About Benoit Guertin

Astronomy Blog: I started out with a 5.1in Newton on EQ3 mount, and developed a passion for photography when I figured how to connect a webcam to the telescope. Ever since I've been hooked. My technology, software and engineering background make this a great match in understanding signal to noise ratio and image processing. Living near a big city, I have little choice but to leave it to the electronic eye and do my "observations" from a computer screen. This blog is about sharing this passion and knowledge with the community.

Star Trails – Quick and Easy

Creating night-time images with star trails is the easiest and should be your first project when getting into astro photography.

Back in the day of film, you had to stomp down the diaphragm and use a shutter actuator to take one VERY long exposure. And if something happened during that long exposure (bird, plane, clouds, etc…) your photo was ruined. With digital, you can instead take LOTS of short exposures and digitally stitch them together, leaving out the ones that got ruined.

Setup your camera to take a series of short exposure photos, 10 seconds is good. For some tips on how to setup your camera, head over to my Astrophotography Cookbook page.

If you are starting out, or want to simply do this quickly, skip taking Bias, Dark and Flat photos. These are used to improve the final image processing and make more sense when you wish to do some deep sky stacking.

For this exercise I configured the intervalometer of the camera to take 10 second exposures with a 1 second pause between (i.e. the shutter is pressed every 11 seconds and each click is a 10 second exposure). I left the camera operating for a little more than one hour, with the result over 400 photos captured.

It’s important to review all the photos and note down the ones to exclude from the final image, things like camera movement because you knocked the tripod, a plane, clouds, etc. It’s possible that from the 438 photos taken, only the range 5 to 352 will be good to build the star trail image as clouds decided to roll into view on the 353rd photo.

The next step is to import the photos into Deep Sky Stacker. This is done by using the Open picture files… command. As I mentioned earlier, the dark, flat and bias can be skipped, these are not required. But if you have them, they will improve the quality of the final image. Don’t forget to select Check all before moving to the next step, and to uncheck any photos you want to exclude if you did a bulk import.

Once the photos are selected, go straight to Stack checked pictures… In the window that pops-up, hit the Stacking parameters… button and select the following:

  • Result – Standard Mode
  • Light – Maximum
  • Alignment – No Alignment

The remaining tabs can remain with the default setting. Hit OK and the program will now start processing all the photos. Note that DSS will still register each image even if you selected No Alignment. If you know how to prevent this waste of time, please tell me in the comment below.

The end result is something like the image below. Base on your the quality of your sky, the camera setting, color balance, etc… various level of work will be required to make it look nice, but you now have something to import into your photo editor and correct all that.

In my Post-processing section of the Astrophotography Cookbook, I provide some tips on how to correct for things like sky gradient.

Clear dark skies!

December 13 – Trying to catch the Geminids

About a week ago I crossed on my news feed that the Geminid meteor shower was peaking on the 13th and 14th and it should be a good year. At the same time I saw some pretty impressive photos of photographers catching spectacular fireballs as these tiny dust and grains of rock plunge into the atmosphere.

Braving the below freezing weather I setup the Canon 80D on a tripod in the back yard to see what I could catch. I read that the best time for the Geminids is 2am, I wasn’t going to stay up that late on a weeknight, so 10pm would have to do.

Wanting to capture as much of the sky as possible, the zoom lens is set to 17mm and wide open at F4. Note that I live in the city with considerable light pollution (I guess that’s what happens when electricity is cheap) which meant only the brightest meteors would be visible. Playing around with the settings I quickly concluded that at ISO1600 10-seconds of exposure would be the longest I should use to avoid having an over exposed sky. Normally it’s best to have the image intensity peak on the left half of the histogram. This can be quickly checked by viewing a captured image and selecting the Info option.

The camera operated for over an hour and managed to take 304 images before the memory card was full. The camera could have kept going much longer had I wiped the card clean before setting up as the battery still had over 25% charge.

Once the photos transferred on computer I reviewed all the images and identified those that had what appeared to be a meteor, plane or clouds such that I could do the necessary processing later on.

I know the chance of catching a spectacular fireball is slim, but it’s still interesting to review the images for any surprised and explore the various types of processing that can be done.

The easiest and quickest thing to do with all these images is a time-lapse movie. This is essentially a no-brainer. I used Canon Digital Photo Professional 4 to perform some color and brightness corrections on the photos prior to creating the movie. The benefit of this software is that you can save the “recipe” you used on one photo and apply it to all. I also did a batch processing to generate individual JPEG with 1080p of resolution to limit the quantity of GB of intermediate files required for this time-lapse movie.

The clouds that showed halfway through the sequence limited what I could do next with regards to “processing”. My next plan was for star trails!

I selected the longest stretch of images without clouds and then stacked them without alignment, using the ADD MAX operation in DSS. The result will be star trails as well as light trails from any passing plane. The image below is 122 individual 10 second exposures for just over 20 minutes total exposure time.

Tracks from two planes are clearly visible over the arc motion of the stars. A third plane much higher and on a different flight path also crossed the image if you pay close attention.

