Re: What is the term for a period of time of extended daylight?

Dear Suzanne,

Thank you for your question. I have tried to find some references to this but not found any. I can, however, say something about the length of the day in a more general sense.

The length of the day is determined by the rotation of the Earth around its axis. A short explanation can be found here [1]. In principle the rotation of the Earth is what is driving the changing of day and night. Furthermore, the place on the globe has some influence. If you are close to the Equator, day and night are both around 12 hours across the year. When you go away from the Equator, the fact the Earth's axis is tilted has some influence, making days longer in Summer and shorter in Winter.

What you are describing sounds like a sudden change in day length. The only thing that could cause this is a slow-down and speed-up of the rotation of the Earth (this would also cause tidal waves). However, the amount of energy required for this is massive. We can compute the amount of energy the rotation of the Earth carries by multiplying the inertia of the Earth with the rotation speed squared. The rotation speed of the Earth is equal to 2 pi divided by the day length, or roughly 7.29x10^{- 5}. The moment of inertia of the Earth is computed using the input from [2] and the calculation in [3]. This gives a number of 9.7x10³¹ assuming the Earth is uniform. In reality, the core is relatively more dense, so the number is slightly lower. Nonetheless, the total amount of energy stored in the rotation of the Earth is 3.76x10²⁴J. This is the energy of 100 billion hydrogen bombs. The only thing that could significantly slow the rotation of the Earth fast is either the Moon being knocked out of orbit or a massive asteroid impact. Either effect would be permanent, unless an equal size and opposite event would happen. Given that this would devastate humanity, and no such devastation is recorded in the annals of history, I would tend to think no such event happened in 1057.

Regards,

Bart Broks

1. http://www.woodlands-junior.kent.sch.uk/time/
2. http://en.wikipedia.org/wiki/Earth
3. http://hyperphysics.phy-astr.gsu.edu/hbase/isph.html