World War I Airplanes

Old Warplanes

During my annual visit to the Military Through the Ages exhibition this year at the Jamestown Settlement Museum I came across two displays I'd never seen before. First was a French biplane shown below.

This plane was armed with a machine gun whose firing mechanism was synchronized with the propeller so bullets wouldn't destroy the blades.

The fabric and wire construction of these planes seems incredibly fragile compared to modern fighters. Cloth and wire weren't much protection from machine gun bullets! Nearby was a German plane from the same war.

A smaller machine gun fired forward from the German plane.

Cockpit controls seem extremely primitive!

The German plane was a Fokker E3 whose features are described below.

Among the many reenactors attending this year's exhibition was a group portraying The Devil's Nightmare Regiment from roughly the year 1529. They always present a colorful display of weapons, costumes, and living customs from this time period. I found their recruitment poster particularly amusing.

It's always a pleasure to visit this wonderful exhibition each year, especially on a mild sunny day!




   

Magnetic Tensegrity Table

Nice Physics Showpiece!

I recently discovered a new physics toy to add to my collection. The beautiful Magnetic Tensegrity Table is shown below. It's made in Britain and comes unassembled in a small box.

The height is about 5 inches, just under 13 centimeters. Many parts and screws were extremely small. They challenged my diminished dexterity during assembly. But the assembly instructions were excellent! In fact, I've never seen a better illustrated, clearly worded, step by step assembly guide!

So how does it work? Three vertical wires evenly spaced around the edges of the circular base and top are under tension. The wires can't support a load by compression, so they are not supporting the top. The small powerful magnets suspended by hooks are attracting each other and would seem to draw the red top and base together. So how does the top stay up?

The curved silver magnet supports are the key. Look at the upper magnet. It is pulled down by the attraction of the magnet below. The downward force on the upper magnet presses its (left) silver support down onto the red base. Now look at the bottom magnet. It is pulled up by the attraction of the magnet above. The upward force on the bottom magnet presses its (right) silver support up against the red top. So the base is pushed down while the top is pushed up! That's why the wires are under tension!

There's enough lift on the top to support extra weight. The next picture shows a 200 gram mass resting on the table top! 

The manufacturer suggested the table would hold up to about 260 grams before collapsing. I foolishly tried 300 grams, and, yes, the whole thing collapsed! It wasn't easy to separate the magnets and reassemble the table, but, after an hour or so, I eventually succeeded. I'll stick to the 200 gram mass from now on. 

Refractor With New Camera

Sky Is Too Bright

I've been impatient to see how a new Nikon Z6 2 camera would work when attached to my 130 mm Stellarvue refractor. Although sky conditions were poor on March 4th, strong winds had diminished, and it wasn't terribly cold. A 94 percent full Moon was present, but I decided to haul out my equipment and see what kind of images were possible. Before sunset I set up the telescope and camera as shown below.

It takes quite a while to assemble the tripod, balance the telescope, hook up the electrical connections, and set up a laptop computer. I used a star diagonal with the camera instead of a straight through attachment because, otherwise, it would be hard to see the camera viewing screen with the scope pointed near the zenith.

The temperature had fallen to about 52 degrees a few hours after sunset, but bright moonlight filled the sky with natural light pollution. I took this single shot 1/60-second picture of the Moon at ISO 100 using a 2X Barlow lens:

I quickly discovered how bright moonlight, neighborhood lights, and lack of flat field frames made all my pictures nearly useless at first inspection. For example, look at this image of the Pleiades star cluster constructed by stacking sixteen, 4-second exposures with ISO set at 51200.

Notice how the background sky looks blue instead of black. Also, notice the bright circular central region caused by uneven illumination of the camera sensor. A flat field frame (image of a uniform light source) would record uneven illumination and allow me to eliminate it. But I didn't record a flat field frame. It took hours of image processing to reduce initially awful unnatural colors. I also cropped out obvious vignetting around the outer edges of the original image. The central circular glow is an image flaw, but the hazy silver glow around three bright stars near the bottom is a hint of real reflection nebulosity.

One of my neighbors had a back yard floodlight shining directly on the telescope from two houses away. This made it impossible to photograph the flame nebula in Orion. All trial images had strange colors and light arcs caused by reflection of the floodlight in the telescope tube. Eventually, Orion rose high enough to avoid unwanted reflections and I was able to get the following picture of the Orion Nebula by stacking two, 15-second exposures at ISO 6400.

