch carrying astronomers of yore. This involves merely comparing the target star to nearby stars of the same brightness. If you have a DSLR or a CCD rig plus a telescope, the AAVSO also has instructions for how to monitor a star’s brightness as well. No pocket watch required.

A homemade interferometer used to measure the separation of close double stars. — A homemade ‘card interferometer’ used to measure the separation of close double stars. Photo by author.

Unless, of course, you want to carry a pocket watch just for good luck. Don’t let the cold January winters keep you from joining the hunt. Let’s make some astrophysical history!

January 13, 2015December 23, 2015 by Nancy Atkinson

Largest Digital Camera Ever Constructed will be Pointed at the Skies in 2022

Artist rendering of the LSST observatory (foreground) atop Cerro Pachón in Chile. Credit: Large Synoptic Survey Telescope Project Office.

The world’s largest-ever digital camera has received the green light to move forward with development. The 3,200-megapixel camera for the Large Synoptic Survey Telescope (LSST) will snap the widest, deepest and fastest views of the night sky ever observed, providing unprecedented details of the Universe. Astronomers say the LSST will help uncover some of the biggest mysteries in astronomy.

The SLAC National Accelerator Laboratory announced this week they have received key “Critical Decision 2” approval from the Department of Energy.

“This important decision endorses the camera fabrication budget that we proposed,” said LSST Director Steven Kahn. “Together with the construction funding we received from the National Science Foundation in August, it is now clear that LSST will have the support it needs to be completed on schedule.”

A rendering of the LSST Camera with a cut away to show the inner workings. Credit: LSST.

Set to begin science operations in 2022, the LSST will create an unprecedented archive of astronomical data that will track billions of remote galaxies, helping researchers study galaxy formation. It will rapidly scan the sky, charting objects that change or move: from exploding supernovae to potentially hazardous near-Earth asteroids and create high resolution time-lapse videos of these objects and a 3-D map of the Universe. It will also help us better understand mysterious dark matter and dark energy, which make up 95 percent of the Universe

The camera itself will be the size of a small car and weigh more than 3 tons. It will be able to take up to 800 panoramic images each night and can cover the sky twice each week. Researchers say it will have the ability to reach faint objects twenty times faster than currently possible over the entire visible sky. Scientists anticipate LSST will generate 6 million gigabytes of data per year.

The unique LSST M1/M3 mirror surfaces being carefully polished. Credit: E. Acosta / LSST Corporation.

The telescope will have an 8.4-meter-diameter primary mirror that has an integrated 5-meter-diameter tertiary mirror. This mirror has already been fabricated at the University of Arizona’s Mirror Lab. The outer ring serves as the first mirror, and is called M1. Another more steeply curved mirror, M3, is carved out of the center. It has a 3-degree field of view.

LSST will be taking digital images of the entire visible southern sky every few nights from atop the Cerro Pachón mountain in Chile.

Cerro Pachon is already home to the Gemini South 8-meter telescope and the SOAR 4.1-meter telescope. This graphic also shows LSST's future site. Credit: C. Claver, NOAO/LSST — Cerro Pachon is already home to the Gemini South 8-meter telescope and the SOAR 4.1-meter telescope. This graphic also shows LSST’s future site. Credit: C. Claver, NOAO/LSST

Amateur and armchair astronomers will be happy to know that data from the LSST will be shared publicly and become available quickly via the internet. Researchers involved are planning to involve the public, including students, by using portals like Google Sky or World Wide Telescope, as well as developing research projects that can be done by students in classroom settings, and the public at home and at settings like science museums. They also hope to utilize citizen science projects like Cosmoquest and Galaxy Zoo.

With the latest approval from the DOE, the LSST team can now move forward with the development of the camera. There will be a “Critical Decision 3” review process next summer, which will be the last requirement before actual fabrication of the camera can begin. Components of the camera will be built by an international collaboration of labs and universities.

