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Why do Mercury and Venus always appear close to the Sun from Earth?

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Nicolaus Copernicus Portrait of Nicolaus Copernicus, 1580, from the Town Hall in Toruń, Poland; in the collection of Muzeum Okręgowe w Toruniu (Regional Museum in Toruń). In his book *De revolutionibus*, he proposed that the Sun was the center of the solar system and that the planets circle the Sun.

Mercury and Venus appear close to the Sun from Earth because they are inferior planets, meaning their orbits lie closer to the Sun than Earth’s orbit.12

Because these planets revolve around the Sun within Earth's orbit, their angular distance from the Sun—known as elongation—is physically restricted. From a terrestrial perspective, Mercury never reaches an elongation greater than about 28°, while Venus reaches a maximum of approximately 48°. Consequently, they are always observed near the Sun in the sky, typically appearing during dusk or twilight.12

While early models like the Ptolemaic system attempted to explain planetary motion using complex geocentric arrangements of epicycles and deferents, the Copernican system later correctly identified that these planets orbit the Sun, naturally accounting for their observed proximity to the solar disk.3