Astronomy Archives

April 1, 2013December 23, 2015 by Nancy Atkinson

How to Reconstruct the Life of a Star

This image of Cep OB 3b was created by combining the light from four separate observations taken through different filters on the 0.9 meter telescope at Kitt Peak. The brightest yellow star near the center of the image is a foreground star, lying between us and the young cluster. The other bright stars are the massive young stars of the cluster that are heating the gas and dust in the cloud and blowing out cavities. Image processing was done by Dr. Travis Rector. Credit: NOAO.

It takes time to understand the life of stars. A star like our Sun takes tens of millions of years to form, and so much like archeologists who reconstruct ancient cities from shards of debris strewn over time, astronomers must reconstruct the birth process of stars indirectly, by observing stars in different stages of the process and inferring the changes that take place.

One of the best places to study the lives of stars is in star clusters. These regions that are rich with young stars provide astronomers much information that is relevant to the study of stars in general, but within a cluster, stars can form during a wide range of time, as a new study of the star cluster named Cep OB3b has shown.

“By studying nearby massive young clusters like Cep OB3b, we can gain a greater understanding of the environments out of which planets form,” said Thomas Allen from the University of Toledo, who is one of the authors of the new paper.

Located in the northern constellation of Cepheus, CepOB3b is similar in some ways to the famous cluster found in the Orion Nebula. But unlike the Orion Nebula, there is relatively little dust and gas obscuring our view of Cep OB3b. Its massive, hot stars have blown out cavities in the gaseous cloud with their intense ultraviolet radiation which mercilessly destroys everything in its path. Cep OB3b may show us what the Orion Nebular Cluster will look like in the future.

Allen and an international team of astronomers have found that the total number of young stars in the cluster is as high as 3,000. Infrared observations of the stars from the NASA Spitzer satellite show about 1,000 stars that are surrounded by disks of gas and dust from which solar systems may form. As the stars age, the disks disappear as the dust and gas get converted into planets or are dispersed into space.

But these observations pointed to a new mystery. Although the stars in Cep OB3b are thought to be about three million years old, in some parts of the cluster most of the stars had lost their disks, suggesting that the stars in those parts were older. This suggests that the cluster is surrounded by older stars, potential relics of previous clusters that have since expanded and dispersed.

To search for evidence for these relic clusters, Allen used the Mosaic camera on the 0.9 meter telescope at Kitt Peak National Observatory to observe wide field images of CepOB3b. These images show hot gas and its interaction with the stars and permit the team to study a curious cavity in the gas for evidence of older, yet still juvenile, stars that have lost their disks of gas and dust.

With these data, the team is searching for the previous generations of star formation in the region surrounding Cep OB3b, and piecing together the history of star formation in this magnificent region. When finished, this may provide clues how previous generations may have influenced the current generation of stars and planets forming in Cep OB3b.

Source:NOAO

March 27, 2013December 23, 2015 by Nancy Atkinson

New Stars: Blazing and Blue

This image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO

A new image from ESO shows a pretty sprinkling of bright blue stars, the star cluster NGC 2547, a group of recently formed stars in the southern constellation of Vela. Even though we recently got a more precise estimate on how old the Universe is from the Planck mission (13.82 billion years), this is a look at some fairly young — new and blue — stars.

But how young are these cosmic youngsters really? ESO scientists say that although the exact ages of these stars remain uncertain, estimates range from 20 to 35 million years old. That doesn’t sound all that young, after all. However, our Sun is 4.6 billion years old and has not yet reached middle age. That means that if you imagine that the Sun as a 40 year-old person, the bright stars in the picture are three-month-old babies.

Most stars do not form in isolation, but in rich clusters with sizes ranging from several tens to several thousands of stars. Clusters are key objects for astronomers studying how stars evolve through their lives. The members of a cluster were all born from the same material at about the same time, making it easier to determine the effects of other stellar properties.

While NGC 2547 contains many hot stars that glow bright blue, also visible are one or two yellow or red stars which have already evolved to become red giants. Open star clusters like this usually only have comparatively short lives, of the order of several hundred million years, before they disintegrate as their component stars drift apart.

