Posted on by VirtualAstro

Coming to a Sky Near You: The Realm of Galaxies

The original Hubble Ultra-Deep Field (Credit NASA, ESA, and S. Beckwith (STScI) and the HUDF Team).

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We live on a planet which orbits a star, and along with a hundred billion other stars, our Sun orbits the centre of our Milky Way galaxy. It doesn’t just stop there; our galaxy is one of hundreds of billions of galaxies in our Universe that gravitationally clump together in groups or clusters.

Throughout Spring in the northern hemisphere, astronomers and people interested in the night sky are going to be in for a galactic treat, as this is the time of year we can see the Coma/Virgo Super cluster or “Realm of Galaxies”.

Galaxies are massive islands of stars, gas and dust in the Universe; they are where stars and planets are born and eventually die. Galaxies are cosmic factories of creation — where it all happens on a very grand scale. To give you an idea of size, it would take you roughly 100,000 years to travel across the disc of the Milky Way at the speed of light!

Andromeda Galaxy.

The Milky Way is the second largest member of our local group of galaxies with Andromeda being the largest. Other members of our local group include the Triangulum galaxy and large and small Magellanic Clouds.

Virgo Galaxy Cluster - NOAO/AURA/NSF

The Coma/ Virgo Super cluster dominates our intergalactic neighbourhood; it represents the physical centre of our Local Super cluster and influences all the galaxies and galaxy groups by the gravitational attraction of its enormous mass.

Unfortunately galaxies are almost impossible to see with the naked eye, so you will need powerful binoculars or a large telescope, such as a Dobsonian to see most of the brighter galaxies in this region.

The cluster contains approximately 2,000 elliptical and spiral galaxies of which approximately 20 or more are observable using amateur equipment. This includes 16 Messier objects such as the Black eye spiral Galaxy M64, and elliptical galaxies, M86 with its plume, massive M87 at its centre and beautiful spiral M88, to name just a few.

From Left to Right M64, M86 and M88 (Credit NASA)

To find the approximate location of the Realm of Galaxies, first find the constellation of Leo – the lion — easily found in the South East this time of year with the backwards question mark overhis head. Go past Leo’s rear end and you will be in the bowl asterism of Virgo, to the bottom left of Leo and the faint constellation of Coma Berenices (Berenices hair) top left of Leo. This is the Realm of Galaxies!

Star Chart to help you find the Realm of Galaxies (Credit Adrian West)

Download a map of this region or use a star atlas to find your way around this area and try and spot as many galactic delights (faint fuzzies) as you can. As a bonus, the ringed Planet Saturn is just below this area too at the moment!

Give yourself plenty of time, wrap up warm and just think, you are looking for the largest structures in the Universe, hundreds of millions of light years away from Earth.

Posted on by VirtualAstro

The Supermoon Illusion

You’ve probably all seen it before, a huge Full Moon sitting on the horizon and you wonder why it looks much bigger than at other times? It isn’t, really; it’s an illusion.

And now, if you have heard about the close approach of the moon, or so called “Supermoon” on March 19th and are concerned about the disasters and mayem it may cause, there is no need to worry. And surely, when this so-called “Supermoon” occurs on March 19th — at its closest approach to Earth in two decades — people will indeed report that the Moon looks much bigger than normal. But it won’t really be much bigger in the sky at all. It’s all an illusion, a trick of the eye.

The moon does have an effect on the Earth with its gravity affecting ocean tides and even land to a lesser extent, but the moon on the 19th won’t interact with our planet any differently than any other time it’s been at its closest (also known as perigee).

If anything we may get slightly stronger tides, but nothing out of the ordinary.

The Moon orbits the Earth in an elliptical orbit, meaning that it is not always the same distance from the Earth. The closest the Moon ever gets to Earth (called perigee) is 364,000km, and the furthest is ever gets (Apogee) is around 406,000km (these figures vary, and in fact this Full Moon on March 19, 2011 will see a slightly closer approach of 357,000km).

So the percentage difference in distance between the average perigee and the average apogee is ~10%. That is, if the Full Moon occurs at perigee it can be up to 10% closer (and therefore larger) than if it occurred at apogee.

