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
If you are able to get out of bed early before sunrise and the sky is clear, you can catch a view of our three closest planets, and if you include Earth that makes 4. Mercury was at the greatest elongation on September 12th (furthest from the Sun when viewed from Earth) which makes it a good time to spot without the glare of the Sun. But it happens that Mars and Venus are also on that same side of the Sun, making a chanced planetary alignment.
The sky map below [click for larger] shows the position of Mercury, Mars and Venus for the morning of the 16 to the 19 of September. Bright star Regulus and our Moon are also there to make this a worth-while event, especially on Monday the 18th.
Mars and Mercury will be closest on the 16th, while the 18th will probably be the most photogenic as the Moon will be a thin crescent in the middle of this alignment.
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
When I took the four shots to create this image below the Moon was just starting to rise above the tree-line behind me. A full moon may be 1,000,000 times dimmer than the Sun it’s still bright enough to cast shadows and considerably light up the scene in a long exposure photo.
Over the mountain top a loose grouping of stars identified as Melotte 111 open star cluster. These are about 40 bright stars laying 280 light years away all moving together. It lies in the Coma Berenices constellation.
Canon Rebel XTi (450D)
20sec @ ISO800
The sky is a stack of 5 x 20sec. The foreground is a single 20sec shot.
The summer is ideal time to view our galaxy. Because of Earth’s position with respect to the Milky Way, it runs north-south across the sky. Anyone with a camera and tripod can easily capture the Milky Way if you are located in a dark area, away for city lights. We were up north in the Malbaie, Québec area for vacation, so I took some time in the early night to observe and photograph the sky. Unfortunately, a full Moon was present in early August and the sky would actually brighten past midnight. The best time was around 11pm for any good viewing and astrophoto. Click on the photo for a high-resolution version.
Milky Way – Sagittarius (just above the trees) to Altair (bright star upper left)
Here is a quick run-down of a quick setup if you want to give it a try:
- Use as short a focal length as you can, 15mm to 25mm is good.
- Set the camera to MANUAL for everything, including the focus and disable any image stabilization. Due to the low light level the camera’s electronic won’t be able to automatically focus or stabilize, so disable them. It’ll just seek and ruin your setup and photos.
- Set the ISO to a high value; 800 on older cameras and 3200 on newer models. Higher ISO will give you a brighter image, but with more noise. You can test various ISO settings to see which one you are comfortable with. If you are planning on taking many images and stacking them, you can run with a higher ISO as the stacking process will increase your signal-to-noise ratio.
- Set the aperture opening as large as possible. Larger openings bring in more light, but depending on the quality of the optics will distort the stars around the edges of the frame. If you see that the stars stretch near the edges, simply stomp it down one or two stops. Trial and error is best to find the right setup. If you’re not sure simply go with a large opening and you can later crop the image if the results isn’t pleasing.
- Set to capture in RAW, this is best for post-processing.
- Look on your lens and set the focus to infinity; this is where you’ll start. If you don’t know where infinity is, look at a faraway object and manually focus on it.
- Mount the camera on a tripod and aim at the desired part of the sky.
- If you have live preview, use it to fine-tune the focus to get the stars as small as possible. Don’t forget that you can often ZOOM in on the live preview screen. If you don’t have live preview (like mine) simply take 3 short test photos (5 seconds each) adjusting the focus in the same direction between each photo. Review the three shots to see which one has the smallest stars and repeat this until you’ve achieved what you believe to be the best image.
- Set the exposure time to 20 seconds. With focal lengths in the 15-25mm range the stars will remain relatively round.
- Take as many photos as you wish.
You can experience with different setups (F-stop, ISO, focal and exposure lengths) and you’ll be able to review and compare later to see which gives you the best image. That way the next time you’ll have your GO-TO setup for great shots.
The above was a stack of 4 images taken 17mm F/4, 20 seconds at ISO 800.
I also identified the constellations and some interesting objects in the above shot.
Objects in the Milky Way