Almanac spreadsheets in 2021

gp_ut

Comparisons with the 2021 Nautical Almanac Commercial Edition show that our spreadsheets remain sufficiently accurate for the year 2021 without the need for any changes or updates in the calculations.

Spreadsheets aries_stars.xls and what_star.xls were modified with the changed spelling of one star’s name (Alnair). Archive TAR and ZIP files were also updated accordingly.

22 February 2015 conjunctions

A recent thread on NavList pointed out that a number of celestial objects appear in close proximity during the second half of February 2015. A quick application of the relevant spreadsheets show Venus and Mars separated by 24.7’, which is less than the apparent Moon disk size. The spreadsheet sailings.xls can be used in this case, since the angle of 1 minute of arc corresponds to the distance of 1 nautical mile on the surface of the Earth.

venus_mars

 

With a Moon crescent in the vicinity of the two planets, it has been mentioned that Uranus is also in the area, separated from the Moon limb by about 2 degrees. While in the first example the parallaxes were essentially negligible (and hence the sailings.xls spreadsheet could be used to calculate the Venus-Mars angular separation), this is not the case for the Moon. Therefore, to compute the lunar distance, there is a dedicated spreadsheet (ld_prec.xls) which takes the viewing location on the surface of the Earth (“AP”) as additional input to account for the parallax effect.

uranus_lunar

Uranus appears slightly to the west of the (almost new) Moon crescent, so the interesting quantity is its distance from Moon’s illuminated near limb. Subtracting the Moon semidiameter (16.4′) from the topocentric centered lunar distance of 2° 15.6′ yields a value that is very close to 2 degrees.

 

Ephemerides for the planet Uranus (along with Neptune and Mercury) are not listed in celestial navigation almanacs, as these objects are not suitable for astronavigation purposes. Nevertheless, we provide almanac spreadsheets for those three planets as well, since their data can be computed from the same VSOP87 planetary theory that we use for the other planets.

Mercury in January 2015

In January 2015 Mercury is visible just northwest of Venus in the evening sky. Its horizontal parallax (HP) is twice that of Venus, so current Earth-Venus distance is about twice the current Earth-Mercury distance. 2015 Nautical Almanac Commercial Edition mentions the two planets in its “Do Not Confuse” paragraph on page 8. Spreadsheets mercury.xls and venus.xls show that the geographic positions (GP) of the two planets are very close to each other at this time.

mercury_jan2015

venus_jan2015

Five years of Navigation Spreadsheets

Navigation Spreadsheets logo
Navigation Spreadsheets

At the fifth anniversary of our website’s launch we review some of Navigation Spreadsheets functions.  All three examples are taken from the 2014 Nautical Almanac Commercial Edition.

1) Ephemeris (almanac data), Venus GP on 2014 May 5 at 13h 15m 18s (p. 256):

venus.xls

Input:
UT: 2014 May 5, 13:15:18

Output:
GHA = 58º 58.0’
Dec = S 0º 14.1’

venus2014

 

2) Sextant altitude corrections (Venus, p. 259)

alt_corr_xls
Input: Hs = 4º 32.6’
Output: Ho = 4º 17.6’

altcorr2014

 

3) The calculated altitude and azimuth (pp. 279-280)

intercept.xls
Input:
GP: GHA = 53º    Dec = S 15º
AP: Lat = N 32º    Long = W 16º
to which we add Ho = 30º 30.0’ in order to allow the calculation of the intercept and the plotting of the LOP.

intercept2014

 

Output:
The resulting LOP (intercept 38 NM away, azimuth 223) is plotted with the T-Plotter.

tplotter1

tplotter2

 

As it was also calculated by intercept.xls this LOP crosses:
the AP’s meridian at 52 NM north of the AP
the AP’s parallel at 56 NM east of the AP

tplotter3

 

(first published on February 15, 2014)