We’ve had an inch-and-a-half of rain over the last 2 days, and when I got up at 4:30 to check the sky, we were still socked in. Went back to bed, woke up a little after 6, and I’ll be darned if the clouds hadn’t cleared out and offered a beautiful view of the earth’s shadow just beginning to take a bite of moon. The photo below is about as deep as the eclipse got for me.
Friends have asked if I got pictures of the comet (Lovejoy C/2014 Q2) and I’ve been reluctant to admit, that, yes, I have, but that they are pretty bad pictures.
The first was a wide field shot in which I imagined seeing the comet’s tail streaming gracefully among the Hyades and the Pleiades. For tracking, I mounted the Canon 60Da piggy back on the Takahashi, set the camera’s intervalometer to take 60 1 minutes shots, and went in the house. About 10 minutes later, I let the dog out, and the sky had socked in, and was spitting snow!. So I shut things down, having got 5 minutes of usable exposure in. There’s the merest hint of a tail, if you look close, and really want to see it. I shot the images at 28mm, f/5.6. The comet is really small in the frame, although it would have worked ok if I could get more exposure. Actually I think the picture captures the impression you get with binoculars.
The next clear night I used the STL 11000, and was able to see really nice detail in the comet’s tail. Unfortunately, the camera was overdue for the annual regeneration of its dessicant plug, and the image is overlain by the shadows of tiny ice crystals. So I took a few pictures and set up for flat fields, hoping I could zero out the frost. The frost is a moving target, and the flats weren’t helpful. So the image below is 5 minutes, dark-subtracted and auto-background-extracted in Pixinsight. The black cuneiform is what frost looks like on a chip. You fix that by removing the desiccant plug from the camera, and popping it in the oven for 4 hours at 350 degrees, which I did the next day.
The third try for Lovejoy was one of those completely abortive observing nights that nobody ever admits to. I planned to use the Canon at 100 mm piggybacked to get Lovejoy with the Pleiades, while exposing the STL11k for the coma and tail. First, the nut that holds the Canon to the mount had come loose and disappeared, and a spare was not immediately at hand. So, I scratched that part of the plan. Then, I could not find Lovejoy in the STL! I had collected coordinates in the house, punched them in, but no comet in the exposure. So I went online in the hut to get updated coords, tried them, and no comet. Tested the overall setup, and made a perfectly lovely, centered shot of Aldebaran. But I apparently had outdated comet info. It was around zero that night, and I was dressed for it, but my feet were getting cold and I was getting frustrated, so I hung it up for the evening with nothing to show for it. That was about a week ago; the forecast suggests that I may get another try on Thursday!
Since I’ve been using the Takahashi FSQ106-ED with the STL11000, I’m getting wide field images, about 3.9 x 2.7 degrees. So the fields contain numerous cataloged objects that would be nice to identify.
Pixinsight offers a workflow to “solve” the image which provides accurate WCS coordinates that are added to the FITS header; and an annotation script that overlays grid, constellation boundaries, and objects from several catalogs.
For narrow field images, the ImageSolver script should work, but it fails pretty regularly on my STL11K pix and really fails on wide field shots made with the Canon 60Da with wide lenses like the one above. Located in the Scripts | Image Analysis menu, the script panel asks for the center coordinates of the image, with a search function so you can choose a known object in the active image. If the script fails, as is likely with wide field images, it is still useful to improve the accuracy of the ManualImageSolver script. To use the ManualImageSolver script is not straight-forward, but it does work pretty well. It’s not straight forward, because, before running it, you need to use the CatalogStarGenerator script to build a synthetic star field image; then use the DynamicAlignment process to manually match stars in the reference image (the synthetic catalog star image) to the target image (your astrophoto). After saving the instance of DynamicAlignment to the workspace, you can run the ManualImageSolver script to provide WCS coordinates to the target image’s FITS header. Honestly, you have to really want it.
