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Gi?i m kho?ng cch t? Tri d?t d?n M?t tr?

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    Posted: 28 September 2012 at 11:25
M?t tr?i l trung tm trong Thi Duong h? c?a chng ta. T?t c? cc thin th? trong Thi Duong h?, bao g?m cc hnh tinh, thin th?ch, sao ch?i, , quay xung quanh n. Kho?ng cch t? Tri d?t t?i M?t tr?i du?c g?i l m?t don v? thin van (AU). M?t don v? AU hi?n du?c xc d?nh b?ng 149.597.870.700 mt.

Theo trang Space, cc nh thin van h?c d s? d?ng don v? AU d? do m?i kho?ng cch trong Thi Duong h?. V d?, sao M?c cch M?t tr?i 5,2 AU trong khi sao H?i vuong cch trung tm Thi Duong h? t?i 30,07 AU. ? ra ngoi cng c?a Thi Duong h?, dm my Oort, noi du?c cho l ci ni c?a cc sao ch?i, cch M?t tr?i 100.000 AU. Kho?ng cch t?i ngi sao g?n nh?t, Proxima Centauri, x?p x? 250.000 AU. Tuy nhin, d? do cc kho?ng cch xa hon, gi?i thin van h?c d s? d?ng nam nh sng hay kho?ng cch nh sng di chuy?n du?c trong m?t nam c?a Tri d?t tuong duong 63.239 AU. V v?y, theo quy d?i, Proxima Centauri n?m cch M?t tr?i 4,2 nam nh sng.



Qu? d?o hnh elip

on v? thin van (AU) l kho?ng cch trung bnh t? Tri d?t t?i M?t tr?i. C? 365,25 ngy t?c l 1 nam, Tri d?t hon thnh m?t vng xoay trn quanh trung tm c?a Thi Duong h?. Tuy nhin, qu? d?o c?a Tri d?t khng ph?i l m?t vng trn hon h?o, m c hnh d?ng gi?ng hnh ovan ho?c elip hon. Trong su?t th?i gian c?a m?t nam, Tri d?t th?nh tho?ng d?ch chuy?n g?n hon t?i M?t tr?i v di khi xa hon. L?n ti?p c?n g?n nh?t c?a Tri d?t t?i M?t tr?i du?c g?i l di?m c?n nh?t, di?n ra vo d?u thng 1 v c kho?ng cch kho?ng 146 tri?u km. Th?i di?m Tri d?t ? xa M?t tr?i nh?t, kho?ng 152 tri?u km, du?c g?i l di?m vi?n nh?t.

Xc d?nh cc kho?ng cch

L?ch s? ghi nh?n, ngu?i d?u tin do kho?ng cch t? Tri d?t t?i M?t tr?i l Aristarchus vo kho?ng nam 250 tru?c Cng nguyn. ?n th?i hi?n d?i, nh thin van h?c Christiaan Huygens d tnh ton kho?ng cch t? Tri d?t t?i M?t tr?i vo nam 1653.

ng s? d?ng cc giai do?n c?a sao Kim d? tm ki?m cc gc trong tam gic sao Kim Tri d?t M?t tr?i. V d?, khi sao Kim xu?t hi?n ? tr?ng thi du?c M?t tr?i r?i sng m?t n?a, 3 thin th? hnh thnh m?t tam gic d?u nhn t? Tri d?t. Ph?ng don kch thu?c c?a sao Kim (m?t cch v tnh l?i chnh xc), ng Huygens d c th? xc d?nh kho?ng cch t? sao Kim t?i Tri d?t, v khi bi?t du?c kho?ng cch d, c?ng v?i cc gc c?a tam gic, ng d c th? do du?c kho?ng cch t?i M?t tr?i. Tuy nhin, v phuong php c?a Huygens m?t ph?n l s?n ph?m mang tnh suy don v khng hon ton d?a trn can c? khoa h?c nn ng thu?ng khng du?c tn nhi?m.


Giovanni Cassini d tm kho?ng cch t? Tri d?t t?i sao H?a tru?c, r?i t? d tnh ton ra kho?ng cch t? Tri d?t t?i M?t tr?i. ?nh: Astronomy for beginners
Nam 1672, Giovanni Cassini d s? d?ng m?t phuong php bao g?m c? th? sai hay sai s? gc, d? tm kho?ng cch t?i sao H?a v d?ng th?i tnh ton ra kho?ng cch t?i M?t tr?i. ng d c? m?t ngu?i d?ng nghi?p c tn Jean Richer t?i vng Guiana thu?c Php trong khi b?n thn ? Paris. H? d do d?c v? tr tuong d?i c?a sao H?a v?i cc ngi sao khc v l?p lu?i tam gic nh?ng k?t qu? do d?c ny v?i kho?ng cch d bi?t gi?a Paris v Guiana. M?t khi n?m du?c kho?ng cch t?i sao H?a, h? cung c th? tnh ton du?c kho?ng cch t?i M?t tr?i. V cc phuong php c?a Cassini mang tnh khoa h?c hon nn ng thu?ng du?c tin c?y.

Phuong trnh m?i

V?i s? ra d?i c?a tu vu tr? v radar, con ngu?i d c trong tay nh?ng phuong th?c d? do d?c tr?c ti?p kho?ng cch gi?a Tri d?t v M?t tr?i. ?nh nghia v? don v? thin van (AU) t?ng l bn knh c?a m?t qu? d?o trn, khng xo tr?n quanh M?t tr?i c?a m?t h?t c kh?i lu?ng v cng nh?, di chuy?n v?i chuy?n d?ng trung bnh 0,01720209895 radian m?i ngy (du?c g?i l h?ng s? Gaussian)".

Ngoi vi?c khi?n m?i th? tr? nn kh m?t cch khng c?n thi?t d?i v?i cc gio su thin van h?c, d?nh nghia trn th?c t? khng ph h?p v?i h?c thuy?t tuong d?i ni chung. S? d?ng d?nh nghia cu, gi tr? c?a AU s? thay d?i d?a vo v? tr c?a ngu?i quan st trong Thi Duong h?. N?u ngu?i quan st ? trn sao M?c s? d?ng d?nh nghia cu d? tnh ton kho?ng cch gi?a Tri d?t v M?t tr?i, k?t qu? s? sai l?ch so v?i con s? tnh ton du?c trn Tri d?t kho?ng 1.000 mt.

Hon th? n?a, h?ng s? Gaussian ph? thu?c vo kh?i lu?ng c?a M?t tr?i, v v M?t tr?i m?t d?n kh?i lu?ng khi t?a ra nang lu?ng nn gi tr? c?a AU thay d?i cng v?i n.

Thng 8/2012, Hi?p h?i Thin van h?c qu?c t? b? phi?u tn thnh chuy?n d?i d?nh nghia v? don v? thin van sng m?t con s? cu, don gi?n hon: 149.597.870.700 mt. Con s? ny d?a trn t?c d? c?a nh sng, m?t kho?ng cch xc d?nh khng lin quan d?n kh?i lu?ng c?a M?t tr?i. 1 mt du?c d?nh nghia l kho?ng cch m nh sng di chuy?n du?c trong m?t mi tru?ng chn khng trong 1/299.792.458 giy.

Tu?n Anh
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