Sunday, January 26, 2014
More Stellar Fingerprints
Unk doesn't always live up to his New Year’s resolutions. At least not right away. The one
about giving up the dadburned cigarettes took dern near a decade to implement
way back when. I am off to a pretty good start with 2014’s Big Resolution, though, “Get out and observe at least once a week, weather
permitting.”
As y’all may
know, I can do very little amateur astronomy of any kind from home. An
occasional look at the Moon from the porch or my annual Christmas Eve peep at
M42 is about it. Too many lights, and, worse, too many trees, huge old oak trees that block the sky in every direction. If I want to see pea turkey, I have to
get to the club dark site.
When I was
working 12 hours a day five (or more) days a week, that was a problem. The best
I could do was a couple of nights a month. I worked a lot of weekends toward
the end of my engineering gig, and by the time I got home I was often too tired
to think about loading up a mess of gear and battling traffic, even for some
blessed hours under the stars. That’s over, now. Since I am retired (well,
semi-retired), there is nothing to keep me from visiting the Possum Swamp
Astronomical Society dark site at least
weekly. Other than the cotton-picking weather, that is.
So it was
that I decided to head out last Saturday evening. The weather was perfect. Only
buzzing bug in the butter? There would be a near full Moon in the sky a couple
of hours after sundown. That was OK, I’d find something to do. I could shoot Jupiter, of course, but I didn't think the
seeing would cooperate enough for that to be worth fooling with. Well, then, it
sounded like an RSpec night.
As I wrote a
couple of weeks back, I’ve begun playing around with spectroscopy using Tom Field's RSpec
software and Robin Leadbeater's Star Analyser diffraction
grating. The grating turns my humble little ZWO planet cam into a spectrograph.
A low-resolution one, sure, but one capable of showing a surprising amount of
detail in stellar spectra, nevertheless. The Moon wouldn’t do a thing to
prevent me from imaging stellar spectra, but seeing was another matter. The consarned Clear Sky Clock (Chart) forecast seeing to be putrid at best. Still, I figgered
giving it a go would be more fun than sitting home watching reruns of Wonder Woman on the cable TV.
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| According to The Cat, he did all the work... |
At 3:45 p.m.
it was time to load up the good, old Toyota, Miss Van Pelt, for the journey
west. What was different from last week? The telescope. Last time, the goal was
lunar and planetary imaging, and I thought my older C8, Celeste, an Ultima 8
OTA, was a better bet than the Edge 800. The reason being the older scope is
set up for a JMI Motofocus, which I figgered might make it easier to focus the
Moon and Jupiter. Turned out not to be the case. In the eight months I’ve had
the new SCT, I’ve become proficient at manual focusing again. I may set the
Edge 800 up for Motofocus one of these days, but I am not missing it too much yet.
I did miss
having Mrs. Peel on the observing field with me last week, no denying it. One big
reason for that, I must admit, is that she is just so doggone pretty and all with her slightly
greenish Takahashi-white tube. I’ve loved orange C8s and black C8s and silver
C8s, but for me white is still the color a telescope tube ought to be. Guess I’ve never forgot the look of the Cave and Unitron tubes of my youth. Appearance ain’t
everything, of course, and there’s more to Emma than just that. Optically this
is the best C8 I have ever owned with the best star test.
“What makes
an Edge different from a regular C8, anyhow, Unk? And how is it different from
Meade’s ACF? I’m confused.” Well, of course you are enthused, Skeezix. Oh, you’re cornfused are you? Well I can
edumacate you about the new SCTs in short order.
Meade’s ACF optics
got there first, coming ‘round about eight years ago in the form of the RCX
SCTs. The RCXs’ optics were different. In addition to having focal ratios of
f/8, the basic optical design was changed. Instead of using a spherical or near
spherical secondary mirror, the RCX used one that was a parabola. The goal was
to reduce coma, which is one of the two things that make stars at the edge of
an SCT’s field look more like comets than stars. An f/10 SCT has coma
equivalent to an f/6 Newtonian. Not bad, in other words, but there.
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| Mrs. Peel... |
As you may
know, the RCX was plagued by Meade missteps, starting with spurious claims,
including that the telescope was some kind of Ritchey Chretien design and that
the secondary was a hyperbola, and ending with horrendous quality control problems.
