Penitenti di ghiaccio al chiaro di luna sul Chajnantor
Babak Tafreshi, uno degli ambasciatori fotografi ESO, ha catturato questo curioso fenomento sull'altopiano del Chajnantor, casa del Atacama Large Millimeter/Submillimeter Array (ALMA).
Queste curiose formazioni di ghiaccio e neve sono conosciute come"i penitenti" sono illuminate dalla luce della luna, visibile sulla destra della fotografia. Sulla sinistra, alte nel cielo si possono vedere la Grande e la Piccola Nube di Magellano, mentre la rossastra Carina Nebula può essere vista a sinistra appena sopra l'orizzonte.
I penitenti sono meraviglie naturali che si possono trovare in regioni con grandi altitudini, come le Ande cilene, che in media superano i 4000 metri sul livello del mare. I penitenti sono sottili punte di ghiaccio o neve indurita, solitamente si formano in grossi gruppi, e puntano al Sole. Raggiungono altezze che variano da pochi centimetri, ricordando l'erba bassa, a cinque metri, dando l'impressione di una foresta di ghiaccio in mezzo al deserto.
I dettagli precisi del meccanismo con cui si formano i penitenti sono ancora misteriosi, per anni le popolazioni andine hanno creduto che i penitenti fossero il risultato dei forti venti che spazzano la zona. Ma i venti hanno solo una piccola parte nella formazione di questi pinnacoli ghiacciati. Oggigiorno è ritenuto che siano la combinazione di vari fenomeni fisici.
Il processo inizia quando la luce del sole irradia la superfice della neve. A causa delle aride condizioni climatiche in questi luochi desertici, il ghiaccio sublima anzi di sciogliersi -- passa da solido a gas senza sciogliersi. I solchi nella superficie del ghiaccio catturano la luce solare riflessa, causando la sublimazione anche nelle parti più profonde, senza questa sublimazione la temperatura e l'umidità aumenterebbero, causando lo scioglimento. Questo fattore positivo accellera la crescita di queste caratteristiche strutture.
Queste statue ghiacciate prendono il nome dai cappelli appuntiti dei "nazarenos", membri di una fratellanza che nel periodo di Pasqua partecipano ad una processione attorno al mondo, non è difficile immaginare queste strutture come un raduno di monaci radunati sotto la luce lunare.
Questa fotografia è stata scattata dalla strada verso il complesso ALMA. L'osservatorio, che ha cominciato l'operazione Early Science il 30 Settembre 2011, una volta ultimato consisterà in un complesso di 66 antenne ad alta precisione che lavoreranno insieme come un singolo enorme telescopio.
ALMA, una struttura internazionale è frutto della della collaborazione di Europa, Nord America, Est Asia e Reppublica del Cile. ESO si rende ambasciatrice per l'Europa come il National Radio Astronomy Observatory (NRAO) lo è per il Nord America e il National Astronomical Observatory of Japan (NAOJ) per l'Est Asia. Assieme queste organizzazioni formano il Joint ALMA Observatory (JAO), controllando e commissionando le operazioni riguardanti ALMA.
Links
Crediti:ESO/B. Tafreshi (twanight.org)
A proposito dell'immagine
| Identificazione: | potw1221a |
| Lingua: | it |
| Tipo: | Fotografico |
| Data di pubblicazione: | Lunedì 21 Maggio 2012 10:00 |
| Dimensione: | 4200 x 3012 px |
A proposito delll'oggetto
| Nome: | Atacama Desert |
| Tipo: | Solar System : Planet : Feature : Surface |
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