Stars are visible all year round, but the night sky changes throughout the year due to the Earth's orbit around the Sun. As the Earth orbits the Sun, different parts of the sky become visible at different times of the year.

In March, the Earth is positioned in its orbit so that the constellation Orion is visible in the night sky. Orion is one of the brightest and most recognizable constellations, and it contains several bright stars, including Betelgeuse, Rigel, and Saiph.

In September, the Earth has moved in its orbit so that the constellation Orion is no longer visible in the night sky. Instead, the constellation Pegasus is visible in the night sky. Pegasus is another bright and recognizable constellation, and it contains several bright stars, including Markab, Scheat, and Alpheratz.

So, while some stars may not be visible in March but are visible in September, it is not because the stars have moved or disappeared. It is because the Earth's orbit around the Sun has changed the perspective from which we view the night sky.