Dear astronauts, during the whole year, from April 2012 until April 2013, we have been visiting the principal constellations which are visible from our latitude in the Northern hemisphere, but mainly from a cultural point of view and without defining whether or not it was the best time for observation. That is why, in order to fulfil our knowledge of the Sierra skies, we will perform another annual journey, indicating this time the best ones to see in each month. I will put in brackets the number of the 27 chapters of the former series where we may see the corresponding constellation, for those who wish to go over the associated references. These may be consulted on the button “El Cielo de la Sierra” (Sierra skies) of “Sierra de Gata Digital”.
Before we begin, here are two commentaries which will correspond to every month:
1. About the time for observation: Although I shall provide the time references adapted to that which our clocks show on each moment of the year (2 hours ahead in summertime and one hour during the winter), the books on this subject usually give the times in T.U. (Universal Time).The history of the exact time measurement has been intimately related to navigational problems and knowledge of LONGITUDE - (the distance to the meridian of reference, measured along the Equator, in hours and minutes) - and anyone interested enough can enjoy reading the book by Dava Sobel “Longitude”, published by the editorial “Debate”. In fact, one of the consequences of this passionate history was that, from the 18th Century, the majority of mariners calculated longitude with respect to the meridian which cuts through the British Astronomical Observatory of Greenwich, very near to London. In 1884, in the International Conference about the Meridian, this was declared the meridian of reference and marked the start of the day to which the rest of the time zones of the world adapted. This is called “Greenwich Mean Time” (GMT). However, as the Earth’s movement - (and consequently the appearance of the sun) - has certain irregularities and the definition of the time needed more precision, taking all this into account, they arrived at the so-called T.U., which is what is used in astronomy. But in our non-professional practice it is practically the same as GMT, which means that in summer, for instance, we just have to go back two hours to be with the T.U. data.
2. About the moment of observation. As we saw in the former series, the constellations appear every day four minutes earlier, or rather, one hour every 15 days, or two hours every month, which is logical as that means 24 hours in 12 months, then everything starts again. That means that, if we are talking about what one can see at a certain hour in a certain week, the following week we would have to look half an hour earlier, and the next, one hour....and so forth, obviously while they are still visible.
And now we start with the month - (word from the Greek, via Latin, where it meant “luna”, or “moon” in English, “Mond” in German, showing us how important our satellite was in the primitive history of the calendar) - of June, known by the Romans as Juno, sister and wife of Jupiter, on which day 21st, at about 7.00 a.m., the Sun, crossing the solstice, will indicate the longest day, which is when our summer begins.
In these skies, three brilliant stars form a famous asterism, which bears the name of the season in which we find ourselves, THE SUMMER TRIANGLE, made up of VEGA, DENEB and ALTAIR - (See Chapter 6 of our former series). We are lucky here in the Sierra to enjoy such a clear sky that we can distinguish the Milky Way, which today will serve as guide to our observations. During this first week of June, and at about 2.0 a.m. (the following week would be at 1.30 a.m., the next at 1.0 a.m., etc) it will extend from North to South and, if we look towards Santibañez el Alto (don’t forget we always take as reference Villasbuenas de Gata) it will be at an approximate height of between two and three hands. Therefore, DENEB will be found a little more than two hands between Cadalso and Torrecilla de Los Ángeles; VEGA at about three and a half hands, a little to the right above Hernan Pérez, and ALTAIR at a little less than two hands, between Villa del Campo and Galisteo.
And now we go to the extreme South of the Milky Way. We already know that SCORPIUS, (Chap. 10), is the zodiacal constellation which is the furthest South, which is why it nearly always escapes us below the horizon. However, in summer it is clearly visible. Its red star, ANTARES, is a little more than a hand above Huélaga, and SHAULA at a little over half a hand above Coria - (we remember also that these open hands are used with the arm fully extended, and measure from the horizon, without taking into account any hills or any other geographical barriers, and correspond to about 20º).
And so that is enough for today. Welcome!