ALMA can actually point at the Sun. But, if the target is not the Sun itself, it is not advisable to point closer to the Sun than a couple of primary beamwidths from the solar photosphere to avoid a large amount of contamination in the observations.
This is because detectable solar emission is seen in the antenna sidelobes up to several degrees away from the Sun, although small grooves or etchings in the antenna surface are designed to ensure that sunlight is not reflected to the secondary subreflector.
How close can ALMA observe to the Sun? - Knowledgebase / General ALMA Queries - ALMA Science
How close can ALMA observe to the Sun?
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- Last updated: Sep 21, 2020 by Anthony Remijan