Re: Why is the Moon so slow today?

> Dear Moongazer and Calendar People
>
> It is the difference between the tidal day and the day that is attributable to the motion of the moon, so a faster motion would lead to a bigger difference regardless of direction of orbit.
>
> Karl
>
> 12(11(18
>
> -----Original Message-----
> From: East Carolina University Calendar discussion List [mailto:CALNDR-L@...] On Behalf Of Victor Engel
> Sent: 07 May 2012 13:56
> To: CALNDR-L@...
> Subject: Re: Why is the Moon so slow today?
>
> You are probably forgetting that the moon goes from west to east, not
> east to west. So if it goes faster, it will take longer to get to the
> same place since the earth rotates the same way. The moon effectively
> is catching up a little bit to the earth, so the earth takes longer to
> lap it.
>
> Victor
>
> On 5/7/12, Moongazer <motti.yarchinai@...> wrote:
>> I was resetting my Time-and-Tide clocks (I have three of them) today after
>> changing the batteries. (It helped that it was Full Moon only yesterday.) I
>> looked up last night's upper transit time of the Moon for my meridian, set
>> the clock to that time and its moon-pointer to the "12 o'clock" (high-tide)
>> position, then adjusted the time (all four clock-hands) forward to the
>> current time-of-day and inserted the battery. I got the upper-transit data
>> from the Data Services section of the US Navy's Astronomical Applications
>> website on  http://aa.usno.navy.mil/data/docs/RS_OneDay.php this page .
>>
>> It then occurred to me to compare the same data for yesterday and today to
>> see exactly how long a tidal day is right now -- i.e. the time between two
>> successive upper transits of the Moon (sometimes erroneously called a lunar
>> day). Its MEAN length is about 24h, 50m. To my surprise, subtracting
>> yesterday's upper transit time from today's gave me a difference of 1:03
>> (i.e. the tidal day is currently 25h, 3m.)
>>
>> Now I know that since the Moon's orbit is an ellipse, not a circle, the
>> Moon's motion is not uniform, i.e. its orbital speed varies. It is at its
>> slowest at apogee and at its fastest at perigee. So, I thought, if the
>> tidal
>> day is currently so much longer than its mean length, the Moon must be
>> moving fairly slowly right now. It must be fairly close to apogee. I then
>> decided to check on this and, to my surprise, I discovered from
>> http://www.fourmilab.ch/earthview/pacalc.html this site   that only
>> yesterday (coincidentally at almost exactly the same time as Full Moon) the
>> Moon was at perigee! If so, I would have expected the current length of a
>> tidal day to be shorter than its mean, not longer. Hence my question: why
>> is
>> the Moon so slow today?
>>
>> --
>> View this message in context:
>> http://old.nabble.com/Why-is-the-Moon-so-slow-today--tp33763520p33763520.html
>> Sent from the Calndr-L mailing list archive at Nabble.com.
>>
>
>
> --
>
> Victor Engel
> http://victorspictures.com/blog
> --
> Scanned by iCritical.