{"id":3576,"date":"2014-03-20T18:13:07","date_gmt":"2014-03-20T18:13:07","guid":{"rendered":"http:\/\/www.benateckyctyrlistek.eu\/?p=3576"},"modified":"2014-12-20T00:23:17","modified_gmt":"2014-12-20T00:23:17","slug":"nastava-jarni-rovnodennost-2014","status":"publish","type":"post","link":"https:\/\/www.benateckyctyrlistek.eu\/?p=3576","title":{"rendered":"Nast\u00e1v\u00e1 jarn\u00ed rovnodennost 2014"},"content":{"rendered":"

\"rocni-doby\"<\/a>Rok co rok se opakuje diskuse nad za\u010d\u00e1tkem jara. Nejinak tomu zajist\u00e9 bude i letos. Ze \u0161koln\u00edch lavic m\u00e1 v\u011bt\u0161ina populace jako za\u010d\u00e1tek jara za\u017eit\u00e9 datum 21. b\u0159ezna, a proto jsou mnoz\u00ed v posledn\u00edch letech zasko\u010deni informac\u00ed, kterou jim poskytuje kalend\u00e1\u0159, uv\u00e1d\u011bj\u00edc\u00ed, \u017ee jaro za\u010d\u00edn\u00e1 ji\u017e o den d\u0159\u00edve. A bude tomu tak i v leto\u0161n\u00edm roce, kdy se jara do\u010dk\u00e1me ji\u017e v tento den. Ti, u nich\u017e tato informace vzbud\u00ed dal\u0161\u00ed z\u00e1jem, se dokonce dopracuj\u00ed ke zji\u0161t\u011bn\u00ed, \u017ee jaro neza\u010d\u00edn\u00e1 20. b\u0159ezna obecn\u011b, ale p\u0159esn\u011b v 17h 56m SE\u010c. Jak to tedy s t\u00edm jarem skute\u010dn\u011b je?<\/p>\n

P\u0159edev\u0161\u00edm si mus\u00edme \u0159\u00edci, o jak\u00e9 \u017ee jaro se n\u00e1m vlastn\u011b jedn\u00e1. Nap\u0159\u00edklad to meteorologick\u00e9 za\u010d\u00edn\u00e1 ji\u017e p\u016flnoc\u00ed 1. b\u0159ezna. To je jednoduch\u00e9 a ka\u017edoro\u010dn\u011b stejn\u00e9. Pokud budete \u0159e\u0161it s n\u011bjak\u00fdm zahr\u00e1dk\u00e1\u0159em jaro vegeta\u010dn\u00ed, m\u00e1te o probl\u00e9m postar\u00e1no. V tomto p\u0159\u00edpad\u011b se toho spr\u00e1vn\u00e9ho data ur\u010dit\u011b nedopracujete. A jaro astronomick\u00e9? To hv\u011bzd\u00e1\u0159i bez probl\u00e9m\u016f spo\u010dtou stovky ba tis\u00edce let dop\u0159edu i dozadu, ale jak se ke sv\u00fdm \u010d\u00edsl\u016fm dopracovali, to v\u00ed jen m\u00e1lokdo.<\/p>\n