This picture was created from images forming part of the Digitized Sky Survey 2. It shows the rich region of sky around the young open star cluster NGC 2547 in the southern constellation of Vela (The Sail). Credit: ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin — This picture was created from images forming part of the Digitized Sky Survey 2. It shows the rich region of sky around the young open star cluster NGC 2547 in the southern constellation of Vela (The Sail). Credit:
ESO/Digitized Sky Survey 2. Acknowledgement: Davide De Martin

The star cluster NGC 2547 lies in the southern constellation of Vela (The Sail), about 1500 light-years from Earth, and is bright enough to be easily seen using binoculars. It was discovered in 1751 by the French astronomer Nicolas-Louis de Lacaille during an astronomical expedition to the Cape of Good Hope in South Africa, using a tiny telescope of less than two centimeters aperture.

Between the bright stars in this picture you can see plenty of other objects, especially when zooming in. Many are fainter or more distant stars in the Milky Way, but some, appearing as fuzzy extended objects, are galaxies, located millions of light-years beyond the stars in the field of view.

Source: ESO

March 27, 2013December 23, 2015 by Jason Major

Book Review: Vistas of Many Worlds

Vistas of Many Worlds: A Journey Through Space and Time by Erik Anderson (Ashland Astronomy Studio)

While many astronomy books are based around images that show us how the Universe appears to us right now, as seen through the sensitive electronic eyes of powerful space telescopes and observatories around the world, Erik Anderson’s Vistas of Many Worlds: a Journey Through Space and Time takes a different, but no less fascinating, approach and shows us what the night sky used to look like, will one day look like, and how it may look from other much more distant worlds.

The nearby orange dwarf star Epsilon Eridani reveals its circumstellar debris disks in this close-up perspective. (Pages 14-15) — The nearby orange dwarf star Epsilon Eridani reveals its circumstellar
debris disks in this close-up perspective. (Pages 14-15)

Written and illustrated by Erik Anderson of the Ashland Astronomy Studio in Ashland, Oregon, Vistas of Many Worlds first takes us on a tour of our local region of the galaxy, introducing us to some of our Sun’s closest neighbors in space. From Alpha Centauri to Altair, we get scientifically-based renderings of several nearby stars as they’d appear close up, along with a detailed description of each — as well as an accurate depiction of the background stars (including the Sun) as they’d appear from such slightly different vantage points. We soon find out there’s an amazing amount of variety in our own stellar neighborhood alone!

Next we get a tour through time itself with images and detailed descriptions of the night sky as it appeared at various points in Earth’s history. Based on the actual movements of the stars across the galaxy, Anderson is able to accurately show the star-filled sky as it looked when the ocean cascaded over the Strait of Gibraltar to fill in the Mediterranean 5.3 million years ago, when the ancestors of modern humans were first learning to use fire 1.5 million years ago… and also what it will look like when the Solar System eventually dips back down into the galactic plane 25 million years from now — a time when nearly all the stars in the sky will be strangers, unfamiliar to us today.

After that Anderson takes us on a hunt for exoplanets, both known and imagined. We first visit the star systems that have been recently discovered to host planets — some a little like Earth, some a little like Jupiter, and some like nothing we’ve ever seen before. Then it’s off to look for truly Earthlike worlds by looking back at how our own planet became so favorable for life in the first place. From a stable parent star like the Sun to the chance birth of a large, stabilizing moon, from the delivery of life-sustaining liquid water (that stays liquid!) to having a protective “big brother” gas giant ready to take the heavy hits, and eventually what first drew organisms up from the sea onto dry land, Anderson speculates about Earth’s distant exoplanetary twins by reflecting on our planet itself.

The Earth's ancient past is depicted as it looked 4.4 million years ago when an ancient ape, "Ardi" the Ardipithecus, roamed Africa. (Pages 36-37) — The Earth’s ancient past is depicted as it looked 4.4 million years ago
when an ancient ape, “Ardi” the Ardipithecus, roamed Africa. (Pages 36-37)

And all the while showing what stars are where in the sky.

Vistas of Many Worlds is a true gem… it inspires imagination with the turn of each page. Anderson’s photorealistic computer-generated illustrations are lush and intriguing, and he does an excellent job combining speculation with scientific knowledge. It’s science as envisioned by an artist as well as art created by a scientist — truly the best of ~~both~~ many worlds.

