Then and Now: Astrophotography on the Simple Side?

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I spent some time this morning with PixInsight on a stack of M-42 images. This is the result. PixInsight is an impressive, though oddly challenging, piece of software. The interface still eludes me at times. The results are splendid, however.

This image was taken through a Nikon D-810a at f/4, 200mm, tracked on an iOptron mount in gusty winds. This piece is the result of three major processes:

  • All images were aligned using stellar centroids.
  • The images were then stacked… this is an image integration of 100 seconds worth of exposures.
  • PixInsight was then used to do a Dynamic Background Extraction to essentially perform a flat field thus removing the lens’ vignetting. I still can’t get over this process: no flat fields required… though I bet real flats would result in a better overall image.

The camera does its own internal bias and dark subtraction. The image was then brought into PhotoShop for adjustment to levels and cropping.

M42 color stack using Nikon D-810a

Now… compare that colorful image with the monochrome one: that was taken way back in 1986 on Tri-X Pan film pushed to about 1000 ASA by boiling it in nitrogen. The image is a 20 minute exposure through a Celestron C-8 at f/10, manually guided with an illuminated reticle eyepiece. I developed this in my bathroom using duct tape and towels to block all external light from entering.

M42 film

What a difference! New technology brings better sensitivity and a whole new world of imaging…. but we knew this. I’ve been playing with CCDs since the early 1990s. No surprises. The real surprise? Cost! All this tech adds up in cost. I am not really sure that it saved me a whole lot of time to make the new image with the new tech… perhaps if both images were color? Then, yes, the new tech has saved me time. Simple? M’eh. It’s about the same level of technical detail. It ends up being about one’s knowledge base: software or film developing? You choose. Certainly some of my best images were taken with film. Which do you prefer? It’s totally up to you. Like vinyl records, film is making a comeback, but hasn’t made its way to the realm of astrophotography again. I am pretty sure that CCDs and CMOS sensors are here to stay for astro-art imaging.

  • PixInsight sounds interesting: check out their site here.
  • iOptron? Check out their site here.

Comatic Aberration and Chromatic Aberration

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These two phrases are pretty much guaranteed to raise the blood pressure of optical aficionados: Comatic Aberration and Chromatic Aberration. There. Did your blood pressure go up? Then it is likely you have dealt with one or both of these issues before… and it is likely that you do not need to read further! For those looking around the internet for an example of these aberrations, seek no more!

Let us start with an image. This shot is of the December sky taken through a wide angle 20mm AFS Nikkor 1:1.8G ED lens on a Nikon D-810. The images were raw NEF files without any processing (except resize), either on board the camera or using software. Click on any image to see it in larger format.

Taurus and comet Wirtanen
Taurus and Comet Wirtanen

The image is a pretty typical night shot: 10 seconds focused at infinity and using 5000 ISO at f/2 (a little stopped down). The constellation Taurus is dominating the right side of the image. There is an airplane top-center moving to the lower left. If you follow the airplane’s future trail it leads to a faint greenish fuzzy object, Comet 46P/Wirtanen. This image is reduced in size…. but upon close, full-scale viewing, this image displays two of the common issues that astronomers and photographers aim to rid themselves of. Funny thing is that this lens gets fabulous reviews on sites like Amazon, and when I complained about these issues I was actually chastised! “Are you kidding? This is such a great lens!” Well, no. It’s not, and for the price, it really should perform a lot better. Add to this story the fact that the Nikkor 16mm fisheye actually is BETTER than this 20mm lens, and there you have an argument to not buy this 20mm lens. So, read on….

May I present to you comatic aberration:

comatic aberration in star images
Classic coma on the images of stars. These should be small round dots, not winged things….

This aberration is off to the sides of the image, off-the central axis. The further from the center, the worse this aberration gets. Some systems sprout seagull like wings from stars. This lens sprouts more than that. Ugly. The cause of this problem is in the optical design and is usually found in parabolic mirror systems like Newtonian reflectors. Alas, it also happens here in lens designs.

May I now present to you chromatic aberration:

Chromatic aberration in star image
An example of chromatic aberration: note the violet halo surrounding the bright star. The violet wavelengths focus at a different distance than all the rest. The fuzzy green object to the left is Comet Wirtanen.

Chromatic aberration has been the bane of the optical world for a long time, starting with those who first pointed telescopes up at the stars (i.e. those like Galileo, etc). A single lens acts very much like a prism in how it bends (refracts) light. The angle of refraction has to do with the light’s wavelength, so not all colors of light will come to focus at the same spot. This is usually handled with complex, multiple-lens systems like Petzval lens groupings using unique glass recipes than minimize chromatic aberration. Well, this lens? It suffers. When pointing at a bright white star, this lens gives an image very much like that of a simple two-lens refracting telescope, what is called an achromatic refractor. Well, they are notorious for having a violet to blue ring of light surrounding bright objects… and halos of blue around the moon and Jupiter. Not fun. Nope. This is why we have monstrously expensive systems like apochromats and Petzvals. We are talking expensive!

