PDA

View Full Version : Phases of the Moon



euclid
12-24-2008, 07:21 PM
1. How do the phases of the moon work? What is the sequence? How long does each phase last? Are there times when the moon is not visible? etc.

2. I there any way to work out the phases of the moon in times past (e.g. in 1096 AD)? If I know the date of Easter in 1096, does that help?

And...Happy Christmas everyone!

DeleyanLee
12-24-2008, 07:23 PM
Here's a starter:

http://www.moonconnection.com/moon_phases_calendar.phtml

pdr
12-26-2008, 02:52 AM
Historical Genre, Resources by Era?

Under General there are a couple of sites mentioned.

One site you can get a calendar showing phases of the moon. I think they back to the year 0!

www.timeanddate.com

BarbaraKE
12-26-2008, 06:24 PM
The problem with trying to determine the phase of the moon at some point in the past has to do with the 'date'.

Ultimately, any way of doing this comes down to calculating the number of days between 'then' and 'some more recent date where we know the phase of the moon'.

So let's say I want the phase of the moon on April 12th, 1096. And I know Sept. 16th, 2000 was a full moon.

We have to calculate the number of days between the two dates. Then we will divide that number of days by the length of the moon's cycle to get the number of moon cycles between the two dates.

The problem comes in with determining the number of days. You can't just take into account the number of years (2000 - 1096) and multiply by 365. Obviously you have to adjust for the month/day (Sept. 16th. vs. April 12th). And you have to adjust for leap years (remembering that every year divisible by 4 is a leap year (i.e. has an extra day) unless it's also divisible by 400 (i.e. 1600) in which case it's not a leap year).

But that's still ok - we can do that.

The problem comes in with the fact that the Gregorian calender (which is what we currently use) started being used at different times in different parts of the ('Western') world. Prior to that, they used the Julian calender. When each country or whatever switched over, they had to adjust their calender a certain number of days (which varied depending on exactly when they changed).

I believe parts of Europe changed as early as some time in the 1500's while Russia didn't change until 1914.

Since you're interested in an earlier date 1096, you would have to take into account how the Julian calender handled things like leap years. (Since I wasn't going back that far, I can't answer that.)

All of this can obviously be done but I'm not up to figuring it out. (Still have a headache from hosting Christmas dinner for the entire family.)

Good luck.

Mike Martyn
12-26-2008, 09:29 PM
Historical Genre, Resources by Era?

Under General there are a couple of sites mentioned.

One site you can get a calendar showing phases of the moon. I think they back to the year 0!

www.timeanddate.com (http://www.timeanddate.com)


Wow! Thanks for that. I've been considering how to show something is terribly out of wack to my inadvertant juvenile time travellers. So here it is. The wolf cub (cub scout in the US) in the group realises that the moon has gone from half back to new overnight!

Chase
12-26-2008, 10:38 PM
All good advice. I include phases of the moon in lots of my stories, so I have software. However, a good freebee is provided by Google Gadgets:

http://www.moonconnection.com/moon_gadget.phtml#rt2ig1_1230316327

Also included are terms. A new moon is of course the dark side to earth. Perhaps a cub scout might easier note a first-quarter half moon one night and then a wanning crescent the next (or diring the same night).

BarbaraKE
12-26-2008, 10:57 PM
One site you can get a calendar showing phases of the moon. I think they back to the year 0!

www.timeanddate.com (http://www.timeanddate.com)

I remember looking at that one. Unfortunately it's based off the Gregorian calender which hadn't even been invented in 1096.

On the other hand, what does it really matter. I like the idea of the cub scout realizing something is wrong because of the moon phase but - in real life - no one is going to sit there and figure out the correct moon phase in 1096.

But it makes a difference in my book since some events take place before the calender change and that difference in dates is important to the story.