Here are more details. Open the target image, the image to be solved. It must be FITS format, because the FITS header is where the WCS coordinates will live. Locate a named object near the center of the image, you will use it the generate a CatalogStar image. I used M8 (Lagoon nebula) in the example. Run the CatalogStarGenerator located in the Script | Render menu). Search for your chosen reference object, which will populate the coordinates fields. Fill in the Dimensions field (from your target image) and provide the Image Scale info. In the Stars panel, choose a catalog, probably the Bright Star catalog. The PPMC catalog is more comprehensive, but is too big for to be practical for wide field images Click OK to run the script, and it will build a reference image of the field. I use the STF panel (‘screen Transfer Function) to adjust the screen stretch so the stars are more easily seen.
Once you have a reference image you’re happy with, you align your target image with it using the
DynamicAlignment process (located in Process | Image Registration menu). When the process panel opens, click the reference image (the synthetic star field); this defines the reference image for the process. Then click the target image (your astrophoto). Now click a star in the reference image that is obvious in the target. This will place an X in the target that you will drag to the corresponding star. The first few alignment points can be surprisingly painful, but once 2 or 3 points are correct, the rest are (usually) placed pretty accurately. However, you MUST check each point since there is generally some distortion in the field.
The other pain point is that for best results, you really need 40 or so points spread over the target. (A shortcut is to use 4 or 5 alignment points and then run ManualImageSolver followed by ImageSolver, which should run happily and produce a pretty good result.) Ok, so you when you have enough alignment points, drag an instance of the DynamicAlignment to the workspace. The instance is represented by the little triangle at the lower left of the process window; when you drag it to the workspace it creates a savable icon with all the details of the alignment session. You need that when you begin ManualImageSolver. located in Script | Image Analysis menu.
Select your DynamicAlignment instance with the Control Points icon, and the catalog star reference image as the Reference Image. You can improve accuracy by raising the Polynomial degree to higher numbers. The residuals image provides an accuracy check; the distortion map shows optical distortion, and the distortion model provides a way of modeling the system to simplify solving other images with the same optical setup. Anyway, now that you have manually solved the image, a set of WCS coordinates have been inserted into the FITS header. And you can run the AnnotateImage script in the Script | Render menu.
The script panel provides an essential preview tool which lets you play with settings without rendering the whole image. You will want to try different settings on labels and markers, but a tip is to use the Graphics Scale slider at the bottom to change everything at once. You can render to a new annotated image, or a transparent overlay. There are issues with label crowding, and it is easier to edit an overlay than the rendered image. It’s still not easy. You could render the grid and the labels into separate overlays which would make the text labels easier to work with. I guess I prefer the transparent overlays, and accept that labels will be crammed together. When you have your overlay, you can apply it with PixelMath.
Accuracy is pretty good. I fear the label crowding is inevitable with this wide of a field. Manual Image Solver is one of the tools in Pixinsight that is actually really well documented, as is Image Solver. For the straight poop see http://pixinsight.com/doc/scripts/ManualImageSolver/ManualImageSolver.html
We had a really clear night June 3rd, following a cold front, so I set up an imaging run on M64, the descriptively named “Black Eye” galaxy. I got a good hour of luminance data, but only about 15 minutes each of RGB. I haven’t made anything acceptable with the color data yet, but the luminance is ok. M64 (aka NGC 4826) is a crowd-pleaser for amateurs because it shows visible structure in modest scopes due to its startlingly obvious dust lane.
But the dust lane wants an explanation. It’s located at the inner third of of a broad disk, and is obvious even at the fairly broad angle at which the galaxy presents itself. The outer disk has suggestions of spiral structure, but the details have apparently softened over time. The explanation is probably related to the observation that the outer part of the galaxy includes a gas disk rotating in the opposite direction of the stars and gas in the inner disk, presumably from accretion or collision at some time in the distant past. From a paper by Corsini, E. M.; Bertola, F, “The Phenomenon of Counterrotation in Galaxies” (http://adsabs.harvard.edu/abs/1998JKPS…33S.574C):
This galaxy contains two nested counter-rotating gaseous disks. Radio and optical observations revealed an inner disk of about 1 kpc radius containing ~107 solar masses in HI and ~108 solar masses in H2 and a counter-rotating outer gas disk extending from 1.5 to 11 kpc and containing ~108 solar masses in HI.
