When it's summer in the Northern Hemisphere...?

Question

is it winter in the Southern Hemisphere??

Answer 1

Yes.

It's summer due to the tilt of the earth in its orbit.  In summer the light from the sun passes through less of the atmosphere than in the winter, hence more energy reaches the earth's surface.

6 months later it's winter because the sun's light has to pass through more atmosphere, less energy reaching the surface.

Answer 2

The period between June to August is considered as summer season in the Northern Hemisphere as the sun shines overhead between the equator and the tropic of cancer(23.5 degree latitude N) during this period whereas the same period is winter season for the Southern Hemisphere