Not all night skies are created equal. Location on earth where you are observing from plays a huge part in making or breaking your viewing experience. But what does location have to do with the night sky? When we dig deeper, we find that night sky viewing location is affected by three main factors including distance from large cities, amount of water in the air, and elevation. Have you ever noticed one of these factors before?
You might have noticed that large cities are set aglow by lights at night, which turns the night sky into an orange orb drowning out fragile star light. This unfortunately, yet reversible downside of cities is known as "light pollution". The next time you are downtown on a cloudless night, look up and see how many stars you can count...5? 20? 30? Depending on the city brightness you may only be able see 20 stars, if not fewer. On the contrary, drive out into the country and you will be overwhelmed with stars on a moonless night. The lack of bright city lights out in the country can make for one memorable night of watching or photographing the night sky. Dark skies out in the country are similar to what our ancestors experienced, thousands of stars strewn across the sky with our Milky Way stretching from horizon to horizon. For more information on light pollution please visit the International Dark Sky website at http://www.darksky.org
While light pollution is the most visible factor changing our view of the night sky based on location, the amount of water vapor present in the atmosphere plays a vital role in determining how "clear" objects in the sky appear. Water vapor in the atmosphere is commonly called "transparency" by astronomers. High water vapor content reduces transparency and low water vapor increases transparency, which is what we want! Imagine swimming in a pool and going under the water, then looking back out through the water. Everything looks distorted and as if it is fluttering around due to what is known as refraction caused by water. Refraction causes light to bend around a medium, such as water in our case (hence why when you put a stick in water it does not look straight anymore, but looks bent!). This is why starlight twinkles in the night sky because of water vapor and temperature changes in the atmosphere. In our analogy the of the swimming pool, the stars would be outside the water (outer space), our water filled atmosphere would be the pool water, and we the observer are at the bottom of the pool looking out through a huge column of water creating distortion. Therefore, in a perfect world we want water vapor to be low in order to experience the night sky where stars are so bright it feels like you can pull them out of the sky. For an interesting article on the effects our atmosphere has on night skies please refer to the article below http://www.skyandtelescope.com/astronomy-resources/transparency-and-atmospheric-extinction/
Water vapor and light pollution can significantly alter our view of the night sky, but one additional key factor is missing and that is elevation above sea level where you are observing from. Traveling to a high elevation location can change our view of the night sky tremendously! Ever notice a trend where professional astronomers build their observatories? Do they place their incredible instruments near large cities at sea level beside oceans? Thankfully not! Observatories are built far from city lights and at very high elevations to reduce the effects of light pollution and atmospheric distortion such as water vapor and temperature gradients. For example, numerous world-class observatories are located at ~14,000 ft elevation on Mauna Kea in Hawai'i and >14,000 ft in the Atacama Desert in Chile. These high elevation locations are far from city lights and also are viewing through less atmospheric distortion, which provides jaw-dropping views of the night sky. For a list of high elevation observatories please see the article below https://en.wikipedia.org/wiki/List_of_highest_astronomical_observatories.
Have you ever heard about the numerous telescopes that are orbiting the Earth such as the Hubble Space Telescope or it's upcoming replacement the James Webb Space Telescope? These space telescopes provide the most detailed, clearest, and highest resolution images of our universe because they are not look through a moisture and pollutant laden atmosphere!
In regards to night skies and locations of excellent star-gazing, this summer I have been teaching astronomy to park visitors at Mount Rainier National Park. Although this location creates it's own weather due to the 14,411 ft mountain, there have been a handful of just spectacular nights for star-gazing. Those nights of great transparency and low humidity were absolutely beautiful. Showing guests how our Milky Way actually "pops" from the black sky background is truly amazing. One of those nights I was running the astrophotography setup and we put together this 6 x 2 (12 minutes total) image of the Lagoon Nebula (Messier 8) below. The Lagoon Nebula image was taken using a Canon 6D (non-modified) at ISO 6400 with a 130mm Takahashi F/7.7 refractor on a EM-200 equatorial mount. Another wonderful night of star-gazing allowed the astronomy program visitors and I to capture the Triffid Nebula (Messier 20) seen below the Lagoon picture. Overall, Mount Rainier is truly a spectacular location to refresh and soak in the beauty of mother nature both during the daytime and also at night under the stars!
The Lagoon Nebula (Messier 8)
The Triffid Nebula (Messier 20)
Experiencing the night sky in a region that might actually scare us with the amount of stars and brightness of the Milky Way, we need to follow three main rules. (1) travel away from light pollution (city lights), (2) travel away from high humidity locations, and (3) gain as much elevation as you can. When we follow these three rules we likely find ourselves near a desert, out in the country, or high up on a mountain with a remarkable night sky few get to experience. What is the darkest place you have been to view the night sky? What was the experience like to you? Please let a description in the comments section below! I'll start, the darkest place I have been to would be Glacier National Park in Montana and I was just amazed at how close the stars appeared due to the high elevation (~5,000-6,000 ft).
As always, thanks for reading and commenting!
~Matt