G\u00f6kbilimciler, uzayda bize yak\u0131n bulunan cisimlerin uzakl\u0131\u011f\u0131n\u0131 hesaplamak i\u00e7in “y\u0131ld\u0131z paralaks\u0131” ya da “trigonometrik paralaks” olarak adland\u0131r\u0131lan y\u00f6ntemi kullan\u0131r. Basit\u00e7e s\u00f6ylemek gerekirse bu y\u00f6ntem, D\u00fcnya G\u00fcne\u015f etraf\u0131nda d\u00f6nerken, bir y\u0131ld\u0131z\u0131n, uzakta bulunan ve daha arkada kalan y\u0131ld\u0131zlara g\u00f6re ters y\u00f6nde olan hareketini \u00f6l\u00e7er.<\/p>\n
Harvard Smithsonian Astrofizik Merkezi’nde astronom olan Mark Reid, paralaks y\u00f6nteminin astronomide uzakl\u0131k hesab\u0131 i\u00e7in en iyi y\u00f6ntem oldu\u011funu s\u00f6yl\u00fcyor. Paralaks y\u00f6ntemi fizi\u011fe de\u011fil, yaln\u0131zca geometriye dayand\u0131\u011f\u0131 i\u00e7in, bu y\u00f6ntemi y\u0131ld\u0131z uzakl\u0131klar\u0131n\u0131 \u00f6l\u00e7mede en ideal de\u011ferlendirme arac\u0131 olarak betimliyor.<\/p>\n
Los Angeles’taki Kaliforniya \u00dcniversitesi’nde profes\u00f6r olan Edward L. Wright’a g\u00f6re bu metot, D\u00fcnya’n\u0131n y\u0131ld\u0131z\u0131n y\u00f6r\u00fcngesinde alt\u0131 ay aral\u0131kla bulundu\u011fu konumlar\u0131n olu\u015fturdu\u011fu iki a\u00e7\u0131n\u0131n ve bu iki konumla beraber y\u0131ld\u0131z\u0131n olu\u015fturdu\u011fu \u00fc\u00e7genin \u00f6l\u00e7\u00fclmesine dayan\u0131yor.<\/p>\n
Y\u00f6ntem \u015f\u00f6yle \u00e7al\u0131\u015f\u0131yor: Elinizi uzat\u0131n, sa\u011f g\u00f6z\u00fcn\u00fcz\u00fc kapat\u0131n ve ba\u015fparma\u011f\u0131n\u0131z\u0131 uzaktaki bir cismin \u00fczerine yerle\u015ftirin. \u015eimdi, sa\u011f g\u00f6z\u00fcn\u00fcz\u00fc a\u00e7\u0131p sol g\u00f6z\u00fcn\u00fcz\u00fc kapat\u0131n. Ba\u015fparma\u011f\u0131n\u0131z hafif\u00e7e yer de\u011fi\u015ftirmi\u015f gibi g\u00f6r\u00fcnecektir. Bu k\u00fc\u00e7\u00fck yer de\u011fi\u015ftirme miktar\u0131n\u0131 \u00f6l\u00e7er ve g\u00f6zleriniz aras\u0131ndaki mesafeyi bilirseniz, ba\u015fparma\u011f\u0131n\u0131za olan uzakl\u0131\u011f\u0131 hesaplayabilirsiniz.<\/p>\n
Bir y\u0131ld\u0131z\u0131n uzakl\u0131\u011f\u0131n\u0131 hesaplayabilmek i\u00e7in astronomlar, D\u00fcnya ve G\u00fcne\u015f aras\u0131ndaki ortalama uzakl\u0131k olan ve yakla\u015f\u0131k 150 milyon kilometreye e\u015fit olan 1 astronomik birimi (AU) baz al\u0131rlar. Ayr\u0131ca alacakaranl\u0131kta olu\u015fan k\u00fc\u00e7\u00fck a\u00e7\u0131lar\u0131, derecenin \u00e7ok k\u00fc\u00e7\u00fck bir kat\u0131 olan ark saniye ile \u00f6l\u00e7erler.<\/p>\n
E\u011fer bir astronomik birimi bir ark saniyenin tanjant\u0131na b\u00f6lersek, 30.9 trilyon kilometre ya da yakla\u015f\u0131k 3.26 \u0131\u015f\u0131k y\u0131l\u0131 sonucuna ula\u015f\u0131r\u0131z. Elde etti\u011fimiz bu uzakl\u0131k birimine paralaks saniyesi ya da parsec (pc) denir. Gelgelelim, en yak\u0131n y\u0131ld\u0131z bile G\u00fcne\u015f’imizden 1 parsec uzaktad\u0131r. Dolay\u0131s\u0131yla, bir y\u0131ld\u0131za olan uzakl\u0131\u011f\u0131 saptamak i\u00e7in g\u00f6kbilimcilerin y\u0131ld\u0131zlardaki bu yer de\u011fi\u015ftirmeleri 1 ark saniyeden daha k\u00fc\u00e7\u00fck bir birim kullanarak \u00f6l\u00e7mesi gerekir ve bu, modern teknolojiden \u00f6nce imkans\u0131zd\u0131.<\/p>\n
Paralaks, kozmik mesafe merdiveninde \u00f6nemli bir basamak. Yak\u0131nlardaki \u00e7ok say\u0131da y\u0131ld\u0131z\u0131n bize olan uzakl\u0131\u011f\u0131n\u0131 \u00f6l\u00e7ebilmemiz sayesinde g\u00f6kbilimciler, y\u0131ld\u0131zlar\u0131n renkleri ve esas parlakl\u0131klar\u0131 -di\u011fer bir deyi\u015fle standart bir uzakl\u0131ktan bak\u0131ld\u0131\u011f\u0131nda g\u00f6r\u00fcnebilecek parlakl\u0131klar\u0131- aras\u0131nda ili\u015fki kurmay\u0131 ba\u015fard\u0131. Bu y\u0131ld\u0131zlar daha sonra “standart mumlar” haline geldi.<\/p>\n
Reid’in s\u00f6yledi\u011fine g\u00f6re e\u011fer bir y\u0131ld\u0131z, paralaks\u0131n\u0131n \u00f6l\u00e7\u00fclebilmesi i\u00e7in fazla uzaktaysa, g\u00f6kbilimciler y\u0131ld\u0131z\u0131n rengini ve spektrumunu bir standart mumunkiyle e\u015fle\u015ftirip esas parlakl\u0131\u011f\u0131 tayin edebiliyor. <\/p>\n