Neutral density filter are mainly used in traditional photography, but are used in astronomy to enhance lunar and planetary observations.

They are usually used for the observation of the Moon, but may also be used for planetary observation.

The instrument is particularly suitable for planetary observations.

This is achieved through year - round semestral astronomy related activities such as conferences, courses, movie debates, planetary observations through telescopes and outings focused on archeoastronomy.

In astronomy, Ibn Abi al-Shukr carried out a large-scale project of systematic planetary observations, which led to the development of several new astronomical parameters.

Then he read about the planetary observations and we all felt distress at what had been discovered.

Accurate planetary observations being collected today will in time lead to more stringent tests for a tenth planet.

The Observers, too rigid in their thinking to understand the planetary observations, have over-ridden the flight plan and passed Proxima Centauri.

"Top priority for planetary observations!"

State briefly, in relation to planetary observations, the advantages of radar over the receipt of naturally emitted radio waves.