(no subject)

[abigailbrady]

Happy solstice everyone!

Random fact: sunrise has already started getting later each day, a few days ago, but sunsets won't start getting earlier for a few days yet [1]. Wonder if those two days (earliest sunrise, latest sunset) have actual names?


1. This may not apply to readers in the southern hemisphere.

Comments

[spindr.livejournal.com]

Random fact: sunrise has already started getting later each day

http://www.guardian.co.uk/britain/article/0,2763,1511179,00.html

now I need to know who's right and who's wrong!!

[abigailb.livejournal.com]

here's a chart. i would guess the 17th or something is actually the earliest sunrise, but it doesn't show seconds. also the latest sunset there is probably the 25th.

[zootalures.livejournal.com]

Hey, i didn't realise that the parhelion and aphelion were timed within a few weeks of the equinoxes (Jan 2, July 2 (in 2004 anyway)). I guess this is just a coincidence though. IIrc the period of our Axial processession is something like once every 26,000 years and the interweb seens to indicate the period of oribital procession to be something like 21,000 years.

Its nice to know that our era is special in some way..

It always amazed me that with everything in geology dating back millions or billions of years that the time frames for a lot of things in celestial mechanics are so small. The fact that there are rocks which are a significant proportion of the (current estimate for the) age of the universe (as we understand it) on earth is neat.

[abigailb.livejournal.com]

I wonder how long the year and day were 4 billion years ago...

[hairyears.livejournal.com]

Tidal drag from the moon slows the Earth's rotation by 16 seconds per million years... But that's nonlinear and it does not imply a four-hour day length four billion years ago! Fossil evidence suggests that in the middle Devonian period, about 375 million years ago, days were about 21.9 hours long, and there were about 400 days in a year. But beyond that I have no idea: ask a geologist.

However, if that calculation is difficult, day length prior to the collision which is believed to have ejected the Moon and given the Earth it's current 24-ish hour day is a matter of speculation.

The year, surprisingly enough, was pretty much what it is today, plus or minus ten percent. At least, since the end of the 'Hadean' era 3.8 Billion years ago, when the planetary bombardment had died down and no further significant exchanges of angular momentum took place.