This is quite a significant difference, and so it is worth pointing out that the Moon does appear to be different sizes at different times throughout the year.

Moon at Perigee and Apogee Credit NASA

But that’s NOT what causes the Moon to look huge on the horizon. Such a measly 10% difference in size cannot account for the fact that people describe the Moon as “huge” when they see it low on the horizon.

What’s really causing the Moon to look huge on such occasions is the circuitry in your brain. It’s an optical illusion, so well known that it has its own name: the Moon Illusion.

If you measure the angular size of the Full Moon in the sky it varies between 36 arc minutes (0.6 degrees) at perigee, and 30 arc minutes (0.5 degrees) at apogee, but this difference will occur within a number of lunar orbits (months), not over the course of the night as the Moon rises. In fact if you measure the angular size of the Full Moon just after it rises, when it’s near the horizon, and then again hours later once it’s high in the sky, these two numbers are identical: it doesn’t change size at all.

So why does your brain think it has? There’s no clear consensus on this, but the two most reasonable explanations are as follows:

  1. When the Moon is low on the horizon there are lots of objects (hills, houses, trees etc) against which you can compare its size. When it’s high in the sky it’s there in isolation. This might create something akin to the Ebbinghaus Illusion, where identically sized objects appear to be different sizes when placed in different surroundings.

Ebbinghaus Illusion – the two orange circles are exactly the same size

  1. When seen against nearer foreground objects which we know to be far away from us, our brain thinks something like this: “wow, that Moon is even further than those trees, and they’re really far away. And despite how far away it is, it still looks pretty big. That must mean the Moon is huge!”.

These two factors combine to fool our brains into “seeing” a larger Moon when its near the horizon compared with when it’s overhead, even when our eyes – and our instruments – see it as exactly the same size.

Source: “Moon Illusion” on Dark Sky Diary Special thanks to Steve Owens

Posted on by Tammy Plotner

Jupiter and Mercury Pair Up in Twilight March 13–16

Credit: Sky & Telescope Magazine

[/caption]According to today’s Sky & Telescope press release, two bright planets will shine close together low in the western twilight from Sunday to Wednesday, March 13th to 16th. Anyone can see them with the naked eye. You’ll just need a clear sky and an open view toward the west roughly 40 minutes after sunset, as twilight fades.

Jupiter is the brighter of the two. “Mercury is pretty hard to spot most of the time, so a lot of people have never recognized it in their lives,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “With Jupiter guiding the way, now’s your chance.”

Jupiter has dominated the evening sky for several months, but now it’s on its way down and out for the season. It’ll be gone in another couple of weeks. Mercury, on the other hand, will climb a little higher in the western twilight by late March. (This refers to viewers in the world’s mid-northern latitudes, including the United States, Canada, southern Europe, and elsewhere between about 30° and 50° north latitude.)

The graphic here shows where to look.

Find a spot with a clear, open view low to the west, and you can watch Mercury passing Jupiter in twilight from March 13 to 16, 2011. Credit: Sky & Telescope magazine

The two planets will appear closest together on Monday and Tuesday, March 14 and 15, when they’ll be only about 2° apart — about the width of your thumb held at arm’s length.

Although the two planets appear close together, they’re not. Jupiter is more than 5 times farther away, at a distance of 550 million miles compared to Mercury’s 102 million miles. That means the light we see from them takes 49 and 9 minutes, respectively, to reach us.

“Don’t miss this chance to do a little astronomy from your backyard, balcony, or rooftop,” says Sky & Telescope associate editor Tony Flanders. “It’s a big universe, and planets await.”

For more skywatching information and astronomy news, visit SkyandTelescope.com or pick up Sky & Telescope, the essential magazine of astronomy since 1941.

