Astronomy Cast Ep. 497: Update on Globular Clusters

Is it globular clusters or is it globeular clusters? It doesn’t matter, they’re awesome and we’re here to update you on them.

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Globular Clusters Might not be as Old as Astronomers Thought. Like, Billions of Years Younger

Globular clusters have been a source of fascination ever since astronomers first observed them in the 17th century. These spherical collections of stars are among the oldest known stars in the Universe, and can be found in the outer regions of most galaxies. Because of their age and the fact that almost all larger galaxies appear to have them, their role in galactic evolution has remained something of a mystery.

Previously, astronomers were of the opinion that globular clusters were some of the earliest stars to have formed in the Universe, roughly 13 billion years ago. However, new research has indicated that these clusters may actually be about 4 billion years younger, being roughly 9 billion years old. These findings may alter our understanding of how the Milky Way and other galaxies formed, and how the Universe itself came to be.

The study, titled “Reevaluating Old Stellar Populations“, recently appeared online and is being evaluated for publication in The Monthly Notices for the Royal Astronomical Society. The study was led by Dr. Elizabeth Stanway, an Associate Professor in the Astronomy group at the University of Warwick, UK, and was assisted by Dr. J.J. Eldridge, a Senior Lecturer at the University of Auckland, New Zealand.

Within larger galaxies, like the Milky Way, globular clusters are part of the galactic halo. Between 150 and 180 are estimated to be part of the Milky Way alone. Credit: ESO

For the sake of their study, Dr. Stanway and Dr. Eldridge developed a series of new research models designed to reconsider the evolution of stars. These models, known as Binary Population and Spectral Synthesis (BPASS) models, had previously proven effective in exploring the properties of young stellar populations within the Milky Way and throughout the Universe.

Using these same models, Dr. Stanway and Dr. Eldridge studied a sample of globular clusters in the Milky Way and nearby quiescent galaxies. They also took into account the details of binary star evolution within globular clusters and used them to explore the colors of light and spectra from old binary populations. In short, binary star system evolution consists of one star expanding into a giant while the gravitational force of the smaller star strips away the atmosphere of the giant.

What they found was that these binary systems were about 9 billion years old. Since these stars are thought to have formed at the same time as the globular clusters themselves, this demonstrated that globular clusters are not as old as other models have suggested. As Dr. Stanway said of the BPASS models she and Dr. Eldridge developed:

“Determining ages for stars has always depended on comparing observations to the models which encapsulate our understanding of how stars form and evolve. That understanding has changed over time, and we have been increasingly aware of the effects of stellar multiplicity – the interactions between stars and their binary and tertiary companions.

An artist’s impression of a millisecond pulsar and its companion. The presence of binaries in globular clusters is a good means of providing age estimates of those clusters. Credit: ESA & Francesco Ferraro (Bologna Astronomical Observatory)

If correct, this study could open up new pathways of research into how massive galaxies and their stars are formed. However, Dr. Stanway admits that much work still lies ahead, which includes looking at nearby star systems where individual stars can be resolved – rather than considering the integrated light of a cluster. Nevertheless, the study could have immense significant for our understanding of how and when galaxies in our Universe formed.

“If true, it changes our picture of the early stages of galaxy evolution and where the stars that have ended up in today’s massive galaxies, such as the Milky Way, may have formed,” she said. “We aim to follow up this research in the future, exploring both improvements in modelling and the observable predictions which arise from them.”

An integral part of cosmology is understanding when the Universe came to be the way it is, not just how. By determining how old globular clusters are, astronomers will have another crucial piece of the puzzle as to how and when the earliest galaxies formed. And these, combined with observations that look to the earliest epochs of the Universe, could just yield a complete model of cosmology.

Further Reading: University of Warwick, arXiv

A Black Hole is Pushing the Stars Around in this Globular Cluster

Astronomers have been fascinated with globular clusters ever since they were first observed in 17th century. These spherical collections of stars are among the oldest known stellar systems in the Universe, dating back to the early Universe when galaxies were just beginning to grow and evolve. Such clusters orbit the centers of most galaxies, with over 150 known to belong to the Milky Way alone.

