Constellations are a celestial backdrop.
Any object in the sky can be said to be “in” a constellation. Fixed stars, such as Betelgeuse in Orion or Sirius in Canis Major, are forever part of the same constellation.
- Planets slowly move across the sky, and so appear against the backdrop of one constellation after another. The fast-moving planet Mercury is generally in a different constellation every two to three weeks, while distant Saturn may appear in the same constellation for years. This photo shows Mars in Gemini.
- The Sun also can be said to be “in” a constellation, although the background stars are not visible during the day. As the year goes by, the Sun, from the vantage point of Earth, appears in a regular sequence of constellations.
Scroll down this page to see a photo of the great planetary alignment of 2002.