Sources: SLAC, LSST FAQ

January 13, 2015December 23, 2015 by Matt Williams

One of the Milky Way’s Arms Might Encircle the Entire Galaxy

Artist's conception of the Milky Way galaxy as seen from far Galactic North (in Coma Berenices) Credit: NASA/JPL-Caltech/R. Hurt

Given that our Solar System sits inside the Milky Way Galaxy, getting a clear picture of what it looks like as a whole can be quite tricky. In fact, it was not until 1852 that astronomer Stephen Alexander first postulated that the galaxy was spiral in shape. And since that time, numerous discoveries have come along that have altered how we picture it.

For decades astronomers have thought the Milky Way consists of four arms — made up of stars and clouds of star-forming gas — that extend outwards in a spiral fashion. Then in 2008, data from the Spitzer Space Telescope seemed to indicate that our Milky Way has just two arms, but a larger central bar. But now, according to a team of astronomers from China, one of our galaxy’s arms may stretch farther than previously thought, reaching all the way around the galaxy.

This arm is known as Scutum–Centaurus, which emanates from one end of the Milky Way bar, passes between us and Galactic Center, and extends to the other side of the galaxy. For many decades, it was believed that was where this arm terminated.

However, back in 2011, astronomers Thomas Dame and Patrick Thaddeus from the Harvard–Smithsonian Center for Astrophysics spotted what appeared to be an extension of this arm on the other side of the galaxy.

*Star-forming region in interstellar space. Image credit: NASA, ESA and the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration*

But according to astronomer Yan Sun and colleagues from the Purple Mountain Observatory in Nanjing, China, the Scutum–Centaurus Arm may extend even farther than that. Using a novel approach to study gas clouds located between 46,000 to 67,000 light-years beyond the center of our galaxy, they detected 48 new clouds of interstellar gas, as well as 24 previously-observed ones.

For the sake of their study, Sun and his colleagues relied on radio telescope data provided by the Milky Way Imaging Scroll Painting project, which scans interstellar dust clouds for radio waves emitted by carbon monoxide gas. Next to hydrogen, this gas is the most abundant element to be found in interstellar space – but is easier for radio telescopes to detect.

Combining this information with data obtained by the Canadian Galactic Plane Survey (which looks for hydrogen gas), they concluded that these 72 clouds line up along a spiral-arm segment that is 30,000 light-years in length. What’s more, they claim in their report that: “The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus (2011) as well as the Scutum-Centaurus Arm into the outer second quadrant.”

Ilustration of our galaxy, showing our Sun (red dot) and the possible extension of the Scutum-Centaurus Arm. CREDIT: Modified from "A Possible Extension of the Scutum-Centaurus Arm into the Outer Second Quadrant" by Yan Sun et al., in The Astrophysical Journal Letters, Vol. 798, January 2015; Robert Hurt. NASA/JPL-Caltech/SSC (background spiral). — *Illustration of our galaxy showing the possible extension of the Scutum-Centaurus Arm. CREDIT: Yan Sun/The Astrophysical Journal Letters, Vol. 798/Robert Hurt. NASA/JPL-Caltech/SSC*

This would mean the arm is not only the single largest in our galaxy, but is also the only one to effectively reach 360° around the Milky Way. Such a find would be unprecedented given the fact that nothing of the sort has been observed with other spiral galaxies in our local universe.

Thomas Dame, one of the astronomers who discovered the possible extension of the Scutum-Centaurus Arm in 2011, was quoted by Scientific American as saying: “It’s rare. I bet that you would have to look through dozens of face-on spiral galaxy images to find one where you could convince yourself you could track one arm 360 degrees around.”

Naturally, the prospect presents some problems. For one, there is an apparent gap between the segment that Dame and Thaddeus discovered in 2011 and the start of the one discovered by the Chinese team – a 40,000 light-year gap to be exact. This could mean that the clouds that Sun and his colleagues discovered may not be part of the Scutum-Centaurus Arm after all, but an entirely new spiral-arm segment.