It took many attempts of trial and error image processing to correct erroneous colors and reduce the effects of sky brightness. You can still see evidence of vignetting and a hazy remnant of light pollution in the previous image. I think I can do better with longer exposures on a darker night.

I pointed the telescope at two star clusters hoping they would show up reasonably well in the bright sky. The image of cluster M37 in Auriga shown in the next image is disappointing because star colors don't seem correct. This image is a stack of twelve, 5-second exposures at ISO 51200.

Inaccurate colors are even more evident in the next image of cluster M35 in Gemini. Smaller, more distant cluster NGC 2158 is visible above M35. This is a stack of 24, 5-second exposures at ISO 51200.

Other star images I've made with this camera under darker skies with different lenses have produced accurate star colors. I'm guessing the camera's white balance was possibly thrown off by bright moonlight and the neighbor's floodlight. Looking back at pictures with correct star colors I noticed how histogram plots for separate red, green, and blue channels significantly overlapped. In these latest incorrectly colored images, however, the red, green, and blue histograms didn't overlap at all! Eventually, I discovered a way to make color corrections using Photoshop. These corrections made the three histograms overlap more. Yet, true colors didn't seem fully restored. I also wonder if I set ISO values too high. I'll have to experiment more when the sky is darker.

After a while I inserted a 2X Barlow lens and tried capturing other celestial targets. All the pictures below were made using the 2X Barlow. Galaxies M81 and M82 in Ursa Major are only about 37 arc minutes apart, so I thought I might fit them in one field of view. For this shot the telescope pointed away from the annoying floodlight and away from the bright Moon. This is a stack of ten, 6-second exposures at ISO 51200. M81 is in the lower right and M82 is in the upper left.

Faint traces of M81's spiral structure are visible, but background sky brightness and short exposure times don't permit visibility of dim details. I'd like to try this again with better conditions. Although the telescope was tracking sky rotation, tracking was inaccurate due to poor polar alignment. Inaccurate tracking limits exposure time. I still don't have a quick, efficient way to get good polar alignment with my non-permanent mount. I found elongated star images in exposures longer than about 8 seconds. If I want to improve image quality, I'll have to find some solution to the polar alignment problem.

Another group of closely spaced galaxies is located in Leo. The next image shows M65, M66, and NGC 3628 together. This is a stack of eight, 8-second exposures at ISO 51200.

Faint edge-on galaxy NGC 3628 is in the upper left, M66 is in the upper right and M65 is below center. Once again, hints of faint spiral arms are present.

Globular cluster M3 in Bootes had risen far enough above the horizon to make the next image possible. This is a stack of eight, 8-second images at ISO 51200.

Finally, planetary nebula NGC 2392 in Gemini is visible in the next picture made from a stack of ten, 6-second exposures at ISO 12800. The 2X Barlow didn't provide enough magnification to show much detail. I also wonder if the color is accurate.

Temperature had dropped to about 47 degrees just after midnight. I was getting tired and chilled, so it was time to quit. All the equipment was bone dry! There was not one drop of dew! Other conditions were imperfect, but I couldn't complain about dew! After I took everything apart and hauled all the gear inside, just as I was closing the door, my neighbor turned off the blasted floodlight!

Departing Sunspots

Afternoon Session

My last solar imaging session was months ago in October!  Thereafter, most days were cloudy, or too cold, or too windy. Finally, on February 18th, a clear day arrived without strong wind or freezing temperature. I waited for afternoon to let temperature rise into the mid-40's and began imaging at 1:45 pm EST. Seeing was mediocre. There were no dramatic prominences, and most sunspots were located in the Sun's western hemisphere where they were destined to depart in the next few days by rotating out of view. The first image below is a 12-panel mosaic showing features in the western hemisphere.

Four sunspots are visible above. The most prominent one is sunspot 3226 in the northwest quadrant. In the southwest quadrant, from left to right, are sunspots 3220, 3217, and 3225. A few dark filaments appear on the disc.

Major sunspot 3226 with a light bridge across the umbra shows up well in the next close image. View it at 100 percent to see all the detail present.

Sunspots 3220, 3217, and 3225 also look nicely detailed when viewed at 100 percent in the following image of the southwest quadrant.

Sunspot 3217 is accompanied by a fan-shaped filament. Sunspot 3225 is closest to the limb where its neighboring white energetic region will rotate out of sight before the following umbra. Sunspot 3220, on the left, has a single umbra.

