occulting disk


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occulting disk

[ə′kəlt·iŋ ‚disk]
(astronomy)
A small metal disk placed in the focal plane of the eyepiece of a telescope, usually to cover a bright object in order to permit observation of a faint one.
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On an average a new member of the Kreutz family is discovered every three days, with some of the larger members being observed for some 48 hours or more before disappearing behind the occulting disk, never to be seen again.
I decided to also keep the black-spot result out of the difference image because the contrast with the protruding disk was more visually appealing--there was no occulting disk involved when recording the images.
Prominences can also be viewed with an H[alpha] coronagraph, a specialized refractor equipped with an H[alpha] filter and an internal occulting disk that simulates a total eclipse.
LASCO's two remaining coronagraphs use an external occulting disk in front of the main lens.
At least the SOHO satellite should have no trouble seeing Venus right up to the edge of its occulting disk.
By carefully controlling scattered light within the instrument, Lyot could use an occulting disk to produce an artificial eclipse that enabled him to view the Sun's prominences and inner corona.
The Baader instrument, in addition to having an occulting disk, relay and projections lenses, and an adjustable iris diaphragm for controlling scattered light, has a narrow-passband H[alpha] filter that greatly increases the contrast of prominences.
Because a coronagraph's occulting disk must precisely match the size of the solar image, the disk must be made for a telescope's specific focal length.
Manipulating the small occulting disk took some practice, especially when fitting it into its Teflon socket in the relay-lens assembly.
As the telescope was slewed and the occulting disk crept across the Sun's face, I felt that I was actually watching the Moon eclipse the Sun.
The instruction manual suggests turning the telescope away from the Sun after 20 to 30 minutes to cool the occulting disk.
Best results require the mounting to be accurately polar aligned so that the occulting disk will stay centered on the Sun without the need for constant guiding.