The timelapse and the star trails are two quick and interesting results from the photo session, but that was not my initial plan. Next I created a “starless” version of my night sky to serve as a background. This was achieved by selecting 8 images 1 minute apart and stacking them using the SIGMA MEDIAN operation. DSS will compare the pixels of all 8 images and if it falls outside a defined sigma distribution, the pixel will be replaced with the median value. As the images are once again not registered or star-aligned, the foreground will remain fix while the stars will move. As the stars move between each image, they will fall outside the sigma distribution and will be replaced by the median value instead.

With my starless image completed, the next step is to use GIMP to blend together the individual meteor trails with the starless nigh sky image. I use a MASK to select just the meteor trail of each photo that I previously identified contained a meteor. Each photo was manually added as a layer to the starless background.

Picture saved with settings applied.

There’s a total of four faint meteor trails as well as one very bright but short lived meteor in the middle. That short bright one ended up being special. Most meteor trails appear only on one frame, but this one left a smoke/dust trail that lingered for a few frames (40 seconds) and can be seen drifting in the high-altitude winds. To best see this, I selected some photos, cropped, enhanced the individual frames and generated an animated GIF.

The last processing I did was select a large sequence of photos that had no clouds or planes but this time register them such that the stars would be aligned between each frame. I simply did an ADD AVERAGE to stack the 62 individual photos, creating the equivalent of a 10 minute exposure of the night sky.

Because the field of view is wide, and I wasn’t in a particularly dark sky area the resulting photo isn’t that interesting, not like some of the other ones of the Milky Way taken while camping away from cities. However I was able to crop the image down to an area that had multiple Open Star Clusters showing up. Swipe to see the photo with the Open Star Clusters identified by their Messier Catalog number.

Click here to enlarge the above photo.

There you have it, a camera outside on a tripod for 1 hour and plenty of interesting results.

August 20, 2021 Not Quite Full

August 20, 2021 Not quite Full

May Lunar Eclipse (Yes a Super Moon)

I hope that some of you will be taking a few minutes this evening to head outside and glance up at the Moon. Not only is tonight a “Super Moon” but depending where you are, you may find the Moon taking on a red hue due to a lunar eclipse.

September 27th 2015 Lunar Eclipse

For tonight’s event, those around the Pacific rim are best located to see the lunar eclipse. On the east coast of North America you might spot the start of the eclipse as the Moon sets in the early morning.

Location of best viewing. Leah Tiscione / S&T; Source: USNO

Even if you are not in a favorable spot, take the time to look at the Moon. There’s this timeless element to it, knowing that it’s been there for millions of years and will continue to be there for many more.

It is also accessible to everyone, no matter how light polluted your sky happens to be.

The best way to see the Moon is with nothing else but your two eyes. Resist the urge to attempt a photo with your phone. That will only end in frustrations. All photographs of the Moon are heavily processed because it’s very hard for a camera to handle both the brightness of a full Moon and the black of the nuit sky, or the glowing halo shining through the thin clouds. And when you do get the brightness under control, all the subtle details of the Moon’s surface is lost. Your eyes are better equipped to handle the large range of brightness and the resolution to really enjoy the sight.

Two separate shots and 15 minutes of processing is required for this, yet your eyes can easily see the details in real time.

2021 Snow Moon

February’s Snow Moon

There’s been lots of attention over Mars this past week. I can’t really blame all the media coverage, the Mars 2020 Perseverance EDL to the Martian surface was really cool and a great feat for NASA. I enjoyed watching it live on the NASA YouTube feed. But this weekend let’s turn our attention to the Snow Moon; the only full moon in February.

The full moon will occur at 3:17am Saturday, so tomorrow evening will be the best time to catch it. There’s nothing particularly special about this full moon, not a Blue Moon (second Full Moon in the month) or “Super Moon”. The name Snow Moon comes from the Farmer’s Almanac as February is normally the month that receives the most snow in North America.

The great thing about full moons is that you don’t need to stay up all night and wait outside in the frigid cold to see it. At this time of year, in the Northern hemisphere, the Moon is visible for more that 12 hours a day.

If you’re tempted to photograph the Snow Moon, leave the mobile phone behind, it’ll just give poor results and you’ll end up frustrated with frozen fingers. Instead just enjoy the view, paying close attention to the various dark “seas” spanning the lunar surface.

If you do try taking a picture, grab a DSLR or compact camera with manual mode. Set the ISO around 200 and the focus to manual. Your shutter speed should be high, around 1/800s; a full moon is surprisingly bright. You’re get better results by slightly under-exposing your shot. If you have a tripod, use it, else try to steady yourself on something (railing, chair, car roof, etc..) Subtle movement can easily ruin the details in you photos.

Clear skies!

