In the Northern Hemisphere, the reason it's so hot in the summer is because the North Pole is tilted toward the Sun! Because of this tilt, the Sun is more directly overhead and its rays hit the Earth at a steep angle. This concentrates the heat in a small area.
During the summer months the Earth’s atmosphere acts like a blanket and holds the heat. Summer begins on June 21-22 in the Northern Hemisphere. Astronomers refer to the arrival of this event as the Summer Solstice. The long daylight hours during the summer months allow the Earth plenty of time to reach warm temperatures as the Sun’s rays beam down. The Sun is extremely hot because of two chemical elements, hydrogen and helium. These elements explode continually causing light and heat. The temperature on the Sun’s surface is 10,000 degrees F!