Which star has successive upper transits at 24 sidereal hours intervals?

Which star has successive upper transits at 24 sidereal hours intervals?

• A. Polaris
• B. Sirius
• C. Aldebaran
• D. Betelgeuse

Answer: (C)

The main idea here is the diurnal motion of the sky caused by Earth's rotation and what happens at the meridian. An upper transit is when a star crosses the local meridian on the upper arc of its daily circle. Because Earth completes one rotation relative to the stars in a sidereal day, the star returns to the meridian after roughly one full rotation. That means successive upper transits occur about 24 sidereal hours apart (actually 23h56m, but we refer to it as a sidereal day). Aldebaran is a good representative example of this everyday pattern: with its mid-declination position, it regularly crosses the meridian while it’s above the horizon for observers at many latitudes, producing a clean, daily upper transit interval of roughly a sidereal day. The same 24-sidereal-hour spacing applies in principle to other stars too, but Aldebaran is a classic, easily observable case that illustrates the standard daily transit behavior.

The main idea here is the diurnal motion of the sky caused by Earth's rotation and what happens at the meridian. An upper transit is when a star crosses the local meridian on the upper arc of its daily circle. Because Earth completes one rotation relative to the stars in a sidereal day, the star returns to the meridian after roughly one full rotation. That means successive upper transits occur about 24 sidereal hours apart (actually 23h56m, but we refer to it as a sidereal day).

Aldebaran is a good representative example of this everyday pattern: with its mid-declination position, it regularly crosses the meridian while it’s above the horizon for observers at many latitudes, producing a clean, daily upper transit interval of roughly a sidereal day. The same 24-sidereal-hour spacing applies in principle to other stars too, but Aldebaran is a classic, easily observable case that illustrates the standard daily transit behavior.