If this is true, than it would mean that our Galaxy has several “outer” arm segments. On the other hand, additional research may close that gap (so to speak) and prove that the Milky Way is as beautiful when seen afar as any of the spirals we often observe from the comfort of our own Solar System.

Further Reading: arXiv Astrophysics, The Astrophysical Letters

January 13, 2015December 23, 2015 by Matt Williams

Faster-Than-Light Lasers Could “Illuminate” the Universe

The Very Large Telescoping Interferometer firing it's adaptive optics laser. Credit: ESO/G. Hüdepohl

It’s a cornerstone of modern physics that nothing in the Universe is faster than the speed of light (c). However, Einstein’s theory of special relativity does allow for instances where certain influences appear to travel faster than light without violating causality. These are what is known as “photonic booms,” a concept similar to a sonic boom, where spots of light are made to move faster than c.

And according to a new study by Robert Nemiroff, a physics professor at Michigan Technological University (and co-creator of Astronomy Picture of the Day), this phenomena may help shine a light (no pun!) on the cosmos, helping us to map it with greater efficiency.

Consider the following scenario: if a laser is swept across a distant object – in this case, the Moon – the spot of laser light will move across the object at a speed greater than c. Basically, the collection of photons are accelerated past the speed of light as the spot traverses both the surface and depth of the object.

The resulting “photonic boom” occurs in the form of a flash, which is seen by the observer when the speed of the light drops from superluminal to below the speed of light. It is made possible by the fact that the spots contain no mass, thereby not violating the fundamental laws of Special Relativity.

An image of NGC 2261 (aka. Hubble's Variable Nebula) by the Hubble space telescope. Credit: HST/NASA/JPL. — *An image of NGC 2261 (aka. Hubble’s Variable Nebula) by the Hubble space telescope. Image Credit: HST/NASA/JPL.*

Another example occurs regularly in nature, where beams of light from a pulsar sweep across clouds of space-borne dust, creating a spherical shell of light and radiation that expands faster than c when it intersects a surface. Much the same is true of fast-moving shadows, where the speed can be much faster and not restricted to the speed of light if the surface is angular.

At a meeting of the American Astronomical Society in Seattle, Washington earlier this month, Nemiroff shared how these effects could be used to study the universe.

“Photonic booms happen around us quite frequently,” said Nemiroff in a press release, “but they are always too brief to notice. Out in the cosmos they last long enough to notice — but nobody has thought to look for them!”

Superluminal sweeps, he claims, could be used to reveal information on the 3-dimensional geometry and distance of stellar bodies like nearby planets, passing asteroids, and distant objects illuminated by pulsars. The key is finding ways to generate them or observe them accurately.

For the purposes of his study, Nemiroff considered two example scenarios. The first involved a beam being swept across a scattering spherical object – i.e. spots of light moving across the Moon and pulsar companions. In the second, the beam is swept across a “scattering planar wall or linear filament” – in this case, Hubble’s Variable Nebula.

Artist view of an asteroid (with companion) passing near Earth. Credit: P. Carril / ESA — *Photonic booms caused by laser sweeps could offer a new imaging technique for mapping out passing asteroids. Credit: P. Carril / ESA*

In the former case, asteroids could be mapped out in detail using a laser beam and a telescope equipped with a high-speed camera. The laser could be swept across the surface thousands of times a second and the flashes recorded. In the latter, shadows are observed passing between the bright star R Monocerotis and reflecting dust, at speeds so great that they create photonic booms that are visible for days or weeks.

This sort of imaging technique is fundamentally different from direct observations (which relies on lens photography), radar, and conventional lidar. It is also distinct from Cherenkov radiation – electromagnetic radiation emitted when charged particles pass through a medium at a speed greater than the speed of light in that medium. A case in point is the blue glow emitted by an underwater nuclear reactor.

Combined with the other approaches, it could allow scientists to gain a more complete picture of objects in our Solar System, and even distant cosmological bodies.