Posted on by Tammy Plotner

Capturing Thor’s Helmut

NGC 2359 - Credit: John Chumack

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It spans nearly 30 light years of space… and resides approximately 15,000 light-years from Earth. Its heartbeat is an extremely hot giant star thought to be in a brief, pre-supernova stage of evolution. Interactions with a nearby dense, warn and large molecular cloud are what may have contributed to its complex shape and curved bow-shock structure. Step back into mythology and see if you have what it takes to capture “Thor’s Helmut”…

Unlike many nebula, this unusual character is the product of the central Wolf-Rayet star, its stellar winds, and the surrounding interstellar matter. The powerful star emits a high velocity wind, pushing matter ahead of it. This process both compresses and expands its ring-like shell. As it grows, it collects even more gas and dust from the interstellar medium. But how many times and how many events?

“We have detected three different velocity components, and determined their spatial distribution and physical properties. The kinematics, morphology, mass and density are clearly stratified with respect to the W-R star.” says JR Rizzo (et al). “These features allow us to learn about the recent evolutionary history of HD 56925, because the multiple layers could be associated to several energetic events which have acted upon the surrounding circumstellar medium. Hence, a careful study of the different shockfronts contain clues in determining the present and past interaction of this evolved massive star with its surroundings.”

While most planetary nebulae contain old stars nearing the end of their lives, the central Wolf-Rayet star in NGC 2359 is very young. Its ultraviolet photons are the fueling source of the emission nebula. Wolf-Rayets are evolved, massive and extremely hot – up to ~50,000 K. Not only that, but their luminosity is incredible, too… up to 10L to the fifth or sixth power. Their surface composition is extremely exotic, being dominated by helium rather than hydrogen and the stars themselves are rare, simply because they are so short-lived. It was only three short decades ago that astronomers also realized that WRs suffered from heavy mass loss as well. Their ejecta bursts outward at speeds comparable to a nova. The whole process of formation simply isn’t clearly understood yet. The layers may be from differential rotation – but they could be the results of the exposed stellar core.

“The overall emission in the nebula is dominated by the overwhelming contribution of the H II region and is characteristic of photoionization processes. The embedded, photoevaporating cloud contributes enough mass over a dynamical lifetime to account for the shell mass of 5.0 solar mass.” says TE Jernigan. “In NGC 2359, imagery reveals variations in density, temperature, and ionization structure on scales ranging from the size of the nebula down to the seeing limit of approximately 2.1 seconds. The structure of the H II region can be understood in terms of a photoionized conical cavity protruding into the surrounding molecular cloud. The emission in the bubble region is characteristic of that produced in the incomplete cooling region behind a stellar-wind shock wave.”

No matter what explanation lay behind it, observing “Thor’s Helmut” is a pure pleasure. You’ll find it located about a fistwidth east-northeast of Sirius (07h 18m 30s, ?13° 13′ 48″). This Herschel object is a delightful 8th magnitude and well worth the effort!

And many thanks to John Chumack of Galactic Images for making the effort and sharing it with us!

Posted on by Nancy Atkinson

Double Spaceship Sighting Alert – and last chance to see Discovery in orbit

Discovery and ISS pass over the UK on March 7, 2011, captured by Will Gater.

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UPDATE: We’ve already got a sighting! The image above was taken this evening in the UK by science writer Will Gater.

Space shuttle Discovery undocked from the ISS on early Monday, March 7, and depending where you live, you might have an opportunity to see the two spaceships flying in tandem. This is an incredible sight, and will be the last opportunity to see Discovery in orbit, as she will be retired after she lands and completes the STS-133 mission. Spaceweather.com reports that the station and shuttle will be flying over parts of the United States and Europe Monday and Tuesday, appearing in the night sky as a closely-spaced pair of bright lights. The ISS is bigger, so will appear as the brighter object trailing the smaller Discovery as they move across the sky.

To find out if you’ll be able to see the two spaceships in your area, there are a few different sites to check out:

NASA has a Skywatch page where you can find your specific city to look for satellite sighting info.

Spaceweather.com, has a Satellite Tracker Tool. Just put in your zip code (good for the US and Canada) to find out what satellites will be flying over your house.

Heaven’s Above also has a city search, but also you can input your exact latitude and longitude for exact sighting information, helpful if you live out in the country.

Seeing the two spacecraft flying closely in tandem is a very unique and thrilling sight. Good luck!

