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

Globular Cluster M15 from Hubble – Credit: ESA, Hubble, NASA

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…

About 

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.

Comments on this entry are closed.

  • SJStar September 17, 2012, 5:43 AM

    Sigh. Oh dear, there are basic errors everywhere here.

    The stellar evolution ideas are plainly wrong. I.e. The clanger here is the “dead helium core.” What? Are white dwarf stars, the only method of “dead helium cores”, cannot be turned into Mira variables.

    As for;

    “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!

    Wow, this is very confusing. The reason why globular star cluster red giants stars last longer is they have a lesser mass. I.e. Ages are proportional to mass. Also the red giants are not on the main sequence!! They have actually evolved away from the main sequence. (80% of the star’s lifetime is on the main sequence). They the move left to right across the H-R diagram into the Red Giant Branch then on to the Asymptotic Giant Branch (AGB), to increase in size and luminosity.

    The reason in not because the stars in globular stars entered the main sequence at the same time, but is really because they are all of similar masses – similar to our Sun’s mass. Few of the stars in globulars are on the main sequence. c.0.7 to 0.8 solar mass stars, while the many of the rest have become red giants.

    High mass stars are never placed on the Main Sequence (and so NEVER exit the Main Sequence), but are in a different luminosity classes like giants (II and III) and supergiants (I), Many of the largest stars never reach the red giant phase but go supernova. I.e. SN 1987A was a blue giant, for example. They move across the HR Diagram not up!

    Another serious confusion is with the RA and Dec. of the objects. They are all over the place. I.e. (Right Ascension: 19 : 43.1 – Declination: +23 : 17) or (RA 20 34 24.00 Dec +28 17 ?0.0)

    Why not write this as (R.A. 20h 34.4m Dec. +28° 17′)
    with degrees as characters & #176; and & #8242;, without my space between the “& #” Negative declinations use the character & minus; I.e. − Simple.

    The statement;

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

    This is not true. (See the USNO page of “Earth’s Seasons 200-2020″)
    It is actually a range of date, so it can be the 22nd or 23rd, and there is no “universal date” (Do you mean universal time?, perhaps) [Really, the Autumnal Equinox can happen on other days of the week, too!]

    • IVAN3MAN_AT_LARGE September 17, 2012, 4:15 PM

      The stellar evolution ideas are plainly wrong. I.e. The clanger here is the “dead helium core.” What? For largish white dwarf stars they are “dead helium cores”. They cannot be turned into Mira variables.

      The only clanger dropped here is yours!

      Delta^2 Lyrae is a class M4II star, not a “largish white dwarf”, and it does, indeed, possess a “dead helium core” – the star’s outer shells are still fusing hydrogen into helium, while the core is inactive helium.

      The reason why globular star cluster’s red giants stars last longer is they have a lesser mass. I.e. Ages are proportional to mass.

      Tammy did not imply that red giants in globular clusters are as massive as other red giants like Betelgeuse and Antares.

      Also the red giants are not on the main sequence!! They have actually evolved away from the main sequence.

      *Sigh* (Jesus H. Christ on a bike!)

      Tammy did not imply that red giants are still on the main sequence.
      I would suggest that you read the article properly, check the facts (on Wikipedia or elsewhere), and fully comprehend it before criticizing it
      .
      As for “Saturday, September 22 – Today marks the universal date of Autumnal Equinox. Enjoy this ‘equal’ period of day and night!”, I presume (and I think most readers here do so as well) that Tammy was referring that date to this particular year.

      • SJStar September 17, 2012, 8:18 PM

        Let’s see. You, like Tammy, are obviously lost when it comes to stellar evolution theory.

        1) ALL stars, including M4II giants, have active cores that are nucleosynthesis.
        Only white dwarfs have inactive cores, where energy is generated by gravitational collapse rather than by fusion.
        Red dwarf stars are fully convective, and helium doesn’t is mixed in the star’s interior. Red giant burn their hydrogen in shells, which is more efficient at a particular depth. The so-called “helium core” contains a higher concentration of helium, but it still contains hydrogen. (The hydrogen converting to helium is inhibited, as the helium gets in the way.) However, the reaction rate is slower, but energy is still being produced there. (By probability, small amounts of helium and other elements can be fused too.)