The 123-page 9″ x 12″ hardcover book can be purchased on the Ashland Astronomy Studio’s website here, as well as on Amazon.com.

An iBook edition is soon to be announced.

A primordial ocean-world orbited by two moons is depicted in Ptolemy's Cluster (star cluster M7). The scene parallels Earth's own natural history, commemorating the origins of watery oceans out of volcanic steam and infalling comets. (Pages 96-97) — A primordial ocean-world orbited by two moons is depicted in Ptolemy’s
Cluster (star cluster M7). The scene parallels Earth’s own natural history,
commemorating the origins of watery oceans out of volcanic steam and
infalling comets. (Pages 96-97)

March 26, 2013April 26, 2016 by Jason Major

Book Review: Your Ticket to the Universe

Your Ticket to the Universe: A Guide to Exploring the Cosmos (Available April 2)

Your Ticket to the Universe is full of images and graphics of astronomical wonders.

Every once in a while an astronomy book comes out that combines stunning high-definition images from the world’s most advanced telescopes, comprehensive descriptions of cosmic objects that are both approachable and easy to understand (but not overly simplistic) and a gorgeous layout that makes every page spread visually exciting and enjoyable.

This is one of those books.

Your Ticket to the Universe: A Guide to Exploring the Cosmos is a wonderful astronomy book by Kimberly K. Arcand and Megan Watzke, media coordinator and press officer for NASA’s Chandra X-ray Observatory, respectively. Published by Smithsonian Books, it features 240 pages of gorgeous glossy images from space exploration missions, from the “backyard” of our own Solar System to the more exotic environments found throughout the Galaxy… and even beyond to the very edges of the visible Universe itself.

Find out how you can win a copy of this book here!

As members of the Chandra team, headquartered at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, Kim and Megan have long had firsthand experience with incredible astronomical images — they previously designed and coordinated the internationally-acclaimed From Earth to the Universe and From Earth to the Solar System photo installation projects, which helped set up presentations of space exploration images in public locations around the world.

Your Ticket to the Universe features images from some of the most recent missions - like MSL! — *Your Ticket to the Universe* even features images from some of the most recent missions – like MSL!

Your Ticket to the Universe takes such impressive images — from telescopes and observatories like Hubble, Spitzer, SDO, Chandra, Cassini, GOES, VLT, and many others, as well as from talented photographers on Earth and in orbit aboard the ISS — and puts them right into your hands, along with in-depth descriptions that are comprehensive yet accessible to even the most casual fans of space exploration.

This is my favorite kind of astronomy book. Although I look at images like the ones in Your Ticket to the Universe online every day, there’s something special about having them physically in front of you in print — and well-written text that can be understood by everyone is crucial, in my opinion, as it means a book may very well become an inspiration to a whole new generation of scientists and explorers.

“The sky belongs to everyone. That’s the premise of this guidebook to the Universe. You don’t need a medical degree to know when you’re sick or a doctorate in literature to appreciate a novel. In the same spirit, even those of us who don’t have advanced degrees in astronomy can gain access to all the wonder and experience that the Universe has to offer.”

Kim K. Arcand holds a copy of her book during a presentation at the Skyscrapers Astronomical Society of Rhode Island — Author Kimberly K. Arcand holds a copy of her book during a presentation at the Skyscrapers Astronomical Society of Rhode Island

I’ve had the pleasure of meeting co-author Kimberly Arcand on several occasions — I attended high school with her husband — and her knowledge about astronomy imaging as well as her ability to present it in an understandable way is truly impressive, to say the least. She’s quite an enthusiastic ambassador for space exploration, and Your Ticket to the Universe only serves to further demonstrate that.

I highly recommend it for anyone who finds our Universe fascinating.

Your Ticket to the Universe will be available online starting April 2 at Smithsonian Books, or you can pre-order a copy at Barnes & Noble or on Amazon.com. Don’t explore the cosmos without it!

March 15, 2013December 23, 2015 by Elizabeth Howell

Why You’ll Never See a Red Comet Like in ‘Game of Thrones’

That red comet is pretty, but perhaps not so realistic. Credit: Game of Thrones Wiki/HBO (Screencap)

A blood-red comet appears in the sky. People quake in its wake.