Below, watch some of the incredible views as Discovery performed the fly-around maneuver of the ISS early Monday.

Posted on by Nancy Atkinson

What’s Up for March?

Jane Houston Jones from JPL provides a video report on the happenings in space this month, and what you can see in the night sky in March: the MESSENGER spacecraft goes into orbit around Mercury on the 18th, and you can see the swift planet in the evening skies, too! Meanwhile, celebrate Sun-Earth day on the 19th, and view the sun through solar safe telescopes.

Jones was also featured on a recent 365 Days of Astronomy podcast, talking with Jane Platt and providing a “Sneak Peek at the Springtime Skies.”

Posted on by Nancy Atkinson

Look to Orion and Help Measure the Darkness of Your Night Sky

Orion as seen from Easter Island. Credit: Wally Pacholka / AstroPics.com / TWAN. Used by permission.

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How dark are your skies? GLOBE at Night wants to know! Join the 6th annual worldwide GLOBE at Night campaign, which is going on right now in the northern hemisphere. “We are running two campaigns this year, from February 22nd to March 6th and from March 22nd to April 4th in the northern hemisphere and March 24th to April 6th in the southern hemisphere,” said Rob Sparks from the National Optical Astronomy Observatory, which is one of the sponsors for this year’s campaign.

By participating in the international star-hunting campaign, you will help address the problems of light pollution locally as well as globally. More participants are needed this year, so sign up to be a citizen scientist today!

Light pollution is a serious and growing global concern. With half of the world’s population now living in cities, many urban dwellers have never experienced the wonder of pristinely dark skies and perhaps, maybe never will. But light pollution is also a concern in areas of safety, energy conservation, cost, health and effects on wildlife, as well as our ability to view the stars.

But this is also one of the easiest environmental problems you can address on local levels.

GLOBE at Night is a wonderful way for everyone around the world to participate to raise public awareness of the impact of artificial lighting on local environments. This event encourages everyone – students, educators, dark sky advocates and the general public – to measure the darkness of their local skies and contribute their observations online to a world map.

The campaign is easy and fun to do, and as in previous years, there are just five easy steps to participate. But this year, there is now an app for that, where participants can submit their measurements in real time if they have a smart phone or tablet.

“There is now a mobile website to submit data,” Sparks told Universe Today. “It will take the GPS data, time and date from your phone and has a cool little graphic to help you determine the brightness of the sky. It even had a red screen feature for night use.” The app can be found at this link.

To participate, you will match the appearance of the constellation Orion in the first campaign (and Leo or Crux in the second campaign) with simple star maps of progressively fainter stars found. Then you submit your measurements, including the date, time, and location of your comparison. After all the campaign’s observations are submitted, the project’s organizers release a map of light-pollution levels worldwide. Over the last five annual 2-week campaigns, volunteers from more than 100 nations contributed 52,000 measurements, one third of which came from last year’s campaign.

The five easy star-hunting steps are:

1) Find your latitude and longitude.

2) Find Orion by going outside an hour after sunset (about 7-10pm local time).

3) Match your nighttime sky to one of the GLOBE at Night magnitude charts

4) Report your observation.

5) Compare your observation to thousands around the world.

Go to the GLOBE at Night website for all the details. There is even a 10-minute audio podcast on light pollution and GLOBE at Night. Or download a 45-minute powerpoint and accompanying audio. GLOBE at Night is also on Facebook and Twitter.

Be a part of GLOBE at Night and help the campaign exceed the 17,800 observations contributed last year. Your measurements will make a world of difference.

Thanks to the GLOBE at Night team for securing permission for Universe Today to post the lead image, from Wally Pacholka from AstroPics.com and TWAN (The World At Night).

Posted on by Tammy Plotner

Naturally Jupiter

As we know, Jupiter’s Southern Equatorial Belt has been missing beneath its icy clouds for almost a year now. While astronomers are able to use instruments like Keck – complete with infrared and adaptive optics – we here on Earth have to take our views of Jupiter a little more naturally.

