{"id":38128,"date":"2019-11-05T03:20:48","date_gmt":"2019-11-05T00:20:48","guid":{"rendered":"https:\/\/bilimvegelecek.com.tr\/?p=38128"},"modified":"2019-11-04T15:25:40","modified_gmt":"2019-11-04T12:25:40","slug":"astronomide-uzakliklar-nasil-olculur","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2019\/11\/05\/astronomide-uzakliklar-nasil-olculur","title":{"rendered":"Astronomide uzakl\u0131klar nas\u0131l \u00f6l\u00e7\u00fcl\u00fcr?"},"content":{"rendered":"

B\u00fct\u00fcn uzakl\u0131k \u00f6l\u00e7\u00fcmlerinin temeli, yery\u00fcz\u00fcn\u00fcn \u00f6l\u00e7\u00fcm\u00fcnde de kullan\u0131lan \u00fc\u00e7genleme (triangulation) y\u00f6ntemidir. Uzakl\u0131\u011f\u0131 \u00f6l\u00e7\u00fclmek istenen (Y) noktas\u0131, aralar\u0131ndaki (AB) uzakl\u0131\u011f\u0131 bilinen iki A ve B g\u00f6zlemci taraf\u0131ndan g\u00f6zlenerek, (YAB) \u00fc\u00e7geninin a\u00e7\u0131lar\u0131 \u00f6l\u00e7\u00fcl\u00fcr. Ancak s\u0131ra y\u0131ld\u0131zlar\u0131n uzakl\u0131k \u00f6l\u00e7\u00fcm\u00fcne gelince, yery\u00fcz\u00fcndeki hi\u00e7bir (AB) uzunlu\u011fu (baz) bu i\u015flem i\u00e7in yeterli de\u011fildir. Daha b\u00fcy\u00fck bir baz elde etmek i\u00e7in, yerk\u00fcrenin G\u00fcne\u015f \u00e7evresindeki y\u00f6r\u00fcngesi \u00fczerinde, alt\u0131 ay ara ile bulundu\u011fu (A) ve (B) noktalar\u0131 (yani yerk\u00fcre-G\u00fcne\u015f uzakl\u0131\u011f\u0131n\u0131n iki kat\u0131) kullan\u0131l\u0131r. Astronomide bug\u00fcn uzakl\u0131k \u00f6l\u00e7\u00fcmlerinde, fotografik y\u00f6ntem kullan\u0131lmaktad\u0131r. Uzakl\u0131\u011f\u0131 \u00f6l\u00e7\u00fclmek istenen (Y) y\u0131ld\u0131z\u0131n\u0131n bulundu\u011fu b\u00f6lgenin alt\u0131 ay ara ile foto\u011fraf\u0131 \u00e7ekilir. Foto\u011fraf plaklar\u0131 \u00fcst \u00fcste kondu\u011fu zaman, \u00e7ok uzak olan y\u0131ld\u0131zlar\u0131n g\u00f6r\u00fcnt\u00fcleri \u00e7ak\u0131\u015f\u0131r (\u00fcst \u00fcste gelir). Daha yak\u0131n olan ve uzakl\u0131\u011f\u0131 \u00f6l\u00e7\u00fclmek istenen (Y) y\u0131ld\u0131z\u0131n\u0131n ise, paralaksal yer de\u011fi\u015fiminden dolay\u0131, birbiriyle \u00e7ak\u0131\u015fmayan farkl\u0131 iki g\u00f6r\u00fcnt\u00fcs\u00fc vard\u0131r. Plak \u00fczerinde, bu g\u00f6r\u00fcnt\u00fcler aras\u0131ndaki uzakl\u0131k \u00f6l\u00e7\u00fclerek, (d\u00fcrb\u00fcn\u00fcn odak uzakl\u0131\u011f\u0131 bilindi\u011finden) (AY) ile (BY) do\u011frultular\u0131 aras\u0131ndaki a\u00e7\u0131 bulunur. Bu a\u00e7\u0131n\u0131n yar\u0131s\u0131, y\u0131ld\u0131z\u0131n p paralaks a\u00e7\u0131s\u0131 olarak tan\u0131mlan\u0131r (Yunanca paralaksis, yer de\u011fi\u015fimi).<\/p>\n

Paralaks a\u00e7\u0131s\u0131n\u0131n maksimum de\u011feri, G\u00fcne\u015f\u2019i (Y) y\u0131ld\u0131z\u0131na birle\u015ftiren (GY) do\u011frusu ile (AB) do\u011frusunun dik oldu\u011fu zamand\u0131r. Bunun i\u00e7in g\u00f6zlem zamanlar\u0131, G\u00fcne\u015f\u2019in ekliptik \u00fczerinde \u00f6l\u00e7\u00fclen boylam\u0131n\u0131n, y\u0131ld\u0131z\u0131n boylam\u0131ndan 90\u00ba ile 270\u00ba b\u00fcy\u00fck oldu\u011fu (aralar\u0131nda alt\u0131 ay s\u00fcre ge\u00e7en) zamanlar se\u00e7ilir.<\/p>\n

