Over-processed! The seeing was atrocious…
C8 Moon
Category: Astrophotography
Peering into the dark with a camera
Afocal Luna
With a few public outreach events this last week I had a few opportunities to hold my phone up to the eyepiece and shoot a few shots of a waxing Moon. The iPhone 5S does have a notably better camera than my old 3S. The afocal method does provide some nice snapshots of the Moon.
As usual I demonstrated the technique to our viewers, showing them how to use their phone to shoot the Moon. The result? Big smiles and happy folks, thrilled to have some great Moon photos of their own.
Luna
Gamma Cygni
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.
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.
The Moon and Mercury
The Earth’s Shadow… Twice
One of the more sublime sights seen from Mauna Kea is the shadow of the mountain rising through the mist and haze at sunset. One of the more sublime sights in the heavens is the Earth’s shadow crossing the face of the Moon, a total lunar eclipse. It is possible to combine these two phenomena if the timing is right, the Earth’s shadow seen twice.
Back on Feb 20th, 2008 the timing was right. A friend of mine, Alex Mukensnable, noted the timing and set up to catch the eclipsed Moon rising in the shadow. The result was a great set of photos. The photo is nice enough as a still, be he did more than that, he shot the event as a timelapse and assembled a video of the rising Moon.
There are several possible variations depending on the timing with this sort of event… If the Moon was at the height of totality rising it would also be right at the tip of the mountain shadow as it rises. This is a relatively rare event as the timing requirements are tight. Unfortunately it would also be quite dim, darkened by the shadow, and not easily seen as it rose.
As lunar eclipses are long events, taking several hours to complete, the likelihood of the Moon being in at least the partial eclipse phase at sunset is fairly good. Still a rare event, but not extraordinarily so. Thus for a single site, the summit of Mauna Kea this even happens in both 2008 and 2015.
As the Earth’s shadow is about 2.6° across at lunar orbit, the closest a partially eclipsed Moon will be seen from the the very tip of the shadow is about 1.3°. This is a bit less than three lunar diameters. Of course these numbers will vary a few percent depending in the distance to the Moon which changes as it makes its elliptical orbit.
The Moon moves slowly across the sky from west to east, thus before totality the Moon would be above the tip of the mountain shadow. After totality, with the eclipse ending, the eclipsed Moon will be in the shadow. Placing the Moon in the shadow also makes it easier to see, the bright crescent a better contrast to the dark shadow. This is the case for the 2008 eclipse captured by Alex.
Of course you could reverse all this timing and watch the event at moonset and sunrise. If the eclipse was just starting at dawn it would again place the eclipse in the mountain shadow.
Another important point to remember is that the shape of the mountain’s shadow has little to do with the shape of the mountain. The shadow will always be a neatly conical form due to the effects of projection.
What brings this event back to the fore is that the timing will soon be correct to see this same event again. The total lunar eclipse of Sept 27th, 2015 will be a bit of a dud for Hawaii, most of the eclipse already over as the Sun sets and the Moon rises over the islands. However, this event will feature very similar timing to the 2008 eclipse. The Moon will still be in partial eclipse when it rises. As it rises a short time after full Moon it will again be deep in the shadow of Mauna Kea as it comes over the horizon.
You know where you will find me on the evening of the 27th. Now I just need some clear weather that day.
Mauna Kea Starscape
With all of the emotion being expressed over telescopes on the mountain this week, just a reminder of why Mauna Kea is the perfect place from which to look to the heavens…