As you can see from this webcam image given to us by John Chumack, even our thin earthly clouds can’t quite hide bright Jupiter. It has returned to the same ruddy, lined face that most of us fell in love with the first time we observed it. Stunning details? No… Because this is how Jupiter really looks when you first glimpse it in the eyepiece.

Right now the westering Jupiter isn’t in the best of positions for extended observing, but it is at a comfortable height and a comfortable time. While it might be tempting to throw a huge amount of magnification its way, it actually makes the view worse rather than improving it. With steady seeing condtions, around 150-200X is ideal – reducing the magnification even lower if the atmosphere is turbulent. You’ll find you’ll also have greater success using your orthoscopic or plossl design eyepieces, too. Got color filters? Go ahead and experiment! Blues, reds and yellows all cause contrast change which can reveal subtle details. As unusual as it may sound, sketching also helps. You don’t need to be a Rembrandt. Just the act of translating what the eye sees onto paper greatly improves your “human” focus.

Don’t forget the galiean moons! As you can see, Europa can look like a world of its own. While larger aperture instruments are able to resolve events like shadow transits, don’t feel left out if you have a small telescope. It’s very exciting to witness one of Jupiter’s satellites being eclipsed by the parent planet – or disappearing as it passes in front. There are even times when the moons eclipse each other! Go on… Take advantage of the early evening hours and enjoy Jupiter.

Because you never know when the perfect moment seeing will arrive…

Many thanks to John Chumack of Galactic Images for sharing his recent image of Jupiter with us.

Posted on by Tammy Plotner

Moon And Venus Steal The Morning Scene…

Venus and Waning Crescent Moon by John Chumack

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If you’re an early riser, then perhaps you’ve noticed Kepler’s Laws in action? No, it’s not a new Bruce Willis movie, just the inevitable pairing of the waning crescent Moon and shining Venus. As you can see from this great photo taken last month by John Chumack, it happens as regular as clockwork… and it’s about to happen again. But what is it about such pairings that command our attention? Step inside and find out!

According to the Sky & Telescope press release, the brightest planet and the eerie waning crescent Moon will create an arresting sky scene low in the southeast in the early dawn of Monday, February 28th, and Tuesday, March 1st. “These are the two brightest astronomical objects in the sky after the Sun,” says Alan MacRobert, a senior editor of Sky & Telescope magazine. “They’ll certainly catch your eye, if you look low in the southeast about 60 to 40 minutes before sunrise — weather permitting.”

Venus will be shining to the Moon’s lower left on the morning of Monday Feb. 28th. The next morning Venus will be to the Moon’s right or upper right. Although they look close together, they’re not. Venus is currently 400 times farther away than the Moon. It’s at a distance of 8.8 light-minutes (the distance light takes to travel that far), compared to the Moon’s distance of 1.3 light-seconds. In miles, that’s 99 million miles for Venus and just 249,000 miles for the Moon. (In fact, you may have driven cars enough miles to get to the Moon.) And despite appearances, Venus is 3½ times wider than the Moon’s diameter.

Locator Chart Courtesy of Sky & Telescope Magazine

“Why do people care about this?” asks MacRobert. “Because some people know we need to look up beyond our own little world — and recognize where we are as part of nature, part of the universe. So many of us live our busy little ant-hill lives without ever noticing the gigantic universe beyond the anthill. A lot of people don’t even know you can see alien planets from your driveway while you’re unlocking the car to go to work.”

But just what is it about such a celestial scene that draws our eye like no other? When it comes to our eyes, almost every photoreceptor has one ganglion cell receiving data in the fovea. That means there’s almost no data loss and the absence of blood vessels in the area means almost no loss of light either. There is direct passage to our receptors – an amazing 50% of the visual cortex in the brain! Since the fovea doesn’t have rods, it isn’t sensitive to dim lights. That’s another reason why the conjunctions are more attractive than the surrounding starfields. Astronomers know a lot about the fovea for a good reason: it’s is why we learn to use averted vision. We avoid the fovea when observing very dim objects in the eyepiece.