This phenomenon, which happens in the second season of the medieval fantasy Game of Thrones, had us all wondering — can you ever actually see a red comet?

We talked to Matthew Knight, an astronomer at the Lowell Observatory in Arizona who observes comets. He gave us some answers just in time for the third season of Game of Thrones, which begins March 31.

At first blush, he said, the comet’s red color wouldn’t be possible because the strongest emissions from comets are in the blue and green regions, mostly from neutral gases such as hydroxide and cyanide.

There is a type of emission that is close to red, called “forbidden oxygen”, which occurs when atoms make a rare energy transition between states of “excitement”. But it’s very faint and short-lived, Knight wrote.

The visible light from a comet comes from a combination of reflected solar continuum (sunlight reflecting off of dust grains) and cometary emission (neutral and/or ionized molecules of gas that emit photons at a particular wavelength). The sunlight reflecting off of dust grains basically looks like sunlight and since the Sun appears yellow/white, this component cannot look red.

A small caveat is that due to the physical properties of dust grains, comet dust often actually does “redden” sunlight slightly when measured with sensitive equipment. However, this reddening is at a very low level and is not enough to cause the reflected sunlight to appear a deep red like in Game of Thrones. The strongest comet emissions in the region where human eyes can see are in the blue and green regions.

Comet Hale-Bopp. which displays the usual cometary colors. Credit: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria

So what ingredients does a comet need to look like the one in Game of Thrones? According to Knight, it would have to meet these criteria:

Be visible in daylight, which really only happens about once a century;
Be close to the sun (he supposes this one is, given how straight the tail is);
Have a “strange composition” that is different from anything we know in the solar system. The composition could be that forbidden oxygen he talked about, coming from a comet whose ices are carbon monoxide and carbon dioxide. But that would be hard, because those types of ices would not survive long when exposed to sunlight.

If we really want to think in a science fiction vein, Knight suggests that maybe the comet could be made up unpredictably:

Alternatively it could be something else entirely unknown in cometary chemistry or dust, with really weird properties causing a much stronger reddening than is normally seen. In any event, the composition would be so anomalous that this comet would almost certainly have originated in another solar system. That would make comet scientists very interested in studying it!

But don’t despair yet. Comet ISON might be bright enough for daylight viewing when it swings by Earth late in 2013. Comets are unpredictable beasts, but we’re pretty sure of one thing: no matter how bright it is, it won’t look red.

March 8, 2013December 23, 2015 by Bob King

A Guide to Help You See Comet PANSTARRS at its Brightest

Comet L4 PANSTARRS setting over Brindabella Ranges to the west of Canberra, Australia on March 5, 2013. The photo gives a good idea of the naked eye of the comet. Credit: Vello Tabur

This is the big week so many of us in the northern hemisphere have been waiting for. Comet C/2011 L4 PANSTARRS, which has put on a splendid show in the southern hemisphere, now finally comes to a sky near us northerners!

Sky watchers in Australia and southern South America report it looks like a fuzzy star a little brighter than those in the Big Dipper with a short stub of a tail visible to the naked eye. The comet should brighten further as it wings its way sunward. Closest approach to the sun happens on March 10 at a distance of 28 million miles. That’s about 8 million miles closer than the orbit of Mercury.

Though very low in the western sky after sundown, the comet should be visible across much of the U.S., southern Canada and Europe beginning tonight March 8.

Comet PANSTARRS will be visible tonight through about March 19 for sky watchers living near the equator. Map is drawn for Singapore. All maps created with Chris Marriott's SkyMap software — Comet PANSTARRS will be visible through about March 19 for sky watchers living near the equator. Map is drawn for Singapore. All maps created with Chris Marriott’s SkyMap software

PANSTARRS’ low altitude presents a few challenges. Approaching clouds, general haziness and the extra thickness of the atmosphere near the horizon absorbs the comet’s light, causing it to appear fainter than you’d expect. A casual sky watcher may not even notice its presence. That’s why I recommend bringing along a pair of binoculars and using the map that best fits your latitude. Find a place with a wide open view to the west, focus your binoculars on the most distant object you can find (clouds are ideal) and then slowly sweep back and forth across the sky low above the western horizon

Comet PANSTARRS map for the southern U.S. March 6-21. Time shown is about 25 minutes after sunset facing west. Map is drawn for Phoenix, Ariz.

