Dew can be an annoying obstacle for astronomers of all levels. Whether you are stargazing in the evening or early morning, dew can form on your optics and ruin your view. Prolonged exposure to dew can also degrade the sensitive inner workings of your telescope over time. Water can be a highly damaging and corrosive substance if it gets into the wrong places. So we learn how to stop dew from forming on your telescope?.
What can you do to prevent dew from forming on your telescope?
What Is Dew?
Dew is naturally condensation the occurs outside under the right conditions. Unlike precipitation which falls from the sky, dew forms naturally on surfaces. To the naked eye, it looks as though the water just appears out of thin air. Usually, dew appears in the early morning in most places but it can form at any time.
When the temperature of the air drops below the dew point, then the temperature will be right to cause the humidity in the air to condense as water on available surfaces. Generally, the higher the humidity the higher the dew point so humid climates will have more dew than drier climates.
One of the easiest ways to prevent dew from forming on your telescope is to properly store it away when you are done using it. Do not leave it outside overnight. If you do need to store it outside, try to find an enclosed space such as a safe shed or barn to keep it in. This will prevent it from being exposed to the natural water in the air.
Enclosed spaces also have less variable temeprature than the outside air so even keeping it in a shed might be enough to save it from any dew formation despite conditions outside.
Many telescopes come with some sort of storage case or bag which you can also put your telescope in. This would also help to prevent it from being exposed to any sort of water.
As we just learned dew forms with changing air temperature and naturally occuring humidity in the air. Learning to store your telescope in places or ways that reduce its exposure to changing air temperature or humidity can go a long way in keeping the dew from ever forming on your expensive device.
Check The Weather
Be sure to check and double check the weather if you are planning on having a long viewing session outside. If you dig a little deeper into the complete weather forecast for your area it will always include the relative humidity and dew point. This information can be extremely valuable in planning your night in order to avoid the dew.
Check the relative humidity. High humidty increases the chance of dew appearing. Then check the dew point. Remember that the dew point is the temperature at which dew will form if the air gets cooler than that number. Now that we know those two numbers, we can check the temperature curve for the evening.
For example, if the humidty is at 75% with a dew point of 68F you can check the evening temperature forecast hour by hour. At 11PM it is supposed to be 72F outside but at 1AM it is supposed to drop to 66F. That means that dew will begin to form around 1AM and probably stick around until morning when the sun rises and raises the temperature again, “burning off” the dew.
This information can be used to accurately plan your views so that you do not have to contend with foggy and dewy optics.
Get A Dew Shield
If all of that sounds too complicated and annoying to deal with, do not worry. Enterprising capitalists have invented all manner of ways to keep the dew at bay. The simplest thing to do might be to purchase a dew shield for your telescope. These nifty upgrades are covers that you can slide over your telescope that will keep the dew off.
Many dew shields are designed so that you can continue to stargaze during the parts of the early morning or evening at which dew forms. These shields will simply give the dew an alternative surface to form on that isn’t your telescope.
These shields are not super expensive and they are easily available online. Simply search for your specific telescope model, type or brand and take a look at what is available. This way, you won’t have to worry about checking the weather or anything like that, simply use the dew shield.
Get A Dew Cap
Another upgrade you can get in conjunction or separately from the dew shield is a dew cap. While a dew shield covers the entire body of your telescope, a dew cap simply protects the most important part of the telescope: the aperture. These caps will protect your optics from getting any dew on them which will keep them dry and clear during the night.
This can be a simple, and cheap, solution to keep water off of your optics. If the rest of your telescope is tight, the dew will simply form on the surface of your optical tube assembly which, in most cases, is harmless. Getting water on or in your lenses and mirror can be a lot more serious. That is where the dew cap comes in.
There are a few more options out there including dew heaters. This keeps the air around your telescope at a temperature higher than the dew point. This is a more involved solution to the dew problem but could be an option for people who are doing very long form viewing or have super sensitive telescopes.
You can also move your telescope periodically. Moving the telescope makes it harder for dew to form on it so if you start getting the first signs of dew, move to a new location. The air temperature is not uniform, especially at night.
In any case, there are multiple ways to prevent dew from forming on your telescope. You can avoid it, plan around it, purhcase accessories to prevent dew formation or simply move around during the night. With these solutions, dew will never have to be a problem again.