Thomas asked, “What is the summer solstice?”
For starters, the summer solstice is the start of summer in the northern hemisphere. It marks the days in Earth’s orbit around the sun and Earth’s rotational tilt coincide with the sun’s rays being directly over the Tropic of Cancer. This is also known as the longest day of the year.
The opposite is true for the winter solstice, which heralds the start of winter and is also the day in which we see the least amount of daylight.
Contrary to popular belief, the hottest days of the year cannot be attributed to the Earth being the closest to the sun during the summer months. In fact, the Earth is actually the farthest from the sun during summer in the northern hemisphere! It is called "apogee."
We are closest to the sun during the month of January, typically the coldest time of the year in the northern hemisphere. That is called "perigee."