Newsgroup: it.scienza.astronomia
Titolo: Per quel famoso secondo di "troppo" ovvero: la nostra pigrizia

Fino a qualche anno fa il secondo intercalare si aggiungeva una volta
all'anno: ora non più. L'ultima volta fu nel 1999. Ne abbiamo parlato
su ISA, ricordate? No?!
Beh, a farla breve vi propongo una serie di indirizzi scelti con
criterio pseudo-casuale ricordandovi che per questo genere di info è
SEMPRE BENE RIFERIRSI A FONTI ATTENDIBILI: la cultura "di riporto" è
perdente fin dal nascere (ed è un insulto nei confronti dei
professionisti).
Ciao
Eliseo
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http://maia.usno.navy.mil/bulletin-a.html
http://tf.nist.gov/
http://www.ien.it/tf/time/index.html
http://hpiers.obspm.fr/eop-pc/
http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/deltaT.html

Eliseo ha scritto:
e ci tiene ad aggiungere per tutti, disattenti in special modo e per
coloro che cadono dalle nuvole:
http://maia.usno.navy.mil/bulletin-a.html
http://tf.nist.gov/
http://www.ien.it/tf/time/index.html
http://hpiers.obspm.fr/eop-pc/
http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/deltaT.html
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La tabella che qui trovi vale fino a 31 Dicembre 2005
http://hpiers.obspm.fr/eop-pc/earthor/utc/TAI-UTC_tab.html
Sito meraviglioso, il seguente!
http://hpiers.obspm.fr/eop-pc/
...all'interno ti dicono come verrà inserito il secondo, leggi qui:
http://hpiers.obspm.fr/eop-pc/
_______________________________________________________________________
_______________________________________________________________________
     INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) 
SERVICE INTERNATIONAL DE LA ROTATION TERRESTRE ET DES SYSTEMES DE REFERENCE
SERVICE DE LA ROTATION TERRESTRE
OBSERVATOIRE DE PARIS                                   
61, Av. de l'Observatoire 75014 PARIS (France)
Tel.      : 33 (0) 1 40 51 22 26
FAX       : 33 (0) 1 40 51 22 91
e-mail    : 
servic...@obspm.fr
http://hpiers.obspm.fr/eop-pc
                                              Paris, 4 July 2005
 
                                              Bulletin C 30
 
                                              To authorities responsible 
					      for the measurement and 
					      distribution of time                                         
                                   UTC TIME STEP
                            on the 1st of January 2006
 
 A positive leap second will be introduced at the end of December 2005.
 The sequence of dates of the UTC second markers will be:		
 
                          2005 December 31,     23h 59m 59s
                          2005 December 31,     23h 59m 60s
                          2006 January   1,      0h  0m  0s
 
 The difference between UTC and the International Atomic Time TAI is:
 
  from 1999 January 1, 0h UTC, to 2006 January 1  0h UTC  : UTC-TAI = - 32s
  from 2006 January 1, 0h UTC, until further notice       : UTC-TAI = - 33s
 
 Leap seconds can be introduced in UTC at the end of the months of
December 
 or June, depending on the evolution of UT1-TAI. Bulletin C is mailed
every 
 six months, either to announce a time step in UTC or to confirm that
there 
 will be no time step at the next possible date.
 
                                              Daniel GAMBIS
                                              Head		
                                              Earth Orientation Center of
IERS
					      Observatoire de Paris, France
_________________________________________________________________________
LEGGI quest'altro passo, te lo consiglio, male non ti fa.......:-) (sullo
stesso sito trovi anche un interessante grafico.....)
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When should we introduce Leap second in UTC ?
On 31 December 1998, the last minute of the day has last 61 seconds. Why ?
leap second : see last last Bulletin C
[ Table 1 : TAI - UTC ] [ Table 2 : offsets of UTC] [Bulletin C] [UTC.html]
--------------------------------------------------------------------------------
The Coordinated Universal Time (UTC, replacing GMT) is the reference time
scale derived from The Temps Atomique International (TAI) calculated by
the Bureau International des Poids et Mesures (BIPM) using a worldwide
network of atomic clocks. UTC differs from TAI by an integer number of
seconds; it is the basis of all activities in the world. 
UT1 is the time scale based on the observation of the Earth's rotation. It
is now derived from Very Long Baseline Interferometry (VLBI). The various
irregular fluctuations progressively detected in the rotation rate of the
Earth lead in 1972 to the replacement of UT1 as the reference time scale .
However, it was desired by the scientific community to maintain the
difference UT1-UTC smaller than 0.9 second to ensure agreement between the
physical and astronomical time scales.
Since the adoption of this system in 1972, firstly due to the initial
choice of the value of the second (1/86400 mean solar day of the year
1820) and secondly to the general slowing down of the Earth's rotation, it
has been necessary to add 21 s to UTC. The last additionnal second has
been introduced on 1 January 1999, at 0h.
The decision to introduce a leap second in UTC is the responsibility of
the International Earth Rotation Service (IERS). According to
international agreements, first preference is given to the opportunities
at the end of December and June, and second preference to those at the end
of March and September. Since the system was introduced in 1972, only
dates in June and December have been used.
The leap second is announced in Bulletin C.
________________________________________________________
________________________________________________________
Queste che hai appena letto NON SONO NOTIZIE DI RIPORTO ma ricavate da
documenti ufficiali pubblicati da Responsabili di Enti che, del tempo
cronologico, ne fanno una Ricerca professionale.
Eliseo
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