One of these clusters is known as NGC 3201, a cluster located about 16,300 light years away in the southern constellation of Vela. Using the ESO’s Very Large Telescope (VLT) at the Paranal Observatory in Chile, a team of astronomers recently studied this cluster and noticed something very interesting. According to the study they released, this cluster appears to have a black hole embedded in it.

The study appeared in the Monthly Notices of the Royal Astronomical Society under the title “A detached stellar-mass black hole candidate in the globular cluster NGC 3201“. The study was led by Benjamin Giesers of the Georg-August-University of Göttingen and included members from Liverpool John Moores University, Queen Mary University of London, the Leiden Observatory, the Institute of Astrophysics and Space Sciences, ETH Zurich, and the Leibniz Institute for Astrophysics Potsdam (AIP).

For the sake of their study, the team relied on the Multi Unit Spectroscopic Explorer (MUSE) instrument on the VLT to observe NGC 3201. This instrument is unique because of the way it allows astronomers to measure the motions of thousands of far away stars simultaneously. In the course of their observations, the team found that one of the cluster’s stars was being flung around at speeds of several hundred kilometers an hour and with a period of 167 days.

As Giesers explained in an ESO press release:

It was orbiting something that was completely invisible, which had a mass more than four times the Sun — this could only be a black hole! The first one found in a globular cluster by directly observing its gravitational pull.

This finding was rather unexpected, and constitutes the first time that astronomers have been able to detect an inactive black hole at the heart of a globular cluster – meaning that it is not currently accreting matter or surrounded by a glowing disc of gas. They were also able to estimate the black hole’s mass by measuring the movements of the star around it and thus extrapolating its enormous gravitational pull.

From its observed properties, the team determined that the rapidly-moving star is about 0.8 times the mass of our Sun and the mass of its black hole counterpart to be around 4.36 times the Sun’s mass. This put’s it in the “stellar-mass black hole” category, which are stars that exceeds the maximum mass allowance of a neutron star, but are smaller than supermassive black holes (SMBHs) – which exist at the centers of most galaxies.

This finding is highly significant, and not just because it was the first time that astronomers have observed a stellar-mass black hole in a globular cluster. In addition, it confirms what scientists have been suspecting for a few years now, thanks to recent radio and x-ray studies of globular clusters and the detection of gravity wave signals. Basically, it indicates that black holes are more common in globular clusters than previously thought.

“Until recently, it was assumed that almost all black holes would disappear from globular clusters after a short time and that systems like this should not even exist!” said Giesers. “But clearly this is not the case – our discovery is the first direct detection of the gravitational effects of a stellar-mass black hole in a globular cluster. This finding helps in understanding the formation of globular clusters and the evolution of black holes and binary systems – vital in the context of understanding gravitational wave sources.”

This find was also significant given that the relationship between black holes and globular clusters remains a mysterious, but highly important one. Due to their high masses, compact volumes, and great ages, astronomers believe that clusters have produced a large number of stellar-mass black holes over the course of the Universe’s history. This discovery could therefore tell us much about the formation of globular clusters, black holes, and the origins of gravitational wave events.

And be sure to enjoy this ESO podcast explaining the recent discovery:

Further Reading: ESO, MNRAS

Messier 12 (M12) – The NGC 6118 Globular Cluster

Welcome back to another edition of Messier Monday! Today, we continue in our tribute to Tammy Plotner with a look at the M12 globular cluster!

In the 18th century, French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky which he originally mistook for comets. After realizing his mistake, he began compiling a list of these objects in order to ensure that other astronomers did not make the same error. In time, this list would include 100 objects, and would come to be known as the Messier Catalog to posterity.

One the many objects included in this is Messier 12 (aka. M12 or NGC 6218), a globular cluster located in the Ophiuchus constellation some 15,700 light-years from Earth.  M12 is positioned just 3° from the cluster M10, and the two are among the brightest of the seven Messier globulars located in Ophiuchus. It is also interesting to note that M12 is approaching our Solar System at a velocity of 16 km/s.

