獲得錯誤的距離在Java中

Question

進入天體座標和視差時

我工作的一個天文數據庫程序，允許用戶創建並輸入自己的恆星和褐矮星，除其他事項外，對於一款入門級編程課程在大學。每個對象都有確定其在空間中的位置，與太陽處於0，0，0光年XYZ座標。然而，由於大量的星形數據庫（例如SIMBAD），維基百科等以視差角度和赤經/赤緯座標給出了天文物體的位置，所以我給了用戶使用添加物體的選項這些參數，如果他們沒有xyz座標。儘管如此，我仍然無法提供準確的值。

下面是進入視差角碼，與選項/進入兩個角秒爲和毫弧秒/ MAS：

/** 
* Notes: 
* scReadIntMM(n1, n2); reads and returns user-entered ints within the range n1 to n2, via Scanner 
* scReadDoubleMM(n1, n2); is the same, only for doubles. 
*/ 

//user chooses units for entering parallax 
System.out.println("Entering parallax and RA/Dec coordinates."); 
System.out.println(); 
System.out.println("Which units do you wish to use?"); 
System.out.println("(1) Arcseconds (1 as = 1/3600 degrees)"); 
System.out.println("(2) Milliarcseconds (1 mas = 1/1000 arcseconds)"); 
userChoice = scReadIntMM(1, 2); //stores user choice 
System.out.println(); 

//user enters angle, converts to distance and stores 
if (userChoice == 1){ 
    //if user chose to enter in arcseconds 
    System.out.println("Set object's parallax angle, in arcseconds."); 
    System.out.println("Maximum: 3.26167 (corresponding to a distance of exactly 1 light year)"); 
    System.out.println("Minimum: 0.006523266 (corresponding to a distance of about 500 light years)"); 
    dist = (3.26167/(scReadDoubleMM(0.006523266, 3.26167))); 
    System.out.println(); 

} else if (userChoice == 2){ 
    //if user chose to enter in milliarcseconds 
    System.out.println("Set object's parallax angle, in milliarcseconds."); 
    System.out.println("Maximum: 3261.67 (corresponding to a distance of exactly 1 light year)"); 
    System.out.println("Minimum: 6.523266 (corresponding to a distance of about 500 light years)"); 
    dist = (3.26167/((scReadDoubleMM(6.523266, 3261.67))/1000)); 
    System.out.println(); 
} 

這兩種給出正確的結果（即3.26167/(angle in as)），當我添加一個額外的println語句在計算後檢查dist的值。例如，輸入Sirius'視差（0.37921爲，379.21 MAS給出了8.60光年的值，這正是我所期待看着它的維基百科頁面後看到的。

下一階段似乎這裏的一切。腳麻，雖然這部分是用戶在其中輸入的座標，它得到一個轉換爲使用上this site列出的程序度，然後得到改變爲弧度一旦一切都被輸入：

//user enters right ascension 
System.out.println("Enter hours of right ascension. (Must be between 0 and 23, whole"); 
System.out.println("numbers only.)"); 
ra = (((double)scReadIntMM(0, 23)) * 15.0); //enters hours 
System.out.println(); 
System.out.println("Enter minutes of right ascension. (Must be between 0 and 59, whole"); 
System.out.println("numbers only.)"); 
ra = ra + (((double)scReadIntMM(0, 59)/60.0) * 15.0); //enters mins 
System.out.println(); 
System.out.println("Enter seconds of right ascension. (Must be between 0 and 59.999999.)"); 
ra = ra + ((scReadDoubleMM(0, 59.999999)/3600.0) * 15.0); //enters secs 
ra = Math.toRadians(ra); //converts from degrees to radians 
System.out.println(); 

//user enters sign for declination (+ or -) 
System.out.println("Is the object's declination positive or negative? (Enter a number.)"); 
System.out.println("(1) Positive"); 
System.out.println("(2) Negative"); 
userChoice = scReadIntMM(1, 2); //stores dec sign 
System.out.println(); 

//user enters declination 
System.out.println("Enter degrees of declination, without positive or negative signs. (Must be"); 
System.out.println("between 0 and 90, whole numbers only.)"); 
dec = ((double)scReadIntMM(0, 90)); //enter degrees 
System.out.println(); 
System.out.println("Enter minutes of declination. (Must be between 0 and 59, whole"); 
System.out.println("numbers only.)"); 
dec = dec + (((double)scReadIntMM(0, 59))/60.0); //enter mins 
System.out.println(); 
System.out.println("Enter seconds of declination. (Must be between 0 and 59.999999.)"); 
dec = dec + (scReadDoubleMM(0, 59.999999)/3600.0); //enter secs 
dec = dec * userChoice; //sets declination sign 
dec = Math.toRadians(dec); //converts from degrees to radians 
System.out.println(); 

然後，RA /月值用於計算X，Y，Z值，還是按照頁面上的說明我掛之前：

//calculates x, y, z coords from ra/dec and distance values 
xIn = ((dist * Math.cos(dec)) * Math.cos(ra)); 
yIn = ((dist * Math.cos(dec)) * Math.cos(ra)); 
zIn = (dist * Math.sin(dec)); 

使用此方法，Sirius（使用維基百科上列出的視差和RA/Dec）的距離爲5.139 ly，而不是使用單獨的視差計算的8.60 ly值。我也越來越低估了更遙遠的事情，比如一個對象，應爲〜388光年遠是幾十光年近。

我實在看不出它可能出現了問題，雖然任何地方。特只有我能想到的事情是RA /月進入H/M或d/M當覆蓋雙打int類型，和我固定在初期（這是造成更大的錯誤）。有什麼我在這裏失蹤？也許只是使用雙打而不是長時間的損失。

Answer 1

從您發佈的鏈接，似乎殷應該是：

((dist * Math.cos(dec)) * Math.sin(ra)); 

而不是

((dist * Math.cos(dec)) * Math.cos(ra));