Topband: recent band openings & distance to terminator

[Eric Scace K3NA]

I've been interested in how early 160m opens for DX.  Here are some results for the last few 
afternoons in which I've been able to get on the air early:

Oct 20:
    first QSO: SM6CMU
    time: 2055z
    distance to sunset termination: 1190 km
    time before local sunset: 1h 0m
    (The band was already open.)

Oct 21:
    first QSO: S58A
    time: 2045z
    distance to sunset terminator: 1350 km
    time before local sunset: 1h 9m

Nov 1:  I was late and the band was already wide open at 2111z.

Nov 3:
    first QSO: G4OBK
    time: 2013z
    distance to sunset terminator: 1540 km
    time before local sunset: 1h 23m
    (Phil reports that my signal was audible around 2005z but not copiable.  The terminator was 1680 
km away at that point.)

I think distance to the terminator is a more appropriate metric than the oft-quoted "I worked him an 
hour before sunset".  Depending on time of year and latitude, a terminator that is 1500 km away 
could reach the station at widely different times:
    Sep 22 on the equator: 52 minutes.
    Dec 22 in London: 2 hours 28 minutes.  (The terminator is never more than 1770 km away, even at 
noon.)

I'd like to encourage others to listen/call early -- perhaps beginning when the terminator is 2000 
km away.  (So far I haven't heard of any DX contacts more than 2000 km into daylight.)

Perhaps, for the purpose of this exploration, we can define a "DX contact" as one with a station 
more than 2500 km away; i.e., clearly more than a single E-hop.

Good luck!

73,
    -- Eric K3NA