Continue reading “Messier 12 (M12) – The NGC 6118 Globular Cluster”

NGC 2419: Wayward Globular or the Milky Way’s Own?

Turns out, we may not know our extragalactic neighbors as well as we thought.

One of the promises held forth with the purchase of our first GoTo telescope way back in the late 1990s was the ability to quickly and easily hunt down ever fainter deep sky fuzzies. No more juggling star charts and red headlamps, no more star-hopping. Heck, it was fun to just aim the scope at a favorable target field, hit ‘identify,’ and see what it turned up.

One of our more interesting ‘discoveries’ on these expeditions was NGC 2419, a globular cluster that my AstroMaster GoTo controller (featuring a 10K memory database!) triumphantly announced was an ‘Intergalactic Wanderer…’

Or is it? The case for NGC 2419 as a lonely globular wandering the cosmic void between the galaxies is a romantic and intriguing notion, and one you see repeated around the echo chamber that is the modern web. First observed by Sir William Herschel in 1788 and re-observed by his son John in 1833, the debate has swung back and forth as to whether NGC 2419 is a true globular or—as has been also suggested of the magnificent southern sky cluster Omega Centauri—the remnant of a dwarf spheroidal galaxy torn apart by our Milky Way. Lord Rosse also observed NGC 2419 with the 72-inch Leviathan of Parsonstown, and Harlow Shapley made a distance estimate of about 163,000 light years to NGC 2419 in 1922.

Created by author
The relative distances of NGC 2419, the LMC, SMC and M31.  Created by author using NASA graphics.

Today, we know that NGC 2419 is about 270,000 light years from the Sun, and about 300,000 light years from the core of our galaxy.  Think of this: we actually see NGC 2419 as it appeared back in the middle of the Pleistocene Epoch, a time when modern homo sapiens were still the new hipsters on the evolutionary scene of life on Earth.  What’s more, photometric studies over the past decade suggest there is a true gravitational link between NGC 2419 and the Milky Way. This would mean at its current distance, NGC 2419 would orbit our galaxy once every 3 billion years, about 75% the age of the Earth itself.

Image credit:
NGC 2419 and the nearby +7 magnitude star HIP 37133. Image credit and copyright: Joseph Brimacombe

This hands down makes NGC 2419 the distant of the more than 150 globular clusters known to orbit our galaxy.

At an apparent magnitude of +9 and 6 arc minutes in size, NGC 2419 occupies an area of the sky otherwise devoid of globulars. Most tend to lie towards the galactic core as seen from our solar vantage point, and in fact, there are no bright globulars within 60 degrees of NGC 2419. The cluster sits 7 degrees north of the bright star Castor just across the border of Gemini in the constellation of the Lynx at Right Ascension 7 Hours, 38 minutes and 9 seconds and declination +38 degrees, 52 minutes and 55 seconds.  Mid-January is the best time to spy NGC 2419 when it sits roughly opposite to the Sun , though June still sees the cluster 20 degrees above the western horizon at dusk before solar conjunction in mid-July.

Image credit: Starry Night Education software
The location of NGC 2419 in the night sky. Image credit: Starry Night Education software

We know globular clusters (say ‘globe’ -ular, not “glob’ -ular)  are some of the most ancient structures in the universe due to their abundance of metal poor, first generation stars. In fact, it was a major mystery up until about a decade ago as to just how these clusters could appear to be older than the universe they inhabit. Today, we know that NGC 2419 is about 12.3 billion years old, and we’ve refined the age of the Universe as per data from the Planck spacecraft down to 13.73 (+/-0.12) billion years.

What would the skies look like from a planet inside NGC 2419? Well, in addition to the swarm of hundreds of thousands of nearby stars, the Milky Way galaxy itself would be a conspicuous object extending about 30 degrees across and shining at magnitude -2. Move NGC 2419 up to 10 parsecs distant, and it would rival the brightness of our First Quarter Moon and be visible in the daytime shining at magnitude -9.5.

