Tag: night photography

International Space Station transit at twilight

The other day the International Space Station (ISS) made a transit of the western sky during twilight. Low on the horizon was the planet Venus with the ISS streaking across the sky above. I’ve been shooting images of the ISS for a year or two but think this is one of the best. It works for a number of reasons. One is the bright twilight on the horizon deepening into dark night sky above. The planet Venus — and its reflection in the water — add a counterpoint.

To create this image I set the camera on continuous shoot and then used the remote release to start. The images are ISO 200, f/4.0, 28mm wide angle lens, and 10s exposures. Five images were taken so this is 50 seconds of transit.

I opened all five images in Photoshop with each image a layer. Because 50 seconds is long enough for stars to leave trails across the sky — even with a wide angle — I wanted to only use one sky layer. In the other four layers I masked the stars and sky and left only the track of the ISS. The result is sharp points for the stars and Venus and a smooth track for the ISS.

Twilight transit of the International Space Station (ISS).
Twilight transit of the International Space Station (ISS).

To get daily updates on transit times of the ISS — and other space satellites — I use the following two web sites:

Spaceweather.com (http://www.spaceweather.com)

Heavens-Above.com (http://www.heavens-above.com)

Light pollution in the night sky

Earlier this month it was apparent that there would be one final night of exceptionally clear skies before the summer monsoon pattern set up and skies would be cloudy more often than clear. I thought another night sky image with reflections of the stars in water might be interesting so I ended up at Lake Mary a few miles southeast of Flagstaff. I was surprised to see how much light pollution there was in the southern sky. This stray light is coming from Phoenix, located over 100 miles to the south. There is so much light that it is even reflected in the lake — as are a few of the stars.

Light pollution from distant Phoenix
Light pollution from distant Phoenix

A very short distance to the north of where this image was taken is the Anderson Mesa astronomical station. It’s hard to believe that they can still gather useful observations of the sky with this much light pollution. Finding truly dark skies is becoming a global challenge.

This is our home!

I have been having a lot of fun taking sky images lately. The newer DSLR cameras (and especially the full-frame cameras) can really push the ISO settings making it easier to take astronomy images with short exposures. The short exposure limits the trails that the stars will make and gives an overall sharper appearance.

This image was shot at ISO 6400, 15s, f/4.0, 28mm focal length. At full zoom, there is only a hint of star trails.

Milky Way Galaxy as seen from northern Arizona.
Milky Way Galaxy as seen from northern Arizona.

The lights along the horizon add interesting texture to the image but even though they were fairly dim the 15s exposure resulted in far too much brightening. After experimenting a bit, I decided to place a credit card in front of the lens blocking the street lights for about 12-13s, then pull it away for the last few seconds. Overall, it did a pretty good job attenuating the street lights but there is also a dark area in the sky just above the lights.

What I should do is get a better neutral density gradient filter that I can slide up and down rather than the screw-on filter that I have now. Then I wouldn’t have to resort to credit card tricks!

Here is another example of what modern DSLR cameras can do. This was taken with the same settings as the image above. Even with a 28-mm wide angle lens, the camera is able to resolve the Andromeda Galaxy which is over 2.5 million light years distant.

Andromeda Galaxy -- our neighbor.
Andromeda Galaxy -- our neighbor.