Pro astronomy je rozhoduj\u00edc\u00ed p\u0159i v\u00fdpo\u010dtu ne dne, ale p\u0159esn\u00e9ho okam\u017eiku stanoven\u00e9ho klidn\u011b s p\u0159esnost\u00ed na sekundy pohyb Slunce po obloze. Za\u010d\u00e1tek astronomick\u00e9ho jara je toti\u017e okam\u017eikem, kdy st\u0159ed slune\u010dn\u00edho kotou\u010de stane p\u0159esn\u011b nad zemsk\u00fdm rovn\u00edkem a Slunce sou\u010dasn\u011b mezi hv\u011bzdami vstoup\u00ed do znamen\u00ed Berana. D\u016fle\u017eit\u00e9 slovo je v tomto p\u0159\u00edpad\u011b slovo \u201eznamen\u00ed\u201c, nebo\u0165 souhv\u011bzd\u00ed Berana se n\u00e1m za v\u00edce ne\u017e dva tis\u00edce let, odkdy po\u010d\u00edt\u00e1me n\u00e1\u0161 letopo\u010det, posunulo vlivem precese a dal\u0161\u00edch drobn\u011bj\u0161\u00edch nepravidelnost\u00ed v pohybu Zem\u011b o zna\u010dn\u00fd kus oblohy d\u00e1l. Tak\u017ee na vysv\u011btlenou \u2013 znamen\u00ed rozd\u011bluj\u00ed ekliptiku, zd\u00e1nlivou dr\u00e1hu Slunce oblohou na dvan\u00e1ct stejn\u011b velk\u00fdch d\u00edl\u016f odpov\u00eddaj\u00edc\u00edch v\u017edy 30\u00b0. Tato znamen\u00ed pak za\u010d\u00ednaj\u00ed pr\u00e1v\u011b znamen\u00edm Berana, kter\u00e9 m\u00e1 svoji hranici na pr\u016fse\u010d\u00edku ekliptiky s nebesk\u00fdm rovn\u00edkem v tzv. v\u00fdstupn\u00e9m uzlu, tedy v m\u00edst\u011b, kde ekliptika p\u0159ech\u00e1z\u00ed z ji\u017en\u00ed polokoule na tu severn\u00ed.<\/p>\n

V okam\u017eiku, kdy se Slunce na sv\u00e9 ro\u010dn\u00ed cest\u011b dostane pr\u00e1v\u011b do tohoto bodu sv\u00e9 dr\u00e1hy, hovo\u0159\u00edme o za\u010d\u00e1tku jara. Vzhledem k tomu, \u017ee ob\u011bh Zem\u011b kolem Slunce, jeho\u017e obrazem je pr\u00e1v\u011b putov\u00e1n\u00ed Slunce oblohou po ekliptice, nen\u00ed d\u00e1n pln\u00fdm po\u010dtem dn\u016f (365 dn\u016f 5 hodin 48 minut a 45,7 sekund), pom\u00e1h\u00e1me si v kalend\u00e1\u0159i p\u0159estupn\u00fdmi roky a z toho z\u00e1konit\u011b plyne, \u017ee za\u010d\u00e1tek jara p\u0159ich\u00e1z\u00ed ka\u017ed\u00fd rok v jin\u00e9m okam\u017eiku. P\u0159esn\u00fd \u010das za\u010d\u00e1tku jara se tak s ohledem na konstrukci p\u0159estupn\u00fdch dn\u016f v kalend\u00e1\u0159i posouv\u00e1 nejen \u010dasov\u011b, ale i datumov\u011b v rozmez\u00ed hned n\u011bkolika dn\u016f. Ve 20. stolet\u00ed za\u010d\u00ednalo astronomick\u00e9 jaro v\u00fdhradn\u011b 21. 3., ov\u0161em jen na po\u010d\u00e1tku stolet\u00ed. Ale u\u017e v roce 1920 se poprv\u00e9 objevuje datum 20. 3., pot\u00e9 se toto datum v seznamu za\u010d\u00edn\u00e1 vyskytovat st\u00e1le \u010dast\u011bji a dnes ji\u017e v\u00fdrazn\u011b p\u0159eva\u017euje. Tak to bude pokra\u010dovat i v budoucnu. Ve 21. stolet\u00ed jsme se naposledy setkali s prvn\u00edm jarn\u00edm dnem 21. 3. v roce 2011. V roce 2048 se p\u0159enese prvn\u00ed jarn\u00ed den dokonce u\u017e na 19. 3. a ke konci 21. stolet\u00ed se 19. a 20. b\u0159ezen budou vyskytovat p\u0159ibli\u017en\u011b ve stejn\u00e9 frekvenci. Tradi\u010dn\u00edho za\u010d\u00e1tku jara 21. b\u0159ezna se na\u0161i potomci do\u010dkaj\u00ed a\u017e v roce 2102.<\/p>\n