One other sunspot of note, 3229, was in the eastern hemisphere. It had emitted a powerful X-class solar flare just a day or two before. On February 18th, however, it appeared like this:

Evidence of 3229's eruptive nature remains in the image above. A dark filament arches above a white active area to the left of the umbra. Shooting straight up are narrow spiky eruptions emerging from the left-most white energetic area. View the image at 100 percent to see this best.

These images turned out remarkably well in spite of sometimes unsteady afternoon seeing. All images were made by stacking the best 400 frames from 4,000-frame videos.
 

Finderscope Experiment

Too Many Aberrations!

When I purchased my 130 mm Stellarvue refractor years ago it came with an 80 mm f/3.75 finderscope. I was curious to see if the finderscope could function as a 300 mm focal length telephoto lens when attached to my new Nikon Z6 2 camera. On February 13th I mounted the combination on a fixed tripod as shown in the picture below and hurried outside to take advantage of some rare clear sky.

Exposure times were limited to two seconds to avoid star trails. I compensated for short exposures by setting ISO at 51200. Focusing was extremely difficult because the finderscope has a helical focus mechanism. Since the camera was fixed to the tripod, I had to turn the entire finderscope to focus. This somewhat stiff rotation caused so much vibration on the unsteady tripod that it was hard to tell if stars were focused. Consequently, star images are a little bloated in the images that follow.

Lens aberrations are immediately apparent away from center in this full frame image of the Pleiades star cluster made by stacking seven 2-second unguided exposures.

The finderscope lens is probably a simple single spherical lens. Only the very center of such a lens is relatively free from aberration. There's a reason good telephoto lenses are so expensive! Unlike the finderscope, quality telephoto lenses contain multiple lens elements which, in combination, correct for the spherical and chromatic aberration seen here. I cropped out the majority of edge distortion and ended up with the next Pleiades image.

In the cropped picture above you can see how individual star images are slightly out of focus and bloated. You can also see a blue fringe on stars from chromatic aberration. On the positive side, the seven-image stack actually captured some silvery reflection nebula around two of the stars! The image scale also nicely includes the entire cluster!

I next tried capturing stars of Orion's belt with a stack of ten 2-second unguided exposures. The same edge aberrations were present in these full frame images, so I cropped out the edges to leave the following central region, slightly more than three degrees across.

The Flame Nebula and Horsehead Nebula are slightly visible on the left near the left belt star, Alnitak.

It's hard to point a camera at Orion without trying at least one image of the Orion Nebula, M42. The final cropped image below is just a single 2-second exposure. Notice blue fringes on stars due to chromatic aberration.

I really like the image scale of these pictures, but the finderscope/camera combination is really impractical. I don't think I'll try this again. Perhaps I'll buy a real 300 mm or 400 mm telephoto lens sometime in the future. For now, I'll look forward to using the camera with my 130 mm refractor for some guided exposures.
 

New Camera and Dobsonian Telescope

Testing a New Combination

Although my 12-inch Dobsonian telescope doesn't track stellar motion caused by Earth's rotation, I thought it would be interesting to test short exposure times with my new Nikon Z6 2 camera attached to this large aperture. On February 6th I gave it a try. A special adapter is required to attach the camera to the scope. The camera would not reach focus with first adapter I purchased. Eventually, I bought another adapter that brought the camera's focal plane a couple centimeters forward, enough to achieve focus.

The telescope effectively acted like a 1500 mm telephoto lens. I quickly discovered stars would trail unless exposures were very short. An approximate rule for avoiding star trails in unguided photos is to keep exposure times in seconds less than 500 divided by the lens focal length. For my telescope the rule said 500/1500 = 0.3 seconds would be the longest exposure I could take. Trial and error proved the rule accurate. To compensate for short exposure time I cranked the ISO up to 51200! The next image is a 0.3-second exposure of the Orion Nebula, M42, at ISO 51200. In spite of background noise associated with high ISO the image captured a lot of detail in only 0.3 seconds!

The Pleiades were high in the sky above most light pollution before the Moon rose. Another 0.3-second exposure at ISO 51200 captured only part of this cluster as seen in the next image. I should have moved the field of view around, taken a series of images, and then combined them to capture the entire cluster. Maybe I'll try this another time. The diffraction spikes on bright stars are kind of pretty!

