Course / Latitude from Polaris

Part II · First sights · Page 4 of 4

The Polaris tables

Latitude = Ho − 1° + a0 + a1 + a2

  • a0: the main term. Find the column for LHA Aries (each covers 10°), then the row for its units of degrees, and interpolate for the minutes.
  • a1: same column, the row for your latitude.
  • a2: same column, the row for the month.

All three are always positive; the tables add 1° in total to make them so, which is why you subtract 1°.

For a star, the main altitude correction is just refraction: the stars and planets column, always minus.

March 14, 2027, 23h41m17s UT, DR longitude W 064°33.5′, DR latitude N 41°12′. Ha 41°26.4'.

GHA Aries 157°20.2' + increment 10°20.9' = 167°41.1'; LHA Aries = 167°41.1' − 64°33.5′ = 103°07.6'

Ho = 41°26.4' −1.1' = 41°25.3'

a0 0°38.2', a1 0.5′, a2 1.0′ (March)

Latitude = 41°25.3' − 1° + 0°38.2' + 0.5′ + 1.0′ = N 41°05.0'

Explore the tables:

Polaris tables, 2027

a0, by the units of LHA Aries (100°–109°; the 10 row is the start of the next column)
LHA Ariesa0
100°0°36.5'
101°0°37.1'
102°0°37.6'
103°0°38.1'
104°0°38.7'
105°0°39.2'
106°0°39.8'
107°0°40.3'
108°0°40.9'
109°0°41.5'
110°0°42.1'
a1, by latitude
Lat.a1
0°0.4′
10°0.5′
20°0.5′
30°0.5′
40°0.5′
45°0.6′
50°0.6′
55°0.6′
60°0.7′
62°0.7′
64°0.7′
66°0.8′
68°0.8′
a2, by month
Montha2
Jan.0.7′
Feb.0.8′
Mar.1.0′
Apr.0.9′
May0.9′
June0.7′
July0.6′
Aug.0.4′
Sept.0.3′
Oct.0.2′
Nov.0.3′
Dec.0.4′

Latitude = Ho − 1° + a0 + a1 + a2. All three are always positive.