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Hack 38 Colorful Star Trails

For most people, stars are decorative points of
light that decorate the night sky. But for you, they can also be
fascinating streaks of light that add dazzle to your
compositions.

Stars might appear as twinkling
points of light to the naked eye, but when you point a camera at them
and leave the shutter open for a while, they transform into colorful
streaks across the sky. Photographing star trails is not only an
artistic endeavor; it can also provide insight into the nature of
stars themselves.

Stars are basically composed of hydrogen and helium, and they burn
intensely. The hotter the star is, the more
bluish its color, and cooler stars tend to be reddish orange. Based
on this information, scientists have formed theories about the age of
the stars we observe. A bright blue star, for example, is considered
at the peak of its life. A duller red star, on the other hand, is
much older.

Thinking about the age of a particular star on a chilly night
probably demands more commitment than the average person cares to
allocate to such matters. But if you point your digital camera upward
and let it record trails of those stars, their colors are much easier
to distinguish in the comfort of your home, gazing at your computer
screen, than they are when you gaze upward into the frigid night.

Take a look at the picture of Orion's belt and sword
in Figure 3-18 (the constellation Orion the Hunter
dominates the winter sky in the Northern Hemisphere). This image is a
four-second exposure (f-1.8 at ISO 800, taken with a
Canon 10D) and is
an enlargement of what you'd observe with your eyes
in the sky. You can see some differences in star colors, but they are
subtle.

Figure 3-18. Stars without trailing effect

Figure 3-19. Stars with trails

In the eight-minute exposure (f-1.8 at ISO 100, taken with the same
Canon 10D) shown in Figure 3-19, the colors of the
stars are easier to determine. The purplish
"star" in the middle of
Orion's sword is actually a
nebula. Clearly, the three stars in his belt are
burning hotter than the three in his sword. You can draw your own
conclusions about the meaning of all of this, such as the age and
distance from Earth of each of these entities. But the point is that
it's much easier to analyze stars if you have more
visual information. And photographing star trails is a great method
for amateur stargazers.

This technique is only for thinking about the temperature of stars relative to one another. All sorts of things happen when dealing with the physics of light traveling through atmosphere that people with years of training think about on a daily basis. That said, we can use these images to play amateur astronomer for a minute.

The three stars that form a diagonal line (Orion's
belt) at the top of Figure 3-19 are (from top to
bottom) Mintaka, Alnilam, and Alnitak. They're about
1,800 light-years away and are much bigger than our own Sun. We can
tell from their intensity that they burn hotly, changing hydrogen
into helium at a furious pace.

But the brightest star in the constellation is Rigel, in the lower
right corner of the frame. It's part of
Orion's left foot (in case you
couldn't tell that was a foot!). Rigel is 1,000
light-years away, but its luminosity is actually 50,000 times
brighter than our Sun. If you study a little star history to learn
more about this beacon of the night sky, you'll find
out that Rigel is actually a triple star (three
stars close together, giving the illusion of being just one).

Last, but not least, the Orion nebula emanates its fuzzy glow in the
lower part of the sword. This area is know as a stellar
nursery, because new stars are formed here within the
masses of gas and dust that are the building blocks of these
entities. Some of these young whipper-snappers are only a million
years old. That might not sound so youthful to you, until you learn
that our Sun is about 4.6 billion years old.

Now, when you look at these images of Orion, those colors begin to
take on new meaning. And this is a satisfying exploration that you
can enjoy until, well, the end of time.

3.11.1 There's More to Stars Than Science

Capturing stars in motion has its artistic side, too, especially when
combined with other elements, such as a desert landscape or dimly
illuminated camp tent. If you put the North Star in the center of
your viewing frame, the star trails will form concentric circles
around it, as shown in Figure 3-20, a picture of the
Canada-France-Hawaii Telescope in Mauna Kea.

