We consider air to be invisible, but, in reality, it is filled with molecules of air and vapor that fog our vision. When we were in Alaska, we were able to see Mt. Denali from the Kashwitna River which is 84 miles (135 km) south of Denali. The day was clear with a blue sky, but, at that great distance, the mountain wasn’t very distinct. Part of it just looked like the sky itself, while other brightly lit parts were more distinguishable. Even when looking through the clear Alaskan air, it’s probably difficult to see farther than 100 miles (160 km).
Most areas of space are so empty that you can see millions of trillions of miles without noticing a fog at all. Space is literally clearer than glass. For example, the Andromeda Galaxy is 14 million trillion miles away, and we can see it easily.
Since space is normally clear, we’re surprised if we see a fog in it. The most commonly noticed fog is the Milky Way band of light.
There’s another band of light that stretches from east to west and is aligned with the plane of our solar system. It’s called the zodiacal light. It’s the result of sunlight being reflected off of tiny dust particles orbiting in the solar system along with all the planets, asteroids, moons, and comets. It’s similar to seeing a cloud of dust being kicked up by vehicles driving a gravel road. No one knows for sure where all the dust comes from, but it might come from things like comet tails and asteroid collisions. It’s extremely faint, so a clear, dark sky is required to be able to see it.
Although the zodiacal light stretches 360° all around us, the brightest part of it is the part closest to the sun. In the morning, that bright section forms a wedge-shaped glow in the east that looks almost like the breaking of day. Because of this, it’s been called the false dawn. The part of the band of light that’s directly opposite the sun has a slightly brighter appearance. It’s called the gegenschein. It reflects light more efficiently since the light in that part is being reflected almost straight back to where it came from.
The best time to look for the zodiacal light is when it’s angled up high into the darker part of the sky. This happens in September in the morning sky. Unfortunately, early morning is usually the time when it’s easiest to be sleeping. Fortunately, it’s up high in the evening as well. After the last glow of light has faded from sunset in March, you can look to the west and try to find the faint glow. You can see Jupiter and Venus there this March as well.
