Saturday, September 9, 2017

Sunspots AR 2679, AR 2675, AR 2673 on 09-Sept-2017

Sunspots AR 2679, AR 2675, AR 2673 on 09-Sept-2017 w/ 127SLT and ASI290MC at prime focus.

Given the unusual sunspot activity over the last few days, I made a Scheiner mask to aid in focusing, since you can't use a Bahtinov mask without a star to focus on. The laptop was set up in the back of our SUV to shield it from glare and I used my DIY solar filter mount w/ Thousand Oaks film on the 127SLT. Best 10% of frames from 1 minute of video.

Tuesday, August 29, 2017

4k wallpaper - Partial Moon

Want some high resolution moon wallpaper? This image is free for noncommercial use.

This picture is a composite from video, taken with a 127SLT and ZWO ASI290MC taken at prime focus. The video was composited with Microsoft's Image Composite Editor (ICE), edited in Gimp to place it on a black background of the right proportions, sharpened with Registax Wavelets, and level adjusted in Gimp.

Download the full resolution image from my Dropbox. In the upper right corner, you'll find a button with two dots. Click it and a dropdown box will open - an option there will let you download the full resolution file.

If you want a similar shot with a fuller moon, I have one here. I personally prefer this one, since it shows features in 3D a bit better due to the more oblique lighting.

Lunar 100 Target 4: Apennine Mountain Range

Image Details: 127SLT w/ 1.5x Barlow and ASI290MC, stacked from one minute of video

Somewhere around 3.75 billion years ago, during the Late Heavy Bombardment, a large asteroid or protoplanet hit the northern hemisphere of the moon. The impact caused an enormous impact crater known as the Imbrium Basin, bordered by high steep walls of rock.

Later lava partially filled in the basin, and hardened to a smooth dark surface known as Mare Imbrium (sea of showers). The Mare Imbrium The Apennine mountains are part of the remainder of the high crater edges. Even though partially buried by lava, the highest peaks are 5 km / 3.1 m high.

The mountain range is about 600 km / 370 m long. It is easily visible with binoculars and is a pretty stunning sight when the terminator line is near it, bringing the 3 dimensional structure into view.

The Apollo 15 mission landed here - the position is marked on the photograph.

Lunar 100 Target 2: Earthshine

Photo Details: 127SLT with SLR at prime focus, stacked from video

Shortly after sunrise or before sunset, when the moon is just a bright sliver, you can sometimes see the dark portion illuminated with a soft, dim glow. To photograph it you have to overexpose the lit portion, resulting in the loss of most detail there.

This dim light is sunlight that has first been reflected from the lit portion of the day side of earth, bounced of the part of the near side of the moon that is not directly lit, and then back down to your retina or camera. Cool, huh?

This diagram from Wikipedia demonstrates the concept very well. 

Saturday, July 22, 2017

Low cost DIY solar filter for small/medium telescopes

Photo Details: 127SLT with SLR at prime focus, stacked from 1 minute of video

In preparation for the coming eclipse, I decided I wanted to get a solar filter for solar observation and photography. What I quickly found was that the actual filter material is not expensive, but buying a filter with a mount designed for your specific telescope can be. I decided to build a mount. Here's one approach that has worked for me.


There are relatively few ways to seriously injure yourself in amateur astronomy, but solar observation and photography is absolutely one of them. All it takes is a glance through an unfiltered telescope to destroy your eye, rendering yourself blind. You remember how you can set ants on fire with a magnifying glass? A telescope is a very large magnifying glass. Read the warnings that come with the solar filter film and follow them. Cover your finder scope! Be careful. Really careful. The information presented here is what worked for me, but your safety is your responsibility alone. If you are not confident in your ability to build a solar filter that will be securely attached to your telescope, don't undertake a project like this. This filter is for occasional use in dry conditions - it will not hold up with exposure to moisture.

This picture shows how the filter mounts - note that you must cover the finder scope before use!

I checked into the various types of solar film, and decided I like the yellow cast that the Thousand Oaks Optical solar film gives. Amazon sells sheets of it in various sizes. I decided that the easiest way to mount it was to buy a sheet larger than my scope's aperture, and sandwich it between two sheets of foam board. I'd then stack some layers of foam board on the back with a cylinder cut out, so that it had a snug friction fit over the telescope's tube. I bought the 8x8" sheet for my 5"/127 mm scope, which cost about $20.

You don't want the filter falling off while you're observing. A gust of wind must not be able to remove it, so I made it as snug a fit as I reasonably could.

Here's the steps I took.I started by cutting two pieces of foam that were a bit larger than my 8x8" solar film. Those two pieces will support the film and serve as the two layers of the foam/film/foam sandwich.

