An artist’s illustration of the exoplanet PH1, Credit: Haven Giguere/YaleDr. Charles Beichman, executive director of NASA’s Exoplanet Science Institute at Caltech, will talk about how the dynamic duo of NASA’s Space Missions and Keck Observatory has led to some of the most exciting astronomy results in recent history.
Tuesday
June 25, 2013
Starts at 7 p.m.
Kahilu Theatre, Waimea
Free and Open to the Public
NASA’s Space Missions have identified more than 3,000 possible planets outside of our solar system and Keck Observatory has confirmed the existence of nearly half of the some 900 proven to exist. Join us for another Astronomy Talk to hear about this fascinating field of science unfolding before us.
These lectures are supported by Rob and Terry Ryan and Keck Observatory’s Rising Stars Fund.
A small, light telescope mount, a small refractor, and a modern autoguider. Seems like a perfect setup! There are a few issues…
The setup is pretty straightforward. A TeleVue 76mm riding atop the iOptron ZEQ25 mount. Atop the TV-76 is a red dot finder and an SBIG STi autoguider. The guider is attached with a bit of custom machining and uses the SBIG accessory kit, including a 100mm lens giving a 2.7 x 2.0 degree field of view. With such a wide field of view the guider also functions as a finder to aid in aligning and framing the photographic telescope.
The iOptron ZEQ25 set up for astrophotography with a TeleVue-76 and Canon 60DThe arrangement is controlled by a laptop, either an older 17″ laptop, finding a second life in the astrophoto rig. Or for a more portable, and less power hungry setup, a small netbook can be used. It may be desirable to set up the iPad for telescope control, removing this function from the laptop. If it were not for guiding the computer could be dispensed with completely. The SBIG STi requires a computer to operate.
Without guiding the performance is not satisfactory. Even with a modest focal length of 380mm there are objectionable guiding errors. The frame at right shows the errors seen during a four minute exposure. Based on my first impressions I would expect to need guiding on any exposure using more than 100mm and a few minutes exposure.
Comet C/2011 L4 PanStarrs, TV-76mm and ZEQ25 mount with no guiding during a 4 minute exposureEverything connects fairly easily, a few more cables than I would like, but it is still marginally portable and not a huge chore to assemble. The challenge now is to verify the setup, configure all of the software, and to take a few photos to prove to myself that it all works properly.
A few steps here have not gone smoothly..
Configuration? There are a lot of setups to check. All of the correct software and drivers… Planetarium software, autoguiding software, camera control, ASCOM, all of the hardware drivers, etc., etc. After everything talks it is a matter of checking settings and tuning the setup with several parameters in the software and on the mount that need to be checked.
I am using PHD to do the guiding, a bit of kit I have used for a while. It works quite well with straightforward controls. It does have quite a few parameters that require checking to tune the control algorithms.
The iOptron controller has a setting for guiding speed in the menus. This is purported to be a fraction of sidereal speed by the manual, up to 100%, but the menu reads as if it is 100x on the controller. I suspect the manual is correct here, will need to test.
The first issue cropped up fairly quickly. I could get no motion from the mount while sending corrections with the STi. PHD was unable to calibrate, no motion. I attempted to use the manual controls in PHD with similar lack of motion. (See update below)
To troubleshoot I needed to make sure that the guide port on the ‘scope worked. I grabbed a Losmandy hand controller and connected it to the ZEQ25 guide port. This worked, the port was working properly and I could see what the guide speed setting on the controller really meant. It looks like 100x is 100% of siderial speed, or close enough.
A copy of Gene Nolan’s USB to ST-4 guiding adapterI have another device I could try, a USB to ST4 adapter designed by Gene Nolan. This is also supported by PHD Guide and ASCOM driver framework is always installed on my imaging computer. After some issues with finding the correct cable setup the USB to ST4 adapter worked just fine.
Parameter
Value
RA Aggressiveness
100
RA Hysteresis
10
Max RA Duration
750ms
Search Region
15pix
Min Motion
0.1pix
Calibration Step
2000ms
Time Lapse
0ms
Dec Guide Mode
Auto
Dec Algorithm
Resist
Dec Slope Weight
5
Max Dec Duration
750ms
Star Mass Tolerance
0.5
Noise Reduction
None
PHD Guiding Paramters for STi w/100mm lens and iOptron ZEQ25
At this point I can calibrate and guide with good results. I am out of USB ports on the laptop, and had to unplug the mouse, but at least it is working.
Some tuning of the parameters in PHD has started to result in very nice guiding graphs and some excellent test images. These could probably be refined a bit more, but they are working for now. The PHD help menu has a fairly good description of each of the parameters, there is also a great guide to PHD on the Rose City Astronomers website.