Still, the idea of a reduced coma SCT was a good one, and the basic design, an
aplantic SCT, not an r/c, was a sound
one. It has lived on at Meade in the form of the f/10 ACF (“Advanced Coma
Free”) SCTs and the new f/8 LX850s and 600s.
As has been
the case for over 30 years, when one SCT maker does something, the other
follows suit; that is the telescope arms race. Celestron was at this time
probably better positioned to respond than Meade would have been if the
situation were reversed. While Meade (who was bought out by the Chinese last
year) was struggling financially, Celestron, who’ve been owned by the Chinese
firm Synta for almost a decade, seemed to be doing well.
They were
certainly doing well enough to one-up the Meadesters. It wasn’t long before Celestron
announced the Edge series of Schmidt Cassegrains. Not only would these
telescopes, which included 8, 9.25, 11, and 14-inch OTAs, correct for coma,
they would, additionally, flatten the naturally curved SCT field, taking the
final step to fix Schmidt Cassegrain edge-of-field performance.
Celestron
took an entirely different path to an improved SCT than Meade. The Edge’s basic
design is almost unchanged. The back-focus distance, the distance from the rear
port to the focal plane been altered slightly, but that is it. To fix coma and
curvature, Celestron incorporated a two-element optical corrector in the baffle
tube. And, though it took them a while to do it, the company also introduced
sophisticated add-on focal reducers for the Edges to bring the f/10 scopes down
to f/7 (but we are still waiting for one designed for the Edge 9.25).
So what is
the Real Deal on these telescopes? The Edges’ images are noticeably better at
the eyepiece field stop than those of the ACFs, but it is not like night and
day. The images in the Meades are very good indeed, with the 10-inch ACF of my
friend Mike Harvey having some of the best SCT optics I’ve seen. Any advantages
the Celestron has may be masked (for visual observing) by aberrations in your
eyes or your eyepieces. In fact, you may find you don’t need either the Edge or the ACF, that you don’t need the More
Better Gooder.
 |
| . |
I will be
the first to tell you that visually the Edge 800 is a dream. You may have heard
that using one is like looking through a superbly corrected 8-inch refractor. That
is true, but what if, like Unk, you don’t do much visual looking? And when you
image, you often use cameras with small chips like planetary cameras or the
Mallincam deep sky video cams? The Edge (or ACF) improvements are at the field
edge, and a small chip camera doesn’t see that. Same goes if you are mainly a
planetary observer. You are concerned with the field center and don’t give a
hoot ‘n holler about the periphery.
And yet, and
yet… While I don’t always take advantage of the innovations inherent in Mrs.
Peel’s optical design, I still love her and have a hard time making myself use any
other telescope. I’ve always loved C8s and she is the best C8 I have ever
loved. She’s the best in part because of the care that was obviously exercised
in her construction. Her finish is beautiful and flawless, and so are her optical
coatings. As above, she shows a terrific star test. And I haven’t even
mentioned her vents that speed cool-down or the mirror locks that eliminate
mirror flop. In my opinion, if you are after a new SCT you owe it to yourself
to at least consider the Edge.
Hokay, glad
we got that out of the way. Where was we? Oh, yeah. I’d just loaded Mrs. Peel
and the VX mount into the 4Runner, shut the tailgate, and made tracks for the
PSAS’ little patch of dark sky heaven. I’d put out an announcement on the club's Facebook page (no more Yahoogroup for we-uns) that I’d be doing spectroscopy
and would be happy to have company. I didn't think I’d get any, though, it being a near full Moon. Unlike Unk, I
would guess most of our members who want to observe Jupiter can do so from
home.
And, indeed,
not a soul other than my favorite yellow tomcat, the airfield’s mascot, greeted
me upon my arrival. He was eager to “help” me, and we soon had Mrs.
Peel on the VX, the camera and the flip mirror on her rear port, and the
computer fired up. As was the case last week, there was not a chance of clouds,
obviously. Was it cold? Unk thought it was, the temperature having PLUMMETED into
the mid 40s shortly after sunset. Luckily, this time I was prepared with a good
sweater, a leather jacket, and a bunch of chemical hand-warmer packs.
As far as
the observing run itself, ain’t much to tell. I was using the ZWO color
cam at f/10 through the flip mirror. I mashed the buttons to go to the first star,
fine tuned the aim a mite with the reticle eyepiece so the star and its spectra
would be centered on the ZWO’s 1/3rd inch chip, flipped the mirror down, and
headed to the computer.