Paralaks a\u00e7\u0131s\u0131 bir yay saniyesi olan uzakl\u0131k, birim olarak kabul edilmi\u015f ve bu birim uzakl\u0131\u011fa parsek (parallax-second\u2019\u0131n k\u0131salt\u0131lmas\u0131) ad\u0131 verilmi\u015ftir. Trigonometriden kolayca bulunaca\u011f\u0131 gibi, bu uzakl\u0131k, G\u00fcne\u015f-Yerk\u00fcre uzakl\u0131\u011f\u0131n\u0131n 206265 kat\u0131d\u0131r. En yak\u0131n y\u0131ld\u0131zlar\u0131n bile paralaks a\u00e7\u0131lar\u0131 bir yay saniyesinden k\u00fc\u00e7\u00fck oldu\u011fundan, bir y\u0131ld\u0131z\u0131n parsek cinsinden uzakl\u0131\u011f\u0131, p paralaks a\u00e7\u0131s\u0131n\u0131n tersi, yani uzakl\u0131k = 1\/p olur. (\u015eekil 1)<\/p>\n

\u00d6rne\u011fin G\u00fcne\u015f\u2019e en yak\u0131n y\u0131ld\u0131z \u201cProxima Centauri\u201dnin paralaks\u0131 p=0,76 yay saniyesi, yani uzakl\u0131k 1,3 parsektir. Y\u0131ld\u0131z uzakl\u0131klar\u0131nda kullan\u0131lan bir uzakl\u0131k birimi de, \u0131\u015f\u0131\u011f\u0131n bir y\u0131lda gitti\u011fi yol olan \u201c\u0131\u015f\u0131k y\u0131l\u0131\u201dd\u0131r. 1 parsek = 3,26 \u0131\u015f\u0131k y\u0131l\u0131 eder. \u0130lk trigonometrik y\u0131ld\u0131z paralaks\u0131 \u00f6l\u00e7\u00fcmleri, 1836 y\u0131l\u0131nda, Almanya\u2019da Friedrich Wilhelm Bessel (1784-1846) ve Rusya\u2019da Friedrich Georg Wilhelm von Struve (1793-1864) taraf\u0131ndan ger\u00e7ekle\u015ftirilmi\u015ftir.<\/p>\n

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Magellan Bulutlar\u0131<\/figcaption><\/figure>\n

Avrupa Uzay Ajans\u0131 (ESA) taraf\u0131ndan 1989 y\u0131l\u0131nda y\u00f6r\u00fcngeye yerle\u015ftirilmi\u015f ve 1993 y\u0131l\u0131na kadar \u00e7al\u0131\u015fm\u0131\u015f olan HIPPARCOS (High Precision Parallax Collecting Satellite) uydusu ile yap\u0131lan paralaks \u00f6l\u00e7\u00fcmleri, yery\u00fcz\u00fcnden yap\u0131lan \u00f6l\u00e7\u00fcmlere g\u00f6re \u00e7ok daha duyarl\u0131d\u0131r ve daha uzak y\u0131ld\u0131zlar\u0131n paralaks a\u00e7\u0131lar\u0131 \u00f6l\u00e7\u00fclebilir. Ancak s\u00f6z konusu galaksiler olunca, o kadar uzaktad\u0131rlar ki, trigonometrik paralaks \u00f6l\u00e7\u00fcmleriyle bir sonu\u00e7 elde etmek olanaks\u0131zd\u0131r. Evvelce de belirtmi\u015f oldu\u011fumuz gibi, Hubble, galaksilerin uzakl\u0131\u011f\u0131n\u0131 saptamak i\u00e7in, de\u011fi\u015fken Sefeid (Cepheid) y\u0131ld\u0131zlar\u0131n parlakl\u0131k de\u011fi\u015fimlerinin periyodu ile mutlak parlakl\u0131klar\u0131 (ger\u00e7ek parlakl\u0131klar\u0131) aras\u0131ndaki ba\u011flant\u0131dan faydalanarak geli\u015ftirilmi\u015f olan y\u00f6ntemi kullanm\u0131\u015ft\u0131r.<\/p>\n

Sefeid de\u011fi\u015fken y\u0131ld\u0131zlar\u0131ndaki parlakl\u0131k-periyot ba\u011flant\u0131s\u0131n\u0131, ilk kez, Amerikal\u0131 kad\u0131n astronom Henrietta Swan Leawitt (1868-1921) Harvard G\u00f6zlemevi\u2019nde, Arequipa (Peru) G\u00f6zlemevi\u2019nde elde edilmi\u015f olan foto\u011fraflar \u00fczerinde Magellan Bulutlar\u0131\u2019ndaki de\u011fi\u015fken y\u0131ld\u0131zlar\u0131 incelerken 1912 y\u0131l\u0131nda saptam\u0131\u015ft\u0131r.<\/p>\n

