Occultations
When one celestial body passes between Earth and another celestial body, we say that the object that is wholly or partially hidden from our view is occulted. Examples of occultations are the moon passing in front of a star or a planet, or a planet passing in front of a star, or one planet passing in front of another planet, such as in 1590 when Venus occulted Mars.
An occultation can provide an unparalleled opportunity to study any existing atmosphere on the occulting planet. As the radiation from the farther object passes through the atmosphere at the limb of the nearer object, that radiation will be influenced according to the properties of that atmosphere. The degree of refraction of the radiation gives information about the atmosphere’s density and thickness. Spectroscopic studies give information about the atmosphere’s composition.