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.



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 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.