Nemiroff’s study accepted for publication by the Publications of the Astronomical Society of Australia, with a preliminary version available online at arXiv Astrophysics

Further reading:
Michigan Tech press release
Robert Nemiroff/Michigan Tech

January 12, 2015December 23, 2015 by Tim Reyes

It Looks Like These Are All the Bright Kuiper Belt Objects We’ll Ever Find

The presently known largest trans-Neptunian objects (TNO) - are likely to be surpassed by future discoveries. Which of these trans-Neptunian objects (TNO) would you call planets and which "dwarf planets"? (Illustration Credit: Larry McNish, Data: M.Brown)

The self-professed “Pluto Killer” is at it again. Dr. Michael Brown is now reminiscing about the good old days when one could scour through sky survey data and discover big bright objects in the Kuiper Belt. In his latest research paper, Brown and his team have concluded that those days are over.

Ten years ago, Brown discovered what is now known as the biggest Kuiper Belt object – Eris. Brown’s team found others that rivaled Pluto in size and altogether, these discoveries led to the demotion of Pluto to dwarf planet. Now, using yet another sky survey data set but with new computer software, Brown says that its time to move on.

Instigators of the big heist - David Rabinowitz, Brown and Chad Trujillo, left to right. The researchers discovered dozens of Kuiper Belt objects (KBO) including six of the eight largest KBOs including the largest, Eris. — Instigators of the big heist – Rabinowitz, Brown and Trujillo, left to right. The researchers co-discovered dozens of Kuiper Belt objects (KBO) including nine of the ten largest KBOs including the largest, Eris.

Like the famous Bugs Bunny cartoon, its no longer Rabbit Season or Duck Season and as Bugs exclaims to Elmer Fudd, there is no more bullets. Analyzing seven years worth of data, Brown and his team has concluded we are fresh out of Pluto or Charon-sized objects to be discovered in the Kuiper Belt. But for Dr. Brown, perhaps it now might be Oort Cloud season.

His latest paper, A Serendipitous All Sky Survey For Bright Objects In The Outer Solar System, in pre-print, describes the completion of analysis of two past sky surveys covering the northern and southern hemisphere down to 20 degrees in Galactic latitude. Using revised computer software, his team scoured through the data sets from the Catalina Sky Survey (CSS) and the Siding Spring Survey (SSS). The surveys are called “fast cadence surveys” and they primarily search for asteroids near Earth and out to the asteroid belt. Instead Brown’s team used the data to look at image frames spaced days and months apart.

Update: In a Twitter communique, Dr. Brown stated, “I would say we’re out of BRIGHT ones, not big ones. Could be big ones lurking far away!” His latest work involved a southern sky survey (SSS) to about magnitude 19 and the northern survey (CSS) to 21. Low albedo (dark) and more distant KBOs might be lurking beyond the detectability of these surveys that are in the range of Charon to Pluto in size.

Animation showing the movement of Eris on the images used to discover it. Eris is indicated by the arrow. The three frames were taken over a period of three hours. (Credit: Brown, et al.) — Animation showing the movement of Eris on the images used to discover it. Eris is indicated by the arrow. The three frames were taken over a period of three hours. More images over several weeks were necessary to determine its orbit.(Credit: Brown, et al.)

Objects at Kuiper Belt distances move very slowly. For example, Pluto orbits the Sun at about 17,000 km/hr (11,000 mph), taking 250 years to complete one orbit. These are speeds that are insufficient to maintain ven a low-Earth orbit. Comparing two image frames spaced just hours apart will find nearby asteroids moving relative to the star fields but not Kuiper belt objects. So using image frames spaced days, weeks or even months apart, they searched again. Their conclusion is that all the big Kuiper belt objects have been found.

The only possibility of finding another large KBO lies in a search of the galactic plane which is difficult due to the density of Milky Way’s stars in the field of view. The vast number of small bodies in the Kuiper belt and Oort Cloud lends itself readily to statistical analysis. Brown states that there is a 32% chance of finding another Pluto-sized object hiding among the stars of the Milky Way.