“Your eye is like a digital camera,” explains Dr. Stuart Hiroyasu, O.D., of Bishop, California. “There’s a lens in front to focus the light, and a photo-array behind the lens to capture the image. The photo-array in your eye is called the retina. It’s made of rods and cones, the fleshy organic equivalent of electronic pixels.” Near the center of the retina lies the fovea, a patch of tissue 1.5 millimeters wide where cones are extra-densely packed. “Whatever you see with the fovea, you see in high-definition,” he says. The fovea is critical to reading, driving and even watching television. The fovea has the brain’s attention. The field of view of the fovea is only about five degrees wide.” When Venus and the crescent Moon are close to that narrow angle, it signals to the brain, “this is worth watching!”

Let’s pretend we’re a photoreceptor. If a light were to strike us, we’d be “on” – recording away. If we were a ganglion cell, the light really wouldn’t do much of anything. However, the biological recorder would have responded to a pinpoint of light, a ring of light, or a light with a dark edge to it. Why? Light in general just simply doesn’t excite the ganglion, but it does wake up the neighbor cells (as does hooting and screaming while pointing at the morning sky). A small spot of light makes the ganglion go crazy, but the neighbors don’t pay much attention (unless you’re in your pajamas cleaning the snow off your car). However, a ring of light makes the neighbors go nuts (and their dogs) and the ganglion turns off. It’s all a very complicated response to a simple scene, but still fun to understand why we are compelled to look!

And perhaps howl just once.

Many thanks to John Chumack of Galactic Images and to Sky & Telescope Magazine for the heads up!

Posted on by Nancy Atkinson

Stunning New Look at Reflection Nebula Messier 78

A visible light image from ESO of the reflection nebula Messier 78. Credit: ESO and Igor Chekalin

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Here’s another “Hidden Treasure” from the European Southern Observatory, from the astrophotography competition where amateurs create images from unused ESO data. In this new image of Messier 78, brilliant starlight ricochets off dust particles in the nebula, illuminating it with scattered blue light and creating what is called a reflection nebula. Almost like fog around a street light, a reflection nebula shines only with the light from an embedded source that illuminates the dust. This image was taken with the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. Comparing this image with others previously taken of Messier 78 shows that remarkably, this object has changed significantly in the last ten years.

This beautiful image was the overall winner of ESO’s Hidden Treasures 2010 astrophotography competition created by Igor Chekalin, who won with his image of this stunning object.

Messier 78 can easily be observed with a small telescope, being one of the brightest reflection nebulae in the sky. It lies about 1350 light-years away in the constellation of Orion (The Hunter) and can be found northeast of the easternmost star of Orion’s belt.

For those of you who want to take a look on your own:
Right Ascension: 05:46.7
Declination: +00:03
Distance: 1.6 (kly)
Visual Brightness: Magnitude 8.3

This image contains many other striking features apart from the glowing nebula. A thick band of obscuring dust stretches across the image from the upper left to the lower right, blocking the light from background stars. In the bottom right corner, many curious pink structures are also visible, which are created by jets of material being ejected from stars that have recently formed and are still buried deep in dust clouds.

Two bright stars, HD 38563A and HD 38563B, are the main powerhouses behind Messier 78. However, the nebula is home to many more stars, including a collection of about 45 low mass, young stars (less than 10 million years old) in which the cores are still too cool for hydrogen fusion to start, known as T Tauri stars. Studying T Tauri stars is important for understanding the early stages of star formation and how planetary systems are created.

Messier 78 region taken in 2006 (below) with the 4-metre Mayall telescope at Kitt Peak, Arizona with a new image from ESO.Credit: ESO/T. A. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF and Igor Chekalin

But this object has changed significantly in the last ten years. In February 2004 the experienced amateur observer Jay McNeil took an image of this region with a 75 mm telescope and was surprised to see a bright nebula — the prominent fan shaped feature near the bottom of this picture — where nothing was seen on most earlier images. This object is now known as McNeil’s Nebula and it appears to be a highly variable reflection nebula around a young star.

This color picture was created from many monochrome exposures taken through blue, yellow/green and red filters, supplemented by exposures through an H-alpha filter that shows light from glowing hydrogen gas. The total exposure times were 9, 9, 17.5 and 15.5 minutes per filter, respectively.

Source: ESO