How Many Stars?


Looking at the sky at night from your backyard you’ll probably be able to see about 50 stars, more if you are away from the city.  So how many do you think is in the frame below?

Portion of the Milky Way near Vulpecula.

Portion of the Milky Way near Vulpecula.

Taking a 200 x 200 pixel sample in the middle I counted 155 stars.  Hence extrapolated to the entire picture comes to 38,000 stars for this 18 x 10 degree portion of the sky.  OK I cheated in taking a picture of a portion of the Milky Way… Nevertheless that is a rather small fraction of the 300 billion stars estimated within our own Milky Way.

Bonus if you can spot the meteor!  Showed up in a single 30sec frame, which I added separately in post processing, else it would have been eliminated from the final image as it’s a random event and I always use a sigma distribution for my stacking.   Hint: it’s located just above open cluster CR399, also known as Brocchi’s Cluster.

Stitching Together the Milky Way


To get a nice view of the Milky Way I would need to get far away from the city lights and a short focal, wide-angle lens.   Also most new DSLR are quite impressive in low light conditions to suppress noise at ISO settings above 1600.  My old Canon XTi (450D) is best kept at 400… but when stacking many frames I can go up to 800 as the noise gets reduced in the process.  Hence when planning of astro-photo session, you need to balance the level of noise and the number of frames you’ll stack.  Also ensure that the light pollution or background brightness level never exceeds 3/4 of your intensity level else you are clipping and loosing information.

The image below is two processed images taken with a 50mm lens on two different days (30 seconds exposure at ISO 800) stitched together the old fashion way: manually in a photo editor.

Milky Way around constellation Vulpecula

Milky Way around constellation Vulpecula – Benoit Guertin

Click on the above image for a a larger version and try to find the planetary nebula Messier 27.  Hint: it’s blue.

Missed the 2016 October Hunter Moon? No Worries


Missed the photo opportunity with the October Hunter Moon?  No worries, while some are claiming it to be a Supermoon, they are mistaken.  November’s full moon will be just 3hrs after perigee (closest to Earth), while the difference was 20hrs for October.  So the November full moon will be larger than the Hunter Moon that just gone by.

So mark November 14th at 13:52 UTC on your calendar!  For North-America, morning of November 14th prior to sunrise will be your best bet.  In Asia it will be in the evening.  Unfortunately for Europe it’ll take place in the afternoon.


Apollo 11 and 17 Landing Sites


What is the smallest detail of the lunar surface can I get with a 80mm telescope (600mm focal length) and Canon 10.1Mpixel camera?  Matching some of the smaller craters in a Moon atlas gives me roughly 6-8km/pixel.  But with image processing anything below 10km doesn’t really show or will blur in the noise.

I tagged a few geological features and dimensioned two craters for reference.  At the same time identified the approximate Apollo 11 and 17 landing sites.  The Apollo Lunar module is only 9.4m wide, hence it is impossible for any Earth bound telescope can possibly pick them up (even Hubble).  However the Lunar Reconnaissance Orbiter (LRO) did manage to pull it off by lowering its orbit as low as 50km above the lunar surface.

Apollo 11 and 17 landing sites and other features

Apollo 11 and 17 landing sites and other features. Moon (October 6th, 2016) – Benoit Guertin

My original photo of the Moon.

Moon – October 6th, 2016


Quick picture of the Moon with the telescope balanced on a railing.  Didn’t trouble getting the mount out.

Moon - October 6th, 2016 - Benoît Guertin

Moon – October 6th, 2016 – Benoît Guertin

October 5th 2016 – Mars, Saturn and the Moon


Didn’t have the luxury to scout a better setting to frame the picture.  In the street was actually better than my backyard with all the electric and utility poles/wires.  But nevertheless took a few minutes to frame the scene down the street while standing under a street light.  Click on the image to expand.

