Namibia 20/26 April 2009, Part
Question: what is the largest galaxy visible in the sky cut? You would think ... NGC 253? Or NGC 4565? Wrong, it is quite simply ... the Milky Way!
And 'This is the main impression that you are viewing the sky from the southern hemisphere: the Milky Way is no longer a simple strip of light but becomes a galaxy in all respects. With the swelling of the nucleus reaches the zenith, it seems to have the copy in the giant NGC 4565, which occupies the entire sky, in a charming scene from science fiction movies!
But first things first. In astronomy which celebrates Galileo, a group of five amateurs, including three from Friuli, a Piedmontese and Padua (myself), decided to celebrate in some way going over the leg of another important astronomer, Nicolas Lacaille. He was the first European to study in detail the Sky South Africa in 1700, and again today for all five of us this was the first time below the equator.
The destination was the Guest- Namibia Farm in Tivoli, located 140 km as the crow flies southeast of the capital Windhoek, a specially equipped place for lovers of the sky because it provides a great deal to hire and variety of tools that would otherwise be impossible to transport by air. For visual observations we used both Dobson, 25 and 50 cm opening!
The weather was all in all favorable, considering that this was not the best season yet and is somewhat 'more difficult to achieve perfect conditions encountered between June and August, the first night was calm but there was a slight haze on the horizon was that blur the Milky Way at around 10 ° and the Magellanic Clouds made invisible when it came to the minimum height (from 23 ° S latitude are circumpolar, but when they touch the horizon in lower culmination).
Then came a slight flick of the tail of the rainy season: the second night, the sky is overcast and we went to bed early disconsolate, but fortunately after midnight one of us was still awake (guess who ...) and had the bright idea to look out and see that the sky had opened, so he (or rather, I) woke up the others and all we could take advantage of the second part of the night until dawn. Which by the way was spectacular because the crescent moon was "a boat" in trio with Venus and Mars, and further down the clouds like those seen in documentaries of the savannah, complete with strings of light rain that evaporates before touching the ground!
Here is the picture:
the third night is even arrivato un temporale, ma anche in quel caso il cielo si è discretamente aperto a mezzanotte. Al quarto giorno altro temporale nel pomeriggio e poi cielo sgombro subito dal tramonto, ma questa volta è stata l’umidità pazzesca, dovuta ai postumi della pioggia, a rendere difficoltose le osservazioni, e verso le ore 2 anche l’asciugacapelli si è arreso e abbiamo deciso di smettere.
Le ultime tre notti finalmente sono tornate nelle condizioni ideali, e anche la trasparenza era migliorata perché rispetto alla prima sera la Via Lattea si avvicinava di più all’orizzonte, le Nubi di Magellano rimanevano sempre visibili per tutta la notte e vedevamo stelle di terza magnitudine alte 1°!
The seeing was disappointing: only the first part of the first night was fantastic and we saw a wonderful Saturn, but toward morning, when Jupiter was rising and the Moon, has come a worthy turbulence of the most disgusting evenings Padua. It was a sign of instability in atmospheric arrival.
Even in the days following the departure of the clouds but there were several changes in wind direction that made the situation unstable and therefore the seeing has never really returned to the top. Evidently there is also the rule of inverse correlation between turbulence and extinction! Have been few moments in which they exploited well 500X sulle nebulose planetarie, e sono sicuro che non fosse colpa dello specchio caldo perché se le stelle apparivano come pallettoni di polistirolo, lo rimanevano anche a fine nottata.
Io spero solo di aver trovato una settimana sfortunata su questo fronte, perché l’altopiano della Namibia dovrebbe avere le carte in regola per dare mediamente molto di più. In ogni caso il seeing è molto difficile da valutare e soprattutto da raccontare, e non potremo fare confronti precisi tra siti e serate diverse finché non inventeranno uno strumento semplice, veloce e oggettivo per misurarlo, come fortunatamente fa l’SQM per il livello di buio.
Arriviamo dunque al punto più interessante della faccenda: la qualità del cielo. E anche qui le sorprese non sono mancate. Ovviamente l’inquinamento luminoso è assente, e così finalmente ho potuto capire com’è fatto un cielo incontaminato e che effetto hanno i soli elementi di luce naturale.
Alla sera si vedeva la luce zodiacale, bassa in Toro e Gemelli, che si incrociava con la Via Lattea, mentre verso mattina era più imponente perché l’eclittica nell’Acquario era perpendicolare all’orizzonte.
Appariva più o meno come in questa foto:
http://apod.nasa.gov/apod/ap090212.html
not end there because there was balance between Spica and the Gegenschein, and the best nights (below describe the changes and issues) you could see the zodiacal light along the ecliptic too! It was clear that the range of Leo and Virgo were clearer than in the parts of Hydra, top, and Pastor / Chioma, below.