As the nights pass, PANSTARRS rises higher in the sky and becomes easier to spot for northern hemisphere observers while disappearing from view in the south. On the 12th, a thin lunar crescent will shine just to the right of the comet. Not only will it make finding this fuzzy visitor easy-peasy, but you’ll have the opportunity to make a beautiful photograph.

Comet PANSTARRS and thin crescent moon should be a striking site about a half hour to 45 minutes after sunset on March 12. Stellarium — Comet PANSTARRS and the thin crescent Moon should make a striking sight together about a half hour to 45 minutes after sunset on March 12. Stellarium

The maps shows the arc of the comet across the western sky in the coming two weeks for three different latitudes. Along the bottom of each map is the comet’s altitude in degrees for the four labeled dates. The sun, which is below the horizon, but whose bright glow you’ll see above its setting point, will help you determine exactly in what direction to look.

One of your best observing tools and the one closest at hand (pun intended) is your hand. Photo: Bob King

A word about altitude. Astronomers measure it in degrees. One degree is the width of your little finger held at arm’s length against the sky. Believe it or not, this covers two full moon’s worth of sky. Three fingers at arm’s length equals 5 degrees or the separation between the two stars at the end of the bowl of the Big Dipper. A fist is 10 degrees. This weekend PANSTARRS will be 2-3 “fingers” high around 25 minutes after sunset when the sky is dark enough to go for it.

The northern U.S. is favored for this leg of the comet's journey. Notice how the comet arcs up higher in the sky compared to the southern U.S. and especially the equator. Map drawn for Duluth, Minn. The comet will remain visible for many weeks. Earth is closest to PANSTARRS on March 5 at 102 million miles. — The northern U.S. is favored for this leg of the comet’s journey. Notice how the comet arcs up higher in the sky compared to the southern U.S. and especially the equator. Map drawn for Duluth, Minn. The comet will remain visible for many weeks. Earth is closest to PANSTARRS on March 5 at 102 million miles.

To find PANSTARRS, locate it on the map for a particular date, note its approximate altitude and relation to where the sun set and look in that direction. Assuming your sky to the west is wide open and clear, you should see a comet staring back. If you don’t find it one night, don’t give up. Go out the next clear night and try again. While Comet PANSTARRS will fade over the next few weeks, it will also rise higher into a darker sky and become – for a time – easier to see. I also encourage you to take out your telescope for a look. You’ll see more color in the comet’s head, details in its tail and an intensely bright nucleus (center of the comet), a sign of how fiercely sunlight and solar heating are beating up on this tender object.

Sound good? Great – now have at it!

March 5, 2013December 23, 2015 by Elizabeth Howell

Book Review: African Cosmos

In 1986, Halley’s Comet captivated a teenager living in a small South African town. Curious about what his nation does in astronomy, he scoured books at the local library and asked questions of his teachers.

It was, however, a tough time to learn about it. Under apartheid, African science was seen as “nothing of merit” until the Westerners colonized the continent two centuries ago.

This tale, told in African Cosmos: Stellar Arts, portrays part of the difficulty of reporting on African science. Turn back to when Egyptians built the pyramids, and you can understand that astronomy goes back thousands of years on the continent. Yet, Africa is under-represented in discussions about popular astronomy. Language, scattered cultures, and distance from the Western world are all barriers.

Creating this volume must have been daunting for Christine Mullen Kreamer and her collaborators, who gathered 20 essays about African astronomy.

But you can see for yourself, as this book is available for free on iPad, and you can download it here.

Africa is a large continent with humans living anywhere from crowded cities to sparse grassland. There are at least 3,000 ethnic groups on that landmass, according to Baylor University, with many of these cultures having separate views in astronomical culture and history.

It’s hard to gather all that information into a single book, but the Smithsonian National Museum of African Art does its best.

