My original Astro Journal with my Equipment and Astro Automation pages: https://SaltwaterWitch.com/astronomy
There’s a beautiful moon out tonight. I shot this with the Nikon D750 + AstroTech AT6RC 1350mm f/9. A nearly full moon always makes deep sky astrophotography difficult, but that’s when you pair a full frame DSLR with a 6" Ritchey-Chrétien. The rest of the sky can wait for the new moon.
In the field--well, not really, but I was a little under a 100 miles away in western Massachusetts testing out the portable narrowband setup with my William Optics GT81 APO refractor, Moonlite automated focuser, ZWO ASI1600MM-Pro Mono camera, iOptron CEM25P mount. It snowed and was cloudy the rest of the time, but I did have a chance to really test out the setup away from the house, and it all worked beautifully. Unfortunately I also forgot to take my Macbook Pro, but ended up running everything from my iPhone using Jump Desktop to remote into the astro system. The weather didn't cooperate, but so what? We had such a fun time down at Lisa and Neil's place this weekend, and just to prove there was at least a little astronomy stuff going on, here's a pic of my setup running in the library.
NGC 2174, the Monkey Head Nebula. I went with the Hubble Palette, SHO, on this one. Exposures: 24 x 120 seconds Ha, 26 x 120 seconds OIII, 24 x 120 seconds SII. Equipment: William Optics GT81 APO refractor, ZWO ASI1600MM-Pro monochrome 16MP camera (unity gain 139/21), Astronomik filters, iOptron CEM25P mount, INDI/Ekos/KStars control software. NGC 2174 is a faint emission nebula located in the constellation Orion, about 6400 light-years away. This was a test of my field setup that I'll taking on the road in a week. I'll have to come back to NGC 2174 with longer exposures--and more of them. And dark frames. I didn't shoot any calibration frames in this run.
Here's my processing of NGC 2174 in Hydrogen-alpha and Oxygen (without the Sulfur frames).
Tonight's setup: William Optics GT81, Moonlite Focuser, ZWO ASI1600MM-Pro, ASI 120MM. This is my narrowband setup, and tonight it's all about the focuser.
I finished the night of Feb 9th with a small batch of frames to process--really only enough for this bi-color Ha-OIII of the Rosette. I also shot some Ha frames of IC 443, the Jellyfish supernova remnant. Both are looking okay, but I need more data. And the weather doesn't look like it's going to cooperate until the weekend--snow and rain. (I was also playing with the old WO 200mm guide scope with this session, and it went well--Total RMS" in the .60s and .70s most of the time. RMS is the Root Mean Square in arcseconds, the standard deviation of the accumulated star movements over a particular guiding session. Lower is better). Exposures: 28 x 240 seconds of Ha, 26 x 240 seconds of OIII. Equipment: William Optics GT81 APO refractor, ZWO ASI1600MM-Pro monochrome 16MP camera (unity gain 139/21), Astronomik filters, iOptron CEM25P mount, INDI/Ekos/KStars running in Stellarmate/Raspberry Pi 3b+
Setup for the night:
Well, maybe. Astronomers in Japan discovered a new Kuiper belt object (KBO), a rock with a 1.3km radius at the edge of our Solar System. That's more than 7.1 billion km, 4.4 billion miles away. What makes this story particularly remarkable is the equipment used to make the discovery, a pair of Celestron 11" RASA astrographs--basically something I can purchase from many astronomy equipment vendors. That's what is so amazing. Equipment powerful enough to detect 1.3 kilometer-sized chunks of rock at the edge of our solar system is easily available to amateur astronomers. This is my "artist's rendering", with the rock occulting a bright background star, which is the method used by the astronomers to detect it. Here's the article in Nature Astronomy: https://www.nature.com/
Our beautiful planet rotates on its axis once every 23.93447 hours (23 hours, 56 minutes, 4.091 seconds). This is one sidereal day--sidereal time is based on the earth's rate of rotation measured relative to the stars that are--for the most part--fixed in position. Here we go: 23.93447 hours = 86164.091 seconds. So, we need to do a 360 degree rotation of the right ascension motor shaft in 86164.091 seconds to match the earth's rotation speed. Sounds simple enough. Backing into the time/revolution (360 deg) before the 100:1 gearhead ratio, we have: 86164.091 / 100 = 861.64091 seconds, or 14.3606 minutes / 360 degrees, which is close to what I'm getting for a full rotation with my current test system: NEMA 11 stepper + 100:1 planetary gearhead and A4988 stepper driver running with 1/16 microstepping. I'm probably going to build the second prototype with a NEMA 17 + 139:1 planetary gearhead, but still waiting on that to arrive. And I will most likely continue to run with 1/16 microsteps. The downside is microstepping significantly reduces torque--I'm sacrificing torque for slower, smoother steps, but I'm thinking I will make up some of this with the 100:1 harmonic drive gearhead (CSF-14-100-GH-F0ACB). The idea is to get the motor with the planetary gearbox to do one rotation in a little over 14 minutes, and then by adding the harmonic drive I'll multiply the rotation time by 100, and we should end up around 86164.091 seconds, or one sidereal day. I think that sounds right? (Also, don't forget the direction is reversed with the harmonic drive--clockwise rotation of the wave generator results in the flexspline moving counterclockwise).
The shot below has my attached 3D printed adapter for a camera mount. Once I test the rotation speed adequately, I will try out some long exposures with the Nikon.
Here's the latest component and wiring setup, driven by an Arduino Nano and A4988 Stepper Driver, with the whole thing running off a single 12vdc power supply. The bottom frame is the entire rotation test taped together and functional.
Star Tracker Build: the 100:1 reduction Harmonic Drive gearhead arrived today, and I'm planning out the mechanics for the direct drive train and structure for a case (3D printing a prototype case that will hold everything together tonight). Harmonic drives are the way to go if you're looking for extreme precision, zero backlash, and just plain cool technology: https://www.youtube.com/watch?v=3mWemlMEzFk I will be using the original iOptron CEM25P saddle for testing, and the threaded holes in the harmonic drive line up neatly. Gearhead specs here: http://www.harmonicdrive.net/products/servo-mount-gearheads/harmonic-drive/csf-gh/14/csf-14-100-gh