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JuliaAstro / AstroTime.jl

Astronomical time keeping in Julia
https://juliaastro.github.io/AstroTime.jl/stable/
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TDB differencing error due to epoch storage #44

Closed bgodard closed 5 years ago

bgodard commented 5 years ago

If I have 2 observers on the surface of the Earth take some measurements at a given TT = tt0 and I want to model a combined observation in the barycentric reference system, I can compute TDB1 (for observer 1) and TDB2 (for observer 2) using an accurate position dependent TDB-TT difference model.

tdb1 = TDBEpoch(tai_offset_observer1,tt0)
tdb2 = TDBEpoch(tai_offset_observer2,tt0)

but then:

julia> tdb2-tdb1
0.0 seconds

julia> tdb2==tdb1
true

but both of these are not correct. The assumption that time can be compared independently of timescale is incorrect (simultaneity is a relative concept).

helgee commented 5 years ago

Fixed in #45