At the
computer, I fired up RSpec, clicked
the “live camera” tab, positioned the star and its spectra so the star was
on the left and the spectra on the right (the program has an image rotation
tool to make that easy), and, voila!,
there was a live spectrum on the program display. I did one thing differently
this time. I thought the spectra I got on my initial outing looked a little
thin, so I upped the exposure a wee bit. Not much. Even at 80 milliseconds the
ZWO is sensitive enough that I was on the verge of overexposing bright stars.
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| Sirius... |
Then it was
just a matter of getting stars in the can. Since I am still just getting
started with this stuff, I stuck to bright suns, the same stars I shot on my
previous RSpec run: Rigel, Capella,
Betelgeuse, and Sirius. The seeing wasn’t perfect, but it was at least a little
better than on the previous RSpec run. Sirius was a little low and twinkling madly, but its spectrum
seemed at least close to “good enough” to me.
“So,
everything went smooth, no hiccups, no disasters, eh, Unk?” Hey! This was an
Uncle Rod observing run. It wouldn’t be normal if something didn't go wrong. The culprit this time was the hand
control extension cable I bought years ago for the CG5. Its flat telephone
style cord gave up the ghost completely yielding lots of “No Response” errors.
I ordered a new and better one from Jim Henson at Scopestuff
as soon as I got back to the Old Manse, since the cords on Celestron’s current
hand controls are so absurdly short that you really cannot get by without an
extension.
Anyhoo, I
persevered despite the HC cable problems, got at least two sequences of each
star, and took a break. My four-footed friend had trotted back to his home in
the nearby hangar. It was dark and it was lonely and it was cold. Did I get
spooked? No, not really. The reason I decided to throw the big switch was because
I didn't really have an agenda left. The old Moon was on the rise, which limited
my options. Given the way Sirius looked onscreen, trying for Jupiter would have
been an exercise in frustration.
If I’d had a
buddy or two on the field with me, I’d no doubt have hung out shooting the
breeze and messing with the scopes a while longer, but I doubt the run would have lasted much
longer even then. By the time I’d finished packing, Luna was up over the
horizon looking in on me, lighting the field like a searchlight. I made tracks
for the Old Manse.
I was back home
in plenty of time for Svengoolie, who was showing yet another 1950s SciFi
“masterpiece,” The Mole People. I
watched it, but it is really almost on the too
freaky side today. It is just freaking odd,
with its introductory lecture by a nervous English professor and an
anti-Shangri-La plot that involves albino Sumerian mole people and a pretty
girl. The film’s ill-concealed viewpoint, that the underground civilization is
just another inferior non-western culture, tends to make us a little uneasy
today, too.
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| Rigel... |
During the
commercials, I must admit I had a peep at my spectra. Just looking at the .avi
files with Windows Media Player, I was somewhat encouraged. There seemed to be
detail in the spectra, more than there was in the ones from my first attempt, I
thought. Also, when I’d been shooting the video, the real time spectrum display seemed to indicate I was picking up absorption lines. But I was really too
distracted by the task of operating the scope to pay close attention. I’d only
know for sure how good or bad they were on the morrow when I ran ‘em through RSpec.
After my
customary Sunday morning bowl of porridge, I pulled out the laptop and got down
to work. Why did I choose to process the files on the laptop rather than on
Chaos Manor South’s famous kitchen workstation, a high-powered Toshiba
wide-screen desktop? Using what is essentially a video camera yields large .avi
video files. At the ZWO’s highest resolution, which is what I habitually use, a
short sequence is a gigabyte in size and transferring a dozen or more of those
files to the desktop is a pain in the you-know-what.
Maybe it’s a
good time to talk about what you can use with the Star Analyser grating other than a planetary webcam-style
camera like Unk’s. If you’ve got a still camera of some kind you can somehow hook to the grating, that’s it. RSpec seems to be
very good regarding the file types it will accept. You can even use that new
DSLR you got for Christmas. Adapters are available for purchase through Tom’s website that allow you to use the grating, which comes in a standard, threaded, 1.25-inch cell, with your camera either by screwing it onto the lens, or
directly to the camera in a T-mount set up.