Then there's the airglow, as expected, becomes brighter as it approaches the horizon as you look through a thicker layer of atmosphere and then there is a greater number of air molecules emit luminescence. This is, however, up to about 5 ° high, because at that point is the extinction to prevail and the speech is reversed, with the band from 5 ° to 0 ° appearing darker. It 'so good to know that even a pristine sky has different gradients of light. All Natural!
But apart from the effect damn nice to have the dark horizon in 99% of the directions (I say 99 because NW is a small speck of Windhoek. It 'is insignificant and not sufficient to generate pollution, however, note) I have not found, fortunately, other differences compared to our abysmal skies of the mountains, as had been heralded by all those who had gone into the desert before. This probably because they were not used to the skies of 21.6 like me.
The real difference between the sky of Namibia and our best sites is therefore not the darkness itself, but is due to the constellations! In fact, the northern sky, with poor Leone as a dead fish floating upside down, there appeared insignificant in comparison to the uproar of stuff that you could see the other side: the area that includes the constellation of Hull, Cross, Centaurus Wolf and Scorpion there is a high concentration of bright stars, so that only the area of \u200b\u200bOrion and Taurus can compete. Ma le costellazioni di prima, oltre a essere molto luminose, sono anche sovrapposte alla meravigliosa e brillantissima Via Lattea australe, che è indubbiamente migliore di quella boreale non solo perché c’è il rigonfiamento del nucleo (che ha uno spessore di oltre 50°!), ma anche perché presenta contrasti molto forti tra nubi chiare e nubi oscure. La Via Lattea “nostra” invece è più diafana e sbiadita: del ramo invernale non ne pariamo neppure, ma perfino il Cigno è stato bastonato dal Centauro, quando verso mattina si vedevano entrambi alla stessa altezza agli antipodi del cielo.
E, come se non bastasse, a completare il quadretto del sud si aggiungono pure le Nubi di Magellano! Prima I read that leaving the amateur Australian experience a sensation of "empty sky" if they go in the northern hemisphere, and now I understand perfectly what they mean.
a monster catching graphics Starry Night, that reproduces in the best possible way (unfortunately I do not know a way to put BN in the Milky Way, leaving the colored stars) the naked eye in the sky which is visible from the latitude to April shortly after midnight.
But back to talk about SQM. Given that you could not use the second part of the night when he went to the Sagittarius zenith, the readings also made away from the Milky Way were a bit 'lower expectations. I thought hard to find 21.9, as I knew to be a pure sky, but we had mean values \u200b\u200baround 21.7. At first not well understood why, because if a non-polluted sky is not entirely clear, in case it should be darker than a perfect and clear. Then we realized that the "fault" was the Milky Way, whose light is diffused in the rest of the air from the atmosphere, just like it does with the Sun and the Moon!
And the humidity level determines the amount of this distribution: the night was the sixth best on Saturday, 25 where we finally reached the fateful 21.9. Even then, however, the maximum darkness lasted only a couple of hours (from 21 to 23), because as he got up Scorpio readings goes down slightly, despite continued to point the instrument to always Hydra / Virgin. This fact confirms the theory.
Needless to say, the brightness of the Milky Way has an effect on the ground: do not even need to adapt to total darkness in order to distinguish good people, telescopes, accessories on the table and walk in the path (made of dark sand, high-contrast with the grass that is clear) without a battery. The torch was necessary only in the apartments, where there are trees.
I also checked the visibility of the shadow of the Milky Way, putting a hand in front of a white sheet, and towards morning the same conversation with Venus. In the first case of course the shadow had faded in the second net.
The darkness comes true if the sky is covered: the third night, as we were finishing up the cover with the Dobson giant tarpaulin to protect them from the imminent storm, came a black cloud of fear, I measured and came out 22.85! There really was almost like being in a dark room and you could not see almost nothing, I did hardly any impression that scene the night sky!
remember, however, also Casera Razzo, when last summer we found a couple of evenings very unfortunate, the clouds were darker than the clear sky, though did not reach the same levels of darkness (22.0), but this fact is always incredible to those accustomed only to polluted skies.
C ol the peaceful little I have said that the difference is even more subtle, and the best nights of the best sites yet Italians fail to ra com pete with the conditions of Namibia, more As one might expect. And this is a very encouraging news. Said other words, even without pollution light is not obvious to find the perfect conditions, for up to 21.5 in artificial light is no longer the main factor that determines the quality of the air but are the natural ones to "control".
final word on the instruments: I liked very much! The fluidity of movement is perfect, the seekers are comfortable and even the optics seem very good. The course is equipped with 50 cm wide and 25 has a chair with adjustable height. early mirrors were very dusty but the owner gave us the distilled water to wash them. The collimation is easily done, just bring home the laser or Cheshire.
In the next describe in detail the episodes that I observed celestial objects, they are more than 450 even if there is a "trick" because thirty are in the small cloud and about 120 in the large!
close with a small photo gallery . I should point out that no picture is mine (I did not need to take away the camera and I had 11 kg of hand luggage!), It's all about their colleagues and when they have completed the development work will also release the astronomical photos and those already submitted on this page with higher resolution.
