Notes
- Times in UT
- Each file : one cycle from NEW MOON
- Data from the USNO
What is UT?
UT means Greenwich Mean Time, but in 24 hour format. Many lunar phase tables
are given in ET (Ephemeris Time) which differs from UT by a second or two.
Our data, in UT, comes directly from the US Naval Observatory website,
aa.usno.nav.mil/data/docs/MoonPhase.html.
What is TLT?
The boundaries of the shadow of night move smoothly across the
face of the Earth. But local time (eg,, Pacific Standard Time in
the USA) changes abruptly, between time zones, by one hour.
A nice discussion may be found at this
NASA site
by David P. Stern.
How to compute your TLT?
To find out the TLT where you are, you need to discover:
- its latitude (this can be done with a map or a GPS appliance), and
- its time zone (eg, from a phone book).
Both may be found (if you are near
a city) from the brilliant
Astro Dienst atlas website.
The latitude (East or West of the prime meridian) divided by
15 (degrees per hour) gives the correction (add if East, subtract
if West) to UT to find TLT. Beware Daylight Saving Time!
We plan to add a conversion utility UT -> TLT soon:
TLTC Calculator.
What is the TLT good for?
Celestial events (eg, a sunspot, eclipse, or meteorite) are timed
in UT, or translated to LT by adding your Time Zone correction.
But terrestrial events (eg, sun directly overhead, or high tide)
need to be corrected to TLT by computing a correction,
the TLTC.
Rev 11 Sep 2003
by Ralph Abraham