Made a quick tutorial on how to remove background gradient with GIMP
You need the GIMP Astronomy Plugin
Made a quick tutorial on how to remove background gradient with GIMP
You need the GIMP Astronomy Plugin
If you’re a fan of shooting stars, and want to catch bits of Comet Thatcher burn up in the atmosphere, you won’t want to miss the Lyrid meteor shower this April. The Lyrids are one of the oldest known meteor showers, dating back to ancient China and they can produce up to 20 meteors per hour at their peak. The meteor shower is caused by leftover debris from Comet Thatcher, a long period comet (415 year) that has only been observed once since discovery in 1861, and is scheduled to return no earlier than 2283.
But how can you enjoy this celestial spectacle if you live in the city, where light pollution can wash out the night sky? Here are some tips to help you catch a glimpse of the Lyrids this year.
Enjoy the show! The Lyrids are known for producing bright and fast meteors, some of which can leave persistent trails in the sky. You might also see some fireballs, which are very bright meteors that can light up the whole sky.
The Lyrid meteor shower is a wonderful opportunity to connect with nature and marvel at the beauty of the cosmos. Don’t let the city lights stop you from experiencing this amazing event. Happy stargazing!
I’m sharing with you a photo I took of the recent Venus and Pleiades conjunction. The closest approach was on April 10th, but I had to wait until the 12th for a clear sky. It was a pretty sight to see the bright planet and the star cluster so close together in the night sky. I used my Canon 80D and a telephoto lens to capture this image. Here are some tips on how I did it:
I was hoping to capture a hint of the nebulosity within the star cluster, but I guess 5 seconds exposures, even when integrated to 6 minutes is not enough to capture that fainter detail. It was around 8:00pm when I took the photos, the sky was not fully dark, making the use of exposure above 5 seconds too bright. However I did manage to capture the colors of the stars down to magnitude 9.
I hope you enjoyed this post and learned something new. If you have any questions or comments, feel free to leave them below. Thanks for reading!
135mm F4.5 telephoto lens
Individual photos: 5 seconds at ISO 1600
6 minutes total integration time
Vixen GP Equatorial Mount (untracked)
Registration and stacking with DSS
GIMP for final adjustment
If you are a stargazer, you might want to mark your calendar for April 11, 2023. At dusk, look west, you will have a chance to see Venus shining bright just 5 degrees left of the Pleiades, a beautiful star cluster also known as the Seven Sisters. Venus is the brightest planet in the sky and it will be easy to spot with the naked eye or binoculars. If you have a clear sight of the horizon and head out early enough, planet Mercury will be visible low in the sky and at a prime time for viewing at 19 degrees from the sun.
The Pleiades, also known as the Seven Sisters, is a famous star cluster in the constellation of Taurus. It is one of the brightest and most easily recognizable clusters in the night sky, visible to the naked eye in both hemispheres. The Pleiades consists of about 1000 stars, but only a few are visible to the unaided eye. The brightest stars are named after the mythological daughters of Atlas and Pleione in Greek mythology: Alcyone, Asterope, Celaeno, Electra, Maia, Merope and Taygeta.
But that’s not all. Venus is also approaching its greatest elongation, which means it is farthest from the sun on the sky’s dome. This will happen on June 4, 2023, when Venus will be 46 degrees east of the sun and will set about three hours after sunset. At that time, Venus will be 49% illuminated and will appear as a first quarter phase through a telescope.
Greatest elongations are important events for observing the inner planets such as Mercury and Venus. They orbit closer to the sun than Earth. Therefore, it always appears near the sun when the sky is still blue and bright or lower over the horizon, and never overhead at midnight.
If you want to learn more about Mercury or Venus and its position in the sky, you can check out some online resources such as EarthSky.org or SkyandTelescope.org. They have detailed information and charts about Venus’s movements and appearances in the sky. You can also use a free online planetarium program such as Stellarium (what I used for the above screen captures) to see how Venus looks from your location at any time.
It’s a interesting to realise that anybody with a smart phone can now photograph our gas giant, Jupiter, located over 865,000,000 km away. You’ll need some better optics to get the moons of Jupiter, but it’s still very impressive that light emitted by the Sun bounced off the planet and traveled space all the way to the small 2mm opening of the lens and sensor on the phone to record a photo.
You’ll have to set the photo app into manual focus and use the “pro” setting to set the ISO and exposure, as the full automatic won’t be able to deal with such small light points in a dark background. But even hand held the results are good, thanks to keeping the exposure above 1/60s.
Below are photos of the Venus and Jupiter in early March taken with nothing more than a Samsung S10. If it wasn’t for Venus being so bright, correctly getting Jupiter would be a greater challenge.
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:
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!
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.
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.
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.
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.
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.
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