ALMA can point at the Sun. Small grooves or etchings in the antenna surface are designed to ensure that optical and infrared sunlight is not reflected to the secondary subreflector, as extreme heat could permanently damage it. On the other hand, the ALMA antenna surface is optimized so that millimeter and submillimeter sunlight is not scattered away, allowing for scientific observations of the Sun.

When the target is not the Sun itself, it is advisable not to point closer to the Sun than 15 degrees from the solar photosphere to avoid a large amount of contamination in the observations. Particularly, it has been found that some antennas show erratic behavior during atmospheric calibration scans when observing targets closer to the 15-degree limit. Contamination from the Sun can cause a temperature increase in the ALMA Calibration Device ambient loads, which can yield faulty system temperature measurements.

This sun avoidance 15-degrees limit is enforced by ALMA's dynamical scheduler by default, except for solar observations. Thus, PIs are advised to consider this when planning their observations and to contact their ARC via the ALMA Helpdesk to discuss the best strategy when observations within the sun avoidance zone are requested (e.g. solar system objects, ToO with limited windows of observability, etc.)

Please see the ALMA Technical Handbook Chapter 8.10 for more information on solar observations.