I was particularly interested to see how Jupiter would look in a short exposure. The following 0.05-second exposure at ISO 500 overexposes the planet but allows all four major Jovian moons to be visible.

Based on the previous picture it looks like this particular telescope/camera combination might be great for capturing certain kinds of planetary conjunctions.

On this night, February 6th, comet C/2022 E3 ZTF was passing near the star, Capella, in the constellation, Auriga. I searched the neighborhood of Capella while looking at the camera's viewfinder screen, but couldn't find the comet. Instead, I took a picture of bright Capella itself with a 0.3-second exposure at ISO 51200. Yellow overexposed Capella shines nicely with accompanying diffraction spikes in the next image.

In my light polluted sky I misidentified the star Almach in Andromeda and photographed Mirach instead. I was surprised to see a faint, fuzzy object to the lower right of bright Mirach in the following image. The faint object is actually the 10th magnitude elliptical galaxy NGC 404! It's amazing how this faint distant object actually showed up in just a 0.3-second exposure at ISO 51200!

Finally, I tried a 0.2-second exposure at ISO 51200 to capture most of the star cluster, M41, in Canis Major. 

Soon after capturing M41 the nearly full Moon rose making the sky even worse for imaging. It was time to quit.

These results with very short exposure times make me wonder how nice it would be to have a 12-inch telescope on a tracking equatorial mount. Longer exposures with no star trailing would really show amazing stuff!

Comet C/2022 E3 ZTF

Partial Success

Almost all comets I've been able to observe have been difficult targets. They usually appear inconveniently close to the horizon, often before dawn when it's hard to get out of bed. Recently, prominent comet C/2022 E3 (ZTF) had an orbit bringing it close to the north celestial pole, so, for a good stretch of days, the comet was located relatively high in the sky to the north.

The comet's unfamiliar name has the following explanation according to earthsky.org: "It was discovered on March 2, 2022 and it was the third such object discovered in the fifth half month (A, B, C, D, E) of the year". (E3) It was discovered by a 48-inch telescope on Mount Palomar which is part of the Zwicky Transient Facility (ZTF). The C indicates it is a non-periodic comet.

I made several attempts to photograph the comet with my new Nikon Z6 2 camera. The first attempt on January 15th was successful as you can see in the following image which was constructed by stacking five 30-second guided exposures with a 70 mm f/2.8 lens at ISO 800.

The green coma and brighter part of the yellow dust tail are visible. Ultraviolet light from the Sun excites diatomic carbon present in gases emitted by the comet. The excited diatomic carbon then emits a green visible color. The dust tail's yellow color comes from reflected yellow sunlight. Darker skies, larger apertures, longer exposures, and telescopic magnification would be needed to reveal the long, dim, wispy ion tail which is not visible above.

I tried again on January 24th when the comet was closer to Earth. The next image is a stack of six 6-second unguided exposures at ISO 6400 with the 70 mm lens set at f/2.8.

Now the comet tail had spread out into a fan shape with a spike pointing ahead of the coma. This is a little easier to see in the following heavily enhanced, cropped image. Enhancing the image to reveal dim details also, unfortunately, brightens background noise. Therefore, the background sky doesn't look as black as it should. (All these images should be enlarged to see the comet in better detail.)

Viewing conditions were much more difficult on January 30th, two days before the comet made its closest approach to Earth. On this night the temperature was wonderfully mild, but the Moon was almost full, and the sky was covered with hazy thin clouds. In addition, it was very humid, and dew rapidly formed on exposed surfaces. Since the comet was closer to the celestial pole this night, I tried a slightly longer exposure time with the unguided camera mounted on an ordinary stationary tripod. The next image is a stack of nineteen 8-second exposures at ISO 6400 with the 70 mm lens at f/2.8.

Unfortunately, haze and moonlight worked together to diminish what should have been a brighter coma and possibly longer dim tail. 

The sky was completely overcast when the comet came closest to Earth on February 1st. After February 1st there were a few more opportunities for interesting comet pictures. For example, on February 6th the comet passed close to the bright star, Capella, in the constellation, Auriga. The Moon was nearly full that night when I tried imaging the comet with a 12-inch Dobsonian telescope. Unfortunately, I couldn't find the comet in the telescope's relatively small field of view. On February 10th the dimming comet passed close to Mars, but the sky was cloudy again. Clouds were forecast for almost every night after February 10th. The comet will rapidly dim as it recedes from the Sun and Earth and travels out into the solar system.