Identifying Stars with Lightroom

This week I’ve been on the hunt for Comet ISON, but that’s a post in itself. This one is about a trick I stumbled upon that helped me determine that I had, in fact, captured ISON this week and it’s interesting enough to me that I thought I would share it.

[If you have trouble seeing detail in the images below, you should be able to click them for a much larger view. I know, internet 101… but a lot of people don’t realize it if you don’t point it out!]

The Problem

It’s not always easy to find the stars in your scene when the contrast is very low – stars fading into a sky brightening from the sunrise, for instance. This morning, the conditions were the best chance I’ve had all week at capturing ISON, but because it was so close to the sun and low on the horizon, it was going to be close. Well, the time came and the sky was clear enough and I shot the part of the sky where it was, but it was so faint that I couldn’t see it on the camera’s LCD to know if I had gotten it.

ISON Visits the Peaks of Otter

ISON Visits the Peaks of Otter

Above is one of the shots from this morning. It’s wider than the usual comet shots because I wanted to give some perspective of ISON against a local landmark. ISON should be in the right side of that image, just down and right of the bright spot (planet Mercury.) I can clearly see Mercury, Saturn, and the star I was using to know where the comet should be, and according to the position of those three, ISON should also be included. Unfortunately, that section of sky is starting to brighten up and wash out the stars so it’s impossible to see it clearly, but I was still curious. Did I capture ISON?

Finding Out

A tight section of sky with reference points and the spot where ISON should have been.

A tight section of sky with the triangle of reference points and the spot where ISON should have been.

Looking at just the section of sky, you can see my three reference points. Mercury (top left), Saturn (lower left), and a bright star to the right of the planes form a triangle. The name of that star is Zubenelgenubi, so I’m just going to refer to it as “the star” if that’s okay with you. Matching those reference points up in Stellarium (planetarium software), we can see where ISON should have been.

A view from Stellarium with the atmosphere turned on to simulate what we should have been able to see.

A view from Stellarium with the atmosphere turned on to simulate what we should have been able to see.

So, we see where ISON should be. It’s in clear sky, but did the camera capture it at all or was it completely washed out?

One of Lightroom’s tricks is a tool that helps you remove spots cleverly named the Spot Removal Tool. When you’re in spot removal mode, there are a number of options that appear along the bottom. The one labeled Visualize Spots is, and I bet you’re way ahead of me here, designed to help you see the spots in your photo that are hard to see when viewing the photo normally… until you’ve printed or uploaded or sent them off to a client, that is. When you check that box, the view switches to a very high contrast view that makes otherwise hard to see specks stand out quite well. Moving the slider left and right allows you to fine-tune the results. This tool is designed for finding things like sensor dust spots against a blue sky, but as it turns out, ┬áit works really well for seeing stars.

So if we click on the spot removal tool (red circle in the top right) and then check the Visualize Spots box (red circle in the lower left), we can now see what’s hiding in our sky.

Lightroom with the Spot Visualization turned on.

Lightroom with the Spot Visualization turned on. (I added the yellow arrows to help mark the specks for this smaller web view.)

Look at those extra dots! And when we compare it to what we see in Stellarium…

The view from Stellarium with the atmosphere turned off and the yellow arrows again to make the specks easier to see.

The view from Stellarium with the atmosphere turned off and the yellow arrows again to make the specks easier to see.

It looks like we caught comet ISON! It’s almost imperceptible, sure, but it’s there!

Conclusion

The Visualize Spots tool is quite handy for bringing out stars and helping you identify what’s in your photo. If you know of other uses for this or have something to add, I’d love to hear your ideas.

And as far as the photo goes, I set out to capture a landscape that included comet ISON against a well-known landmark. While it’s not a giant-tailed comet shining bright in the sky (like we hope it becomes in the next week as it passes around the sun), there are definitely photons from ISON in what my camera captured. So, while I wouldn’t tout this image as a clear shot of ISON, I’m definitely chalking it up as a technical victory.

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