Artists concept of the view from Eris with Dysnomia in the background, looking back towards the distant sun. Credit: Robert Hurt (IPAC)

Dr. Brown also released a blog story in celebration of the discovery of the largest of the Kuiper Belt objects, Eris, ten years ago last week. Ten years of Eris, reminisces about the great slew of small body discoveries by Dr. Brown, Dr. Chad Trujillo of Gemini Observatory and Dr. David Rabinowitz of Yale Observatory.

Brown encourages others to take up this final search right in the galactic plane but apparently his own intentions are to move on. What remains to be seen — that is, to be discovered — are hundreds of large “small” bodies residing in the much larger region of the Oort Cloud. These objects are distributed more uniformly throughout the whole spherical region that the Cloud defines around the Sun.

Furthermore, Dr. Brown maintains that there is a good likelihood that a Mars or Earth-sized object exists in the Oort Cloud.

Small bodies within our Solar System along with exo-planets are perhaps the hottest topics and focuses of study in Planetary Science at the moment. Many graduate students and seasoned researchers alike are gravitating to their study. There are certainly many smaller Kuiper belt objects remaining to be found but more importantly, a better understanding of their makeup and origin are yet to be revealed.

Artist's concept of the Dawn spacecraft at the protoplanet Ceres Illustration of Dawn's approach phase and RC3 orbit This artist’s concept of NASA’s Dawn spacecraft shows the craft orbiting high above Ceres, where the craft will arrive in early 2015 to begin science investigations. (Image credit: NASA/JPL-Caltech) — Artist’s concept of the Dawn spacecraft at the protoplanet Ceres Illustration of Dawn’s approach phase and RC3 orbit This artist’s concept of NASA’s Dawn spacecraft shows the craft orbiting high above Ceres, where the craft will arrive in early 2015 to begin science investigations. (Image credit: NASA/JPL-Caltech)

Presently, the Dawn spacecraft is making final approach to the dwarf planet Ceres in the Asteroid belt. The first close up images of Ceres are only a few days away as Dawn is now just a couple of 100 thousand miles away approaching at a modest speed. And much farther from our home planet, scientists led by Dr. Alan Stern of SWRI are on final approach to the dwarf planet Pluto with their space probe, New Horizons. The Pluto system is now touted as a binary dwarf planet. Pluto and its moon Charon orbit a common point (barycenter) in space that lies between Pluto and Charon.

So Dr. Brown and team exits stage left. No more dwarf planets – at least not soon and not in the Kuiper belt. Will that upstage what is being called the year of the Dwarf Planet?

But next up for close inspection for the first time are Ceres, Pluto and Charon. It should be a great year.

The relative sizes of the inner Solar System, Kuiper Belt and the Oort Cloud. (Credit: NASA, William Crochot)

References:

A Serendipitous All Sky Survey For Bright Objects In The Outer Solar System

Ten Years of Eris

2015, NASA’s Year of the Dwarf Planet, Universe Today

What is the Kuiper Belt?, Universe Today

January 12, 2015December 23, 2015 by Elizabeth Howell

NASA Space Shots Inspire This Brilliant Video Of Universal Wonders

A still from Lucas Green's video "Space Suite", on Vimeo.

Moons pass by Saturn’s rings. An eclipse takes place on Jupiter. We see these shots every day in images from space agencies, but how would it be to actually float in a nearby spacecraft and watch these in action?

An incredible new Vimeo video called “Space Suite” shows off what it actually could be like. And here’s the neat thing — it is heavily based on those very same jaw-dropping shots space agencies regularly release.

“I created the video above as a visual proof-of-concept for a project I’m currently working on with Two Story Productions. The project relies heavily on space visuals, and I wanted to demonstrate that compelling footage could be created quickly and easily by mining the impressive image libraries of NASA (and others) for stunning photography, and then bringing them to life with simple 3d ‘tricks’,” wrote creator Lucas Green in a blog post last week.

