Sentinel
Category: Astronomy
Exploring the cosmos
Gamma Cygni
Sacred Summit
The summit of Mauna Kea stands behind the uprights of an ancient ahu or shrine.
SBIG ST-i Camera Mount
The SBIG ST-i is a useful little camera, I have enjoyed using mine. I usually use the camera for autoguiding, but it can also be used for basic astrophotography and even some science. In preparation for using the ST-i with a group of students I had need to make a couple additional mounts. After I go to the effort of designing a simple solution to my problem I may as well share the solution.
ST-i camera mount mechanical drawing
I have included the mechanical drawing for the mount in the link above. I machined this from a block of aluminum. There is no reason it could not be made of wood or plastic to allow fabrication with whatever equipment is available. For wood you may need to make the block a little longer and use inserts for the threading. Plastic could be done pretty much as drawn.
The version I made was milled from a solid chunk of aluminum, but a good version could be easily cut from wood and assembled with brass inserts. The design could also be 3D printed without much loss in mechanical robustness.
To mount a c-mount lens you will need the adapter ring sold by SBIG to convert the 1.25″ filter thread found on the camera to the 1″ c-mount thread. Still, at $40 this ring is a lot less than the $350 guiding kit. Good c-mount lenses can be found from many sources for less than $100. You will need a focal length between 75 and 150mm for a nice image scale and as wide an f/ratio as you can find. The kit includes a 100mm f/2.8 lens which I find is quite useful in guiding my Televue 76mm or the AT6RC.
Geminid Meteor Shower
The annual Geminid meteor shower is one of the most reliable annual meteor showers. The shower is noted for a steady stream of bright meteors with rates of well over 100 per hour.
The shower peak is predicted for December 14th, at around 18:00UT (14Dec 08:00HST). For viewers in the central Pacific this favors the evening of Dec 13th into the morning of Dec 14th, starting around 8pm as Gemini rises in the east. The peak is broad, with near peak rates occurring a day either side of the maximum, thus allowing everyone with a dark sky to enjoy this event. Thus the evening of the 14th may also provide a good viewing opportunity.
Even from more southerly sites, this is an excellent stream of often bright, medium-speed meteors, a rewarding event for all observers, whatever method they employ. The peak has shown slight signs of variability in its rates and timing in recent years, with the more reliably-reported maxima during the past two decades (HMO, p. 171) all having occurred within λ⊙ = 261.5° to 262.4°, 2015 December 14, 01h30m–23h UT. Near-peak Geminid rates usually persist for almost a day though, so much of the world has the chance to enjoy something of the shower’s best, regardless of when the maximum actually happens. Mass-sorting within the stream means fainter telescopic meteors should be most abundant almost a day ahead of the visual maximum, with telescopic results indicating such meteors radiate from an elongated region, perhaps with three sub-centres. Further results on this topic would be useful. The 2015 peak arrives just three days after new Moon, so observing conditions are ideal. – IMO 2015 Meteor Calendar
As noted by the IMO calendar entry above, new Moon will be on the 11th, placing the peak just a few days after new, a thin crescent in the evening sky that will set early. This leaves a perfect dark sky to enjoy the meteor shower. In the islands Gemini will rise around 8pm, bringing the constellation Gemini and the shower radiant over the horizon and marking the start of the show.
Watching meteors requires no more equipment than your eyes and a dark sky, and can be enjoyable for just about anyone.
A Camera Security Device
Taking astrophotos or time lapse often involves leaving a camera out in the dark for long periods. Cameras are somewhat more robust than humans, tolerating the cold for a bit longer. As a result often the cameras are unattended while the human seeks shelter in some warmer place. This can result in the theft of the unattended camera.
On the mountain is not the only place this risk exists. I have often left a camera operating for hours in my driveway at the front of my house attached to a telescope. In an attempt to make it somewhat more difficult to simply grab and run I designed a simple security device. A little block of aluminum with a slot that accommodates a standard computer cable lock.
