ISS transiting the Sun between two huge sunspot groups. Credit: Dani Caxete

0.5 seconds in the Sun

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It’s funny — in astronomy, you wouldn’t think split-second timing would be all that critical for getting a good shot of some cosmic object. After all, the galaxies, stars, planets, and more have been around for billions of years. What’s the hurry?

But then, you have to remember that not everything is just sitting out there waiting for the shutter to snap. Some things are moving pretty rapidly, and if they’re close enough to us then the difference between getting a nice shot and a fantastic one can take less than a second.

Here, I can show you. Check this out!

ISS transiting the Sun between two huge sunspot groups. Credit: Dani Caxete

ISS transits the Sun between two huge sunspot groups. Credit: Dani Caxete

That is the Sun (duh), taken by Spanish astrophotographer Dani Caxete. He took this on September 5, 2017. At the time, those two big sunspots groups were visible (called Active Regions 12673 and 12674, the former of which flared several times just days later) — in fact, they were big enough to be spotted with no optical aid; I saw them myself using my eclipse glasses left over from August.

But that’s not all that’s in the shot. Look again: Between the active regions is a decidedly more artificial spot:

Close-up of the ISS transiting the Sun between two huge sunspot groups. Credit: Dani Caxete

Close-up of the ISS transiting the Sun between two huge sunspot groups. Credit: Dani Caxete

 

Yup, Caxete caught the International Space Station as it transited the Sun! The ISS is orbiting the Earth at about 8 kilometers per second at a height above ground of just over 400 km (about 500 km from Caxete, who was in Madrid when he took the shot due to his angle). At that speed and distance, it takes very roughly a half a second to cross the face of the Sun.

To capture it, you can’t rely on tripping the shutter at the right time; it’s better to take video, and then select the frames that show the ISS. This image shows one such frame. Caxete made a nice little video showing his travel across the city, the equipment-setting-up, and then getting the shot:

 

Coooool. I like his ‘scope, too; it’s a Long Perng 80 mm f/6.8 refractor with a Lunt Solar Systems Herschel wedge (which filters the sunlight down to acceptable levels), and a Nikon D610 camera. There’s no substitute for good optics!

As Dani told me, he has something of “an obsession with the ISS.” He took this shot as well:

ISS transits the Moon

ISS transits the Moon. Credit: Dani Caxete

 

Nice. And he has lots of other such images he’s taken (including one I featured on the blog back in 2011, though the ISS had a visitor that day), and I suggest you scroll through them, because they’re very pretty.

Getting a shot like this takes some planning, too. The sky is big, and you have to be at the right spot at the right time to catch the ISS moving across a target like the Sun or Moon. Happily, software packages like CalSky (which is what Caxete uses) make that a lot easier; you give it a location and it can calculate what’s visible in the sky and where, including the Sun, Moon, planets, asteroids, and satellites (including potential transits near your location). It’s not too hard to use and fun to play with, so give it a try.

Not that getting a shot like this is easy. But with all this lovely tech we have handy, it’s a lot easier than it used to be. Still, it takes a lot of experience and perseverance … and a deep love of the chase. I don’t mind a chase myself, given the right circumstances (I traveled to Wyoming for the eclipse last month, after all), but in this case, I’m just glad experts like Caxete and others are willing to drop everything, even for just a short while, to provide the rest of us with such lovely images.