Editor’s note: It has come to our attention that some of the visuals used in this video were taken from previously pre-processed files by Stephen van Vuuren, who used a painstaking proprietary method for creating the feature I-MAX Film, “In Saturn’s Rings.” The files were acquired and re-purposed by Lucas Green, without permission.

Green has now added notation on his webpage that ” In addition to the libraries of NASA and ESA, some of the more striking imagery was created by Stephen van Vuuren, who meticulously stitched together thousands of raw images to use in his film ‘In Saturn’s Rings’. Watch some clips on his website – his work makes ‘Space Suite’ look like a fuzzy picture on an old television screen.”

“In Saturn’s Rings” is still in production, scheduled for release this year, and Universe Today will provide updates on the film.

“The demo footage probably won’t make it into the final project, so I wanted to show it off here, and give a short breakdown of some of my favorite shots. All of the imagery in the video is sourced directly from actual photographs, with minimal retouching. Most of the shots make use of photogrammetry, or ‘projection-mapping’, in order to rapidly block out the source images as virtual scenes.”

His blog includes details of the shots he chose and how he converted them to the incredible 3-D effects you can see in the video above. Enjoy!

January 10, 2015December 23, 2015 by Bob King

How to Find and Make the Most of Comet Lovejoy

This photo map shows Comet Lovejoy's nightly position among the winter stars through January 19th as it travels across the constellation Taurus not far from Aldebaran and the Pleiades star cluster. Click to enlarge. Credit: Bob King

Comet Q2 Lovejoy passed closest to Earth on January 7th and has been putting on a great show this past week. Glowing at magnitude +4 with a bluish coma nearly as big as the Full Moon, the comet’s easy to see with the naked eye from the right location if you know exactly where to look. I wish I could say just tilt your head back and look up and bam! there it would be, but it’ll take a little more effort than that. But just a little, I promise.

Comet Lovejoy and its spectacular "lively" ion tail photographed on January 8th by Nick Howes at Tzec Muan Network at Siding Spring Australia — Comet Lovejoy and its spectacular “lively” ion tail photographed on January 8th by Nick Howes at Tzec Muan Network at Siding Spring Australia

Last night, under a dark rural sky, once I spotted the comet and noticed its position in relation to nearby bright stars, I could look up and see it anytime. Finding anything other than the Moon or a bright planet in the night sky often requires a good map. I normally create a star-chart style map but thought, why not make a photographic version? So last night I snapped a few guided images of Lovejoy as it glimmered in the wilds of southern Taurus and then cloned the comet’s nightly position through onto the image. Maybe you’ll find this useful, maybe not. If not, the regular map is also included.

Comet Lovejoy position is shown for each night tonight through January 23rd. The comet should remain in the 4-5 magnitude range throughout. Click for a larger map you can print out and use outdoors. Click to enlarge and print for use outdoors. Source: Chris Marriott’s SkyMap software — Comet Lovejoy’s position is shown for each night tonight through January 23rd. The comet should remain in the 4-5 magnitude range throughout. Lovejoy is currently high in the southeastern sky at nightfall and crosses the meridian due south around 9 o’clock local time. Click for a larger map you can print out and use outdoors. Source: Chris Marriott’s SkyMap software

To see Comet Lovejoy with the naked eye you’ll need reasonably dark skies. It should be faintly visible from outer ring suburbs, but country skies will guarantee a sighting. I’ve been using bright stars in Orion and Taurus to guide binoculars – and then my eye – to the comet. Pick a couple bright stars like Aldebaran and Betelgeuse and extend a line from each to form a triangle with Lovejoy at one of the corners. If you then point binoculars at that spot in the sky, the comet should pop out. If you don’t find it immediately, sweep around the position a bit. After you find it, lower the binoculars and try to spot it with the naked eye.

