Betelgeuse Fading

Something is definitely not right with Orion. For anyone familiar with the sky the constellation just looks wrong with Betelgeuse at half its normal brilliance.

We have long known Betelgeuse is a dying star, in the last stages of its life. Old stars tend to be unstable, changing in brightness. Betelgeuse has always varied a bit, but this is the largest change on record.

The magnitude of Betelgeuse over the past 35 years, data from the AAVSO
The magnitude of Betelgeuse over the past 35 years, data from the AAVSO

It is odd to see such an iconic star change so dramatically, a reminder that not even the stars are permanent.

Orion with a faint Betelgeuse changing the appearance of this familiar constellation
Orion with a faint Betelgeuse changing the appearance of this familiar constellation, photo taken December 29, 2019

The photo tends to flatten the magnitude of stars, the difference is not as obvious. You need to step outside and look for yourself. Orion currently rises late in the evening.

Orion Revisited

The Great Nebula of Orion is a beautiful object, the brightest nebulae in the sky. It is also quite easy to photograph, making it somewhat of a standard target. I, like many astrophotographers, use the nebula as something of calibration target to check new equipment and processes.

This shot was taken with a Canon 6D and a TV-76mm telescope, a combination I want to work with this summer. I also changed up my processing flow a bit, re-ordering the steps, to achieve better calibration. The result is a more neutral color tone in the original, I can then saturate the image to taste for display or printing. Th original might be a bit closer to true color. Of course, “true color” is a bit of an illusion in astrophotography, where everything is relative.

Orion Nebula
M42, The Orion Nebula, Canon 6D and TV-76mm, 16x240s+10x60s+10x15s @ISO6400

Postcard from the Universe – Orion Nebula with the EOS-M

The first astrophoto taken with the EOS-M. Considering the trouble it is to manually trigger the exposures without proper camera control, I am surprised I stuck it out to take 40+ subs. Since 30 seconds was the longest I could program the camera for I simply maxed out the ISO and took a lot of subs plus a dozen darks. There is still way too much noise in the resulting frame. Still, the ISO 12,800 frames are not all that bad, better than I expected. If this camera had remote control it would be a decent little astro camera. Longer subs and a lower ISO would deliver decent results.

NGC1976 The Orion Nebula
The Orion Nebula with and EOS-M, 40x30s exposures @ ISO12,800, AT6RC and 0.8x focal reducer, a set of 12x4s exposures used to reveal detail in the core.

Better Elevation Bearings for an Orion XT8

A telescope needs to move smoothly, without any binding or sticking. The elegantly simple bearing design used in dobsonian telescopes uses a smooth surface riding on a small pad of some low friction material. This requires a pad of some material that slides smoothly and does not stick, to provide the motion. The standard answer of telescope builders is polytetrafluoroethylene, simply referred to by the acronym PTFE or the trade name Teflon.

Orion Elevation Pads
Elevation bearing of an Orion XT8 8" dobsonian telescope
I recently spent some time rebuilding a small dobsonian telescope, one of the telescopes that belongs to the Mauna Kea VIS and is used every night in the public program. The ‘scope is a commercial unit built by Orion Telescopes, an 8″ f/6 ‘scope. These telescopes are quite popular, with good reason… low cost, decent performance and very easy to use. The 8″ version I was working on retails in price for about $330.

The price is excellent for an 8-inch telescope, but there is some sign of cost cutting in the more recent versions. One interesting difference I found in this ‘scope was the bearing material. The bearing pads that are supplied do not appear to be PTFE, but instead a much harder material, possibly HDPE instead, which would be cheaper than PTFE. replacing these with PTFE results in a nice improvement in the smoothness and ease of movement of the telescope.

This particular telescope was missing two bearing pads, so some replacement was required, whatever the material. Without access to the original parts it was necessary to obtain whatever material was available, and that would be PTFE. Since it came in a different thickness than the original bearing it was also necessary to replace all four pads.

Elevation Pad
Elevation bearing pad on an Orion XT8 8" dobsonian telescope
Teflon in sizes suitable for bearing pads can be ordered from a number of suppliers across the web. The material shown here was purchased from Scopestuff, where a 12″ x 3/4″ strip of 1/8″ thick PTFE is available for $11, just the right size to cut bearing pads for the Orion XT series telescopes.

In place of the original staples, a small flat head screw is used to secure the Teflon in place. The soft material is easy to work. As long as the tools are sharp drilling and countersinking the pieces is easy. Best use a new drill bit if you have one, or grab one of the odd sizes that never seem to be used.

Position of the bearing around the radius of the trunnion have some impact into how easily the telescope will move. Positioned closer together and closer to the bottom of the bearing and the telescope will move more easily. Positions further part and higher on the bearing sides will result in more friction as the trunnion presses outwards against the pads.

The repair worked quite nicely, with a ‘scope that move smoothly across the sky. A bit more cleaning and a few minutes collimating the optics had the small telescope again ready for the sky.