Astronomy Observing Conditions

Astronomers, both amateur and professional, work with the Earth’s thick atmosphere every time they gaze up at the stars. And, as you might guess from the song “Twinkle, twinkle little star, how far can you see?” the clarity of that atmosphere plays a major role in the success or failure of your observing session. While absolutely clear skies are necessary, they’re not enough. A lot of external factors like cloud cover, transparency and seeing also play a role in the quality of your observations or images.

Luckily, there are tools that you can use to monitor these conditions. Many apps will provide a 96 hour forecast for your local area, allowing you to see how much the conditions are expected to change in that time period. These apps are especially helpful if you’re looking for the ideal night to set up your telescope and observe an event.

While a clear sky is essential, it is important to note that the quality of your observing depends not only on the clarity of the sky but also on its stability and the degree to which its transparency has been impaired by atmospheric turbulence. This is called the “seeing” of the sky, and most of the Astronomical League’s Observing Programs require you to evaluate and record your seeing and transparency in your observation log.

To judge the quality of your observing conditions, you can try a simple test: look at a nearby star and see how easily it splits into two stars with the naked eye. This is a good indication of the level of turbulence present in the atmosphere, which will cause the light moving through it to jump around. The better the seeing, the less turbulence there is.

Another thing to keep in mind is the temperature of your telescope optics, and whether you’re observing over surfaces that retain heat (such as asphalt or concrete) which can create “temperature waves.” If you’re using a high magnification, these waves will interfere with the image. You can minimize this effect by observing at the same time of day, such as during twilight, or when the Sun and Moon are near the horizon.

Finally, if you have the opportunity, try to visit an observatory on a mountaintop. This is because a higher elevation generally means a lower humidity, which in turn makes for better seeing conditions.

Regardless of where you observe, remember that the most important factor is to have fun! Observing is a great way to share in the fascination of our universe, and there’s never been a better time to take advantage of the technology available to us now. So, go outside and enjoy the stars! They’re worth it.