Guiding Test: 240sec with a TV-76 and 60D on a ZEQ25 mountA 100% crop of an image is included at the left, nothing exciting, just a section of starfield near Vega. What is nice about the images is the perfectly round stars. The image was taken at 384mm effective focal length. Will need to do this again with the AT6RC at 1096mm for a more stringent test.
It is really necessary to set the autoguide rate to 100% when using shorter focal lengths. Otherwise the mount does not move very far during each calibration step, as a result calibrations take a very long time and will sometimes fail.
Another observation. When guiding near the pole, shooting comet PanSTARRS at near +80° declination, I encountered very regular declination errors using PHD. Every couple minutes the dec error would deviate by about a pixel, alternating in each direction. Shutting off the declination correction worked pretty well, the mount was polar aligned accurately enough that there was very little declination drift.
I still have yet to understand just why the STi will not directly interface with the ZEQ25, something in the ratings of the photo-isolators used in the STi? The manual simply states these are good to 25mA and 25V, which seems generous for the task. It may be in the voltage levels, I did discover that the iOptron uses 3.3V on the guide port. Perhaps the STi will not pull down low enough for a valid low logic level? I built the USB to ST-4 adapter with MOSFET optocouplers, these can switch harder than standard photo transistors.
UPDATE– The interface issue was just a cabling problem. The same cable I use with my Losmandy G11 does not work, it is flipped from the pinout needed for the ZEQ25. With a corrected cable I now connect the STi directly to the guide port on the ZEQ… It works.
With the Moon and Jupiter having departed the sunset stage, Mercury and Venus continue their dance. This evening finds the two about 4° apart with the dimmer Mercury higher in the sky. Mercury has dimmed over the last few weeks and is now only 0.7 magnitude, far dimmer than Venus at -4 magnitude.
Over the coming days the pair will draw closer, passing within 2° on June 19th. As the month wanes the two will then separate ending the dance.
I saw it on Facebook first, shared by a family member… The meme that will not die…
The usual Super Moon hype as found on Facebook, source unknownSuperMoon is back!
The claims are the usual… The Moon will be huge in the sky. The Moon will be closer than is has been in some huge time span.
There is some truth here, the June full Moon will be a bit bigger and brighter than usual. And it will be closer to the Earth than it has been in a long time, if you consider 27.5 days to be a long time.
The SuperMoon meme exaggerates the truth to varying degrees.
It all relates to lunar apogee and perigee. As the Moon’s orbit is elliptical, it does get a little further and closer during each orbit, but the difference is fairly minor, the distance varies from 405,000km (251,000miles) to 360,000km (223,000miles) from the Earth. This difference in distance results in the Moon appearing up to 12% larger at perigee compared to apogee. For a better explanation you can go to another post that explains this more fully, with graphics.
12% difference, noticeable if you look close, but hardly a “SuperMoon”.
The Moon passes through perigee, the closest point every 27.5 days, about once each orbit. Not a very long time. But SuperMoon only occurs if perigee happens to coincide with full Moon. As these two cycles are usually out of sync with each other people do not usually notice. About once a year the two cycles coincide and we get a slightly larger, brighter full Moon… The SuperMoon. Interesting, but not as dramatic as the hype.
The apparent size of the moon as seen at perigee versus apogeeAnother theme that pops up in the SuperMoon meme is a prediction for more earthquakes or volcanic eruptions. I found this one again touted in some YouTube video on the June 2013 full Moon. This claim would at least seem to be somewhat logical, lunar tidal forces do have notable effects on the Earth.
Geologists have studied the lunar earthquake/volcano possibility for decades with varying results. Indeed, some older studies seemed to indicate a link. More recent studies have pretty much ruled out any association, better data associated with more instrumentation and improved worldwide coverage has shown that if there is any effect it is quite small.
Besides, if there were a link, the earthquakes should occur every 27.5 days as the Moon passes through perigee, they do not. There is no reason to make anything special of the full Moon/perigee synchronicity.
June 23rd will offer a nice, bright full Moon. A great time to take a moonlit walk, or a night dive. Ignore the scaremongers, and use this as an excuse to enjoy our beautiful universe.
Today Mercury reaches maximum elongation, the furthest point it will reach from the Sun in our sky and the highest it will be above the sunset for this evening apparition. The planet is easily visible as a bright, starlike object about 24° above the setting Sun as twilight begins. Over the next couple weeks Mercury will slide back into the sunset, heading for inferior conjunction on July 9th.
A rigid mount to adapt the TeleVue-76 to the SBIG STi autoguider? I need such a solution, I have both of these bits of kit that need to be wed together for the minimal astrophoto setup. As I am unlikely to find such a part commercially, I would have to make it myself.
