Keijusalamat saapuvat keskikesän öiden myötä – Harvinainen ilmiö napattiin kuvaan La Sillalla
Tässä ainutlaatuisessa ja vaikuttavassa kuvassa ESO:n La Sillan observatoriolta nähdään pilvetön taivas, jota värjäävät punainen ja vihreä ilmahehku ja koristavat taivaan kohteet. Taivaallisen kokoonpanon joukossa ovat Pieni ja Suuri Magellanin pilvi kuvan keskustan oikealla puolella, useiden tähtien syntyalueiden ruusunpunainen hehku, ja Linnunradan vasemmalla puolella meteorin himmeä vihreä viiru. Kuitenkin tätä hämmästyttävää taivaallista kantajoukkoa himmentää jokin vaikeasti tavoitettava, meitä paljon lähempänä oleva kohde.
Pääkuvan alla olevat kuusi paneelia näyttävät suurennettuina sarjan äärimmäisen harvinaisesta ilmakehän ilmiöstä, keijusalamasta. Muutamaa tuntia ennen päivänkoittoa – josta Linnunradan alalaidasta nouseva eläinratavalon seiväs ilmoittaa - voimakas ukkosmyrsky ilmestyi kaukaiseen horisonttiin, ja loi Maan yläilmakehästä leikkikentän näille häilyville ilmiöille.
Shakespearen juonittelevien haltijoiden, Kesäyön unelmanXPuckin ja MyrskynXArielin mukaan nimetyt keijusalamat aiheuttavat korkealla myrskypilvien yläpuolella noin 80 km korkeudessa olevat ionosfäärin epäsäännöllisyydet. Keijusalamat havaitaan yleensä punaoransseina välähdyksinä ja ne ovat seurausta positiivisesta pilvestä maahan lyövistä salamoista. Nämä ovat harvinaisempia kuin niiden negatiiviset vastineet, koska salamanisku alkaa pilven yläosista, jotka ovat kauempana maanpinnasta. Lyhyen purkauksen aikana keijusalama etenee nopeasti alaspäin luoden riippuvia punaisia rihmoja ennen katoamistaan.
Tässä kuvatut keijusalamat havaittiin noin 40 minuutin aikana ja ne olivat todennäköisesti yli 500 km päässä (vertaa satelliittikuvaan, joka näyttää myrskyn Argentiinan yläpuolella). Jokainen niistä ylsi jopa 80 km korkeuteen kestäen vain sekunnin murto-osan. Nämä erittäin vaikeasti muilla kuin tieteellisillä erikoislaitteilla kuvattavissa olevat epätodelliselta tuntuvat keijusalamat palkitsivat ESO:n valokuvalähettilään, Petr Horálekin kärsivällisyyden tällä uskomattomalla kuvasarjalla.
Petr kuvasi myös toisen upean keijusalamakuvan La Sillalla ja muutamaa päivää myöhemmin Paranalilla VLT:n tasanteella hän sai tämän mahtavan otoksen, joka on peräisin tästä myrskystä.
Linkit:
- Punaiset keijusalamat La Sillan Observatoriolla
- Keijusalamat Paranalin Observatoriolla
- Keijusalamat La Sillan Observatoriolla
P. Horálek/ESO
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