Weekly SkyWatcher’s Forecast: September 10-16, 2012

Greetings, fellow SkyWatchers! With very little Moon to contend with this week, it will be a great time to take on some challenging studies like the Helix Nebula, Saturn Nebula, Stephen’s Quintet and more. It’s time to get out your big telescope and head for some dark skies… Because this week isn’t for the beginner! Whenever you’re ready, I’ll see you out back…

Monday, September 10 – Today is the birthday of James E. Keeler. Born in 1857, the American Keeler was a pioneer in the field of spectroscopy and astrophysics. In 1895, Keeler proved that different areas in Saturn’s rings rotate at different velocities. This clearly showed that Saturn’s rings were not solid, but were instead a collection of smaller particles in independent orbits.

Now, let’s head on to Capricornus and drop about four finger-widths south of its northeastern most star – Delta – and have a look at M30 (Right Ascension: 21 : 40.4 – Declination: -23 : 11). Discovered in 1764 by Charles Messier, binocular observers will spot this small, but attractive, globular cluster easily in the same field with star 41. For telescopic observers, you will find a dense core region and many chains of resolvable stars in this 40,000 light year distant object. Power up!

Let’s get some more practice in Capricornus, and take on a more challenging target with confidence. Locate the centermost bright star in the northern half of the constellation – Theta – because we’re headed for the “Saturn Nebula”.

Three finger-widths north of Theta you will see dimmer Nu, and only one finger-width west is NGC 7009 (Right Ascension: 21 : 04.2 – Declination: -11 : 22). Nicknamed the “Saturn Nebula”, this wonderful blue planetary is around 8th magnitude and achievable in small scopes and large binoculars. Even at moderate magnification, you will see the elliptical shape which gave rise to its moniker. With larger scopes, those “ring like” projections become even clearer, making this challenging object well worth the hunt. You can do it!

Tuesday, September 11 –Today celebrates the birthday of Sir James Jeans. Born in 1877, English-born Jeans was an astronomical theoretician. During the beginning of the 20th century, Jeans worked out the fundamentals of the process of gravitational collapse. This was an important contribution to the understanding of the formation of solar systems, stars, and galaxies.

So, are we ready to try for the “Helix”?

Located in a sparsely populated area of the sky, this intriguing target is about a fist width due northwest of bright Formalhaut and about a fingerwidth west of Upsilon Aquarii. While the NGC 7293 (Right Ascension: 22 : 29.6 – Declination: -20 : 48) is also a planetary nebula, its entirely different than most… It’s a very large and more faded edition of the M57! On a clear, dark night it can be spotted with binoculars since it spans almost one quarter a degree of sky. Using a telescope, stay at lowest power and widest field, because it is so large. It you have an OIII filter, this faded “ring” becomes a braided treat!

Wednesday, September 12 – Today in 1959, the USSR’s Luna 2 scored a mark as it became the first manmade object to hit the moon. The successful mission landed in the Paulus Putredinus area. Today also celebrates the 1966 Gemini 11 launch.

Tonight let’s take the time to hunt down an often overlooked globular cluster – M56. Located roughly midway between Beta Cygni and Gamma Lyrae (RA 19 15 35.50 Dec +30 11 04.2), this class X globular was discovered by Charles Messier in 1779 on the same night he discovered a comet, and was later resolved by Herschel. At magnitude 8 and small in size, it’s a tough call for a beginner with binoculars, but is a very fine telescopic object. With a general distance of 33,000 light-years, this globular resolves well with larger scopes, but doesn’t show as much more than a faint, round area with small aperture. However, the beauty of the chains of stars in the field makes it quite worth the visit!

While you’re there, look carefully: M56 is one of the very few objects for which the photometry of its variable stars was studied strictly with amateur telescopes. While one bright variable star had been known previously to exist, up to a dozen more have recently been discovered. Of those, six had their variability periods determined using CCD photography and telescopes just like yours!

Thursday, September 13 – Today in 1922, the highest air temperature ever recorded at the surface of the Earth occurred. The measurement was taken in Libya and burned in at a blistering 136F (58C), but did you know that the temperatures in the sunlight on the Moon double that? If you thought the surface of the Moon was a bit too warm for comfort, then know surface temperatures on the closest planet to the Sun can reach up to 800F (427C) at the equator during the day! As odd as it may sound, even that close to the Sun – Mercury could very well have ice deposits hidden below the surface at its poles.

