COORDINATE TRANSFORMATIONS

Chapter 31 Generalised coordinate transformations

Practical Astronomy with your Calculator or Spreadsheet

Fourth Edition

Peter Duffett-Smith and Jonathan Zwart

HOR = horizon coordinates (A(zimuth), a(ltitude))

EQU = equatorial coordinates (H(our angle), δ (declination))

ECL = ecliptic coordinates (λ (ecliptic longitude), β (ecliptic latitude))

GAL = galactic coordinates (l (galactic longitude), b (galactic latitude))

From horizon to equatorial : enter φ (geographical latitude)

From horizon to ecliptic : enter φ (geographical latitude), ST (local sideral time), ε (obliquity of the ecliptic)

From horizon to galactic: enter φ (geographical latitude), ST (local sideral time), ε (obliquity of the ecliptic)

From equatorial to horizon: enter φ (geographical latitude)

From equatorial to ecliptic: enter ε (obliquity of the ecliptic)

From equatorial to galactic: no φ, ε nor ST required

From ecliptic to horizon: enter φ (geographical latitude), ST (local sideral time), ε (obliquity of the ecliptic)

From ecliptic to equatorial: enter ε (obliquity of the ecliptic)

From ecliptic to galactic: enter ε (obliquity of the ecliptic)

From galactic to horizon: enter φ (geographical latitude), ST (local sideral time), ε (obliquity of the ecliptic)

From galactic to equatorial: no φ, ε nor ST required

From galactic to ecliptic: enter ε (obliquity of the ecliptic)

For a link to a schematic view of the chapter 31 theory and matrices: link schematic

For a link to a worked-out example : link example