        This core shrinks under gravitation, increasing the temperature, that in turn expands the star. If the density and temperature gets high enough, the helium can then be burnt into carbon, oxygen or nitrogen.

        My exact point was that the only Helium white dwarfs can be considered “dead helium cores”! What makes them dead is the end of nucleosynthesis and fusion. These cores are mostly formed by the intermixed hydrogen diffusing from the core out to the surface.

        • IVAN3MAN_AT_LARGE September 18, 2012, 12:48 AM

          Let’s see. You, like Tammy, are obviously lost when it comes to stellar evolution theory.

          Really? Well, Prof. James B. Kaler (University of Illinois), when referring to the M4II class star Delta-2 Lyrae, used the term “dead helium core” to describe its current state, and he also stated: “It may be preparing to become a much more obvious pulsating variable like Mira.”

          So, Mr. Know-It-All, is Prof. Kaler “obviously lost” as well?

          • SJStar September 18, 2012, 3:46 AM

            I have never claimed nor said that Delta-2 Lyrae would not turn into a Mira. I only said “dead white dwarfs” cannot turn into Miras. I.e. The star has expelled all there outer gas into space. The debate is on the interpretation of “dead helium cores”, which I have clearly shown are not a permanently dead as one might think. I made that perfectly crystal clear.

            To make this clear again.

            Again, I think you don’t understand what is happening. Kaler is using this terminology in a different context – ambiguously used by Tammy. Here he means the helium in inactive as it has neither the temperature or pressure to burn into carbon, oxygen and nitrogen. It is in comparison to the active hydrogen burning on the shell above it.

            He clearly says; http://stars.astro.illinois.edu/sow/star_intro.html

            “As their dead helium cores contract, heating and firing to fuse the helium to carbon and oxygen, the stars expand to approach the sizes of the orbits of the outer planets, becoming distended red “supergiants.”

            How can the Helium be dead if the core can be burnt if the temperature and pressure exceeds a certain limit?

            [When it does it is called the helium flash, several of which can occur, but this is short-lived.]

            Also the book “Stars: A Very Short Introduction
            By Andrew King, pg.50 (2012) describes; “This ‘dead’ helium core resembles a small star growing in mass…“, properly differentiating its meaning.

            The term ‘dead’ also has been used mainly to replace an older term, which describes the created helium ash sinking towards the core. I.e. The excellent pdf on stellar evolution is useful here, which also uses “helium ash.”

            If you dead your dead, but blow me down, we can also have resurrected helium too! (Matching your Jesus reference.)

            (The term is probably an in-joke, being like cremated ashes – based broadly on the traditional comparison that stars are comparable to the range of types of people. Frankly, it would be better to say ‘inert’ or even ‘resting’ IMO. I.e. It ain’t dead, it’s only resting!)

            A definition of a “dead star” are more typically described as white dwarfs. For example, in a Science Daily Article :Anomalous White Dwarfs: Largest Collection Of White Dwarfs Made Of Helium Discovered; 26th April 2009 describes;

            The stars are white dwarfs, a common type of dead star, but they are odd because they are made of helium rather than the usual carbon and oxygen. This is the first extensive sequence of helium-core white dwarfs to be observed in a globular cluster, a dense swarm of some of the oldest stars in our galaxy.

            Yet, better still, I actually explained the process properly, and yet you still think it smart without even bothering to understanding the origin of common terms!

            (Kaler is also probably doing this to sort out the plagiarists where terms are just inserted to catch out those using other ideas or works. Thanks for confirming that, BTW.)

          • IVAN3MAN_AT_LARGE September 18, 2012, 4:45 AM

            The term “dead” has many definitions, not just “no longer living; deprived of life” (sense #1); it also means (sense #11) “not moving or circulating; stagnant; stale”; or (sense #15) “lacking the customary activity; dull; inactive”; or (sense #17) “sudden or abrupt, as the complete stoppage of an action”; or (sense #18) “put out; extinguished”; et cetera.

            Therefore, you’re just being bloody pedantic!