October 5th, 2016 - Mars, Saturn and the Crescent Moon

October 5th, 2016 – Mars, Saturn and the Crescent Moon

Almost in the same horizontal plane, you have Mars on the left and Saturn close to the Moon.

As it wasn’t fully dark yet, and I was on a tripod the exposure was rather short: 1/2sec at ISO 400.  Hence no rich star field this time around.  But you do see some of the bright stars such as Antares below Saturn.  Below is an overlay with a star chart.

Overlay with star chart - October 5th, 2016

Overlay with star chart – October 5th, 2016

If you missed it, there is still tomorrow… the Moon will have moved to a position above Saturn.

October 5th 2016 Photo Opportunity 

Great photographic opportunity tonight and tomorrow with a crescent Moon near Saturn in the early evening sky.  Mars is also visible a bit further east and if you have a clear view of the horizon you may catch a glimpse of Venus before it sets.

Octobre 5th 2016 Southwest Evening Sky

Octobre 5th 2016 Southwest Evening Sky (


Layers and Blurring


We spend lots of money on expensive optics and hours trying to get the focus spot-on or the mount alignment/guiding perfect for smooth tracking to avoid blurry and stretched stars.  So why would you want to blur your final image?

Consider the images below.  The one of the left is softer and more pleasing to the eyes, yet the stars remained sharp.


Side-by-side compare of blurred and the original image

One way to obtain this effect is by creating copies of the image, applying varying blur to each and then adding them from heaviest to the least blur using the Lighten only layer mode.

Take your original image and duplicate as required (in my example I blurred two layers, hence need a total of three identical layers).


Original image (centered on Constellation Vulpecula)

Apply heavy blur to the bottom layer.  At the same time, reduce the color saturation and adjust the levels to get nice blacks.  You want the blacks to be nice and dark such that the general shape of the cloud-like structures appear due to the bright and dark zones.  In this example, the blur was applied to a level of 80 pixels.


Heavy blur to the bottom layer, and reduced color saturation

Repeat the same for the middle layer, but with less blur (level of 20 pixels).  If you want the colors of the stars to pop out, increase the color saturation.  It will create an effect of nebulosity around bright stars.  Once again, adjust the levels as required.


Medium blur to create nebulosity effect

Finally, the top layer don’t apply any blur, adjust the curves to reduce the faint portion of the image as you don’t need to keep this portion of the image.  You only want to keep the nice bright stars.  The dim structures are kept in the lower two blurred layers.

Adjust the % between the layers to get the desired effects  The pixel intensity from bottom (most blurred) to the top will be kept only if the result is brighter than the previous layer.  The sharp and bright stars are from the top layer, while the overall dim structures are from the blurred lower layers.


Final result after blending the 3 layers

Turn the various layers on/off to see what is the contribution of each.  It’s a lot of trial and error depending what you accentuate versus what you want to fade into the background.  Play with the level of blur, the curves and the % layer blending until you get the effect you desire.

For more information on the original image, see my post on Vulpecula.

Wide Field Around Vulpecula


Continuing my wide field photography of the Milky Way I centered on the constellation Vulpecula (little fox) located in the middle of the Summer Triangle.

In the same frame, three Messier objects are identified:  globular cluster M56 and M71; planetary nebula M27.  Interesting fact is star HD189733 (second bright star above M27 in the framed portion) is the nearest extra-solar planet (63 light years) where the presence of water was detected.  But at 700degC, chances for life are pretty slim.


Left to Right: Globular Cluster M71 in Sagitta; Planetary Nebular M27 in Vulpecula; Globular Cluster M56 in Cygnus

The three constellations from left to right are: Sagitta, Vulpecula and Cygnus (also know as Northern Cross).

As a footnote, this was captured with nearly a full moon in a heavily light polluted suburb.  At 30 seconds of exposure time, the luminosity peak was around 75%.

Canon XTi (450D)
50mm F3.2 (ISO 800)
46 x 30sec (23 minutes)