Executing a telescope observation session

As the Observation Secretary at the Cambridge University Astronomical Society, I had to plan and execute numerous observation sessions – both as a public advertised event, and as a small group with my friends. There are several aspects to consider when stargazing – from the weather conditions to photographing the objects that you’re observing. Here are some of the main points to think about for a night of stargazing.

Weather conditions

This is usually the most frustrating aspect of planning an observation night. Cloudy skies or precipitation are astronomers’ largest enemies. Weather conditions can change quite rapidly depending on your location, and the weather forecast may not be accurate beyond a day or two into the future. We usually plan our observations only a few days in advance and frequently check the forecast to see if there are major changes to the weather.

Certain bright objects such as the Moon and planets can be observed even with the presence of some thin high-altitude clouds. These objects are large and bright enough for these clouds to only slightly distort their view.

Visibility of the targets

All objects in the sky rise and set at a certain time. Observing conditions are ideal when the object is high above the ground. This is because when objects are close to the ground, their light has to travel a greater distance through our atmosphere, which causes distortions. Faint objects are affected more by this and appear quite blurry through a telescope. Free software such as Stellarium can be used to check the movement of objects in the sky at any place on any day.

Deciding suitable equipment

The two main factors to consider when deciding what equipment to use are the object’s brightness and angular size. Binoculars offer a lower magnification than most telescopes, which makes them ideal for observing larger objects like the Moon and the Pleiades star cluster. These objects appear quite large and usually don’t fit in the small field of view offered by higher magnification telescopes. Telescopes have a larger aperture, which means that they collect a lot more light and enable us to observe fainter objects. The Ring nebula is an example of a small and faint object that will benefit from a telescope’s higher magnification and larger aperture.

Recording observations

The most rewarding part of observing is looking at the object directly through the eyepiece of the telescope. The level of detail that can be seen on large objects such as the Moon and the Orion nebula is astonishing. The usual method of recording these observations is either through sketches or photographs. Sketching details on the object requires patience and some amount of drawing skills. The alternative is to take a photograph through the telescope. There are multiple ways of taking pictures. The easiest way is to just place a phone camera in front of the telescope’s eyepiece. For best results, however, a digital camera can be attached to the telescope using a camera adapter. A lot of modern observatories have sophisticated telescopes that have built in cameras which are computer controlled and can be used for obtaining high-resolution photographs.

Sharing observations

There are several platforms that can be used to share photographs and sketches of celestial objects. Online astronomy forums, such as Stargazers Lounge (https://stargazerslounge.com/), is an easy way for amateur astronomers to share their observations with the world. Many astronomy magazines, such as Astronomy Now and Sky & Telescope, also accept submissions from the public. For more advanced observers, there are databases that one can contribute to, such as the Comet Observation database (COBS - https://cobs.si/) – which contains the brightness measurements of many comets.


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