What are the 5 largest constellations that one can see from the Pacific Northwest? This is a great question as the largest constellations visible from the Pacific Northwest happen to be the largest constellations in the sky. However, these are not necessarily native to the northern hemisphere, as Hydra, Virgo, and Cetus are considered Southern Constellations.

Here is a summary of the largest constellations visible in the Pacific Northwest.

Constellation	IAU Rank	Best Time To View	Where In The Sky	Interesting Fact
Hydra	1st	March/April	Southern Sky Close To Horizon	Hindu and Chinese astronomers had myths related to these stars
Virgo	2nd	May	Southern Part Of The Sky	The ecliptic intersects the celestial equator within this constellation. Spica is an easy way to find it.
Ursa Major	3rd	April	Directly Overhead	This is part of the Big Dipper.
Cetus	4th	November	Southern Sky Close To Horizon	Cetus is in the region of the sky that contains other water-related constellations.
Hercules	5th	July	Overhead/Mid-sky	Hercules has no first or second magnitude stars

Interesting Trivia:

The largest northern constellations are Ursa Major, Hercules, Pegasus, Draco and Leo, all of which are visible from the Pacific Northwest.

All of these listed were known to the Greek, listed by Ptolemy in his Almagest in the 2nd century AD. They have been known since ancient times. The largest constellation that has not been known since antiquity is Lynx.

To find out which ones have Messier objects, check out this article. For a different spin on things, check out this article from astronomy.com.