Comet Lovejoy last night January 9th around 8 p.m. (CST) shows a bright coma and faint ~1.5-degree-long tail. This photo, made with a 200mm lens, gives a good idea of what the comet looks like in 50mm binoculars. Details: f/2.8, ISO 800, 2-minute exposure. Credit: Bob King

This week, as Lovejoy continues trekking north, you can use bright orangey Aldebaran in Taurus and the Pleiades, also called the Seven Sisters star cluster, to “triangulate” your way to the comet. Look for a glowing fuzzball. In 10×50 and 8×40 binoculars, it’s obviously different from a star — all puffed up with a brighter center. The 50mm glass even shows a hint of the coma’s blue color caused by carbon molecules fluorescing in ultraviolet sunlight and a faint, streak-like tail extending to the northeast. With the naked eye, at first you might think it’s just a dim star; closer scrutiny reveals the star has a hazy appearance, pegging it as a comet.

Comet Lovejoy sketches from last night made using a 15-inch telescope. The coma is big - almost a half-degree across. The drawing shows the bright nuclear region and tiny "false nucleus". At right, a suspected plume extends to the southwest of the false nucleus. Color is how the comet really looks in the telescope. Credit: Bob King — Comet Lovejoy sketches from last night made using a 15-inch telescope. The coma is big – almost a half-degree across. The drawing shows the bright nuclear region and tiny “false nucleus”. At right, a suspected plume extends to the southwest of the false nucleus. Color is how the comet really looks in the telescope. South is up. Credit: Bob King

Through a telescope the coma is a HUGE pale blue tiki lamp of a thing with a small, much brighter nuclear region. The rays of the ion tail, so beautifully shown in photographs, are indistinct but visible with patience and a moderate-sized telescope under dark skies. At low magnification, the nucleus – the false nucleus actually, since the real comet nucleus is hidden by a shroud of dust and gas – looks like a misty star of about magnitude +9. On close inspection at high magnification (250x and up), you penetrate more deeply into the nuclear zone and the star-like center shrinks and dims to around magnitude +13.

Fascinating plumes of dust recorded by Gianluca Masi on January 6th. South is up, west to the left. Credit: Gianluca Masi

If the seeing is good and comet active, high magnification will often reveal jets or fans of dust in the sunward direction, in this case west of nucleus. I’ve been studying the comet the past couple nights and am almost convinced I can see a short, very low contrast plume poking to the south of center. Generally, plumes and jets are subtle, low-contrast features. Challenging? Yes, but with Lovejoy as close as it’s going to get, now’s the time to seek them.

In this photo taken January 8th, the comet's tail is caught in the act of separated from the head or coma. Magnetic fields embedded in the stream of particles from the Sun occasionally reconnect on the rear side of a comet and pinch off its tail. Credit: Rolando Ligustri — In this photo taken January 8th, the comet’s tail is caught in the act of separated from the head or coma. Magnetic fields embedded in the stream of particles from the Sun occasionally reconnect on the rear side of a comet and pinch off its tail. A new one quickly grows to replace the old. Credit: Rolando Ligustri

Just before Christmas, fluctuations in the solar wind snapped off Comet Lovejoy’s tail. Guess what? It happened again on January 8th as recorded in dramatic fashion by astrophotographer Rolando Ligustri. An ion or gas tail like the one in the photo forms when cometary gases, primarily carbon monoxide, are ionized by solar radiation and lose an electron to become positively charged. Once “electrified”, they can be twisted, kinked and even snapped off by magnetic fields embedded in the Sun’s particle wind.

Of course, the comet didn’t miss a breath but grew another tail immediately. Look closely at the photo and you see another faint streak of light pointing beyond the coma below and left of the bright nuclear region. This may be Lovejoy’s dust tail. Most comets sport both types of tails – gas and dust – since they release both materials as the Sun heats and vaporizes their ices.

Lovejoy’s been a thrill to watch because it’s doing all the cool stuff that makes them so fun to follow. Gianluca Masi, an Italian astrophysicist and lover of all things cometary, will offer a live feed of the comet on Monday January 12th starting at 1 p.m. CST (7 p.m. UT). May your skies be clear tonight!