Ask Ethan # 33: flying without stars

Do not cling to particulars, but strive to fly up to where the open view of the whole problem opens, even if this view is not the most clear.
- Ludwig Wittgenstein

The reader asks:

On a clear night in the city of Yonkers, I see several stars. In Monroe, I see even more. Why I do not see them, while on the plane, above the clouds? I thought there would be a planetarium right there ??

Difficult problem. Think about it.



From places with strong light pollution (most cities) only the brightest stars and planets are visible. Starlight has to compete with all other light sources. In New York, Chicago or Los Angeles, the sky is so bright that you can only see a couple of dozens of stars.
')
This pollution is so strong that you will not even notice the difference in the presence or absence of the moon in the sky.



For places more distant from the city, this is no longer the case. Of course, there is some light pollution, but the number of visible stars will increase from a few dozen to a thousand. In addition, the brightest nebulae, such as the Andromeda nebula, can be seen with the naked eye in the absence of the Moon. The difference is huge - but not so much, if you compare it with the case when you find a really dark place to observe.



The number of visible stars increases to numbers from 6000 to 45000 , the Milky Way becomes visible, and it becomes possible to distinguish the colors of the stars.

But there are also " super-dark " places.



We measure the darkness of the sky on the Bortl scale . In the super dark sky, the color of the Milky Way and such rare species as zodiacal light and glare (sunlight reflected from dust in the plane of the solar system) are noticeable.

But even with such a sky you can be prevented by the simplest natural phenomenon.



These are of course clouds. As well as strong turbulence in the atmosphere.

All of these factors — light pollution, clouds, and turbulence — affect what the observer can see. And when using a telescope, these factors will influence the observations even more. Therefore, for good observations it is necessary to go to such places.



You find a high space, above the cloud line and most of the atmosphere. It is far from cities and other sources of light pollution, and where the air behaves calmly.

Better than this will only launch a telescope into space.



Mindful of the above, one would think that a night flight by plane at a height of 9 kilometers above the ground is the ideal time to observe the sky.

But if you looked out of the plane at night, you could see the moon, a couple of planets - and that’s all. Apart from the lights on Earth.



But why?

It's pretty easy to understand if you remember the night you spent in your house. If you turn on the light inside, and the outside is dark - what will you see from where?



The observer outside the house sees everything that happens inside. But to see what is happening outside, you need to turn off the lights in the house.

Usually in the place where you look from, it should be darker than where you look.

So what's up with the plane?



There is always a light on the plane and this greatly limits your ability to observe. And this is the only reason that you do not see the night sky from an airplane.

If you persuade the team to turn off the lights in the cockpit, or you get yourself a plane of release before 1940, without lights, you can see the same sky as in the next photo.



In the early years of aviation, pilots took sextants with them and were guided by the stars - just like sailors in those days when there was no GPS. Here is a photo of a navigator reading the sextant from a 1940 British military aircraft.



If it were not for the light in the plane, you would have watched the sky at its best. Astronomers are aware of this, and NASA even has a special telescope mounted on an airplane - SOFIA .



So, if you want to see the stars from the airplane window - ask the team to turn off the lights in the cabin, and the Universe will be yours!