Arocket is launched to a height of 210 kilometers above sea level. what level of the atmosphere has it entered?

The rocket has entered the thermosphere.

Explanation:

Thermosphere starts at around 90 km to 1000 km above the sea level. It is present between Mesosphere and Exosphere, The temperature climbs sharply from lower to higher and it get impacted by the solar temperature heavily. In the lower level of thermosphere almost till 500 km resides the ionization/ ionosphere. This area is ionized by solar activities and the cause of Aurora.

So if the rocket launched the height of 210 km, so it has reached the thermosphere and might also touched the ionosphere and aurora  

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