Primary minimum

Primary Minimum
In the light curve of an eclipsing binary, the deeper eclipse.
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When the cooler component passes in front of the hotter one, part of the latter's light is blocked, and the total brightness of the binary, as viewed from Earth, temporarily decreases. This is the primary minimum of the binary.

to the line of sight, the star dims noticeably when the dimmer component passes in front of, or eclipses, the brighter component, and dims again very slightly when the brighter component eclipses the dimmer one (see eclipse); the primary minimum, ...

See also: Period, Variable star, Earth, Binary star, Magnitude