Humans have used the stars for navigation, divination, and religious practices for hundreds of years. Studying the stars and the planets also helped establish civilizations and pave the way for astronomy, not to mention astrology. With the invention of the telescope, studying heavenly bodies became more convenient, particularly with the integration of technological advances that make viewing and making calculations easier. While today’s telescopes boast of a number of features that make sky gazing far more enjoyable, it is not a perfect machine. The temperature within and outside the telescope can affect how it performs. Let’s take a look at why this is critical.
How Telescopes Work
Telescopes use a combination of mirrors or lenses to focus light so that distant objects may be viewed. The lenses are carefully shaped and positioned so they can focus light well enough to allow objects to appear closer than they really are. When the telescope is aimed at a distant object, such as a star or planet, light from these objects enter the telescope and is focused by the lenses. This produces an image of the objects that can be viewed through the eyepiece.
Certain factors affect the way the telescope works, especially if you are taking it outside after having kept it indoors for some time. Telescopes, like most types of equipment, work best in optimal conditions. Certain factors are difficult to control and some, such as cloud cover and atmospheric conditions, are downright impossible to change, but there are certain things that can be achieved to keep your telescope working properly. One of these is thermal equilibrium.
What is Thermal Equilibrium?
Thermal equilibrium refers to the relationship between two objects or systems that are in contact, wherein no heat energy is exchanged between them. In this condition, both objects or systems have the same temperature and thus, in thermal equilibrium or optimization. This is also the ideal thermal condition for telescopes, allowing for the best images to be produced and reducing the effects of convection currents and dew. If thermal equilibrium is maintained inside the telescope, it will be able to produce clear and crisp images consistently.
Why Do Telescopes Need to Cool Down?
Thermal dynamics can affect how the telescope produces images. Problems with temperature can lead to blurry and distorted views. The interior of the telescope is not a vacuum, so air is present inside. It changes temperature, depending on the current conditions. Because warm air is less dense, it will rise from hot/warm components inside the telescope, creating tube currents.
The problem is that these currents are trapped inside the sealed environment of the telescope, which means it will take a while for the currents to cool down. Warm air and cool air do not have the same refractive power, which explains why the images may appear distorted or unclear due to the refraction of the light that passes through. The greater the difference is between the air temperatures, the more issues will occur with the telescope’s performance.
To explain further, let’s take a look at how tube currents work. Tube currents are convection currents that are specific to telescopes. These currents form when heat from a telescope escapes to the surrounding air. However, warm air remains trapped inside the telescope. If the telescope is used under these conditions, light from the object being viewed will pass through the cooler air outside the telescope and on through the warm air inside. Since warm air affects light in a different way compared to cold air, the image that will be produced is blurry or distorted. Keep in mind that the telescope collects and focuses light. If the light itself is degraded, the telescope will fail at focusing it well enough to create the best image of the object being viewed.
How Is a Telescope Cooled Down?
Thermal optimization may be achieved by simply allowing the telescope to cool down on its own. When placing the telescope outside, leave it for about 30 minutes or so to allow the components within to cool down. You may have to check your telescope from time to time to determine if the images are optimized since the rate at which the components cool down will depend on the size of the telescope.
How Long Should the Telescope Be Allowed to Cool Down?
In general, smaller or mid-sized telescopes will require at least 30 minutes to allow the equipment to reach the ideal temperatures. Larger telescopes often take longer to cool down. On average, these will require about 45 minutes to an hour or more, although the exact time will depend on the type of telescope you have. In some cases, you may even need to use a fan to help the cooling process along.
Other than tube currents, you may also have a problem with dew. Dew is condensation that forms on the lens of the telescope when the temperature of the lens dips lower than what is called the dew point. Some telescopes tend to be more prone to condensation than others, usually by virtue of their design. The problem with dew is that it not only distorts the image and creates haze, it can also make the image disappear completely, especially when condensate covers the whole lens.
To fix this problem, you will have to increase the temperature of the lens to remove the condensate. This can be done using a simple hairdryer or an appliance that can produce controlled heat. If the problem persists or is common, using a dew shield and a dew heater connected to a battery will help keep the lens at the right temperature and prevent the formation of condensate.
Storing Your Telescope Correctly
Where a telescope is stored will have a direct impact on the temperature of its components. It is best stored in a cool (often dark) space where the temperature of the air matches the ambient air. Avoid placing the telescope next to a window or close to a vent or heater. Do not cover it with plastic or thick fabric because these materials trap heat.
Maintaining Thermal Equilibrium
Hazy, blurry, distorted, or cloudy images can often be blamed on thermal imbalance in the telescope. With some basic knowledge in thermodynamics, you should be able to fix the problem quickly. Optimizing thermal equilibrium is actually fairly easy, as long as you understand how the environment affects the telescope and its components. Keeping the components in thermal equilibrium will ensure that the telescope is in top condition so it can produce clear images when required.