Tonight we’ll move on to Aquila and look at the hot central star of an interesting planetary nebula – NGC 6804 (Right Ascension: 19 : 31.6 – Declination: +09 : 13). You’ll find it almost 4 degrees due west of Altair. Discovered by Herschel and classed as open cluster H VI.38, it wasn’t until Pease took a closer look that its planetary nature was discovered. Interacting with clouds of interstellar dust and gases, NGC 6804 is a planetary in decline, with its outer shell around magnitude 12 and the central star at about magnitude 13. While only larger telescopes will get a glimpse of the central, it’s one of the hottest objects in space – with temperatures around 30,000K!

If that’s not “hot” enough for you, then take a look straight overhead at brilliant star Vega. It is a “Sirian type” star and with a surface temperature of about 9200 degrees Kelvin, it’s twice as hot as our own Sun. At around 27 light years away, our entire solar system is moving towards Vega at a speed of 12 miles per second, but don’t worry… It will take us another 450,000 years to get there. If we were to arrive tonight, we’d find that Vega is around 3 times larger than Sol and that it also has a 10th magnitude companion that can often be resolved in mid-sized scopes. It’s one of the first stars to ever be photographed. Back in 1850, that simple star – Vega – took and exposure time of 100 seconds through a 15? scope. How times have changed!

Friday, September 14 – Tonight’s destination is not an easy one, but if you have a 6? or larger scope, you’ll fall in love a first sight! Let’s head for Eta Pegasi and slightly more than 4 degrees north/northeast for NGC 7331 (Right Ascension: 22 : 37.1 – Declination: +34 : 25).

This beautiful, 10th magnitude, tilted spiral galaxy is very much how our own Milky Way would appear if we could travel 50 million light years away and look back. Very similar in both structure to ourselves and the “Great Andromeda”, this particular galaxy gains more and more interest as scope size increases – yet it can be spotted with larger binoculars. At around 8? in aperture, a bright core appears and the beginnings of wispy arms. In the 10? to 12? range, spiral patterns begin to emerge and with good seeing conditions, you can see “patchiness” in structure as nebulous areas are revealed and the western half is deeply outlined with a dark dustlane. But hang on… Because the best is yet to come!

Saturday, September 15 – In 1991 the Upper Atmosphere Research Satellite (UARS) was launched from Space Shuttle Discovery. The successful mission lasted well beyond its life expectancy – sending back critical information about our ever-changing environment. After 14 years and 78,000 orbits, UARS remains a scientific triumph.

If you’re up early, why not check out Mars? While the red planet is visible, it’s also rather small at the moment, with an apparent diameter of less than .5”. Can you still spot some surface details?

Tonight return to the NGC 7331 with all the aperture you have. What we are about to look at is truly a challenge and requires dark skies, optimal position and excellent conditions. Now breathe the scope about one half a degree south/southwest and behold one of the most famous galaxy clusters in the night.
In 1877, French astronomer – Edouard Stephan was using the first telescope designed with a reflection coated mirror when he discovered something a bit more with the NGC 7331. He found a group of nearby galaxies! This faint gathering of five is better known as “Stephan’s Quintet” and its members are no further apart than our own Milky Way galaxy.

Visually in a large scope, these members are all rather faint, but their proximity is what makes them such a curiosity. The Quintet is made up of five galaxies numbered NGC 7317, 7318, 7318A, 7318B, 7319 and the largest is 7320 (Right Ascension: 22 : 36.1 – Declination: +33 : 57). Even with a 12.5? telescope, this author has never seen them as much more than tiny, barely there objects that look like ghosts of rice grains on a dinner plate. So why bother?

What our backyard equipment can never reveal is what else exists within this area – more than 100 star clusters and several dwarf galaxies. Some 100 million years ago, the galaxies collided and left long streamers of their materials which created star forming regions of their own, and this tidal pull keeps them connected. The stars within the galaxies themselves are nearly a billion years old, but between them lay much younger ones. Although we cannot see them, you can make out the soft sheen of the galactic nucleii of our interacting group.

Enjoy their faint mystery!

Sunday, September 16 – It’s New Moon! For those of you who have waited on the weekend to enjoy dark skies, then let’s add another awesome galaxy to the collection. Tonight set your sights towards Alpha Pegasi and drop due south less than 5 degrees to pick up NGC 7479 (Right Ascension: 23 : 04.9 – Declination: +12 : 19).

