Discover our tips on how to best observe objects in the Solar System such as planets and the Moon.
The major planets of the Solar System - Venus, Mars, Jupiter, and Saturn - are very small objects, and observing their details requires using the most appropriate techniques:
It is essential for the telescope optics to be in thermal equilibrium with the environment. Therefore, leave the telescope outdoors at the observation site for at least 30 minutes, but for some closed-tube telescopes like many Schmidt-Cassegrain or Maksutov-Cassegrain catadioptric designs, a much longer time may be necessary, up to 2 hours or more.
For a telescope to perform at its best in terms of sharpness and contrast, its optics must be perfectly collimated. Collimation is particularly critical with telescopes equipped with non-spherical (aspheric) optics that do not allow for degrees of freedom, and where images degrade significantly even with small alignment errors. Therefore, before each high-resolution observation, perform a careful collimation check and make any necessary adjustments, at high magnification (at least 10-15 magnifications per centimetre of aperture).
If possible, schedule high-resolution observation on a night when the atmosphere is calm, without wind, and with stars that twinkle as little as possible. A quick check at 150-200x will dispel any doubts.
If possible, try to schedule your observations when the planet is at its highest point in the sky (culmination) because this is the position where it is least disturbed by layers of the Earth's atmosphere, both in terms of turbulence and differential refraction.
If you have multiple telescopes available, use the one with the largest aperture (objective diameter) to achieve higher resolution.
The optimal magnification is the one that allows you to fully utilize the telescope's resolution under the atmospheric turbulence conditions of a given evening. Therefore, it is useful to have many combinations of eyepieces and Barlow lenses to find the most useful magnification allowed by the atmospheric conditions (and the type of subject). Generally, Mars and Saturn can tolerate very high magnifications (up to 3 times the telescope's diameter in mm), while Jupiter is less "tolerant" due to its blurred details.
To observe the most challenging details, it can be helpful not to keep the planet perfectly centred in the eyepiece field (which happens with telescopes equipped with efficient tracking motors) but, on the contrary, obtain a better view of the details by slightly moving the planet within the field (using the keypad controls or micrometric mechanical adjustments). This technique takes advantage of a characteristic of human vision, which makes moving objects more visible.
In some cases, it can be useful to use specialized optical filters for planetary observations. Generally, the most useful ones are called "contrast filters," of the interference or dielectric type, which increase the contrast of certain colours at the expense of others. For example, the most commonly used filters increase the contrast of red or brown details, allowing for better highlighting of Mars' albedo features or Jupiter's Great Red Spot.
Credit: The Telescope Doctor – Plinio Camaiti, Auriga (www.auriga.it)
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