The book opens with lengthy explanations of the Egyptian and Babylonian contributions to astronomy. The Babylonians, for example, observed the strange backwards motion of Mars when our planet “catches up” in our smaller orbit to Mars’ larger one. The Egyptians used the sky to develop a 12-month calendar to track important feasts and the time for harvests.

Retrograde motion of Mars. Image credit: NASA

This information is readily accessible elsewhere, but the art makes it stand out. Flip the pages, and you’ll gaze at period art, maps and even astronomical tables that were on display at the museum for a 2012 exhibition.

Perhaps the most fascinating historical chapter is Cosmic Africa, which traces the development of a film of the same title. Anne Rogers and her film team did field research in seven countries to narrow down which tribes to focus on. Eventually, they settled on the Ju/’hoansi in Namibia, the Dogon in Mali and (through archaeology) the area of Nabta Playa in Egypt.

There aren’t many explanations of these peoples in the historical record, so it’s neat to see how their culture is shaped by the stars and nebulas they see. Adding to the interest, the team deliberately visited the Ju/’hoansi during a partial solar eclipse to learn how the tribe reacts to more rare astronomical events.

You’ll see a lot of tribes in this large volume, and will also get hints of the latest art and science surrounding African astronomy. The most current astronomical information is sparse, perhaps out of recognition that the information would go out of date very quickly. It might have been interesting nevertheless to include more information about the Square Kilometer Array, the world’s largest telescope, that is under development in both Africa and Australia.

For more information on the book, check out the online exhibition from the Smithsonian.

February 23, 2013April 26, 2016 by Dan Majaess

Nearby Ancient Star is Almost as Old as the Universe

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions. Credit: NASA/ESA/A. Felid (STScI)).

A metal-poor star located merely 190 light-years from the Sun is 14.46+-0.80 billion years old, which implies that the star is nearly as old as the Universe! Those results emerged from a new study led by Howard Bond. Such metal-poor stars are (super) important to astronomers because they set an independent lower limit for the age of the Universe, which can be used to corroborate age estimates inferred by other means.

In the past, analyses of globular clusters and the Hubble constant (expansion rate of the Universe) yielded vastly different ages for the Universe, and were offset by billions of years! Hence the importance of the star (designated HD 140283) studied by Bond and his coauthors.

“Within the errors, the age of HD 140283 does not conflict with the age of the Universe, 13.77 ± 0.06 billion years, based on the microwave background and Hubble constant, but it must have formed soon after the big bang.” the team noted.

Metal-poor stars can be used to constrain the age of the Universe because metal-content is typically a proxy for age. Heavier metals are generally formed in supernova explosions, which pollute the surrounding interstellar medium. Stars subsequently born from that medium are more enriched with metals than their predecessors, with each successive generation becoming increasingly enriched. Indeed, HD 140283 exhibits less than 1% the iron content of the Sun, which provides an indication of its sizable age.

HD 140283 had been used previously to constrain the age of the Universe, but uncertainties tied to its estimated distance (at that time) made the age determination somewhat imprecise. The team therefore decided to obtain a new and improved distance for HD 140283 using the Hubble Space Telescope (HST), namely via the trigonometric parallax approach. The distance uncertainty for HD 140283 was significantly reduced by comparison to existing estimates, thus resulting in a more precise age estimate for the star.

Age estimate for HD 140283 is 14.46+-0.80 Gyr. On the y-axis is the star's pseudo-luminosity, on the x-axis its temperature. An evolutionary track was applied to infer the age (credit: adapted by D. Majaess from Fig 1 in Bond et al. 2013, arXiv). — HD 140283 is estimated to be 14.46+-0.80 billion years old. On the y-axis is the star’s pseudo-luminosity, on the x-axis its temperature. Computed evolutionary tracks (solid lines ranging from 13.4 to 14.4 billion years) were applied to infer the age (image credit: adapted from Fig 1 in Bond et al. 2013 by D. Majaess, arXiv).

The team applied the latest evolutionary tracks (basically, computer models that trace a star’s luminosity and temperature evolution as a function of time) to HD 140283 and derived an age of 14.46+-0.80 billion years (see figure above). Yet the associated uncertainty could be further mitigated by increasing the sample size of (very) metal-poor stars with precise distances, in concert with the unending task of improving computer models employed to delineate a star’s evolutionary track. An average computed from that sample would provide a firm lower-limit for the age of the Universe. The reliability of the age determined is likewise contingent on accurately determining the sample’s metal content. However, we may not have to wait long, as Don VandenBerg (UVic) kindly relayed to Universe Today to expect, “an expanded article on HD 140283, and the other [similar] targets for which we have improved parallaxes [distances].”