They are coplanar to the stellar disk. Stars co-rotate with the inner gas but beyond the dust lane less than 5% of them (~108M) co-rotate with the outer gas. The kinematical features of NGC4826 are interpreted considering an original gas-poor galaxy with prograde gas which slowly acquires a comparable mass of external retrograde gas. The new counterrotating gas settles in the outer parts of the stellar disk,leaving undisturbed the galaxy morphology.
The galaxy is now relatively isolated, so there is no obvious smoking gun. The culprit may have been a counter-rotating dwarf galaxy in orbit around M64, which has now completely lost its identity, and is suggested only by the Black Eye.
After the crazy weather we’ve been having , it was a treat to see Venus, Jupiter and Mercury crammed together into a neat triangle after sunset. Mercury can be hard to find in the twilight, and it sure makes it easier to have Venus or Jupiter as a marker. Tonight we have both! Mercury is the faintest of the three, at the top of the triangle.
Last year I discovered that the Geological Society of America (GSA) has annual regional meetings with really great field trips to local geological locations of interest. So I joined up, and last year paid a visit to the Serpent Mound Disturbance, a fairly ancient meteor impact site in southeastern Ohio.
This year a trip was offered to the Kentland, Indiana impact site. The trip was ably led by Dr John C. Weber, Professor of Geology at Grand Valley State University, Allendale, Michigan.
The site is located in the flat Indiana farm land typical of the north western part of the state, and the only clue about the area’s unusual geologic history is a limestone quarry, now called the Newton County Stone Quarry, operated by the Rogers Group. The surrounding landscape is covered by Pleistocene glacial deposits to considerable depth, which is the source of the rich soil that makes this such productive farm land.
Beneath the soil and glacial till, I’m told, are tidy, virtually horizontal layers of Middle-Lower Paleozoic bedrock that slope very gently from the Kankakee-Cincinnati Arch southwest to the Illinois basin.
Apparently there was a limestone outcrop that was obvious to local residents early on; the site has been a quarry since the 1880’s.
Geologists recognized that explanation was required both for the raised bedrock, and for the very un-tidy, not-horizontal placement of the strata within the formation.
Why is Kentland important? The impact site currently has no surface signs of a crater. However the impact uplifted the strata at the center of the site, providing a handy outcrop of limestone for local use. The resulting quarry is exactly why the impact effects are so accessible; the site is a laboratory for studying impact-deformed strata. Geologist love roadcuts because they expose strata that are normally covered by earth or vegetation. The quarry is like a continually expanding roadcut that regularly reveals new windows on the tortured layers of the site.
R.S. Dietz, one of the early proponents of impact geology, studied Kentland’s impact structures in place, especially shatter cones, and found the orientation of the cones were invariably normal (perpendicular) to the bedding:
“The orientation of the shattercones suggests that, assuming that the beds were essentially horizontal prior to deformation, the shock force resulted from some type of explosion directly above the beds rather than from a crypto-volcanic explosion below the beds.” (Science 10 January 1947: 42-43.)
Along with Meteor Crater in Arizona, Kentland provided the essential clues to put “crypto-volcanic” theories to rest.
The site was carefully described and mapped by R.C. Gutshick from the 1960’s to late 1980s. He showed that the quarry is at the apex of a structural dome, the central uplift area of a complex crater.
