Auroras start at altitudes of about 80 to 600 kilometers (50 to 370 miles) above Earth's surface.

Here's a breakdown:

* Lower boundary (80 km): This is the region where the atmosphere is dense enough for auroral particles to collide with air molecules and produce light.

* Upper boundary (600 km): This is the limit of where the auroral particles can penetrate.

However, it's important to note that most of the auroral activity happens between 100 to 300 kilometers (60 to 190 miles). This is where the most intense auroral displays occur.