Figure 3-20. The Canada-France-Hawaii Telescope (photo by Jean-Charles Cuillandre)

Pointing your camera at other parts of the sky produces different
streaming effects. This is truly trial-and-error
fun at its best. The thing to keep in mind is that you
want to find an interesting landscape element that
isn't too brightly lit and that complements the
streaking stars above.

3.11.2 Get Your Equipment Together

Unlike some of the other hacks, where you could employ workarounds
for your point-and-shoot digicam, this technique requires a camera
that enables you to control the shutter. Manual
mode (where you control shutter and aperture independently) is the
absolute best for star trails. Your exposures will be anywhere from
30 seconds to hours in duration.

I also prefer a real cable release that allows me to lock the shutter
open. I've been using the Canon Remote Switch
RS-80N3 with the Canon 10D for my long exposures. The Remote
Switch has a locking button, so I can trip the shutter and keep it
open until I unlock the button on the switch.

Battery power becomes a real issue for this type of shooting. Prior
to digital imaging, many photographers would use older mechanical
bodies that didn't require any type of power at all.
They would lock the shutter open with a cable release, time the shot
with their watch, then close the shutter when time was up.

But digital cameras need juice for any type of shooting. And when
you're making long exposures on a cold night, those
batteries seem to drain pretty fast. To help deal with this
situation, I recommend you have two or three extra batteries with
you. Even better, consider an auto-adapter kit that allows your
camera to tap power through the cigarette lighter. For the Canon 10D,
I also use the Battery Grip BG-ED3 that holds two
lithium-ion power cells.

Once you have your power under control, turn your attention to dew
and condensation management. I suggest you keep a multicoated
protection filter, such as a skylight or UV, and a lens hood on your
camera at all times. The lens hood helps block out stray light and
reduces the amount of moisture that accumulates on the glass part of
the lens. The protection filter keeps dew and debris off the actual
front lens element. And it's much easier to clean
the filter than the lens itself.

Make sure you have a sturdy Ziploc bag in your camera case. When
you're done shooting outside, put your camera in the
bag and zip it up. Once you bring your rig indoors, the condensation
will form on the bag, not in the camera. Leave it in the bag until
the camera reaches room temperature. Be sure to remove your memory
card before putting the camera in the plastic bag, so you
don't have to wait until it warms up to room
temperature before you can start viewing the images you captured.

To begin your shoot, attach your camera to a sturdy tripod, point it
upward to an interesting group of stars, and set it to Manual
Exposure mode. If you have a 50mm lens, start with that and open the
aperture all the way to its widest settingusually, f-1.7 or
so. If you have only a zoom lens, set it to a mid focal length, such
as 50mm, and open the aperture all the way.

Set the shutter
speed to Bulb setting; this is often denoted by the letter B. That
setting means that for as long as you hold down the shutter release,
the shutter will stay open. You can already see the advantage of
having a locking release: you don't have to stand
next to your camera, holding the button down for 30 minutes.

Make your first exposure for five minutes and review the result in
your LCD monitor. This will give you a point of reference for
experimentation. You don't have to take notes about
your exposure times, because your camera is recording that
information and attaching it to the image.

3.11.3 A Few More Tips

When scouting for a location for your star shooting, try to find
somewhere that has little or no light pollutionthe darker, the
better. A little light pollution makes a big impact on long
exposures.

Be sure to bring at least one flashlightpreferably, one with a
red lens that enables you to keep your night vision while working. A
piece of red tissue paper and a rubber band over the flashlight lens
will do in a pinch.

Another accessory that makes shooting more comfortable is a
right-angle finder that slips over your
eyepiece. This enables you to view the sky more comfortably by
looking down into the finder, as you would with a quality telescope.

Gloves, hat, hot cocoa, and all the cold weather comforts will make
this assignment more enjoyable. If you have a photo buddy, star
shooting is a great opportunity to catch up with each
otheryou'll have quite a bit of time on your
hands during those two-hour exposures.