Image Credit; Starry Night Education Software
The view of the Milky Way galaxy as seen from NGC 2419. Image Credit; Starry Night Education Software

And ironically, another 2007 study has suggested that the relative velocity of Large and Small Magellanic Clouds suggest that they may not be bound to our galaxy, but are instead first time visitors passing by.

And speaking of passing by, yet another study suggests that the Milky Way and the Andromeda galaxy set on a collision course billions of years hence may be in contact… now.

Image credit: Starry Night Education software
The view of the Andromeda galaxy as seen from NGC 2419. Image credit: Starry Night Education software

Mind not blown yet?

A 2014 study looking at extragalactic background light during a mission known as CIBER suggests that there may actually be more stars wandering the universe than are bound to galaxies…

But that’s enough paradigm-shifting for one day. Be sure to check out NGC 2419 and friends and remember, everything you learned about the universe as a kid, is likely to be false.

Can Stars Collide?

Imagine a really bad day. Perhaps you’re imagining a day where the Sun crashes into another star, destroying most of the Solar System.

No? Well then, even in your imagination things aren’t so bad… It’s all just matter of perspective.

Fortunately for us, we live in out the boring suburbs of the Milky Way. Out here, distances between stars are so vast that collisions are incredibly rare. There are places in the Milky Way where stars are crowded more densely, like globular clusters, and we get to see the aftermath of these collisions. These clusters are ancient spherical structures that can contain hundreds of thousands of stars, all of which formed together, shortly after the Big Bang.

Within one of these clusters, stars average about a light year apart, and at their core, they can get as close to one another as the radius of our Solar System. With all these stars buzzing around for billions of years, you can imagine they’ve gotten up to some serious mischief.

Within globular clusters there are these mysterious blue straggler stars. They’re large hot stars, and if they had formed with the rest of the cluster, they would have detonated as supernovae billions of years ago. So scientists figure that they must have formed recently.

How? Astronomers think they’re the result of a stellar collision. Perhaps a binary pair of stars merged, or maybe two stars smashed into one another.

Professor Mark Morris of the University of California at Los Angeles in the Department of Physics and Astronomy helps to explain this idea.

“When you see two stars colliding with each other, it depends on how fast they’re moving. If they’re moving at speeds like we see at the center of our galaxy, then the collision is extremely violent. If it’s a head-on collision, the stars get completely splashed to the far corners of the galaxy. If they’re merging at slower velocities than we see at our neck of the woods in our galaxy, then stars are more happy to merge with us and coalesce into one single, more massive object.”

There’s another place in the Milky Way where you’ve got a dense collection of stars, racing around at breakneck speeds… near the supermassive black hole at the center of the galaxy.

This monster black hole contains the mass of 4 million times the Sun, and dominates the region around the center of the Milky Way.

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech
Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech

“The core of the Milky Way is one of those places where you find the extremes of nature. The density of stars there is higher than anywhere else in the galaxy,”Professor Morris continues. “Overall, in the center of our galaxy on scales of hundreds of light years, there is much more gas present than anywhere else in the galaxy. The magnetic field is stronger there than anywhere else in the galaxy, and it has it’s own geometry there. So it’s an unusual place, an energetic place, a violent place, because everything else is moving so much faster there than you see elsewhere.”

“We study the stars in the immediate vicinity of the black hole, and we find that there’s not as many stars as one might have expected, and one of the explanations for that is that stars collide with each other and either eliminate one another or merge, and two stars become one, and both of those processes are probably occurring.”

Stars whip around it, like comets dart around our Sun, and interactions are commonplace.

There’s another scenario that can crash stars together.

The Milky Way mostly has multiple star systems. Several stars can be orbiting a common center of gravity. Many are great distances, but some can have orbits tighter than the planets around our Sun.

When one star reaches the end of its life, expanding into a red giant, It can consume its binary partner. The consumed star then strips away 90% of the mass of the red giant, leaving behind a rapidly pulsating remnant.

What about when galaxies collide? That sounds like a recipe for mayhem.
Surprisingly, not so much.