The crater itself has long since eroded away (hence, “impact structure”), along with evidence of exactly when the impact occurred, and how large the crater was. The glacial till that covers the neighborhood is about 50,000 years old; the upper layers of bedrock are of Silurian age, about 300 million years old. At some time in this 300 million year gap, an object made a sudden stop in Indiana – from maybe 20 km/sec to 0 in less than a second- and created a 6-13 km (3.7 to 8 miles) diameter crater. The center of the impact was raised by 600 meters by the rebound, and created a chaos of the formerly tidy Silurian and Ordovician layer cake. Then all evidence of the crater, the outer rim and glassy melts were eroded away, both here and over the surrounding region. Much later, glaciers covered the area, leaving behind a layer of debris that has become home to corn and soybeans.
How do you figure out the size of a crater that has long since eroded away? The Earth Impact Database gives a diameter of 13 km probably based on Gutschick’s mapping. However Gutshick also measured the uplifted Ordovician Shakopee dolomite to be about 600 meters above its un-deformed counterparts. Applying impact models developed by HJ Melosh, GS Collins, and RA Marcus (http://impact.ese.ic.ac.uk/ImpactEffects/effects.pdf), a 13 km crater should show a central uplift of 1 to 1.3 km. A crater of 6 to 7 km would have a central uplift that more closely matches Gutschick’s measurement. You can play with the various impact parameters with the online Impact Effects Program at http://impact.ese.ic.ac.uk/ImpactEffects/
For me, the highlights of seeing this place first hand, were the incredible, and obvious distortions of the rock layers; the numerous shattercones, now considered an icon of impact geology; and the impact breccia, another hallmark of impacts, but not at all unlike volcanic breccia to my eyes.
I think I expected to get some understanding of a “system” that would describe the disturbed strata. Nope. I liked Weber’s description from his field guide: “It is a steeply dipping, bedding sub-parallel, folded fault that juxtaposes the St Peter Sandstone with the Middle Ordovician Platteville Group” But I must admit this doesn’t seem to do the chaos justice. Here’s a St Peter sandstone – Platteville sequence that is turned on its side, and then repeats. The St Peter sandstone is the distinctive white layer. At its base, it’s pulverized to a flour consistency, which is characteristic of other impact sites. I don’t know if that accounts for this occurrence, or if it has just weathered.
Here’s a detail of a section with Platteville and St Peter sandstone. There are shatter features, breccia dikes with hefty clasts, and a general sense of craziness.
Similarly, Maquoketa shale and Galena Platteville. The Ordovician black Maquoketa shale is, I believe, a member of the Richmond formation. It’s another distinctive marker bed, and quickly weathers into talus slopes.
More Maquoketa shale and Galena showing the MFS (Marine Flooding Surface):
The north-east pit is working Silurian carbonates. I don’t believe it’s been mapped; I don’t which Silurian formations are presented.
Some really big clasts thrown into Maquoketa shale:
Shakopee dolomite is the oldest exposed layer.
One of the definitive, but not exclusive, indicators of impact are breccias. At Kentland there are dikes filled with polymict breccias that were apparently forced into fissures and voids opened by the rearrangement of massive blocks by the impact.
Inside, the breccias have a fairly fine grained matrix with clasts that are familiar from the neighborhood: St Peter Sandstone and various carbonate chunks, with conspicuous voids.
I haven’t gone into the studies of microscopic features of this site. Weber authored an interesting study (“Kentland Impact Carater, Indiana: An Apatite Fission-Track Age Determination Attempt” ; Weber, et al) using fission tracks in apatite grains in the St Peter SS to attempt to find an impact date. The fission tracks would show a thermal reset, possibly at the time of impact. Unfortunately, the reset seems to occur regionally, so presumably local evidence has eroded away. There are several GSA Field Guides available from http://fieldguides.gsapubs.org/ (by subscription).
I intended to get a good hour in for LRGB on this, but as it turned out the guiding was intermittent and I really only got 4 each good RGB frames for 20 minute total exposure. So the image is not deep.
