Beneath the Vortex

Humboldt County, California

It was a clear, still night at Moonstone Beach. The tide was out, and my brother and I could hear the surf roaring in the distance. An occasional rogue wave would send a low sheet of water sliding across the sands to replenish the glossy surface and worry our toes. Overhead the stars were bright in the moonless sky, and up the coast the remnants of the season’s Milky Way stood on the horizon above the lights of Trinidad. It felt good to be on the north coast.

To the trained astronomer there was probably much more to see and understand in the starry night than I knew, though I did arrive with some knowledge gleaned from my photographic studies of it. There were a few objects in the sky that I hoped to include in an image. To the left of the Milky Way I looked to find the spiral galaxy Andromeda. To the right of the Milky Way and a little farther away was Polaris, the north star. And in the middle of the Milky Way just above the horizon I was able to catch the star Deneb, home to the infamous Denebian slime devils that nearly killed Spock in an old Star Trek episode. Deneb was nearly swallowed up in the lights of Trinidad.

There are no planets in these photographs, for the planets, the Moon, and the Sun travel across our sky in a consistent pathway known as the ecliptic, which off the left edge of these images to the south.

In previous pages I have mentioned how differently our human eyes see in low light from the way the camera sees. The images here represent a couple of the ways in which the camera takes in a nighttime scene differently from your eye or mine. The camera’s shutter can be left open for extended periods, each moment of which will add light and detail to the image being recorded on the sensor or piece of film. Our eyes don’t work that way. They see moment by moment, not allowing the image brightness to build up over time. An extended exposure in the camera can also allow moving objects like stars to become streaks, while our eyes see the stars as points.

The image with the stars as points was the shorter exposure at 30 seconds, and that time combined with a fairly wide aperture and a high ISO captured the stars and distant lights brightly. The 30 seconds was not so much time that the stars became streaks in their slow flight across the sky, though a close examination reveals that they do become slightly elongated.

The vortex image used a much longer shutter speed of 14 minutes, which allowed the stars to become distinct streaks as Earth’s rotation carried us beneath them. Earth revolves like a wheel on an axel that runs through the planet from pole to pole. The vortex shows the stars revolving around Polaris, the north star or polestar. Polaris is at the center of the vortex because its location is almost directly on our northern polar axis. When photographing the night sky, the stars move the shortest distances in a given length of time closer to the polar axes. They travel the longest distances farther from the axes. We can’t see the southern polar axis from our northern position on the globe; when we look to the south at night the stars are making a wide arc as they rise in the eastern skies to their zenith before sinking into the western horizon.