Venus

Venus is the brightest planet, easily visible to the naked eye as the "morning star" or "evening star". Through a telescope, its most striking feature is the phase cycle.

Phase Cycle — Venus goes from a tiny, nearly full disk near superior conjunction to a large, thin crescent near inferior conjunction. The phase and apparent size have an inverse relationship: as Venus approaches Earth, it appears larger but shows less illuminated surface.

Dichotomy (Schroter Effect) — Venus reaches half-phase (dichotomy) several days before or after the geometrically predicted date. This optical illusion, known as the Schroter Effect, is caused by Venus's thick atmosphere scattering sunlight along the terminator.

Maximum Brightness — Venus reaches peak brightness (about mag -4.9) roughly 36 days before or after inferior conjunction — not at greatest elongation. At this point it's a bright crescent about 25% illuminated.

Equipment — A small telescope at 50-100x easily shows the phase. Use a blue or violet filter to enhance cloud features. Observe in twilight or daytime to reduce glare. A neutral density filter helps when Venus is very bright.

Venus has a synodic period of about 584 days. Each apparition follows a predictable sequence:

Superior Conjunction — Venus is behind the Sun, invisible. It appears as a tiny, nearly full disk.

Evening Star — Venus emerges east of the Sun, visible in the evening sky. Over several months it moves away from the Sun, reaching greatest eastern elongation (~47°).

Greatest Elongation (East) — Best evening visibility. Venus appears as a half-lit disk (dichotomy), about 24″ across.

Inferior Conjunction — Venus passes between Earth and Sun. It appears as a large thin crescent up to 60″ across, but is close to the Sun's glare.

Morning Star — Venus appears west of the Sun, visible before dawn. Reaches greatest western elongation, then slowly returns toward superior conjunction.