It's difficult to say definitively what the "third largest" constellation is because there isn't a universally agreed-upon way to measure constellation size. Here's why:

* No official boundaries: Constellations are not defined by precise boundaries like countries on a map. Their shapes are more conceptual and have evolved over time.

* Different measurement methods: You could measure a constellation's size by:

* Area of sky: This would be the total area of the sky encompassed by the constellation's stars.

* Number of stars: This could be based on how many stars are traditionally included in the constellation.

* Linear distance: This could be measured by the distance between the constellation's farthest points, but this would be subjective.

Here are some of the constellations often considered large:

* Hydra: One of the largest constellations by area of sky covered.

* Ursa Major: Known for its recognizable "Big Dipper" asterism.

* Virgo: Also covers a large area of the sky.

* Centaurus: Another constellation known for its size.

Ultimately, the "third largest" would depend on the method you use to measure constellation size.