Yes, today is the world’s longest day. June 21st marks the Summer Solstice and people in the Northern Hemisphere of planet Earth will experience longer daylight than every other day. Well, countries like United States, Canada, Russia, Turkmenistan, Azerbaijan fall into the north of the equator, these will experience the longest day of year 2016.
It is not necessary that every year summer solstice occur on June 21. It is a simple and usual phenomenon which can happen in between June 20 to 22 of every summer.
A solstice occurs when the sun is at the highest point in the sky relatively to the equator. This means today Northern Hemisphere is tilted fully towards the sun. And because North Pole is tilted to its extremes towards the sun, Arctic Circle will see 24 hours of daylight.
Well, make sure that June 21st is longest but not the hottest one. Earth only absorbs maximum sunlight! Interestingly, today people also witnessed the longest Roza too. It will be 15 hours long Roza.