CARTES CÉLESTES ROB WALRECHT

There is a wide selection of rotating celestial maps (sometimes also called celestial planispheres) disseminated in bookstores and specialty stores, classic bookstores, nature stores, web sites, etc. Among these, the models proposed by Rob Walrecht are very good value for money… Made of plastic (insensitive to humidity and night rosé), they are well readable with diameter of about 25 cm, display the hours and dates (to view the exact sky at the time of observation), and celestial coordinates (to point on the map an object that is not there but with celestial coordinates). Another extremely interesting point: they are available in different models adapted to different latitudes of observation (20, 30, 40, 50, 60 ° North, 20, 30 and 40 ° South)… What does that mean? Celestial maps present the sky only for a given average latitude (for example, for metropolitan France, about 47 ° N). However, if we look at a place far north or farther south, the sky becomes even worse (some constellations are no longer visible because disappearing below the horizon, while others appear above the opposite horizon). In practice and as an example, if the constellation of the Grande Ourse can be easily traced from the Metropole, the constellation of the South of Chile will hardly be accessible. Conversely, if from the island of Réunion (located at the Tropic level of Capricorn, that is to say, 20 ° south latitude) an observer can admire the famous constellation of the Southern Cross, this same constellation will be strictly invisible from Marseille, Paris or Lille! In fact, it is imperative to choose its rotating celestial map so that it matches the visible sky from the latitude of the place of observation.