In the "Columns" drop-down menu, you can choose which columns to display.
The times for moonrise and moonset are based on the ideal situation, where no hills or mountains obscure the view and the flat horizon is at the same altitude as the observer. Moonrise is the time when the upper part of the Moon is above the horizon, and moonset is when the lower part of the Moon is about to disappear below the horizon. However, the Moon might not be visible ― even if it is above the horizon ― if it is in a phase near the new moon or if the weather is not clear.
If the horizon in the moonrise/moonset direction is at a higher altitude than that of the observer, moonrise will be later and moonset earlier than listed (and the reverse: on a high mountain where the horizon is below the observer, the moonrise will be earlier and moonset later than listed).
The Earth's atmosphere refracts the incoming light from the Moon in such a way that the Moon is visible longer than it would be without an atmosphere. The refraction depends on atmospheric pressure and temperature. These calculations use the standard atmospheric pressure of 101.325 pascal and temperature of 15°C or 59°F. A higher atmospheric pressure, or lower temperature than the standard, means more refraction and the moonrise will be earlier and moonset later. In most cases, however, this would affect the rising and setting times by less than a minute. Near the North and South Poles this could have greater impact, because of low temperatures and the slow rate of the Moon¢s rising and setting.
Because the Moon rotates around the Earth, its position in the sky relative to the Sun changes rapidly. Within a 24-hour period, its horizontal position, relative to the Sun, changes by about 12 degrees in a counterclockwise direction. In most cases, this causes the moonrise and moonset to occur later than the day before. As the time between moonrise occurrences is more than 24 hours, there are days when the Moon will not rise so the event will not occur until the day after. When this happens, a minus sign (-) is shown. On a day when the moonset occurs before the moonrise, additional minus signs are added and the moonrise is shown on a separate line below the moonset.
For regions near the North or South Pole, the Moon might be up all day or down all day. If this is the case, the Moon Calculator will show "Up all day" or "Down all day."
The azimuth displayed is the horizontal direction of the Moon at moonrise or moonset, at the times displayed in the Moonrise and Moonset columns. As on a compass, the azimuth is measured in degrees, with 360 in a full circle, counting in a clockwise direction starting from north. North has an azimuth value of 0 degrees, east is 90 degrees, south is 180 degrees, and west is 270 degrees. A small arrow is displayed after the azimuth value to indicate the map direction where the Moon will rise or set (for a map where north is upward).
The times used for the moonrise and moonset time calculations are also used for the azimuth calculations, such that the actual height of the horizon and refraction, as described for the Moonrise and Moonset columns, can influence the real direction where the Moon rises or sets.
It is important to note that the directions refer to true north and not to magnetic north. True north refers to north according to the earth’s axis, not magnetic north. Magnetic north refers to the direction in which the north end of a compass needle will point in response to the earth’s magnetic field.
"Meridian Passing" shows four columns calculated at the time the Moon passes the meridian of (or same longitude as) the observer. These columns consist of the local time and the altitude, distance, and fraction of the Moon illuminated at the meridian passing.
"Time" shows the local time of the moment when the Moon's position will be above the horizon either directly north or directly south (except for Polar Regions, where the Moon might be down all day during the winter). For locations near the equator, the Moon can be right over one's head, at the point nearest the zenith position (altitude 90 degrees).
"Altitude" shows the altitude of the Moon's center above the ideal horizon at the passing time. Typically this is the highest position it reaches in the sky that day (except near the South and North Poles, where the altitude often increases or decreases all day and night). The altitude takes into account typical refraction in the Earth's atmosphere. If the Moon is below the horizon all day, the altitude will be labeled "below."
"Distance" is the distance from the Earth's center to the Moon's center in kilometers. To compare, the Earth has an equatorial diameter of 12,756 km and the Moon an equatorial diameter of 3,476 km.
If the Moon does not pass through the meridian on a given date, the columns are empty. This occurs once every Moon cycle.
The "Phase" column will be displayed only on days when a certain Moon phase event occurs. The local time will be displayed after one of these Moon phases:
Times are rounded to the nearest minute and should generally match closely with those listed in the annual Astronomical Almanac by H.M. Nautical Almanac Office in the U.K. and the United States Naval Observatory.
A representative sample set of 100 records consisting of times for moonrise and moonset was compared with times listed in The Astronomical Almanac for 2007. Most of the records were the same, but five differed by one minute each.
Governments introduce changes to Daylight Saving Time and can change a location's time zone, sometimes on short notice. Therefore, there is a significant chance of errors for future dates due to unforeseen time changes. Known future changes in Daylight Saving Time are adjusted for.