          • SJStar September 18, 2012, 5:38 AM

            No I’m not being pedantic. You just have missed the central point here. It is important to explain what you exactly mean in science. A novice reading this might be easily be confused (it confused me), and core subjects like stellar evolution are centrally important. For example, it is a subject taught and examined in schools. Concepts, like the basic definition of the main sequence, when scrambled can lead to real misunderstandings. This is obvious here.

            I’m very pleased you got the point that the stellar evolution process is actually means inactive. I just wish that Tammy would take more effort with this kind of detail instead of carte-blanch rehashes from multiple sources, especially the often unreliable Wikipedia.

      • SJStar September 17, 2012, 9:05 PM

        2) I said; “The reason why globular star cluster’s red giants stars last longer is they have a lesser mass. I.e. Ages are proportional to mass.”

        Tammy did not imply that red giants in globular clusters are as massive as other red giants like Betelgeuse and Antares.

        Correct. No she didn’t. Tammy said nothing about massl!

        Clearly you have missed the point. Today’s globular cluster red giant stars had the original mass, when they were on the main sequence, of about 1.0 to 0.8 solar masses. The rate of their evolution is therefore about 10 to 13 billion years old and have aged into red giant stars.

        Large stars like Betelgeuse and Antares are about 15 and 12 solar masses, respectively. These stars are likely to last between 8 and 15 million years before ending their lives as supernovae.

        Logically, this explains the mass is the difference

        Yet Tammy statement instead explains;

        “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!”

        This reasoning does not explain or give the primary reason to the question. Rates of evolution is based on mass and not brightness or luminosity. I.e. The mass of stars stays fairly constant until the very end of their lives. Brightness and luminosity changes during the life time of the star depending on the changes in energy production in the core of the star.

        (In fact, the Luminosity Class I and II stars are Giants and Supergiants, and were never on the Main Sequence! Clearly Luminosity class V (5) stars are classed as Main Sequence stars!!)

        [Globular star clusters once also had large more massive stars too, but they had a shorter life span, and were extinguished.]

        3) As for sighing at;
        “Also the red giants are not on the main sequence!! They have actually evolved away from the main sequence.”

        The third way to say this;

        Stars begin their lives on the main sequence, spend 80% of their time there, before evolving away from the main sequence, to increase in size and luminosity and evolve into red giants along the red giant branch.
        Don’t believe me. See http://en.wikipedia.org/wiki/Red_giant and the HR Diagram on this page shows the line on the main sequence. The figure on http://en.wikipedia.org/wiki/Stellar_evolution (under chapter ‘Mid-sized stars’, shows five places across the H-R Diagram. Points 3 to 4 shows the stars on the main sequence, and the position of the red giants. Red giants are clearly not on the main sequence!!

      • SJStar September 17, 2012, 9:29 PM

        4) “As for “Saturday, September 22 – Today marks the universal date of Autumnal Equinox. Enjoy this ‘equal’ period of day and night!”, I presume (and I think most readers here do so as well) that Tammy was referring to that date for this particular year.”

        You presume wrongly. It is the imprecision that is the problem.

        Please pray tell what “universal date” actually mean?

        Sure it is a precise moment that happens all over the world at the same universal time *UT”), but the observed time varies from year to year and varies in local time across the world.

        (I.e. I did qualify it by saying;”Do you mean universal time, perhaps?”)

        Also depending where you live in the world, this date could be either 22nd or 23rd.

      • SJStar September 17, 2012, 9:40 PM

        As I read you reply I notice you continue to use words that are either sacrilegious or profane in some of your replies. While it doesn’t really bother me, it may offend some, it may bother others or children that might read it.

        You might be justifiably cross or angry at me or others but there is no excuse to use commonly unacceptable language like swearing or taking the Lord’s name in vain.

