Let'sgoflying! said:
so if the sun is setting still, then you would be x degrees S of the arctic circle?
x=? (can we derive it from the given ~3hrs of night?)
1. Calculate an initial value for t from
t = N + (6h + L)/24
(for morning phenomenon)
t = N + (18h + L)/24
(for evening phenomenon)
where N is the day of the year.
2. Calculate M and [FONT=Symbol,sans-serif]l[/FONT].
3. Solve for [FONT=Symbol,sans-serif]a[/FONT], noting that [FONT=Symbol,sans-serif]a[/FONT] is in the same quadrant as L.
4. Solve for [FONT=Symbol,sans-serif]d[/FONT].
5. Solve for H; the correct quadrant for H is given by the following rules:
rising phenomenon: H = 360 - arccos x
setting phenomenon: H = arccos x
6. Calculate T.
7. Calculate UT. To convert to the local time see the standard time conversions in Section 1.16.
Enter Data
Year:
Month:
Day of the Month:
Latitude:
Longitude:
Observer's height above horizon (meters):
Observer's location:
MMT Observatory, Arizona
Calculations
Intermediate Variables
Convert to decimal form:
The functions necessary to convert between sexagesimal and decimal form are defined past the right margin of the page.
The day of the year N:
First, calculate the
Julian Date for the calendar date at 0h UT:
Then calculate the
Julian Date for the calendar date on 0 January, 0h UT for the given year:
Define an initial value for t, the approximate time of the phenomena:
(for morning phenomena)
(for evening phenomena)
The
zenith distances for the phenomena:
for Sunrise or Sunset
for civil twilight
for nautical twilight
for astronomical twilight
Calculate the Morning Phenomenon
Convert the time T to a range between 0 and 24h:
Calculate UT of the phenomenon. If UT is greater than 24h , the phenomenon occurs on the following day, Greenwich time. If UT is negative, the phenomenon occurs on the previous day, Greenwich time.
but I am about 2 degrees, 45 minutes south of the Arctic Circle.