Gallery of photos

Manually Processing Comet Images

Looking back, the “Great comet of 2020″ C/2020 F3 NEOWISE was a fantastic sight and well worth the 3am alarm to snap some photos back in July. But comet images are notoriously difficult to work with. Should I also add that in older times, comets were often seen as a bad omen, the bearer of bad news? Cough, cough COVID-19 cough…

Anyways, back to astronomy… There are essentially two types of photo registration (alignment) software out there: 1) Deep Sky which uses pin-point stars to perform alignment; 2) Lunar/Planetary uses the large “disk” of a planet or Moon to align based on surface details.

So when you capture long wispy comets like the RAW image below, software like DSS or Registax just can’t cope.

RAW image : Canon 80D 300mm f/5.6 5 seconds exposure at ISO3200 (09-jul-2020)

I turned to standard photo-editing software for a manual alignment and stacking. This is essentially opening one “base” image and then adding a 2nd image as a new layer. I change that 2nd layer to be overlaid as a “Difference” and manually align this 2nd layer to match the base layer. Once that is done I change the layer mode to Addition, and then hide this 2nd layer. Repeat the steps for a 3rd, 4th, 5th, etc. layers until you’ve added all your images. Always aligning with the “base” image to ensure no drift.

If you simply add all those layers up, you will get one very bright image because you are adding pixel intensities. You can do that and then work with the Levels and Curves to bring it back down, or if like me, working with GIMP, then use the Py-Astro plug-ins to do the merging and intensity scaling in a single step with a Merge all layers. Py-Astro can be downloaded here. I haven’t explored all that the plugins have to offer, that will hopefully be in another blog.

Stacking 11 individual frames results in an improvement over a single RAW image (image below). With the stacked image, I’m able to work with the intensities to darken the sky while keeping the comet tail bright.

After merging 11 images manually aligned in GIMP

However the sky gradient is pretty bad, due to the camera lens and because at 4am the sun is starting to shine on the horizon. So off to IRIS to correct the background gradient. From GIMP I save the files as a 16BIT FIT that I can use in IRIS. For steps on how to do this, see my blog about how to remove the sky gradient.

After a quick spin in IRIS, I’m back in GIMP for final color and intensity adjustments, I boosted the BLUE layer and adjusted the dark levels for a darker sky.

C/2020 F3 NEOWISE from 09-JUL-2020 by Benoit Guertin
Final Processed image of C/2020 F3 NEOWISE from 09-JUL-2020

“7 Minutes of Terror”

The folks at JPL created a short film showcasing Perseverance’s critical descent phase for the Mars landing. If everything goes according to plan, we shall have a new rover on Mars at 3:40pm EST on February 18, 2021.

Perseverance is currently “cruising” at 84,600km/h through space with Mars as a target. To give you an idea of what kind of speed that is, here are a few benchmarks:

  • The fastest commercial jet: the Concord flying at Mach 2.04 is just under 2,200km/h
  • Space Shuttle re-entry speed: 28,100km/h
  • Voyager 1, leaving our solar system : 61,500 km/h
  • Parker Solar Probe (fastest man-made object) : +250,000km/h

Perseverance was launched on July 30th, 2020 from Cape Canaveral Air Force Station, Florida, on top of a Atlas V-541 rocket.

Animation of Mars 2020’s trajectory around Sun, Data source: HORIZONS System, JPL, NASA

The only way the rover will be able to decelerate from its current cruising speed is by plunging into the Martian atmosphere at the right angle and using the atmospheric friction to slow it down. That “7 minutes of terror” is the time the rover will spend on re-entry, from approaching Mars at the right angle, to landing in the desired spot on the Martian surface.

Lots of steps need to go right, timed correctly to have a successful landing. Only 22 of the 45 landers sent to Mars have survived a landing. The US is by far the country with the most success (sorry Russia, you’re space program is awesome, but you suck at landing on Mars)

Glancing up at the night sky that February 18, 2021 evening will be very easy to spot Mars, but also the Pleiades star cluster (Messier 45). Mars will be about 5 degrees north of a almost half-illuminated moon. And if you keep looking higher up by 10 degrees you’ll see the famous open star cluster nicknamed the Seven Sisters, also used as the Subaru emblem.

My First Photoshopped Moon

Ever since Photoshop (and other editing software) allowed user to manually manipulate pixels there has been edited pictures. And with the computing power available at our fingertips and some built-in tools it’s surprisingly simple to “stich” together two photos. So full disclosure, the image below is “Photoshopped”.

I decided as an exercise to see how to insert into a nighttime skyline a photo of the Moon photo taken with my telescope.

The New York city skyline was taken by me a visiti of the Empire State Building in October last year (pre-pandemic) with a Canon 80D, 17mm F4.0 lens at 1/50s ISO 6400. The Moon is with the same camera body, but paired to a Skywatcher 80ED and I had the settings at ISO 200 and 1/20s. There is no software scaling of either photos, they are stitched “as is”.

This image was done with GIMP, I also inserted 2 “blurred” layers to create a small amount of haze around the moon to make it look a little more natural. The Moon was purposely placed “behind” a skyscraper to give it an element of depth and lowered the color temperature.

So dig through some of your old photos and start experimenting…