~ 大约太阳正午
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
作为更新，部分混乱可能是太阳正午是所有
计算从公元前4713年1月1日格林威治中午开始。
Date.ordinal_to_jd 的正确使用并没有弥补这一事实。所以通过
像这样添加或减去 12 小时：
jdn = Date.ordinal_to_jd(Time.now.year, Time.now.yday) - 0.5
我们应该减少错误。自从我们的计算以来，我们只是使用哪个
从昨天中午开始？
该代码是从本页的两个方程推导出来的日出方程 http://en.wikipedia.org/wiki/Sunrise_equation.
我从这里的用户那里得到的第一个答案是我们不明白
0.0009 和 lw / 360。lw / 360 看起来是弧度的小数日
本初子午线。至于0.0009，它一定是一个很小的方差
自公元前 4713 年 1 月 1 日格林威治中午以来的秒数。请参阅 IAU 标准了解更多信息
我根据这个算出是0.007776秒page http://en.wikipedia.org/wiki/Julian_Day.
我有一些来自 Date 类的信息，不包括方法细节。
=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
附带说明一下，Ruby 有一种计算儒略日期的方法真是太好了。
我正在研究 Javascript 代码NOAA http://www.srrb.noaa.gov/highlights/sunrise/sunrise.html.
这是我受链接启发而写的一个课程。
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
现在这让我到达那里，但我仍在研究返回这样的数字的方法
作为由最上面的方程计算的那个。尝试一下我们可以看到我们做到了
在 JDN 中获得 0.5 分。谁是对的？红宝石还是 NOAA？
NOAA 使用 2000 年 1 月 1 日的值 2451545.0 从 jd 中减去该值来获取时间
像这样的分数世纪
def calcTimeJulianCent(j)
t = (j - 2451545.0)/36525.0
return t
end