“That’s actually a very interesting question, because if you imagine two galaxies colliding, you’d imagine that to be an exceptionally violent event,’ Professor Morris explains. “But in fact, the stars in those two galaxies are relatively unaffected. The number of stars that will collide when two galaxies collide is possibly counted on the fingers of one or two hands. Stars are so few and far between that they just aren’t going to meet each other with any significance in a field like that.”

Galaxy mergers, such as the Mice Galaxies will be part of Galaxy Zoo's newest project.  Credit: Hubble Space Telescope
The Mice galaxies merging. Credit: Hubble Space Telescope

“What you see when you see two galaxies collide, however, on the large scale, is that the tidal forces of the two galaxies will rip each of the galaxies apart in terms of what it will look like. Streams of stars will be strewn out in various directions depending on the precise history of the interaction between the two galaxies. And so, eventually over time, the galaxies will merge, the whole configuration of stars will settle down into something that looks unlike either of the two initially colliding galaxies. Perhaps something more spheroidal or spherical, and it might look more like an elliptical galaxy than the spiral galaxy that these two galaxies now are.”

Currently, we’re on a collision course with the Andromeda Galaxy, and it’s expected we’ll smash into it in about 4 billion years. The gas and dust will collide and pile up, igniting an era of furious star formation. But the stars themselves? They’ll barely notice. The stars in the two galaxies will just streak past each other, like a swarm of angry bees.

Phew.

So, good news! When you’re imagining a worse day, you won’t have to worry about our Sun colliding with another star. We’re going to be safe and sound for billions of years. But if you live in a globular cluster or near the center of the galaxy, you might want to check out some property here in the burbs.

Thanks to Professor Mark Morris at UCLA – visit their Physics and Astronomy program homepage here.

Weekly Space Hangout – September 13, 2013: Voyager is Out, LADEE Launches (a Frog), Asteroid 324 Bamberga

Once again, we have gathered together the forces of space journalism to report on the big news stories of the week. And there were lots of big stories indeed, with the launch of NASA’s LADEE mission to the Moon, and the awesome fact that Voyager 1 has totally left the Solar System.

Host: Fraser Cain

Journalists: Amy Shira Teitel, Nicole Gugliucci, Matthew Francis, David Dickinson, Nancy Atkinson

Frog Launches with LADEE
LADEE Launch Trajectory
Asteroid 334’s Close Approach
Voyager Has Left the Heliosphere
New Comet Lovejoy Discovered
Lots of Globular Clusters

We record the Weekly Space Hangout every Friday at 12 pm Pacific / 3 pm Eastern as a live Google+ Hangout on Air. You can watch the show from right here on Universe Today, or on our YouTube channel.

Beautiful Star Cluster Looks Surprisingly Youthful

This view of the globular cluster NGC 6362 was captured by the Wide Field Imager attached to the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile. Credit: ESO/J. Emerson/VISTA. Acknowledgment: Cambridge Astronomical Survey Unit

Past observations of globular star clusters have revealed that they are some of the oldest objects in the Universe, with most of the stars originating around the same time — some are more than 10 billion years old. And this new image of NGC 6362, a ball of stars found in the constellation of Ara, definitely shows its age, with many yellowish stars in the cluster that have already run through much of their lives and become red giant stars. But astronomers are seeing some curious stellar activities in this cluster that appears to indicate younger, bluer stars are part of the mix, too.

So how can this be, since all the stars in a cluster formed at the same time from the same cloud of gas?

NGC 6362 is home to many blue stragglers — old stars that succeed in passing for a younger age. Blue stragglers are bluer and more luminous — and hence more massive — than they should be after ten billion years of stellar evolution. Blue stars are hot and consume their fuel quickly, so if these stars had formed about ten billion years ago, then they should have fizzled out long ago. How did they survive?

Right now astronomers have two main theories about blue stragglers and how they maintain their youthful appearance: stars colliding and merging, and a transfer of material between two companion stars. The basic idea behind both of these options is that the stars were not born as big as we see them today, but that they received an injection of extra material at some point during their lifetimes and this then gave them a new lease of life.