Comet 64P/Wirtanen

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Comet Wirtanen has been giving us a moderate showing this time around the Sun. As it has been closer to Earth than it usually gets, we are enjoying a comet that might just get bright enough by December 16th to see without a pair of binoculars.  Last night we checked it out through the school’s 16″ telescope and took some images as well.

Comet 46P/Wirtanen: One is through the 16″, the other is a wider field view through a telephoto lens. The brilliant green color is striking and caused by the excited gases: cyanogen (CN)2 and diatomic carbon (C2).

Wirtanen

20-21 January 2019: Total Lunar Eclipse

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We have a splendid opportunity to see a total lunar eclipse this January. It will be taking place late on a Sunday night into the early hours of Monday morning. That Monday is also Martin Luther King, Jr. Day here in the USA, so many schools will not have classes that day. Eclipse timings are given in the above graphic, in Universal Time.  Converting that to the various USA time zones: 

Event Pacific Mountain Central Eastern
Partial eclipse starts 7:34 pm 8:34 pm 9:34 pm 10:34 pm
Total eclipse starts 8:41 pm 9:41 pm 10:41 pm 11:41 pm
Total eclipse ends 9:43 pm 10:43 pm 11:43 pm 12:43 am
Partial eclipse ends 10:51 pm 11:51 pm 12:51 am 1:51 am

Usually the real eclipse visibility starts to take place late in the penumbral phase approaching the first contact of the umbra. If you have not seen a lunar eclipse before, it is quite a special event. The moon will appear to have a charcoal chunk missing from it as the eclipse progresses.  Deeper into the eclipse, the moon will take on a rusty red hue caused by the sunlight passing through the earth’s atmosphere before arriving at the moon. Telescopes are not required, as one can see the whole event easily with the eye. Binoculars and telescopes will offer a nice closeup view.  Photography of the event is a relatively simple affair. A good tripod and telephoto lens will work well with the moderate shutter speeds required.  Tracking is not needed.  An example of a series of photos I took of the last total lunar eclipse is below. The camera was a Nikon D7000 with 200mm telephoto on a tripod. Click for a larger image.

The Annual Leonid Meteor Shower is Upon Us

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It is that time of year again when we get to enjoy one of the best meteor showers, the Leonids. This one peaks mid-November and stems from the remains of Comet Tempel-Tuttle which has left its debris in a massive orbital path through which our planet passes yearly. This November the peak is on the mornings of November 17th and November 18th.  This is not likely to be a storm shower, as we have enjoyed in the past. This is more likely to produce anywhere between 10 to 15 meteors per hour. As with all meteor showers, you will see more if you are far away from city and town lights and have clear, transparent skies. Here in the state of New Hampshire, it will also be chilly, so you’ll want a coat, sleeping bag, and some warm food/drink to enjoy while looking up. The meteors will appear to stream out of the head of Leo, the Lion. This is the sky for those mornings (click to enlarge):

Looking southeast on the morning of November 17th: The Leonids will seem to originate from Leo's head.

Looking southeast on the morning of November 17th: The Leonids will seem to originate from Leo’s head.

A New and Potentially Bright Comet!

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Don Machholz, Shigehisa Fujikawa and Masayuki Iwamoto have confirmed a new comet which might very well become bright enough to see without optical aid. Stand by for updates here in the coming days as the orbital elements and ephemeris are corrected. The comet has been designated:

MPEC 2018-V151: COMET C/2018 V1 (Machholz-Fujikawa-Iwamoto)

More information from the Minor Planet Center here: https://www.minorplanetcenter.net/mpec/K18/K18VF1.html?fbclid=IwAR2ZmjuWzNVq4QQb4mZNGeVtJdyEhnjZEgmyj08SsUtCcTL_NFqkq5bRUFc

A Winter Comet: 46P/Wirtanen

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It appears that we might just have a bright comet for the end of 2018 and into the start of 2019: Comet 46P/Wirtanen. With a short period of just about 5.4 years, this time around the Sun, it will be very close to Earth (a mere 0.07AU or 11.6 million km) and enjoying its perihelion, too….. Predictions at this stage suggest a magnitude 3 object, well within the visibility range of the human eyeball.  When and where to look?  Here is an overall map of the comet’s path through December. Note that the perihelion date in December 16th, then the comet should be near its brightest:

Comet 46P/Wirtanen throughout December 2018.

Comet 46P/Wirtanen throughout December 2018. (click to enlarge)

On the night of 16 December for mid-latitude northern observers, looking south, this is what you should see…a lovely view of Orion and surrounding constellations. The comet should be near the Pleiades, making for a fine photographic opportunity.

