With the Geminids peaking tonight and a clear sky after two nights of snow, I charged the camera battery and got a quick setup going to take some pictures of the sky. As for any nigh sky photo, both lens stabilizer and auto-focus is set to OFF and focused manually at infinity. Then found a corner of the yard shielded from stray lights and planted the tripod, roughly aiming the camera 70deg up and pointing east (the constellation Gemini was rising at 10pm).
However at -15C outside, the old battery wouldn’t last very long. I left it running for about 30 minutes, taking 20 seconds exposure at ISO 800 with a 17mm F4 lens. The camera is now thawing (covered with frost after bringing it indoors) and will wait until tomorrow before checking the pictures out.
Setup for the 2017 Geminids
In the brief moments that I was outside I caught a 2-3 meteors and one really bright one (easily visual magnitude -4). So even living in the city, the Geminids are visible and accessible to all. With my feet deep in snow I wasn’t dressed well enough to hang around in the cold wind to watch the show for long. So I hope the camera managed to capture a few.
Today I got an e-mail from Gary that a photo of the Big Dipper that I had submitted a few months ago got selected for this week’s column on SkyNews. Couldn’t be happier. I wish all my weeks could start this way.
Astrophotography is a combination of equipment, experience, location/timing and luck. With this photo I just happen to hit everything right and was lucky.
Using the best equipment helps, but for this photo it was the simplest of setup: my very worn Canon Rebel XTi DSLR with a zoom lens set to 17mm F4 mounted on an old steel camera tripod my father used in the 60s. So nothing special, and within everyone’s reach.
OK, for the next part I had experience on my side. It allowed me to pick the right camera settings, but was also lucky as my photo viewing was limited to that small LCD screen on the camera. I had no laptop to fully explore and review the photos and make the necessary adjustments. Even the focus was reviewed through the small camera LCD. That night I only took 4 images with 20 second exposure crossing my fingers that I would have something worthwhile once back home.
And then there is the post-processing on the computer, which is a lot of trial-error. In image processing doing steps A + B will not give you the same results as performing B + A. We all have our “recipes” for what produces good results, but every photo ends up being a unique project. With this one, I knew there was good potential.
Finally there is the location and timing. I was up in cottage country, away from city lights, and a clear sky. However there was a full moon rising, couldn’t wait too long as the sky would start to brighten. A Big Dipper low in the sky next to the trees framed everything very well.
Thanks Gary and SkyNews for selecting my photo. For all the experimentation that I do with the camera, once in a while I get everything right. I’m just happy someone noticed and said “Hey, that’s a great photo we could use.”
The Moon is white right? OK, OK… it only looks white because of the high contrast with the dark sky, it’s more grey. What? No? You mean it has color?
From samples returned by the Apollo missions we know that two of the main minerals making up the lunar regolith is titanium oxide (TiO2) and iron oxide (FeO) based basalts. While TiO2 is quite white and used in many household products from white toothpaste to white kitchen tiles, FeO is rust and closer to orange-brown (think Mars). On the Moon the result is a slightly blue-ish color in the areas with high TiO2, and more of a brown-red for the higher FeO and low TiO2 zones.
A normal image of the moon taken with DSRL, the different in hues is subtle as seen below.
Moon Natural Color (November 7, 2017) – Benoit Guertin
But it can be exaggerated by playing with the color saturation, and you get the image below, where various hues of blue-grey, orange and brown become apparent. The sharp boundaries between colors are caused by the different mineral make-up of the lava flows during the early formation of the Moon. Common interpretation of the age of the lunar surface is that the blue-grey areas are “younger” than the orange-brown.
Moon with exaggerated colors
Who says you can’t pull scientific information with simple backyard astronomy gear? The same technique, but with narrow-band filters is used by NASA and other space and research agencies to catalog the make-up of the lunar surface.
So if you are planning lunar prospecting for future mining rights, all you need is a telescope and a DSLR.
Not too far my previous post’s open cluster lies a smaller and younger NGC 6709. Both were imaged on the same evening, but I only got 15 minute of integration due to advancing clouds. However with these open clusters, I don’t think a greater number of frames would amount to much more details.
Open Cluster NGC 6709
Canon Rebel XTi
30 x 30sec (ISO 400)
Image is cropped and scaled 50%.
Open star clusters are the galaxy’s youngest stars. They are created from the collapse of giant molecular gas clouds, often forming large and very hot stars shinning brightly in the blue-white part of the spectrum. As they are rapidly consuming their fuel, they are also short-lived. By ending as a super nova, they create the heavier elements beyond carbon that exists all around us.
Below is open star cluster NGC 6633, estimated to be 660 million years old (our solar system is 4.6 billion years old). The cluster is of a decent size covering just about the size of a full Moon in the night sky. The brighter and whitish stars stand out against older and further stars in the background.
Open Star Cluster NGC 6633
Younger star clusters such as the Pleiades (Messier 45) have yet to burn away their molecular gas clouds. However there is no hint of glowing gas (nebula) with NGC 6633.
Canon Rebel XTi
51x30sec (25.5 minutes) ISO 400
Some constellations are easier to spot than others. Cassiopeia with its distinctive W is visible year round in the northern hemisphere above the 34th parallel. In the image below it easily stands out from the fainter background stars.
Cassiopeia above the three line – Benoit Guertin
The five stars drawing a W in the sky are all naked eye magnitude 3 and brighter stars, and in the image above I used a layering technique to increase the color and brightness of those stars to really make them stand out.
- Duplicate your base image, and set this layer to lighten only
- Apply a blur to the top layer(about 8-12 pixels)
- Increase the color saturation and brightness. Play with the curves to brighten the bright stars, but not the background sky.
- Use a mask as required to filter out the bright foreground elements, such as light reflecting off a building roof-line in my image above.
Canon Rebel XTi
4 x 20sec ISO800
Ursa Major, or Big Dipper is one of the most recognizable constellation in the Northern hemisphere. People often use it to locate Polaris, the North Star. Can you find Polaris? (Hint: upper right)
Ursa Major (Big Dipper) low in the sky in late summer around 11pm
Canon Rebel XTi (450D)
Stacking of 4 x 20 seconds @ ISO800
Post processing with GIMP