问对天文数据使用Ruby Date类

EN

lw = 88.743  # my longitude

jdate = Date.ordinal_to_jd(Time.now.year, Time.now.yday)
n = (jdate - 2451545 - 0.0009 - lw / 360).round  # lw is users longitude west of 0.
j_noon = 2451545 + 0.0009 + lw / 360 + n 
puts j_noon

=> 2455616.24740833

jdn = Date.ordinal_to_jd(Time.now.year, Time.now.yday) - 0.5

        =begin
--------------------------------------------------------------------- Class: Date
Class representing a date.

See the documentation to the file date.rb for an overview.

Internally, the date is represented as an Astronomical Julian Day Number, ajd. 
The Day of Calendar Reform, sg, is also stored, for conversions to other date formats. 
(There is also an of field for a time zone offset, 
but this is only for the use of the DateTime subclass.)

A new Date object is created using one of the object creation class methods named  
after the corresponding date format, and the arguments appropriate to that date
format; for instance, Date::civil() 
(aliased to Date::new()) with year, month, and day-of-month, or Date::ordinal() with
year and day-of-year.

All of these object creation class methods also take the Day of Calendar Reform as an
optional argument.

Date objects are immutable once created.

Once a Date has been created, date values can be retrieved for the different date
formats supported using instance methods. For instance, #mon() gives the Civil month,
#cwday() gives the Commercial day of the week, and #yday() gives the Ordinal day of
the year. Date values can be retrieved in any format, regardless of what format was
used to create the Date instance.

The Date class includes the Comparable module, allowing date objects to be compared
and sorted, ranges of dates to be created, and so forth.

---------------------------------------------------------------------------------

Includes:
Comparable(<, <=, ==, >, >=, between?)

Constants:
MONTHNAMES:      [nil] + %w(January February March April May June July August
                            September October November December)
DAYNAMES:        %w(Sunday Monday Tuesday Wednesday Thursday Friday Saturday)
ABBR_MONTHNAMES: [nil] + %w(Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec)
ABBR_DAYNAMES:   %w(Sun Mon Tue Wed Thu Fri Sat)
ITALY:           2299161
ENGLAND:         2361222
JULIAN:          Infinity.new
GREGORIAN:       -Infinity.new

Class methods:
_load, _parse, _strptime, ajd_to_amjd, ajd_to_jd, amjd_to_ajd, civil, civil_to_jd,
commercial, commercial_to_jd, day_fraction_to_time, gregorian?, gregorian_leap?, jd,
jd_to_ajd, jd_to_civil, jd_to_commercial, jd_to_ld, jd_to_mjd, jd_to_ordinal,
jd_to_wday, julian?, julian_leap?, ld_to_jd, mjd_to_jd, new, now, ordinal,
ordinal_to_jd, parse, s3e, strptime, time_to_day_fraction, today, valid_civil?,
valid_commercial?, valid_jd?, valid_ordinal?, valid_time?

Instance methods:
+, -, <<, <=>, ===, >>, _dump, ajd, amjd, asctime, civil, commercial, ctime, cwday,
cweek, cwyear, day, day_fraction, downto, england, eql?, gregorian, gregorian?, hash,
hour, inspect, italy, jd, julian, julian?, ld, leap?, mday, min, mjd, mon, month,
new_offset, new_start, next, next_day, offset, ordinal, sec, sec_fraction, start,
step, strftime, succ, time, to_s, to_yaml, upto, wday, weeknum0, weeknum1, wnum0, 
wnum1, yday, year, zone

=end

class JulianDayNumber

  def initialize(year = 2000, month = 1, day = 1) #defaults to Jan. 01, 2000
    @year = year
    @month = month
    @day = day
  end

  def calcJDN

    if (@month <= 2) then 
      @year -= 1
      @month += 12
    end

    varA = (@year/100).floor
    varB = 2 - varA + (varA/4).floor

    jdn = (365.25*(@year + 4716)).floor \
           + (30.6001*(@month+1)).floor \
           + @day + varB - 1524.5

    return jdn
  end

end

jd = JulianDayNumber.new(2011, 3, 2)
julianday = jd.calcJDN
puts julianday

=> 2455622.5

    def calcTimeJulianCent(j)
      t = (j - 2451545.0)/36525.0
      return t
    end