The constellation Libra is not defined by a specific number of stars. Instead, it's a pattern of stars as seen from Earth.

Here's why:

* Constellations are patterns: Constellations are groups of stars that appear close together in the sky from our perspective on Earth. They don't necessarily have any physical connection to each other, they just happen to be in the same line of sight.

* Different cultures, different patterns: Different cultures throughout history have seen different shapes in the stars, leading to variations in constellation definitions.

* Modern boundaries: The International Astronomical Union (IAU) has established official constellation boundaries, but these boundaries are based on dividing the sky into areas. There's no set number of stars that must be within a constellation boundary.

So, while you might find some sources referencing a specific number of "main stars" in Libra, it's more accurate to say Libra is a pattern of stars that includes both bright and faint stars within its boundaries.