Magellan Bulutlar\u0131\u2019n\u0131n uzakl\u0131\u011f\u0131 o zaman bilinmedi\u011finden, Leawitt\u2019in yapm\u0131\u015f oldu\u011fu g\u00f6zlem, Sefeidlerin \u0131\u015f\u0131k-de\u011fi\u015fim periyodu ile \u201cg\u00f6r\u00fcnen\u201d parlakl\u0131klar\u0131 aras\u0131ndaki ba\u011flant\u0131d\u0131r. Bu y\u0131ld\u0131z topluluklar\u0131ndaki y\u0131ld\u0131zlar\u0131n hemen hemen hepsinin ayn\u0131 uzakl\u0131kta olduklar\u0131 varsay\u0131labilece\u011finden, Leawitt hakl\u0131 olarak, bu periyot-g\u00f6r\u00fcnen parlakl\u0131k ba\u011flant\u0131s\u0131n\u0131n, ayn\u0131 zamanda periyod-mutlak parlakl\u0131k aras\u0131nda da ge\u00e7erli olaca\u011f\u0131na dikkati \u00e7ekmi\u015ftir. Ancak bu ba\u011flant\u0131n\u0131n \u201ckalibrasyonu\u201d (yani g\u00f6r\u00fcnen parlakl\u0131klar\u0131n mutlak parlakl\u0131klara d\u00f6n\u00fc\u015ft\u00fcr\u00fclmesi) i\u015flemi kalm\u0131\u015ft\u0131r.<\/p>\n

Onu da, Wilson Da\u011f\u0131 G\u00f6zlemevi\u2019nden Harlow Shapley, ba\u015fka y\u00f6ntemler kullanarak, Samanyolu i\u00e7erisindeki baz\u0131 Sefeidlerin uzakl\u0131klar\u0131n\u0131 saptamak yolu ile 1918 y\u0131l\u0131nda ger\u00e7ekle\u015ftirebilmi\u015ftir. De\u011fi\u015fken Sefeid y\u0131ld\u0131zlar\u0131n\u0131n \u0131\u015f\u0131k de\u011fi\u015fim periyodu kolayca g\u00f6zlenir. I\u015f\u0131k \u015fiddeti de uzakl\u0131\u011f\u0131n karesi ile ters orant\u0131l\u0131 olarak de\u011fi\u015fti\u011fine g\u00f6re, periyot-mutlak parlakl\u0131k ba\u011flant\u0131s\u0131ndan elde edilen mutlak parlakl\u0131k ile g\u00f6r\u00fcnen parlakl\u0131k k\u0131yaslanarak, uzakl\u0131k hesaplanabilir. Sefeidler genelde \u00e7ok parlak y\u0131ld\u0131zlar olduklar\u0131ndan, galaksiler gibi \u00e7ok uzak g\u00f6kcisimlerinin uzakl\u0131k tayininde \u00e7ok \u00f6nemli rol oynamaktad\u0131rlar.<\/p>\n

Sefeidlerin bile g\u00f6zlenemeyece\u011fi kadar uzak olan galaksiler i\u00e7in ise, s\u00fcpernovalar veya galaksinin toplam parlakl\u0131\u011f\u0131 gibi de\u011fi\u015fik y\u00f6ntemler geli\u015ftirilmi\u015ftir.<\/p>\n

Kaynak:<\/strong> Metin Hotinli, 50 Soruda B\u00fcy\u00fck Patlama Kuram\u0131, Bilim ve Gelecek Kitapl\u0131\u011f\u0131, 2. Bask\u0131, Aral\u0131k 2012, S. 70-73<\/p>\n","protected":false},"excerpt":{"rendered":"

B\u00fct\u00fcn uzakl\u0131k \u00f6l\u00e7\u00fcmlerinin temeli, yery\u00fcz\u00fcn\u00fcn \u00f6l\u00e7\u00fcm\u00fcnde de kullan\u0131lan \u00fc\u00e7genleme (triangulation) y\u00f6ntemidir. Uzakl\u0131\u011f\u0131 \u00f6l\u00e7\u00fclmek istenen (Y) noktas\u0131, aralar\u0131ndaki (AB) uzakl\u0131\u011f\u0131 bilinen iki A ve B g\u00f6zlemci taraf\u0131ndan g\u00f6zlenerek, (YAB) \u00fc\u00e7geninin a\u00e7\u0131lar\u0131 \u00f6l\u00e7\u00fcl\u00fcr. Ancak s\u0131ra y\u0131ld\u0131zlar\u0131n uzakl\u0131k \u00f6l\u00e7\u00fcm\u00fcne gelince, yery\u00fcz\u00fcndeki hi\u00e7bir (AB) uzunlu\u011fu (baz) bu i\u015flem i\u00e7in yeterli de\u011fildir. Daha b\u00fcy\u00fck bir baz elde etmek i\u00e7in, yerk\u00fcrenin […]<\/p>\n","protected":false},"author":429,"featured_media":38129,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[19],"tags":[248,1748,5518,5472],"class_list":["post-38128","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-bilim-gundemi","tag-astronomi","tag-samanyolu","tag-seferid","tag-uzaklik"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/38128","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/users\/429"}],"replies":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/comments?post=38128"}],"version-history":[{"count":0,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/38128\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media\/38129"}],"wp:attachment":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media?parent=38128"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/categories?post=38128"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/tags?post=38128"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}