Machined from aluminum the block took very little time to make and provides a great deal peace of mind. It is not impervious to a determined attack, but does prevent the camera from simply walking away. In place of aluminum it could probably be 3D printed if you do not have a machine shop available. With a little more patience it could be manufactured with simply hand tools.
Mechanical design for the CamLockBlock
The slot is the standard Kensington security slot, a 3mm x 7mm slot as found in almost all laptop computers. The locks are available from just about anyplace that sells computer accessories.
The screw I use is a tamperproof button head screw, one that requires a special tool to remove. A standard hex button head screw would probably work in most situations, it is unlikely that an opportunistic thief will have a set of allen keys handy.
The block can be used on a telescope, with the cable wrapped around a tripod leg. It can also be used on a tripod, a ¼-20 hole is tapped to allow the block to sit between the camera and the tripod head. The security cable can then be secured to anything available. Atop Mauna Kea there are many railings, guardrails and signposts that would provide a solid locking point. In nature there are fewer steel poles, but a tree trunk or something similar would also serve.
The design can be modified to suit ones needs, the mechanical drawing above shows the device in its simplest form. As you can see in the photo my prototype block includes two screw holes for the camera and a 3/8″ threaded hole for larger tripods. I also put a second lock slot on the bottom to have the option of having the lock stick out in a different direction.
Check the dimensions of your camera, tripod head or favorite adapter plate to insure that the lock will fit without interference. You can always adjust the dimensions or the mounting hole positions to accommodate your setup.
A LED Streetlamp Replacement
It may be the day after Thansgiving, but that did not stop the electrical contractors installing new streetlamps in Waikoloa Village.
We are not sad to see the old low pressure sodium light go, it has been a nuisance. The poorly designed sodium lamp creating glare into our windows We had called to complain with the county, but nothing was ever done. The glare intruded on our bedroom window, a real issue, somewhat alleviated by the growth of our plumeria along the front blocking the light, a deliberate solution on my part.
The big question is whether the new LED light improves the astronomy situation from my driveway. The old sodium lamps along the street made it impossible to do visual observing, there was simply too much glare. The new lamps should darken the sky and create far less light directed at my driveway.
Even better, the lamps in question are C&W Energy Star Friendly® units with reduced blue emissions. Elimination of almost all of the blue light greatly reduces scatter in the atmosphere and is better for the observatories.
With the old light I was able to do astrophotography from the driveway using an LPR filter that blocked the 589nm of sodium light. The new lights will have a broader spectrum and be more difficult to block. On the other hand they send very little light upwards, possibly improving the situation. It will be interesting to see what the difference is. When the Moon is a few days further gone I will have to setup the camera and find out.
It may also be a good idea to check the old CloudCam images against new images as the replacement continues. It will be interesting to see if the emissions from the neighborhood are effectively reduced as seen from the top of the mountain.
Mercury Appears in the Evening Sky
The planet Mercury is starting an evening apparition. The planet should become visible this week just above the fading glow of the setting Sun as a magnitude -1 object. The planet is moving about 1° further from the Sun and higher in the sunset each day, reaching a maximum elongation of 20° on December 28th.
Full Moon
Hawaii Discovers: The World’s Leading Observatory Was Born in Hawaii 25 Years Ago
W. M. Keck Observatory press release…
Twenty-five years ago in 1990, the average US house cost $123,000, the Dow Jones averaged 2633 and gasoline cost a little more than a dollar-thirty a gallon. Saturn wasn’t just a planet: it was now a newly launched car company from GM, The Simpsons was aired for the first time and the Space Shuttle Discovery placed the Hubble Space Telescope into orbit.
Want Of Light
Before the W. M. Keck Observatory was built, the 200-inch Hale Telescope at Palomar Observatory reigned supreme. It was the largest telescope in the world, but after 50 years, progress in astronomy was flattening out because the instruments needed more photons than the 5-meter mirror could provide.
The biggest hindrance to an explosion of discoveries was a want of light and the telescopes themselves were the problem. Mirrors larger than Palomar’s could not be made and supported at the exacting levels needed for astronomy.
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