表达式17: "A" Subscript, "c" "o" "s" , Baseline left parenthesis, "x" , right parenthesis equals left brace, "x" greater than or equal to 1 : 0 , left brace, "x" less than or equal to negative 1 : 180 , cos to the negative 1st power left parenthesis, "x" , right parenthesis , right brace , right braceAcosx=x≥1:0,x≤−1:180,cos−1x
17
Duration of daylight (hours)
18
表达式19: "T" left parenthesis, "t" , "h" , right parenthesis equals 2 "L" left parenthesis, "t" , "h" , right parenthesis times StartFraction, 24 Over 360 , EndFractionTt,h=2Lt,h·24360
19
Civil twilight
20
表达式21: "T" left parenthesis, "x" , negative StartFraction, 50 Over 60 , EndFraction , right parenthesis less than or equal to "y" less than or equal to "T" left parenthesis, "x" , negative 6 , right parenthesisTx,−5060≤y≤Tx,−6
21
Nautical twilight
22
表达式23: "T" left parenthesis, "x" , negative 6 , right parenthesis less than or equal to "y" less than or equal to "T" left parenthesis, "x" , negative 12 , right parenthesisTx,−6≤y≤Tx,−12
23
Astronomical twilight
24
表达式25: "T" left parenthesis, "x" , negative 12 , right parenthesis less than or equal to "y" less than or equal to "T" left parenthesis, "x" , negative 18 , right parenthesisTx,−12≤y≤Tx,−18
25
Night
26
表达式27: "T" left parenthesis, "x" , negative 18 , right parenthesis less than or equal to "y" less than or equal to 24Tx,−18≤y≤24
27
Horizontal equilux line
28
表达式29: "y" equals 12y=12
1212
1212
29
Vertical solstice lines
30
表达式31: "x" equals StartFraction, left bracket, negative 3 , negative 1 , positive 1 , positive 3 , right bracket Over 4 , EndFraction "Y"x=−3,−1,+1,+34Y