This new image shows the entire cluster against a rich background of the carpet of stars in the Milky Way. It can be easily seen by amateur astronomers with a small telescope.

This video zooms into the cluster, starting with views from the La Silla Observatory and ending with a detailed view of the center from the Hubble Space Telescope:

Source: ESO

Weekly SkyWatcher’s Forecast – September 17-23, 2012

Greetings, fellow SkyWatchers! This looks like a great week to take in some galactic star clusters and enjoy the Andromeda Galaxy! Some lucky viewers are in for a Mars occultation event and everyone wins with a meteor shower. What’s that, you say? Darn right. This week is also the time of the Autumnal Equinox! When ever you’re ready to learn more, just meet me in the back yard…

Monday, September 17 – Today in 1789, William Herschel discovered Saturn’s moon Mimas.

Tonight we’ll hunt with the “Fox” as we head to Vulpecula to try two more open star cluster studies. The first can be done easily with large binoculars or a low power scope. It’s a rich beauty that lies in the constellation of Vulpecula, but is more easily found by moving around 3 degrees southeast of Beta Cygni.

Known as Stock 1, this stellar swarm contains around 50 or so members of varying magnitudes that you will return to often. With a visual magnitude of near 5, loose associations of stars – like Stock clusters – are the subject of recent research. The latest information indicates that the members of this cluster are truly associated with one another.

A little more than a degree to the northeast is NGC 6815 (Right Ascension:19 : 40.9 – Declination: +26 : 51). While this slightly more compressed open cluster has no real status amongst deep sky objects, it is another one to add to your collection of things to do and see!

Tuesday, September 18 – Tonight we’ll start with an asterism known as the “Coat Hanger,” but it is also known as Brocchi’s Cluster, or Collinder 399. Let the colorful double star Beta Cygni – Albireo – be your guide as you move about 4 degrees to its south-southwest. You will know this cluster when you see it, because it really does look like a coat hanger! Enjoy its red stars.

First discovered by Al Sufi in 964 AD, this 3.5 magnitude collection of stars was again recorded by Hodierna. Thanks to its expansive size of more than 60 arc minutes, it escaped the catalogues of both Messier and Herschel. Only around a half dozen stars share the same proper motion, which may make it a cluster much like the Pleiades, but studies suggest it is merely an asterism…but one with two binary stars at its heart.
And for larger scopes? Fade east to the last prominent star in the cluster and power up. NGC 6802 (Right Ascension: 19 : 30.6 – Declination: +20 : 16) awaits you! At near magnitude 9, Herschel VI.14 is a well compressed open cluster of faint members. The subject of ongoing research in stellar evolution, this 100,000 year old cluster is on many observing challenge lists!

Wednesday, September 19 – On this day in 1848, William Boyd was watching Saturn – and discovered its moon Hyperion. On this date a moon will be on everyone’s mind as our Moon occults Mars (Pacific, South America, SW Atlantic). Be sure to check information such as the International Occultation Timing Assoication (IOTA) for specific details in your area. Even if you aren’t in a position to catch the occultation, it will still make a splendid scene! Also today in 1988, Israel launched its first satellite. How long has it been since you’ve watched an ISS pass or an iridium flare? Both are terrific events that don’t require any special equipment to be seen. Be sure to check with Heavens Above for accurate times and passes in your location and enjoy!

Tonight we again visit the M15 (Right Ascension: 21 : 30.0 – Declination: +12 : 10) globular and learn more about the scale of the Universe – circa 1900. On a decent night, a modest telescope will resolve about a dozen 13th magnitude stars outside M15?s core region. Most of these stars are red giants with absolute magnitudes of -2. Such stars appear 15 magnitudes fainter than they would be if they were at an astronomically standardized distance. Based on this 15 magnitude loss in intensity, we should be able to figure out how far away M15 is, but this is circular reasoning. In the early 1900s, astronomers didn’t know that the brightest stars in M15 were absolute magnitude -2. They first needed to know how far away the globular was to make sense of that.

Here’s where the H-R diagram helps out.

