REM PROGRAM SEASONS
REM THIS PROGRAM ANIMATES THE ROTATING EARTH
REM IT HAS 12 MERIDIANS LINES
REM COULD ADD COLORS FOR DIFFERENT TIMES OF DAY
REM COULD ADD OTHER SPOTS AT DIFFERENT LATITUDES - CONTINENTS
PI = 3.141593: DRC = PI / 180
XC = 160: YC = 240: R = 50: RSPOT = 5
KFIN = 40
DIM AMP(20), AMPOLD(20), M$(20)
DLTA0 = 23.5 * DRC
M$(1) = "MARCH": M$(2) = "APRIL": M$(3) = "MAY"
M$(4) = "JUNE": M$(5) = "JULY": M$(6) = "AUGUST"
M$(7) = "SEPTEMBER": M$(8) = "OCTOBER": M$(9) = "NOVEMBER"
M$(10) = "DECEMBER": M$(11) = "JANUARY": M$(12) = "FEBRUARY"
SCREEN 12
LOCATE 3, 25: PRINT "MARCH OF THE SEASONS"
LOCATE 11, 16: PRINT "NORTH POLE"
LOCATE 20, 16: PRINT "SOUTH POLE"
FOR ROT = 1 TO 300
GOSUB 1000
FOR I = 1 TO 8
THPHASE = I * PI / 96
DLTA = DLTA0 * SIN(PI / 48 * (ROT + I / 8))
XSUN = XC + 300 * COS(DLTA)
YSUN = YC - 300 * SIN(DLTA)
CIRCLE (XSUN, YSUN), 10, 14
PAINT (XSUN, YSUN), 14
ROT2 = ROT MOD 12
THSPOT = THPHASE + ROT2 * PI / 12 - PI / 2 + .13
XSPOT = XC + R * SIN(THSPOT)
AMPSPT = ABS(1 / COS(THSPOT))
IF XSPOT > XC THEN HUESPT = 10 ELSE HUESPT = 2
CIRCLE (XSPOT, YC), RSPOT, HUESPT, , , AMPSPT
PAINT (XSPOT, YC), HUESPT
FOR J = 0 TO 11
AMP(J) = R * SIN((J - 6) * PI / 12 + THPHASE)
FOR K = 0 TO KFIN
PHI = (K - KFIN / 2) * PI / KFIN
X = XC + AMP(J) * COS(PHI)
X1 = XC + AMPOLD(J) * COS(PHI)
Y = YC + R * SIN(PHI)
IF X >= XC + (Y - YC) * TAN(DLTA) THEN HUE = 14 ELSE HUE = 9
PSET (X1, Y), 0
PSET (X, Y), HUE
NEXT K
AMPOLD(J) = AMP(J)
NEXT J
REM WHILE INKEY$ = "": WEND
CIRCLE (XSUN, YSUN), 10, 0
PAINT (XSUN, YSUN), 0
CIRCLE (XSPOT, YC), RSPOT, 0
PAINT (XSPOT, YC), 0
CIRCLE (XC, YC), R + 2, 5
CIRCLE (XC, YC), R + 1, 5
HUENP = 7.5 + SGN(DLTA) * 6.5
HUESP = 7.5 - SGN(DLTA) * 6.5
LINE (XC - 1, YC - R - 3)-(XC + 1, YC - R - 8), HUENP, BF
LINE (XC - 1, YC + R + 3)-(XC + 1, YC + R + 8), HUESP, BF
NEXT I
NEXT ROT
END
1000 REM PRINT MONTH
NMON = INT((ROT + 5) / 8) MOD 12 + 1
LOCATE 16 - 8 * SIN(PI * (NMON - 1) / 6), 62: PRINT M$(NMON)
LOCATE 16 - 8 * SIN(PI * (NMON - 2) / 6), 62: PRINT "           "
RETURN