As noted at the outset, analyses of globular clusters and the Hubble constant yielded vastly different ages for the Universe. Hence the motivation for the Bond et al. 2013 study, which aimed to determine an age for the metal-poor star HD 140283 that could be compared with existing age estimates for the Universe. The discrepant ages stemmed partly from uncertainties in the cosmic distance scale, as the determination of the Hubble constant relied on establishing (accurate) distances to galaxies. Historical estimates for the Hubble constant ranged from 50-100 km/s/Mpc, which defines an age spread for the Universe of ~10 billion years.

Age estimates for globular clusters were previously larger than that inferred for the Age of the Universe from the Hubble constant (NASA, R. Gilliland (STScI), D. Malin (AAO)) — Age estimates for the Universe as inferred from globular clusters and the Hubble constant were previously in significant disagreement (image credit: NASA, R. Gilliland (STScI), D. Malin (AAO)).

The aforementioned spread in Hubble constant estimates was certainly unsatisfactory, and astronomers recognized that reliable results were needed. One of the key objectives envisioned for HST was to reduce uncertainties associated with the Hubble constant to <10%, thus providing an improved estimate for the age of the Universe. Present estimates for the Hubble constant, as tied to HST data, appear to span a smaller range (64-75 km/s/Mpc), with the mean implying an age near ~14 billion years.

Determining a reliable age for stars in globular clusters is likewise contingent on the availability of a reliable distance, and the team notes that “it is still unclear whether or not globular cluster ages are compatible with the age of the Universe [predicted from the Hubble constant and other means].” Globular clusters set a lower limit to the age of the Universe, and their age should be smaller than that inferred from the Hubble constant (& cosmological parameters).

In sum, the study reaffirms that there are old stars roaming the solar neighborhood which can be used to constrain the age of the Universe (~14 billion years). The Sun, by comparison, is ~4.5 billion years old.

The team’s findings will appear in the Astrophysical Journal Letters, and a preprint is available on arXiv. The coauthors on the study are E. Nelan, D. VandenBerg, G. Schaefer, and D. Harmer. The interested reader desiring complete information will find the following works pertinent: Pont et al. 1998, VandenBerg 2000, Freedman & Madore (2010), Tammann & Reindl 2012.

February 22, 2013December 23, 2015 by Elizabeth Howell

In Reality, Nebulae Offer No Place for Spaceships to Hide

The nebulas in Battlestar: Blood and Chrome make for nice scenery, but they're a lot brighter than the truth, according to a Harvard astronomer. Credit: Battlestar Galactica: Blood and Chrome/Machinima (screencap)

In the Battlestar: Galactica universe, nebulas are a nifty spot to hide from the Cylons that are plotting to kill humanity. There’s just one problem with the hypothesis, though — these diffuse areas of gas in our universe are actually very faint, even if you get close up. Probably too faint for a hiding spot.

Prequel Battlestar Galactica: Blood and Chrome (released on DVD this week) shows the young William Adama flying around the universe with pretty nebulas in the background. That’s not anywhere near the truth, Harvard astronomer Peter Williams told Universe Today.

In an e-mail, Williams explained that bright nebulas are a common misperception seen in Star Wars, Star Trek and a host of other sci-fi series.

The big issue is that nebulae are just too faint for the human eye to see. And while it’s tempting to think that they’d look brighter from up close, in fact this isn’t actually true — they actually look just as bright from any distance! This is a law of optics, known in the jargon as the “conservation of surface brightness”. The key is that there are two competing effects in play. Imagine that you can see a nebula that’s, say, the size of the full moon.

Yes, if you get closer, your eye will receive more total power from the nebula. But the nebula will also look bigger, so that energy will be spread out over a larger visual area (technically: “solid angle”). The physics tells you that the power per solid angle in fact stays exactly the same, and this quantity is precisely the “brightness” of an object. So if nebula are too faint for to see from Earth with the naked eye — and they are — getting up close and personal doesn’t help any.