The most massive and swollen red giants (those nearing the end of their lives such as Betelgeuse and Antares) can be as luminous as absolute magnitude -6, but you can’t assume that the brightest red giants in a globular cluster are as bright as Antares and Betelgeuse. Why? Because we later discovered that all stars in a globular cluster entered the main sequence about the same time – some 12 billion years ago. Meanwhile, the very brightest ones – the Denebs – are no longer around. They exited the main sequence, became red giants and exploded a long, time ago, and possibly in a dwarf galaxy far, far away!

Now let’s take a a stellar tour of Lyra! First we’ll look at a double which has a close separation – Epsilon Lyrae. Known to most of us as the “Double Double,” look about a finger width northeast of Vega. Even the slightest optical aid will reveal this tiny star as a pair, but the real treat is with a telescope – for each component is a double star! Both sets of stars appear as primarily white and both are very close to each other in magnitude. What is the lowest power that you can use to split them?

Now let’s head for the northeast corner of the little parallelogram that is part of Lyra for easy unaided eye and binocular double Delta 1 and 2 Lyrae.

The westernmost Delta 1 is about 1100 light-years away and is a class B dwarf, but take a closer look at brighter Delta 2. This M-class giant is only 900 light-years away. Perhaps 75 million years ago, it, too, was a B class star, but it now has a dead helium core and it keeps on growing. While it is now a slight variable, it may in the future become a Mira-type. A closer look will show that it also has a true binary system nearby – a tightly matched 11th magnitude system. Oddly enough they are the same distance away as Delta-2 and are believed to be physically related.

Thursday, September 20 – Now let the Moon head west, because on this night in 1948, the 48? Schmidt telescope at Mt. Palomar was busy taking pictures. The first photographic plate was being exposed on a galaxy by the same man who ground and polished the corrector plate for this scope – Hendricks. His object of choice was reproduced as panel 18 in the Hubble Atlas of Galaxies and tonight we’ll join his vision as we take a look at the fantastic M31 – the Andromeda Galaxy.

Seasoned amateur astronomers can literally point to the sky and show you the location of M31 (Right Ascension: 0 : 42.7 – Declination: +41 : 16), but perhaps you have never tried. Believe it or not, this is an easy galaxy to spot even under the moonlight. Simply identify the large diamond-shaped pattern of stars that is the “Great Square of Pegasus.” The northernmost star is Alpha, and it is here we will begin our hop. Stay with the north chain of stars and look four finger-widths away for an easily seen star. The next along the chain is about three finger-widths away… And we’re almost there. Two more finger-widths to the north and you will see a dimmer star that looks like it has something smudgy nearby. Point your binoculars there, because that’s no cloud – it’s the Andromeda Galaxy!

Friday, September 21 – And what was Sir William Herschel doing on this date a couple of centuries ago? You can bet he was out telescoping; and his discoveries on this night were many. How about if we take a look at two logged on September 21 which made the Herschel “400? list?

Our first stop is northern Cygnus for NGC 7086 (RA 21 30 30 Dec +51 35 00). Located on the galactic equator about five degrees west of Beta Cephei, our target is an open cluster. At magnitude 8.4, this loose collection will be difficult for the smaller scope, and show as not much more than an arrow-like asterism. However, larger scopes will be able to resolve many more stars, arrayed in long loops and chains around the brighter members. Although it’s sparse, NGC 7086 has been studied for metal abundance, galactic distance, membership richness, and its luminosity function. Be sure to mark your notes for H VI.32, logged by Herschel in 1788.

Now hop on over to Andromeda for NGC 752 (RA 01 57 41 Dec +37 47 06). You’ll find it just a few degrees south of Gamma and in the field north of star 56. Located 1300 light-years away, there’s a strong possibility this cluster was noted first by Hodierna before being cataloged by Herschel on this night (1786). At near magnitude 5, this “400? object is both large and bright enough to be seen in binoculars or small telescopes, and people have often wondered why Messier did not discover it. The star-studded field containing about 70 members of various magnitudes belong to H VII.32 – a very old cluster which has more recently been studied for its metallicity and the variations in the magnetic fields of its members. Enjoy them both tonight! Sir William did…

Saturday, September 22 – Today marks the universal date of Autumnal Equinox. Enjoy this “equal” period of day and night!

