"Psi" is a Greek letter, not a measurement of a star's brightness. You're likely thinking about "magnitude," which is the way we measure a star's apparent brightness.

Here's the breakdown:

* Magnitude: A system of measuring a star's apparent brightness from Earth. Brighter stars have lower magnitudes (e.g., -1, 0, 1). Dimmer stars have higher magnitudes (e.g., 5, 10, 15).

* Psi: The 23rd letter in the Greek alphabet, often used to label stars within constellations. For example, "Psi Draconis" is a star in the constellation Draco.

To find the magnitude of a specific star, you would need to look it up in a star catalog or database. For example, you could search for "Psi Draconis magnitude" online.