Why is 21 June the longest day?

Related questions

1. Which is the place where sun never rises?
2. Which country has no daylight?
3. What is belye Nochi?
4. Why do white nights happen?
5. Where on earth does it never get dark?
6. Where do white nights occur?
7. What country is always dark?
8. Which country has long nights?
9. What is the longest day in 2019?
10. What is the official first day of spring?

Tags

1. #countries
2. #sunset
3. #happen
4. #solstice
5. #northern
6. #longest
7. #early
8. #latitudinal
9. #location
10. #hemisphere
11. #between
12. #considered
13. #depends
14. #sunrise
15. #country
16. #though
17. #doesn