Tonight we’ll return again to Vulpecula – but with a different goal in mind. What we’re after requires dark skies – but can be seen in both binoculars and a small telescope. Once you’ve found Alpha, begin about two fingerwidths southeast and right on the galactic equator you’ll find NGC 6823 (Right Ascension: 19 : 43.1 – Declination: +23 : 18).

The first thing you will note is a fairly large, somewhat concentrated magnitude 7 open cluster. Resolved in larger telescopes, the viewer may note these stars are the hot, blue/white variety. For good reason. NGC 6823 only formed about 2 billion years ago. Although it is some 6000 light-years away and occupies around 50 light-years of space, it’s sharing the field with something more – a very large emission/reflection nebula, NGC 6820 (Right Ascension: 19 : 43.1 – Declination: +23 : 17).

In the outer reaches of the star cluster, new stars are being formed in masses of gas and dust as hot radiation is shed from the brightest of the stellar members of this pair. Fueled by emission, NGC 6820 isn’t always an easy visual object – it is faint and covers almost four times as much area as the cluster. But trace the edges very carefully, since the borders are much more illuminated than the region of the central cluster. Take the time to really observe this one! Its processes are very much like those of the “Trapezium” area in the Orion nebula. Be sure to mark your observing notes. NGC 6823 is Herschel VII.18 and NGC 6820 is also known as Marth 401!

Now we’re off to a spectacular open cluster – NGC 6940. At close to magnitude 6, you’ll find this unsung symphony of stars around three fingerwidths southwest of Epsilon Cygni (RA 20 34 24.00 Dec +28 17 -0.0).

Discovered by Sir William Herschel on Oct 15, 1784, and logged as H VIII.23, this intermediate aged galactic cluster will blow your mind in larger aperture. Visible in binoculars, as size increases the field explodes into about 100 stars in a highly compressed, rich cloud. Although it is not an often visited cluster, it is part of many observing challenge lists. Use low power to get the full effect of this stunning starfield!

Sunday, September 23 – On this day in 1846, Johann Galle of the Berlin Observatory makes a visual discovery. While at the telescope, Galle sees and identifies the planet Neptune for the first time in history. On this day in 1962, the prime time cartoon “The Jetsons” premiered. Think of all the technology this inspired!

Rather than doing lunar work tonight, why not wait until the Moon has westered and have an “Autumn Planetary Marathon”? Start easy with M57 between Gamma and Beta Lyrae. Head north-northwest to the “Cat’s Eye” (NGC 6543) roughly between Delta and Zeta Draconis – you’ll need your charts for this one! Now southwest to the “Blinking Planetary” (NGC 6543) – found less than three degrees east-southeast of Iota Cygni. Continue east-southeast a little less than 6 degrees past Deneb to the “Box Planetary” – NGC 7027. Now on to the brightest of the ten – M27. The “Dumbbell Nebula” is located a little more than 3 degrees north of Gamma Sagittae. Now drop two hand spans south to the “Little Gem” (NGC 6818) – around 7 degrees northeast of Rho Sagittarii.

One hand span east of the “Little Gem” leads you toward the “Saturn Nebula” in Aquarius – a little more than a degree west of Nu. Now it’s a huge jump of more than two hand spans west-northwest to tiny NGC 6572 – located around two finger-widths south-southeast of 72 Ophiuchi. Continue on to compact NGC 6790 a finger-width south of Delta Aquilae. Did you find them all? Well, if the “Cat’s Eye” is the toughest to locate, then NGC 6790 is the hardest to identify. Good going! But don’t stop now… Two hand spans west-northwest leads to NGC 6210 – best located using pointer stars Gamma and Beta Herculis. Excellent work!

Ready for the finale? Now, kick back… relax… and watch the Alpha Aurigid meteor shower. Face northeast and look for the radiant near Capella. The fall rate is around 12 per hour, and they are fast and leave trails!

Until next week? Wishing you clear skies…