I then cut four more pieces that were a little smaller than 8x8" to serve as the friction mount on the tube. I used the telescope cap as a guide - remember that you want the inside diameter of the cap, though, not the inside diameter.  I traced the outside diameter and then conservatively freehanded the inside diameter. I cut to the inside diameter, leaving a small amount of material. Remember, we want a snug fit - we can't have this thing falling off and letting the sun burn a hole in our retina or camera sensor. Safety first!

The two sandwich pieces should have a hole cut that is smaller than the tube diameter, because you want the filter mount to slide over the tube and then stop. You want it to hit foam board before it hits film.

I stacked four of the smaller friction mount pieces and glued them together hot glue, and then carefully sanded the inner hole until it fit very snugly over the optical tube. I then hot glued the stack to one of the sandwich mount pieces.

I then sandwiched the film in between the two front sandwich mount pieces, and taped them together securely with electrical tape.  Here you see the finished filter face down, from the back/telescope side. Remember to observe the orientation of the film as specified in the film's instructions!

Your finder scope must be covered, or have a filter of its own. You can get the alignment close by watching the shadow cast by the scope. I usually remove the filter and put the protective cap on the telescope (to protect the optics and against mistakes) and then move the scope until the shadow is a round circle. That gets you pretty close. Then I remove the cap and quickly install the filter.

Go slow, and think through every move before you make it - your natural temptation is to look up at your target. If there are kids or adults who are unfamiliar with telescopes and solar observations with you, be cautious and communicate the hazards to them.

I really enjoy using the filter for both observing and photography. Here's the video that the first image was stacked from, just to give you an idea of what to expect. Be careful, and have fun!

Saturday, July 15, 2017

Lunar 100 Target 15 - The Straight Wall

Photo Details: Celestron 127SLT, ZWO ASI290NC, 1.5x Barlow, stacked from 1 minute video

View Full Size Image

Midway across the moon's southern hemisphere, just north of Tycho crater, is an odd sight. On a lunar surface pocked with round craters, a seemingly straight line cuts across one of the dark, smooth cooled lava plains. This is Rupes Recta, or the Straight Wall. It's the best example of a linear fault line to be seen on the moon with a small telescope.

A fault is a crack in an otherwise continuous in a section of rock. In this case, it is thought that the crack resulted from tension in the crust. The rock would have deformed at first, and then broken. One side drops, exposing a rock face called a scarp. The "wall" looks nearly vertical, but is known to have a slope ranging from 7-20 degrees. It is about 110 km/ 68 miles long and 2.5 km/1.5 miles wide. Estimates of its height range from 240m/800 ft to 500m/1640 ft.

The Straight Wall was first recorded in a drawing by Christiaan Huygens in 1686.

Friday, June 30, 2017

Lunar 100 Target 3 - Mare/highland dichotomy

Photo Details: Celestron 127SLT, ZWO ASI290MC, composite from video
03-Apr-2017, cropped from full disk.

A very large high resolution version of this image is available for download.

Note: As mentioned in the first post, these posts will not list the Lunar 100 features in order because the features are not always visible at different times. Item 2, moonshine, will be posted when viewing conditions allow.

The third target on the Lunar 100 list is the mare/highland dichotomy. When you look at the surface of the moon, you'll notice two distinctive surface types. Smoother dark areas, the maria, are so named because they were mistaken for actual seas by early astronomers. The cropped photo above highlights the Mare Crisium. It is approximately 550 km wide. The maria are relatively smooth plains of basaltic rock that formed from cooling lava produced by volcanic eruptions between 3 and 4 billion years ago. It is believe that deep impressions formed by impacts were filled in with magma, and then hardened to form the maria. Higher concentrations of titanium and iron make this rock significantly darker than the rest of the surface of the moon. They are the youngest lunar surfaces, and show significantly less crater activity from impacts than the lunar highlands.

The darker, smoother mare shows a lower density of impact craters than the surrounding lighter highlands

The lighter areas of the lunar surface are significantly older. They are believed to have formed between 4 and 4.5 billions years ago when the surface of the moon was still molten. They are composed primarily of anorthosite, which is an igneous rock. Anorthosite forms when molten rock cools more slowly than in the formation of basalts. This indicates that the highlands solidified under different conditions than the maria. The highlands formed very early in the formation of the solar system, which is itself estimated to be 4.6 billion years old.

Notably, the rocks from the lunar highlands are older than the oldest Earth rocks found this far. On earth, the igneous rocks formed at the beginning of the Earth's life have been predominately covered by tectonic activity and sedimentary rock formation. The moon has cooled sufficiently that it has no significant tectonic activity, and the lack of water and atmosphere make sedimentary rock formation impossible. The oldest rocks on the moon are still exposed.