  • Aqua4U September 17, 2012, 5:09 PM

    Thanks Tamster… You always inspire me to take out my telescope to view the glories above! How’s about tying in some of the observations made at the ‘Star Party Hang Out’ in your review? The co-ordinates for objects viewed are not always given due to the ‘fast pace’ or limited time of the show? I like the idea of ‘newbies’ getting used to using co-ordinates…

    Yesterday I made/cut out a 3 inch secondary mirror for the 12 1/2″ Newt. I’m building. Ever cut glass? It’s trick, fur shore. The mirror blank I used I got way back in 1984 while working for a semiconductor company. One of the scientists ran a test in a vacuum deposition chamber by vaporizing aluminum on FLAT glass plates. He knew I was ‘into’ astronomy, so he gave me one of the test samples. It’s been holding up spider webs in my garage for years.. so… now I have a ‘test bench’ secondary. I cut the oval with a minor axis of 3″ and major axis of 4.246″, which gives me a 3″ secondary at the required 45 degrees. Now all I’ve got to do is set it up in my test bench….

    My main mirror was ground and polished by another scientist friend, back in the 70’s. He never built the scope he’d planned – babies and career got in the way….so I bought that mirror from him for $200 and HOPE he got it right! f 3.6 is kind of fast… so if it isn’t near perfectly shaped… uh ohhhh. So… testing, then I’ll send it out to be coated, IF everything checks out. Otherwise, I’ll have to refigure it… dzzzzzzz.

    • Aqua4U September 19, 2012, 5:32 PM

      Yesterday I mounted the uncoated main mirror into my scope. With the secondary I made and focuser with a typical eyepiece inserted, I finally have most of the weighting I need to balance this (ala) german equatorial mounted scope. All that’s left is to add the weight of a finder scope? I am attempting to make one today from a pair of el cheapo plastic 50mm Chinesean binoculars I bought at a garage sale several years ago. Those binocs NEVER focused properly.. so… here goes nothing! ~@: 0

      So far, I’ve spent about $300 US building this 12 1/2″ Newt. I COULD have saved a lot of time making it into a Dobson style mount but opted for the G.E. mount because I like the idea of possibly putting a mechanical clock drive on it later… tick-tock, tick-tock, tick-tock.

  • SJStar September 17, 2012, 10:45 PM

    Tammy says this about M15;

    Tonight we again visit the M15 … globular and learn more about the scale of the Universe – circa 1900.

    Q. When did you last visit M15?

    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.

    Fair enough.

    Such stars appear 15 magnitudes fainter than they would be if they were at an astronomically standardized distance.

    What astronomical standardised distance? (10 parsecs, but that isn’t mentioned in the text.) BTW, the term arcsec wasn’t used in 1900, but was suggested by a Professor Turner in 1913.

    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.

    What circular reasoning? (15 magnitude loss means nothing without a standardized distance. If you don’t know this state distance, then there cannot be a distance scale. This is not circular, it is plainly unknown!)

    Amazingly you then say;

    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.”

    Eh? The H-R Diagram didn’t appear until Hertzspung and Russell until around 1910, and even then, they didn’t have much knowledge of stellar luminosities except via trigonometric parallaxes. (M15 showed no parallax.) Also the first diagram was a colour-magnitude diagram, which has the visual magnitudes plotted against star colours (found by differences of star colour by measuring the magnitude difference between blue and red plates.)

    You then go on to explain as given in my earlier postings, the nature of the H-R DIagram in terms of luminosity, but don’t really explain anything stated above about M15. Both paragraphs are frankly disconnected.

    However, what is more confusing is that although M15 was one the first globular cluster to have its distance calculated (it is often the globular mentioned in textbook because of it), but you still don’t even mention the actual finally distance of M15!

    The answer of course is about 10 kiloparsecs (10 kpc.) or 10000 parsecs, but the text here makes no mention of this. Furthermore what has this to do with;

    – The Scale of the Universe in 1900?
    – The circular reasoning?
    – The connection / explanation between absolute magnitudes and the H-R Diagram (you never actually say but only imply it is something to do with distance, but also leave no answer.)
    – The explain it all away as having something to do with a mash of absolute magnitudes, differences between Antares and Betelgeuse galactic red giants and bright red giants in globulars, main sequences — all ending in a quip about some dwarf galaxy.

    It makes no sense to me, and I totally suspect, absolutely no sense to a observational novice in which this series is supposedly aimed.

    It is obvious this text has been cobbled together from many sources then condensed. It is the only plausible explanation I can think of.

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