Another
popular option is Meade’s no longer produced DSI series of camera. While they've been gone for a while, many were made and it’s easy to find one of
these basic CCD cams for sale in used venues. Certainly, you can use a big-boy
camera like an SBIG with RSpec, too. RSpec
can be configured to work in conjunction with CCD camera control programs like CCDsoft.
For me,
though, the ZWO is easier to use. With video coming straight into the program,
I can see the spectrum live on the computer display (remember, this program’s
subtitle is “Real Time Spectroscopy”) and it’s obvious whether or not I’ve got
everything working more or less correctly. Also, being able to take many frames
and stack them with RSpec’s “Average”
function makes it easier to deal with the punk seeing we get this time of year.
Yes, even way down in the Swamp, seeing can be a problem in the depth of winter,
especially a nasty winter like this one has been.
 |
| The ZWO...recommended! |
I could see how
just how bad the seeing had been when I began looking at my Rigel and Sirius
sequences on RSpec. Their graphs moved
up and down in “amplitude” like crazy. Not to worry. I clicked the Average
button and their spectra, their graphs, settled right down. OK, time to
calibrate, to change the pixel scale of the graph to angstroms (or nanometers
if’n you prefer) so it would mean something. I’d just…I’d just… Suddenly Unk realized
he was in over his head. I had absolutely no idea where the hydrogen beta line
was and couldn’t click on it to complete the calibration process.
The more I
looked at my spectra, the more confused I became. They looked different from
the examples in Tom’s videos, and attempting to calibrate by guessing at the
h-beta line led to crazy results. There was only one thing to do, run crying
and screaming to Mr. Field and see if he could make heads or tails of my .avi
files.
Indeed he
could, and far more quickly than I could have dreamed of or asked for. In short
order, Tom got me going again. Part of my problem was seeing. It was, if not as
poor as on my initial RSpec outing, bad
enough to complicate things. What was also confusing me was that I was seeing
the second order spectrum peeking in on the right. Once Tom educated me about
these things and a few other factors and I was back on track. Next time I will
try to work under better seeing and see if I can eliminate that intrusive and
confusing second order spectra.
Anyhoo,
after Mr. Field got me calmed down, seeing straight, and thinking right I was
able to successfully calibrate my spectra and pick out the Balmer Series lines and
other things. Again, what I mostly think will help is better seeing—and more
experience, of course. I’ve still got a lot to learn, but I sure am having fun
doing it.
Though my
results were a little indifferent this time, muchachos, they weren't that bad, I thought. MOst importantly,
I’d had fun, learned a lot, and, wonder of wonders, found something I could do
on a winter’s night with the full Moon in the sky and the jet stream overhead.
You cannot beat that with a stick, muchachos, you cannot beat that with a
stick.
Nota Bene: One of the things I love about being an astronomy writer is that I get to do a lot of traveling to clubs and star parties to give talks. I know, however, that some clubs just can't afford to fly me in and put me up. I would much rather address your club in person, but if that is just not possible, I have a DVD video of my Herschel Project presentation I can send your way. It's not Cecil B. Demille quality, and I can do a better job live, but y'all may like it anyhow. Just ask...
Nota Bene: One of the things I love about being an astronomy writer is that I get to do a lot of traveling to clubs and star parties to give talks. I know, however, that some clubs just can't afford to fly me in and put me up. I would much rather address your club in person, but if that is just not possible, I have a DVD video of my Herschel Project presentation I can send your way. It's not Cecil B. Demille quality, and I can do a better job live, but y'all may like it anyhow. Just ask...
Next Time: Atlas Rides Again…
Comments:
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Great to see some articles on spectroscopy from you...amazing to see how you can do some real science with not too much gear or expense. Something I have been interested in for many years and your articles may just be the boost I need to get into it seriously here in New Zealand.
Hi Ivan... If I am understanding your question correctly, it's taken into account because of the calibration you do...
It appears that the calibration based on the user's identification of a known wavelength calibrates the camera pixels into wavelength units. And from what I have seen (I don't have the program), this calibration seems to do only that. If the user wants to identify absorption or emission lines, this is all that's needed. But the camera's spectral sensitivity curve affects, and largely determines, artifactually, the shape of the star's spectrum displayed by the program as a plot (intensity vs. wavelength).
Ivan, seeing as how I am very new to the program, I think you'd be better off asking the author, Tom Field. He can be contacted through the RSpec website, or on the RSpec Yahoogroup.
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