Moon chart accuracy?

Question

Okay I asked this question yesterday but I forgot to add the link to the moon chart thing. I reposted it but no one has responded to it. Anyways how accurate would you say that this moon chart is? And another thing how would I use the chart in day light savings time. I'm not sure weather GMT has daylight savings. Should I use the chart to a clock that been set back an hour or do I use it to a clock that has been set foward? here is the link. Thanks in advance
http://www.cycletourist.com/moon/index.php

I'd also like to add that i am in southern california we set are clocks foward in the summer and back in the winter.

Answer 1

I didn't check their numbers, but since precise lunar phase times are readily available I would expect their times are accurate to the precision given (1 minute).

California time is currently Pacific Daylight Time (PDT), or GMT -7:00. GMT does not go on daylight savings time, so when you go back to standard time you will need to use GMT - 8:00.

Answer 2

You have to take Daylight time and your meridian position into account, down to the second.

You have to convert GMT to LMT (Local Mean Time).

That is if you want to be accurate.

Meridian time can be as much as 30+ minutes off LMT

What this means is if you want to start watching an ECLIPSE you can be as much as 30+ minutes off seeing the actual start.

This is why people go out and find the moon partially covered already, because they didn't compute LMT they use ST (standard time or MERIDIAN time).

In the case of an OCCULTATION (the moon going in front of a star) this is VERY important.

YOu need to know your longitude and how many minutes of time change for each degree from 0 or GMT or UT

UT and GMT are almost identical

But for an OCCULTATION the error of UT and GMT can mean you don't see the star disapear.

This is all about time changes

GMT to LMT and if the calculations are UT then you must take the small UT to GMT factor into account.

Answer 3

"How accurate"? Well coming from the USNO I'd say it's reliable.

If you're still in Daylight Saving Time, then go to the drop-down list and choose "GMT - 7.00 (PDT)". Because the items in the list show PDT, MDT, etc, I assume that it's still Daylight Saving. I happen to know that if Pacific time is 7 hours behaind GMT, then it must be Daylight Saving. Your normal time zone is GMT minus 8 hours.

When Daylight Saving ends, that list will probably default back to Standard times, which will show as PST, MST, etc.

Answer 4

This chart takes the time from your computer's clock, so as long as your clock is set correctly, you won't need to do any calculations. For instance, where I am it's now 6 pm EDT, and it's showing the phase correctly, along with the correct difference (-4 hours) between EDT and GMT. Yours should show -7 hours for PDT.

Answer 5

The phases of the moon have been studied and measured in minute detail for years.
As long as there is no human error in creating the chart (such as a keying error or incorrect link), its as accurate as any other such chart.

The times given are GMT (UTC), so for the time in your area you will need to convert to your local time (there are conversion charts online). Most conversion charts include the time with and without DST (Daylight Savings Time).
UTC is a constant, it doesn't use DST.

Answer 6

I checked the numbers with the U.S. Naval Observatory, and they are accurate to plus or minus 1 minute. If you need that type of accuracy or better, you need to learn the ifs, ands, and buts about the moons position. Such as geocentric observations, atmospheric conditions, etc.

Answer 7

GMT does not have daylight savings.

Use this link and you can put in where you are and the date. That's all you need.

http://aa.usno.navy.mil/data/docs/RS_OneDay.php

And it is the U S Navy, so I think it can probably be trusted.....