Moon phases

Moon phases are caused by the different perspectives of Sun's illuminated Moon, as seen from Earth while our satellite follows its orbit around us, as shown by the diagram below:

Dates and times for the four phases are given throughout the year. See the timescales section for greater detail about the given times.

Lunar eclipses

Lunar eclipses happen when the Earth totally or partially prevents Sun's light from arriving to the moon. Our planet produces an umbral cone, within which the Sun is invisible, and a penumbral zone where the Sun is only partially visible. During an eclipse, the Moon may just enter the penumbra but not the umbra, or may enter the umbra, totally or partially. This classifies lunar eclipses in three categories (see the diagram):

• Total, when the Moon totally enters the umbral cone.
• Partial, if only part of the Moon entered the umbra.
• Penumbral, if it enters the penumbra but not the umbra.

Both total and partial eclipses have a penumbral phase when the Moon is inside the penumbra but not the umbra, and total eclipses have a partial phase when our satellite is only partially inside the umbra. While total or partial eclipses are noticeable and easy to observe, penumbral ones are not detected by the human eye.

The ephemerides list the circumstances of the eclipses, with the dates and times of the contacts of the lunar limb with the umbra (for total and partial eclipses) and the penumbra. The magnitude of the umbral eclipse (defined as the fraction of the lunar diameter that is obscured by the umbra at the time of maximum eclipse) is also given. A total eclipse has a magnitude greater or equal to 1, while a partial one has a magnitude below 1.

You can find other eclipse predictions here:

• Eclipses Online.
• IAU Working Group on Solar Eclipses Home Page.
• IMCCE (France, in French).
• GSFC Sun-Earth - Eclipse Homepage at NASA/GSFC Sun-Earth Connection Education Forum (Fred Espenak).
• Xavier Jubier's Solar Eclipse Interactive Google Maps.
• Arnold Barmettler's Maps for all Solar Eclipses in the 20th and 21th Century.

Geocentric planetary phenomena

The geocentric planetary phenomena include the times for equinoxes and solstices.

The maximum elongations are the best epochs for inner planet observation, while the opposition dates provide the best circumstances for outer planets.

In the case of planet Mars, the best date is that of 'minimum distance', which in fact accounts for the instant where the light-time between the centers of Mars and the Earth is minimum; then, Mars's apparent diameter is greatest.

Meteor showers

For the main annual meteor showers, the radiant name, activity interval and the date of maximum are given, together with other data:

• R.A. and Decl.: Right ascension and declination of radiant at maximum, referred to ICRS. ICRS is the reference system used by modern star catalogs.
• Vg: Geocentric velocity in km/s, without accounting for acceleration due to Earth's gravity field.
• ZHR: Zenith Hourly Rate. It is the maximum number of meteors that an observer could see under ideal conditions, with clear skies and the radiant at zenith.
• % Moon: Percentage of Moon's illumination at 0h TT of maximum's day.

The home page includes a daily ephemeris for annual showers. Due to their nature, meteor shower predictions are approximate, so the appropriate caution must be taken when using the ephemerides. ZHR prediction is notably difficult, and is consequently omitted sometimes.

Predictions are based on data from:

• International Meteor Organization.
• IAU Meteor Data Center.
• IAU Telegrams.

Timescales

Dates are given in Universal Time (UT) and (with the exception of those dates that include decimals, like the eclipse contacts) have not been rounded, but truncated. For example, a Moon's phase taking place at 23:53:59 UT is listed as 23:53 UT. Similarly, if a radiant's maximum occurs at 23 hours of day 18th, it is not rounded to 19th, but the 18th is given.

Universal Time is a scale based on Earth rotation, and the different local times are based on applying one or more timezones to it.