Another couple hours in the machine shop were in order, another small pile of aluminum chips. This actually went pretty quickly, these are easy cuts to make. No tapping is required, the four holes are simply drilled through. The two hours included design and cleanup for a quick project.
The SBIG STi to TelevVue TV-76 mountMechanical drawing for a mount to attach an SBIG STi autoguider to a TeleVue refractorI came up with the design on the fly. A piece of aluminum from the scrap bin and a couple quick measurements of the ‘scope and guider. I simply cut aluminum until it seemed about right. It was only after the fact that I produced a drawing of the finished item.
The TV-76 has a rather non-standard mounting point on top for accessories like this. A pair of #10-32 threaded holes, 0.75″ apart and located in a slot 0.625″ wide milled into the mounting ring. This seems simple enough. An adapter made for the TV-76 should work with any of the TeleVue refractors that use this mounting. Another concern is that the solution must also be very rigid, any flexure between the autoguider and the telescope will result in smeared stars.
The design assumes that you have the additional guiding kit sold by SBIG for the STi autoguider. This provides the mounting rings that clamp the camera body.
The hardware required will be two ¼-20 x 1½” socket head cap screws, and two #10-32 x 1″ socket head cap screws. A pair of plastic press on caps convert the #10 screws to knobs. All parts you can find in a neighborhood hardware store.
The mount is 1.5″ high to set the autoguider away from the main OTA, as to not encounter any vignetting. This also allows space to get fingers onto the mounting knobs. The dimensions are chosen so that standard screws protrude by just the right amount. I messed this up on the one I made, machining the center to far. As a result a few washers are needed for the screws that mate with the refractor. This is fixed in the mechanical drawing.
To co-boresight the TV-76 with the autoguider it was necessary to slip a 1/4″ washer between the mount and the rear ring as a shim. With that in place the same object is centered in both fields of view. The STi has a 2.7° x 2.2° field when used with the 100mm lens supplied in the SBIG accessory kit. With this wide field of view it also serves as a finder to locate and frame the photographic target.
It assembles nicely, a good start. The true test will be the quality of the images produced by the rig.
The least massive galaxy in the known universe has been measured by UC Irvine scientists, clocking in at just 1,000 or so stars with a bit of dark matter holding them together.
This image shows a standard prediction for the dark matter distribution within about 1 million light years of the Milky Way galaxy. Image credit: Garrison-Kimmel, Bullock (UCI)The findings, made with the W. M. Keck Observatory and published today in The Astrophysical Journal, offer tantalizing clues about how iron, carbon and other elements key to human life originally formed. But the size and weight of Segue 2, as the star body is called, are its most extraordinary aspects.
“Finding a galaxy as tiny as Segue 2 is like discovering an elephant smaller than a mouse,” said UC Irvine cosmologist James Bullock, co-author of the paper. Astronomers have been searching for years for this type of dwarf galaxy, long predicted to be swarming around the Milky Way. Their inability to find any, he said, “has been a major puzzle, suggesting that perhaps our theoretical understanding of structure formation in the universe was flawed in a serious way.”
It began, as all these things do, with a phone call from Liz…
“It’s stuck”
“What is stuck?”
“SFP won’t move in K2AO.”
“Do not try to move it any further, I am up tomorrow for SegEx, I will go look at it.”
Looking into the partially disassembled side of the Keck 2 AO BenchLast time we tried to free up the SFP stage when it was stuck we carved an L shaped gouge in the cover plate. This is the hazard of optics that move under computer control. We tell the computer to move these optics under the assumption that the encoder position indication is correct, sometimes it is not. In reality there is no way to actually see where the stage is, an optical assembly moving deep within the AO optical bench. For most of the optical stages this is not a problem, if the encoder is not correct you can just reinitialize it and regain the position, the stage can not actually hit anything.
SFP is different, it can crash into the rotator if it gets lost. There is no real way to fix this issue, it has to be this way. SFP stands for Simulator Fiber Positioner, an artificial star created with a optical fiber. Placing the tip of the fiber at the telescope focus creates a bright dot of light that we can use to align and calibrate the AO system. The three axis stage can move the fiber into the light path and accurately position it just where you need it for system tests. There is also a diagonal mirror used to inject light from the telescope simulator and the spectral calibration source mounted atop the simulator.
This evening the Moon will join the ongoing dance of planets in the sunset. A very thin crescent Moon will be 13° above the horizon at sunset and 6° below and south of the brilliant Venus. 5° above Venus will be Mercury notably dimmer at only 0.4 magnitude.
Tomorrow the Moon will be a bit higher and show a little more crescent at 6% illuminated. It will be above Venus and about the same elevation as Mercury, if 7° further to the south.
Jupiter is still present, but probably too low into the sunset to spot at only 6° from the setting Sun. Maybe with perfect conditions?