Jak u\u017e bylo \u0159e\u010deno, za posun za\u010d\u00e1tku jara jsou zodpov\u011bdn\u00e9 p\u0159estupn\u00e9 dny, respektive po\u010det dn\u016f v jednom kalend\u00e1\u0159n\u00edm roce, kde se st\u0159\u00edd\u00e1 podle p\u0159esn\u011b definovan\u00e9ho syst\u00e9mu po\u010det 365 a 366 dn\u016f. Proto se okam\u017eik jarn\u00ed rovnodennosti, \u0159\u00edd\u00edc\u00ed se pouze ide\u00e1ln\u00edm pohybem Slunce po ekliptice, opo\u017e\u010fuje ka\u017ed\u00fd n\u00e1sleduj\u00edc\u00ed rok o on\u011bch p\u0159eb\u00fdvaj\u00edc\u00edch 5h 49min. Za\u0159azen\u00edm p\u0159estupn\u00e9ho roku se pak okam\u017eik jarn\u00ed rovnodennosti \u201ep\u0159edb\u011bhne\u201c o 24h m\u00ednus 5h 49min, tedy 18h 11min. V n\u00e1mi pou\u017e\u00edvan\u00e9m \u0159eho\u0159sk\u00e9m kalend\u00e1\u0159i vystupuje 400let\u00fd cyklus. Rokem 2000 jsme vstoupili do nov\u00e9ho cyklu a na jeho za\u010d\u00e1tku vzniknou nejv\u011bt\u0161\u00ed rozd\u00edly.<\/p>\n

V souvislosti s rovnodennost\u00ed se tak\u00e9 \u010dasto do\u010dteme klasickou u\u010debnicovou pou\u010dku tvrd\u00edc\u00ed: \u201eden a noc jsou o rovnodennosti stejn\u011b dlouh\u00e9\u201c. Zn\u00ed to naprosto logicky, ale ani to ov\u0161em nen\u00ed tak \u00fapln\u011b pravda. V den rovnodennosti je skute\u010dn\u011b geometrick\u00fd st\u0159ed Slunce nad obzorem po dobu t\u00e9m\u011b\u0159 p\u0159esn\u011b 12 hodin a z toho by m\u011blo vypl\u00fdvat, \u017ee d\u00e9lka dne, tedy po\u010det hodin denn\u00edho sv\u011btla, a noci bude prakticky stejn\u00e1. M\u00e1 to v\u0161ak sv\u00e1 ale. Prvn\u00edm probl\u00e9mem je skute\u010dnost, \u017ee slune\u010dn\u00ed disk m\u00e1 \u00fahlov\u00fd pr\u016fm\u011br kolem p\u016fl stupn\u011b a svoji roli hraje tak\u00e9 zemsk\u00e1 atmosf\u00e9ra zp\u016fsobuj\u00edc\u00ed lom sv\u011btla. Kombinace t\u011bchto vliv\u016f vede ke skute\u010dnosti, \u017ee v den rovnodennosti setrv\u00e1v\u00e1 Slunce na na\u0161\u00ed obloze p\u0159ibli\u017en\u011b 12 hodin a 10 minut zat\u00edmco pod ide\u00e1ln\u00edm horizontem z\u016fst\u00e1v\u00e1 jen 11 hodin a 50 minut.<\/p>\n

