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2.4 The SunRise and NewMoon Functions

Precise times for common solar and lunar events are provided by the SunRise, SunSet, NewMoon, and FullMoon functions.

Determining the precise times of common events.

Sunrise and sunset times are computed according to your current location and time zone as set previously with SetLocation. The location used throughout this user's guide is Melbourne, Australia.

On 1993 November 17, sunrise at Melbourne is about 06:00 (or 6:00am).

In[17]:=SunRise[{1993,11,17}]

Out[17]=

Sunset is about 20:10 (or 8:10pm).

In[18]:=SunSet[{1993,11,17}]

Out[18]=

The SunRise and SunSet functions take into account atmospheric refraction. When light passes along the horizon to reach you, it is refracted by about 0.5 degrees, so that sunrise occurs about two minutes earlier than the time you would expect from simple geometry. Similarly, sunset occurs about two minutes later. You can use the option Refract->False to suppress refraction.

Related functions are NewMoon and FullMoon.

The new moon nearest to 1993 November 17 occurs on November 14.

In[19]:=NewMoon[{1993,11,17}]

Out[19]=

The nearest full moon occurs fifteen days later on November 29.

In[20]:=FullMoon[{1993,11,17}]

Out[20]=

All the dates and times returned are accurate to within one minute.

As with all the functions in Scientific Astronomer, if you omit the date or near date argument, the current date (as calculated from Date[]) is always used. Thus, SunSet[] returns the time when the Sun will set today, and FullMoon[] returns the date of the nearest full moon.

You can use the NewMoon function to calculate the date of the Chinese New Year. As a general rule, Chinese New Year begins on the new moon nearest to February 4 in any given year. Thus, a definition is ChineseNewYear[year_] := NewMoon[{year, 2, 4}].

A related event is a Harvest Moon, which occurs on the day of a full moon nearest the northern autumnal equinox. On the evening of a Harvest Moon the Sun sets directly in the west at the same time as a full moon rises in the east, thus extending the light at the end of the day. This symmetry greatly impressed ancient civilizations, many of which supposedly used the extra light to harvest crops. More often though it was used as the time of a celebration. A definition is HarvestMoon[year_] := FullMoon[{year, 9, 23}].

Related functions, which are built into Scientific Astronomer, include VernalEquinox[date], AutumnalEquinox[date], SummerSolstice[date], and WinterSolstice[date].

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