Looking up at the colors of space

“It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so.”

— Anonymous quote, often attributed to Samuel Clemens — nom de plume Mark Twain.

Such are many common perceptions and misperceptions of the night sky.

Color for example, or lack thereof, is one. Most everyone has looked up at the night sky while on summer vacation at the beach, and the sky seems white on black. Seemingly, there are countless white stars and clouds of the Milky Way on a black background (if you’re lucky enough to be far away from the local beach town’s light pollution). That would be incorrect. The

That would be incorrect. The actual color, even as seen from space, is a dark blue-grey.

And the moon? I would guess if seen from high overhead, a full moon would look pearly white. If seen near the horizon, it appears reddish or orangish. The horizon colors are mostly because of the much thicker atmosphere you’re looking through near the horizon. As it travels this path, more of the shorter, blue wavelengths of light are scattered away, leaving more of the longer, redder wavelengths. (Dust or pollution can also deepen the reddish/orange color.)

But looking overhead, we see the true color of white, correct? No grasshopper, incorrect. As any astronaut who has traveled to the moon can attest, it’s one of the greyest objects in the solar system. Astronauts who orbited or landed on the moon wasted their color film on it’s monochromatic surface. As I heard Neil Tyson say at a presentation, “Once in a blue moon?” Hahaha.

The universe, however, does have a favorite color. That color is red, always the same red, a medium deep shade that occurs at a specific wavelength of 6,563 angstroms.

Many spectacular deep space objects, like the Great Nebula in Orion (M42), aren’t bright enough to visually see their true colors. With a large enough telescope, generally larger than your typical backyard variety, you can manage to see a weak greenish glow. Yet in digital images, we see purples, reds, blue-greys, but no greens at all. Those are it’s true colors. The eye is preferentially sensitive to the green part of the spectrum at low light levels.

One big disappointment as the budding amateur astronomer looks through the telescope is the expectation of seeing colorful objects as seen in magazines. The young astronomer is puzzled. Nothing is wrong with their telescope or eyes. Humans can’t perceive colors under low light levels. Everything appears grey. Film or digital cameras can do what the eye cannot: “accumulate light.”

And the sun is always perceived as yellow. Wrong again, grasshopper.

That yellow color is an artifact of our own atmosphere. As light pen etrates our atmosphere, the shorter (blue) wavelengths are bounced around by the atmosphere, giving us the blue sky and contributes to the sun looking more yellow than it actually is. Its true color is more like snow, which does a good job of reflecting all colors equally (hence its white).

The sun’s actual color becomes obvious when seen above our atmosphere. Astronauts report the sun is a pure-white star. But even that is an illusion, as white is made up of all colors, wheels within wheels of optical deception.

Now, let’s lend a little mystery to one of our nearer neighbors, the planet Saturn, which lies only 79.3 light minutes away.

The full moon on August 12 will be very close in the sky to Saturn, which is at opposition at that same time. Essentially this will be a double opposition. Being at opposition occurs when the moon or a planet is directly opposite in the sky from the sun’s position.

With the outer planets (Mars thru Neptune), opposition typically occurs once a year. When at opposition, the object will rise about when the sun sets and will be directly overhead or directly south at midnight.

In this case they will be in the southern sky in Capricornus. Speaking of colors, this is one object which your small telescope will visually show Saturn to be a creamy yellow, which is correct and rather an egg yoke yellow. This is caused by the giant planet’s atmosphere which is made of hydrogen, helium, ammonia, & hydrocarbons.

And in closing, the next good opportunity to get away from the city and enjoy the moonless night sky will be the weekend of Aug. 27-28. The annual Perseid meteor shower should peak on the night of Aug 12-13 will be greatly diminished from our viewpoint by the full moon.