Z\u00e1pad\/v\u00fdchod Slunce je toti\u017e definov\u00e1n jako okam\u017eik, kdy se horizontu r\u00e1no p\u0159i v\u00fdchodu \u010di ve\u010der p\u0159i z\u00e1padu horizontu dotkne nikoliv st\u0159ed Slunce, ale jeho horn\u00ed okraj. V obou p\u0159\u00edpadech je tedy v tomto okam\u017eiku je\u0161t\u011b st\u0159ed Slunce pod obzorem. Je\u0161t\u011b v\u011bt\u0161\u00ed vliv m\u00e1 pak lom sv\u011btla. To kdy\u017e vstupuje do atmosf\u00e9ry Zem\u011b, tedy hust\u0161\u00edho prost\u0159ed\u00ed, n\u00e1m nad obzorem slune\u010dn\u00ed paprsky \u201ezdvih\u00e1\u201c p\u0159ibli\u017en\u011b o cel\u00fd pr\u016fm\u011br Slunce (0,5\u00b0). P\u0159esn\u00e1 hodnota pak z\u00e1vis\u00ed i na stavu atmosf\u00e9ry (atmosf\u00e9rick\u00fd tlak, teplota), a proto je prakticky nemo\u017en\u00e9 ji zcela exaktn\u011b stanovit. Obecn\u011b ov\u0161em lze \u0159\u00edci, \u017ee d\u016fsledkem lomu sv\u011btla je, \u017ee Slunce ka\u017ed\u00fd den a tedy i p\u0159i rovnodennosti z\u016fst\u00e1v\u00e1 nad obzorem o p\u0159ibli\u017en\u011b 6 minut d\u00e9le, ne\u017e kdyby Zem\u011b sv\u016fj plynn\u00fd obal nem\u011bla.<\/p>\n

P\u0159i rovnodennosti tedy stejn\u00e1 d\u00e9lka dne a noci nen\u00ed. Tak\u017ee kdy tedy plat\u00ed konstatov\u00e1n\u00ed, \u017ee den a noc se rovnaj\u00ed? Z\u00e1le\u017e\u00ed na tom, kde na Zemi to sledujeme. V rovn\u00edkov\u00fdch oblastech se d\u00e9lka dne a noci v pr\u016fb\u011bhu roku p\u0159\u00edli\u0161 nem\u011bn\u00ed. Naopak u p\u00f3l\u016f, kde nast\u00e1v\u00e1 pol\u00e1rn\u00ed noc a pol\u00e1rn\u00ed den, se jich prakticky nedo\u010dk\u00e1me. U n\u00e1s ve st\u0159edn\u00ed Evrop\u011b, tedy na p\u0159ibli\u017en\u011b 50\u00b0 severn\u00ed zem\u011bpisn\u00e9 \u0161\u00ed\u0159ky, se skute\u010dn\u00e9 \u201erovnodennosti\u201c do\u010dk\u00e1me ka\u017edoro\u010dn\u011b ji\u017e kolem 17. b\u0159ezna. Ale berte tento datum se stejnou rezervou jako za\u010d\u00e1tek jara 21. 3., rok od roku se m\u016f\u017ee v \u0159\u00e1du a\u017e dn\u016f posouvat.<\/p>\n

P\u0159evzato: Zpravodaj Hv\u011bzd\u00e1rny v Rokycanech.<\/p>\n

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Rok co rok se opakuje diskuse nad za\u010d\u00e1tkem jara. Nejinak tomu zajist\u00e9 bude i letos. Ze \u0161koln\u00edch lavic m\u00e1 v\u011bt\u0161ina populace jako za\u010d\u00e1tek jara za\u017eit\u00e9 datum 21. b\u0159ezna, a proto jsou mnoz\u00ed v posledn\u00edch letech zasko\u010deni informac\u00ed, kterou jim poskytuje kalend\u00e1\u0159, uv\u00e1d\u011bj\u00edc\u00ed, \u017ee jaro za\u010d\u00edn\u00e1 ji\u017e o den d\u0159\u00edve. A bude tomu tak i v […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":false,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[8],"tags":[],"class_list":["post-3576","post","type-post","status-publish","format-standard","hentry","category-clanky"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_shortlink":"https:\/\/wp.me\/p4YkmD-VG","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/posts\/3576","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=3576"}],"version-history":[{"count":1,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/posts\/3576\/revisions"}],"predecessor-version":[{"id":3578,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=\/wp\/v2\/posts\/3576\/revisions\/3578"}],"wp:attachment":[{"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3576"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3576"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.benateckyctyrlistek.eu\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3576"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}