Those bright colors surrounding Battlestar's ships are not actually what you would see if nestled in a nebula, according to Harvard astronomer. Credit: Battlestar Galactica/SciFi (screencap) — The opening sequence in Battlestar: Galactica shows the ships hiding in a bright nebula. Credit: Battlestar Galactica/SciFi (screencap)

Further, Williams, explains, the bright colors we’re used to seeing in Hubble Space Telescope images are just an approximation of what a nebula actually looks like.

Reproduced images of nebulae don’t portray their colors accurately. As you may know, some astronomical images use “false color” to represent wavelengths of light that humans can’t even see. This does happen with images of nebulae, but nebulae really are colorful, and many nebula images try to reproduce those colors faithfully. No current reproduction, however, can be truly accurate.

The Crab Nebula. Image credit: NASA/Hubble Space Telescope.

The problem is that the colorful nebular emission comes from reactions that produce light at a few, specific wavelengths; meanwhile, our inks and pixels emit over much broader wavelength ranges. We can mix these broad ranges in ways that approximate the narrow ones, but the results aren’t quite the same.

For an entertaining look at the science of nebulas, Williams recommends this entertaining video by astronomer Phil Plait, a long-time friend of Universe Today who is best known for his Bad Astronomy blog (now at Slate). “If you were inside [the nebula and looked down], you wouldn’t see it,” Plait says in this 2008 clip.

Guess it’s time to find another spot to hide.

January 18, 2013December 23, 2015 by Nancy Atkinson

Astronomy Photographer of the Year Competition Now Open for 2013

Winning photograph in the Earth and Space category in the 2012 Astronomy Photographer of the Year Competition, 'Star Icefall' by Masahiro Miyasaka (Japan).

It’s back! The 2013 Astronomy Photographer of the Year competition is now open and accepting submissions. This is the fifth year of the competition, which is is run by the Royal Observatory Greenwich in association with Sky at Night Magazine. Every year it produces some of the most beautiful and spectacular visions of the cosmos, whether they are striking pictures of vast galaxies millions of light years away, or dramatic images of the night sky taken much closer to home.

“Every year brings something new to see in the sky and the arrival in March of the predicted Comet C/2011 PANSTARRS will hopefully inspire some memorable pictures in this year’s competition,” said Dr. Marek Kukula, Public Astronomer at the ROG and judge in the competition. “It will be great to see even more entries from talented young photographers and newcomers to astrophotography who prove year after year that all you need to do is pick up a camera.”

Entries to the competition must be submitted by June 13, 2013. There are some great prizes, too. The overall winner will receive £1,500. Category winners will receive £500. There are also prizes for runners-up (£250) and highly commended (£125) entries. The Special Prize winners will receive £350, with an £125 prize for the People and Space Special Prize runner-up. All of the winning entries will receive a one year subscription to Sky at Night Magazine.

Astronomy Photographer of the Year 2013 has four main categories:

Earth and Space – Photographs that include landscape, people and other earth-related things alongside an astronomical subject ranging from the stars, the Moon or near-Earth phenomena such as the aurora.

Our Solar System – Imagery which captures the Sun and its family of planets, moons, asteroids and comets.

Deep Space – Pictures that capture anything beyond the Solar System, including stars, nebulae and galaxies.

Young Astronomy Photographer of the Year – Pictures taken by budding astronomers under the age of 16 years old.

There are also three special prizes: People and Space recognizes the best photo featuring people in the shot; Best Newcomer is awarded to the best photo by an amateur astrophotographer who has taken up the hobby in the last year and who has not entered an image into the competition before; and Robotic Scope, is awarded for the best photo taken using one of the increasing number of computer-controlled telescopes at prime observing sites around the world which can be accessed over the internet by members of the public.

The winning images will be showcased in the annual free exhibition at the Royal Observatory Greenwich from September 19, 2013 to February 23, 2014.

Find more info and enter online by visiting www.rmg.co.uk/astrophoto . Each entrant may submit up to five images to the competition.

To view the entries submitted so far, visit www.flickr.com/groups/astrophoto

So get out there with your camera! And good luck!