I’ve started using CCDStack and, when calibrating the frames, was getting a “negative ADU” alert when applying the flats. This was quite mystifying. It turns out I was not making flats with enough exposure. I resolved it by re-exposing the flats with the 40 watt bulb (instead of 15 watts), increasing the exposure so I was getting about 60% full well capacity. That satisfied CCDStack, and should make a better flat. I’m still seeing irregularities in the background areas, which were repaired in Photoshop with Astronomy Tools from ProDigital Software.
M99 is a “grand design” spiral, except for its crazy arm which has presumably been distorted by a close encounter. Because it presents itself so well, it’s been the subject of a lot of research, mainly concerned with the distortion of the spiral. This gets interesting because HI (neutral hydrogen) mapping from Areceibo showed a massive (about 100 million solar masses) rotating accumulation of neutral hydrogen fairly nearby, dubbed VirgoHI21.
There’s nothing to see of Virgo HI21, it seems to be mass without stars, which only shows up in radio survey. From its mass, it should be a 12th mag galaxy. The discovery of VirgoHI21 was greeted with great excitement, because it was thought to be the first candidate for a dark matter galaxy, which maybe it is. Would that be cool! But it seems that dark matter refuses to reveal itself that easily. Evidence is mounting that the VirgoHI21 is a tidal tail, probably from M99, the result of nearby NGC 4262 gliding thru the neighborhood 280 million years ago. This is all gleaned from the detail page on M99 from WikiSky.
NGC 4298 and 4302 are a lovely pair that I will image soon, if it ever clears up.
We’ve had a rainy week and 5 or 6 inches of rain, but it cleared up nicely. I planned a run on M99, which I had botched a few weeks before. i unparked the scope, fired up the camera & coolers, opened the roof and aimed at Denebola to check the aim. That accomplished, I headed inside to do the rest from the living room.
I stepped out of the Hut into a lovely twilight and had to just stop to take in the Big Picture, which is so often lost when futzing with gear.
I heard peepers chorusing across the field and the redwings calling in the bamboo patch. Then coyotes had a brief earnest discussion. I haven’t processed the M99 frames yet. Will put them up soon.
In my continuing, ongoing shakedown, I set up a full LRGB series of M65 (NGC 3623) on the clear, moonless night of April 3. The forecast was good, so I set things running and went to bed. Somewhere in the green series, things murked up a bit, and the tracking crapped out for some of the greens and all of the blue.
The luminance looked pretty good, except for the usual annoying, slightly oval star images. But wow, quite by accident, the image shows Supernova 2013am, discovered on
March 30 by M. Sugano (Japan). I’m probably the only one who didn’t know this was now playing in one of Leo’s Kodak Photo Spots. Still, hitting it by accident means I could have discovered it! Well, if I had actually noticed it! I found out about the supernova via a casual mention on a mailing list, and thought, “didn’t I just image that?”
I had a few hours before moonrise, and wanted another stab at NGC 4435 & 4438. I thought I had good focus, and was getting about 5.5 FWHM on the focus run, but it looks like the focus drifted quite a bit during the run.
And for some reason Maxim refused to connect to the mount, so the exposures are unguided. I got 5 sort of acceptable 300 second frames. NGC 4438 is one abused galaxy. It seems likely but not certain that NGC 4435 is responsible. From ESO (http://www.eso.org/public/news/eso1131/) :
“NGC 4435 could be the culprit. Some astronomers believe that the damage caused to NGC 4438 resulted from an approach between the two galaxies to within about 16 000 light-years that happened some 100 million years ago. But while the larger galaxy was damaged, the smaller one was significantly more affected by the collision. Gravitational tides from this clash are probably responsible for ripping away the contents of NGC 4438, and for reducing NGC 4435’s mass and removing most of its gas and dust.”
The dark patches on 4438 are enormous clouds of visually opaque dust. I believe the fuzzy patch just to the right of 4438 is a small companion galaxy.