Looking south of 16 December.

Looking south of 16 December. (click to enlarge)

Orionid Meteors 2018

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A good meteor shower to watch is the annual Orionids. This one originates from the famous comet:  1P/Halley – yep, that one!  As the comet orbits the Sun, little particles are left behind all over the place along the path.  When our planet orbits through this debris, we see a meteor shower. This year, the peak night will be October 21-22, 2018… some time around 2:00am will be when the shower radiant is high in the sky. All you need is a good dark sky to view from. No optical gear is needed. Suggestions for those nearing winter:  A sleeping bag, hot drinks, and some snacks. The image below shows that evening at about 1:30am local time with Orion rising in the southeast. The small red circle is the radiant from which the Orionid meteors will seem to emanate.

Orionid radiant

Looking southeast at 1:30am local time to see Orion and the Orionids radiant (red circle).

 

What is a Quindar Tone?

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Ever watched footage of the Mercury, Gemini or Apollo space projects? When Houston talks to the astronauts, there is a beep, then some talking then another beep? Yep – those beeps are Quindar Tones. If you listen carefully, the tones are not the same pitch: there are two distinct tones, one at 2525Hz and the other at 2475Hz. They are both 250ms in length…. like these:

What are these tones for? What’s going on? Why the beeps?  Well, it all boils down to older technology. Back when they were shooting astronauts into space on top of missiles (some more controlled than others), eventually they got people into orbit. As astronauts orbited the Earth, they needed some way to talk to them, even when their space capsules were not within the line of sight of Mission Control in Houston, Texas. Communications centers and tracking stations were built around the world, each with the ability to talk directly to the space capsule as it orbited on by. Mission Control then had telephone lines to each of these stations around the world. These lines were dedicated lines, and expensive. The tones were used as a method to control when the remotely located transmitter was transmitting, and used the phone lines to send these remote control tones as audible beeps. Both tones originated at Mission Control…. like this:

  1. Mission control needs to say something to the astronauts in space. They push the push-to-talk switch.
  2. This send a 2525Hz intro tone to the system.
  3. The remote communications station receives the intro tone, and turns on the transmitter to the radio antenna aimed at the space capsule.
  4. Voice communications takes place.
  5. When done, Mission control releases the PTT switch, and the 2475Hz outro tone is sent, thus turning off the system. The remote transmitter is off.

An example for you is below. Note that the Quindar tones only take place just before and after Mission Control speaks. The astronauts do not initiate any of the tones. They make all radio calls into the “blind” so to speak, hoping that some ground tracking station is picking them up.

Now, you might wonder about the issues here. If an astronaut were to also talk at the same time, they might pick up a Quindar tone on their audio and retransmit it back to the ground and cause all sorts of troubles down on the Earth side of things. Yep – that was a problem(!) so engineers made their best effort to prevent the tones from even reaching the astronauts by placing a filter into the stream of all uplinked audio sent to the capsule. These filters were simple notch filters centered on the tone frequencies…. not perfect, by any means, but it worked, generally.

The name “Quindar”?  That came from the organization that invented the system, Quindar Electronics. You can visit their site at:  http://www.qeiinc.com/History.aspx  to see some of their excellent history.

What now?  Quindar tones were used from the early flights of Merucry through the Space Shuttle program. With new methods of telecommunications (i.e. fiber optics, satellite feeds, etc), sending command and control statements to remotely located transmitter sites is a lot easier. There is no need for audible tones these days.

 

 

Cleaning Time!

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Every observatory needs basic maintenance, and those here at PEA are no different. I usually cringe at the thought, but cleaning is a part of the requirement… not that I dislike cleaning. I actually really find it meditative, and a clean observatory dome makes me smile. The cringe-feeling comes from the prospect of kicking up a ton of dust, pollen, cob webs, and such… all of which will have to come to rest some place: Hopefully not on any optics! EEEK! Scheduling the cleaning is a whole other game to play, as well. School ends in early June. A few weeks later, the summer school program begins, and then runs for 5 more weeks. Grass is growing and getting cut throughout June and summer, so, why clean if it’s going to get even more dusty and grassy and pollen-dusty…? So… I wait until the end of summer, when there is a cool, dry, sunny day, like today!

Step – one – cover the optics. Then cover the telescope tubes and mounts with trash bags. Open the dome and aperture.

Two – Vacuum the whole place from top to bottom. We have open studs, so there are a lot of nooks and crannies to work through.

Three – Damp wipe of surfaces, and then a scrub of the floor.

Four – wipe down the ladder and other step-stool devices used by observers throughout the year.

Five – wait for everything to be dry. A light breeze and sunny, dry weather help here. Today was a perfect day.

The result? A clean observatory with a bunch of displaced spiders and no more wasp nests. Webs are gone. Pollen and dust are gone. Happiness!

IMG_1947

A clean machine!