Interpreting the Results of the Sunrise/Sunset Calculator

Sunrise/Sunset Tables

Accuracy

The rising and setting times given in these tables refer to the appearance and disappearance (respectively) of the upper limb of the sun as observed at sea level on a refracted (apparent) sea horizon. Because of irregularities of terrain, these theoretical times will only approximate the rising and setting times observed on land. Even on a perfect (sea) horizon, variations in the atmospheric temperature profile can cause the amount of atmospheric refraction of light to vary, such that observed rise and set times may deviate from the computed values by one or two minutes. Hence the rise and set times are only calculated to the nearest minute, based on average atmospheric refraction. If an event occurs twice on the same date, the program identifies only the first occurrence. For example, the start of civil twilight may occur twice on a single calendar day. This could occur on as many as two days per year at certain high latitudes.

Usages

They are important in relation to safe driving practices (eg., headlights on after dark), aviation practices, hunting regulations, etc. For mountain-top observatories, a correction is made to the sunrise/set times for the dip of the horizon, which depends on the altitude of the site above the surroundings.

Information for Hunters

Hunting regulations typically restrict hunting and/or the discharge of firearms to certain periods of the day. Some provinces define these periods in relation to the times of sunrise and sunset, which can be obtained from the advanced options page. Select your location of interest by typing the name of the nearest town or city. If the area is not near a town or city, or if the nearest town or city is not in our database, you can select the area of interest by longitude and latitude. There is no need to change any of the default settings and only the sunrise and sunset times are relevant (local noon and twilight times etc. may be ignored). The times shown are in Standard Time, so one hour must be added for those dates that daylight savings time is in effect.

It is worth noting that some provinces, e.g., Nova Scotia and New Brunswick, publish official times of sunrise/sunset in their hunting regulations. Hunters in such provinces should not rely on our data but respect the official times.

Definitions

The SUNRISE-SUNSET table gives the following times for each day of the year.

• LOCAL NOON occurs when the sun is due south, and highest in altitude above the horizon for that day. Local noon will generally differ from 12:00 because of:
  
  1. a longitude correction from the standard meridian of your time zone, and
  2. the correction to sundial, due to the sun's non-uniform eastward motion along the ecliptic throughout the year (which in turn arises from the earth's orbit about the sun being slightly eccentric, and inclined to the earth's equator)
• SUN RISE and SUN SET are the true rising and setting times.
• TWILIGHT START and TWILIGHT END times are tabulated for both Civil Twilight (when the centre of the sun's disk is 6 degrees below the horizon) and Nautical Twilight (sun 12 degrees below the horizon). For observatories, Astronomical Twilight (sun at 18 degrees below the horizon) as well as Nautical Twilight are tabulated.

Note that for extreme northern (or southern) latitudes, on the summer solstice the sun will not set above latitude 65.7 degrees, and Civil and Nautical twilights will not end above latitudes 60.6 degrees and 54.6 degrees respectively. At the winter solstice, sunrise will not occur above latitude 67.4 degrees. In such seasons and circumstances, times are not given in the table.

All the above values are tabulated in Standard Time; when Daylight Savings Time is in effect one hour must be added to all the above times in the sunrise-sunset table. Since 1987, Daylight Savings Time is observed from the first Sunday in April to the last Sunday in October in most North American jurisdictions.

• HOURS OF ILLUMINATION gives for each day the duration of daylight hours from sunrise to sunset, and the duration of Civil twilight (summed for morning and evening), when sky illumination is present, and their total.
• LST or Local Sidereal Time, is the right ascension on the meridian, i.e., the angle from the meridian, measured westward along the celestial equator, to the vernal equinox (the sun's position at the start of northern hemisphere spring). It is given for 00:00 standard time each day, and increases by 24 hours 03 minutes and 56 seconds for each 24 hours of solar (standard) time. Local Sidereal Time is used by observers of the night sky, as it measures the rotation of the earth relative to the fixed stars.

For intermediate latitudes, the times in the sunrise-sunset table for a given location repeat from year to year to within about 2 minutes. Hence, a sunrise-sunset table may be used for any year, within this accuracy.

Sun Directions Tables

Accuracy

These tables provide information on the direction and length of the shadow cast by the sun at given times of the day, for the 21st day of each month. (It is near that day in June and December that the sun reaches its most extreme positions.) Data are listed for the standard time in the given time zone. The angles are accurate to about 0.5 degrees (the sun's diameter), except when the sun is at the horizon where the accuracy decreases slightly due to atmospheric refraction, which is not taken into account in these calculations.

Usages

These tables are important in relation to driving just before sunset or just after sunrise, the maximum permitted height of a new building, etc.

Definitions

The shadow direction, in the second to the last column, is measured from the North through East. The length of a shadow cast by any object is equal to the height of the object multiplied by the shadow length factor, tabulated in the last column.