Discovered by William Herschel in 1784. this tantalizing 11 magnitude barred spiral galaxy has had a supernova in its nucleus as recently as 1990. While the 16th magnitude event is no longer visible, smaller telescopes will easily pick out bright core and elongation of the central bar. Larger aperture will find this one a real treat as the spiral arms curl both over and under the central structure, resembling a ballet dancer “en pointe”. Congratulations! You’ve just observed Caldwell 44.

Until next week? Wishing you clear skies!

Written by Tammy Plotner. NGC 7009 Image Credit: NOAO/AURA/NSF

3-D View From Subaru – Stephan’s Quintet

Composite tricolor images of Stephan's Quintet using H? filters with a recession velocity of 0 (left image) and a recession velocity of 4,200 miles per second (right image).


While this isn’t a true “cross eye” image, you can darn sure open the larger version, set it to screen size, cross your eyes and get a pretty astonishing result. If you don’t “get it”, then don’t worry. Just look at the pictures separately, because the Subaru Telescope has added a whole new dimension to a seasonal favorite – Stephen’s Quintet. Located in the constellation of Pegasus (RA 22 35 57.5 – Dec +33 57 36), this awesome little galaxy group also known as HIckson Compact Group 92 and Arp 319. In visual observation terms, there’s five – but only four are actually a compact group. The fifth is much closer…

While literally volumes could be written about this famous group, the focus of this article is on the latest observations done by the Subaru Telescope. Each time the “Quints” are observed, it would seem we get more and more information on them! By employing a variety of specialized filters with Subaru’s Prime Focus Camera (Suprime-Cam), the two above images reveal different types of star-formation activity between the closer galaxy – NGC7320 – and the more distant members. It captures Stephen’s Quintet in three dimensions.

So how is it done? Suprime-Cam has the capability of wide field imaging. By utilizing specialized filters, researchers can narrow the photographic process to specific goals. In this instance, they use narrowband filters to reveal star-forming regions within the grouping and their structures. These H-alpha filters are very specific – only allowing a particular wavelength of light to pass through – revealing the hydrogen emissions of starbirth. But here’s the tricky part. The images were taken with two different types of H-alpha filters – each one with a different recession velocity. With a setting of zero, we have an object which is moving away from the observer and close. The other has a greater recession velocity of 4200 miles (6,700 km) per second. This is an indicator of distant objects. For a color palette, red indicates the H-alpha emission lines while blue and green colors assigned to the images from the blue and red filters captured light so that the composite tricolor images aligned with human color perception in red, green, and blue.

When processed, we get the two different views of Stephen’s Quintet as seen above. Says the imaging team; “The image on the left shows the galaxies when the observers used the Ha filter with a recession velocity of 0 while the one on the right shows them when they used the Ha filter with a recession velocity of 4,200 miles per second. The left image shows Ha emissions that indicate an active star-forming region in the spiral arms of NGC7320 in the lower left quadrant but not in the other galaxies. The right image contrasts with the left and shows a region of H-alpha emissions in the upper three galaxies but none from NGC7320. Two (NGC7318A and NGC7318B) of the four galaxies are shedding gas because of a collision while a third (NGC7319) is crashing in, creating shock waves that trigger vigorous star formation.”

But that’s not all. In the figure below we can see the relationship of the galaxies. “Gas stripped from these three galaxies during galactic collisions is ionized by two mechanisms: shock waves and strong ultraviolet light emanating from the newborn stars.” reports the Subaru team. “This ionized gas emits bright light, which the H-alpha filter reveals. Thus the researchers believe that NGC7319 as well as NGC7318A/B are driving the star-forming regions in the Ha emitting region around NGC7318A/B.”

A diagram of the member galaxies of Stephan's Quintet. NGC7320 is a closer galaxy and has a recession velocity of 0. The remaining four are a group of more distant galaxies 300 million light years away. The researchers believe that the merging of NGC7318A/B and NGC7319's crashing into them are responsible for the active star formation regions in the Ha emitting region around NGC7318A/B.

But star-forming activity isn’t all you can derive from these images – they are also an indicator of distance. By exposing opposing recession velocities in the same image, observers are able to deduce where objects are located at different distances, yet close to each other. “The contrasting images show that NGC7320 is closer than the other galaxies, which show active star formation at a significantly higher recession velocity (4,200 miles per second) than NGC7320 (0).” explains the team. “NGC7320 is about 50 million light years away while the other four galaxies are about 300 million light years away. This explains the intriguing arrangement of the galaxies in Stephan’s Quintet.”

Now is a great time to observe this cool cluster of galaxies for yourself… Before the Moon interferes again!

Original Story Source: Subaru Telescope Press Release.