Tuesday, February 03, 2009

Seasons and Photoperiods

We started the Journey North Mystery Class today by learning about seasons at this Liverpool Museums site. We also used a globe to reinforce the concept that the tilt of the earth on its axis is what causes seasons.

Then, we had to find our local sunrise and sunset time for Monday. We looked in Monday's newspaper, but it only had Monday's sunset and Tuesday's sunrise. Our recycling bin had already been picked up, so we had to go online to find Monday's sunrise. We went to this site and found both our sunrise/sunset times online.

Then, we had to calculate our photoperiod, or length of daylight. There are other methods, but we did this by writing our time as if it were a 24-hour clock. Then, we subtracted. BUT, remember you cannot borrow as if it was based on 100. These are hours and minutes, so you must borrow as a group of "60."

Here's an example:
sunrise: 7:25 am (stays 7:25)
sunset: 6:10 pm (so change to 18:10)

So, you'd subtract 18:10 - 7:25. You can't have 10 minutes and subract 25. So, you actually have to change it to 17:70 - 7:25. Then, just subtact! In this case, your photoperiod would be 10:45 or 10 hours and 45 minutes. Hope this helps, as I was a little confused at first. We'll have plenty of time to practice when we get our set of 10 sunrises/sunsets data on Friday!

Our photoperiod was 10 hours 49 minutes. Alexandra was really surprised as she thought we always had 12 hours of sunlight and 12 hours of darkness. So, she's already learning something! (And, so am I as I learned to calculate photoperiods.)


Rhonda said...

Some great learning going on. I also wanted to stop by and thank you for the links to the MTH. I loved looking at the activities that you and Alexandra did.

Robin said...

Yep, I remember learning that valuable "borrowing" lesson. Our poor data sheet looked pretty mucked up for the first couple of weeks.
Did you already get the mystery locations?

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