Preface

NASA Reference Publication 1349

Twelve Year Planetary Ephemeris: 1995 - 2006

Fred Espenak

Planetary research programs often require detailed solar system ephemerides to assist in long range planning for telescope time at major astronomical observatories or for Earth orbiting and interplanetary spacecraft missions. The planetary community's chief source for such information is the Astronomical Almanac (or AA) which is prepared jointly by the U. S. Naval Observatory and the Royal Greenwich Observatory. Since the AA is not available more than ten months before the beginning of each year, there exists a need for accurate ephemeris data in hard format one or more years in advance.

With proliferation of personal computers over the past decade, a number of ephemeris programs have become available which allow anyone to quickly calculate planetary circumstances for any date in the near future with reasonable accuracy. Nevertheless, many researchers find it useful to have a planetary ephemeris in hard copy so that they can quickly and more conveniently make comparisons between different observing seasons or planets. Since the publication of Ten Year Planetary Ephemeris: 1986 - 1995 [Espenak, 1986], many of my colleagues in the AAS/DPS¹ have urged me to update it and make it available to as large a segment of the planetary community as possible. However, the new publication should overcome a number of its predecessor's shortcomings by adding a lunar ephemeris and by including physical aspect geometry data for the planets. It should utilize the most accurate planetary ephemeris available and should provide these data at a temporal frequency higher than 5 days.

The Twelve Year Planetary Ephemeris: 1995 - 2006 (or TYPE) is an attempt to address these requirements and provide accurate solar system ephemerides during the next twelve years. It is not meant to replace AA since it does not provide planetary ephemerides as frequently nor with as much detail. For instance, TYPE does not include heliocentric coordinates, natural satellite or minor planet ephemerides. Nevertheless, TYPE does present accurate geocentric positions as well as physical aspect geometry's for the Sun, the Moon and the eight major planets: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Furthermore, TYPE includes one particularly useful parameter missing from AA. The geocentric radial velocity of a planet is of special interest to high resolution spectroscopic investigations, particularly at infrared, microwave, sub-millimeter, millimeter, and radio frequencies. Although not listed in AA, geocentric radial velocities are essential to the successful planning, data reduction and analysis of such investigations. In addition, TYPE includes the solar elongation or geocentric angle between the Moon (or planet) and the Sun. Elongation's are measured from 0¡ to 180¡, east or west of the Sun. Eastern elongation's place the planet in the evening sky, while western elongation's place the planet in the morning sky. Elongation's of 0¡, 90¡E, 180¡ and 90¡W correspond to solar conjunction, eastern quadrature, opposition and western quadrature, respectively. The value of the elongation is that it quickly gives the position of the planet with respect to the Sun without comparing the specific coordinates of the two bodies.

The fundamental ephemerides of the Sun, Moon and planets are based on the JPL DE200/LE200² [Standish, 1982a, 1982b] and include the effects of lighttime travel, nutation and the aberration of starlight. Since both TYPE and AA use the JPL DE200/LE200, the geocentric apparent coordinates in TYPE and AA for 1995 are in perfect agreement to within the precision of the published values (0.1 arc-seconds). It should be noted that AA positions for Pluto are astrometric, while TYPE positions are apparent for true equator and equinox.

The first three sections of TYPE constitute the greater portion of this work and consist of ephemerides for the Sun, the Moon and major planets, respectively. The final two sections tabulate the Moon's phases, and identify notable planetary configurations. Throughout TYPE, a bold header at the top of every page quickly identifies the planet and year. Each section is described in more detail as follows.

Section 1 is a twelve year geocentric ephemeris for the Sun tabulated at 2-day intervals. It lists both the Gregorian and abbreviated Julian dates, the right ascension and declination of the Sun for the true equinox of date at 00:00:00 TDT (Terrestrial Dynamical Time), the distance of the Sun from Earth, the geocentric radial velocity, and the apparent angular diameter. Finally, the physical aspect geometry gives the heliographic latitude and longitude of the sub-Earth point of the solar disk, followed by the position angle³ of the Sun's rotation axis. Physical aspect geometry is calculated with elements from Carrington [1863].

Section 2 provides a twelve year geocentric ephemeris for the Moon. Due to it's rapid apparent motion, the Moon's ephemeris is given at 1-day intervals. The lunar tables include the Gregorian date, the right ascension and declination of the Moon for the true equinox of date at 00:00:00 TDT (Terrestrial Dynamical Time), the distance of the Moon from Earth, the equatorial horizontal parallax, and the apparent angular diameter. The physical aspect geometry gives the lunar libration (optical + physical) in latitude and longitude plus the position angle of the Moon's rotation axis. The Sun's selenographic colongitude and the position angle of the midpoint of the Moon's bright limb follow. Finally, the Moon's age, phase and elongation from the Sun are listed. Optical librations are calculated from the formulae of Encke [1843].

Section 3 contains a twelve year geocentric ephemeris for the major planets of the Solar System: Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Ephemerides for the five classic planets (Mercury through Saturn) are listed at 2-day intervals. Due to their slow apparent motion, ephemerides for Uranus, Neptune and Pluto are tabulated at 4-day intervals. The planetary tables include the Gregorian date, the right ascension and declination of the planet for the true equinox of date at 00:00:00 TDT (Terrestrial Dynamical Time), the distance of the planet from Earth and from the Sun, the geocentric radial velocity, the apparent visual magnitude, and the apparent equatorial angular diameter. The physical aspect geometry gives the phase, the planetocentric latitude and longitude of the sub-Earth point on the planetary disk, and the position angle of the planet's rotation axis. Finally, L_s (planetocentric orbital longitude of Sun) and the planet's elongation from the Sun are listed. Visual magnitudes for the planets were calculated using expressions from Harris [1961]. The planetary aspect geometry was calculated via algorithms from the Explanatory Supplement [1974] with orbital elements from Meeus [1991] using cartographic coordinates and rotational elements published by Davies et al. [1989]. At the beginning of sections 1, 2 and 3, special keys give definitions or descriptions of every column in each table. Additional information, explanations and descriptions of these parameters may be found in section L of AA.

Section 4 presents the phases of the Moon from 1995 through 2014. During this twenty year period, the dates and times of New Moon, First Quarter, Full Moon and Last Quarter are tabulated for each lunation. This section should be useful for dark moon scheduling or observations where the Moon is needed as a calibration source. Algorithms for calculating lunar phases are based on Meeus [1991] and agree to within ±2 minutes of values published in AA for 1995.

Section 5 presents a range of different planetary phenomena occurring from 1995 to 2010. They are arranged in chronological order with one page per year. Algorithms for calculating planetary phenomena are based on Meeus [1991]. Among the planetary configurations listed during this period are:

	- solstices and equinoxes (Earth)
	- aphelion and perihelion (Venus, Earth, Mars, Jupiter and Saturn)
	- phases of the Moon
	- apogee and perigee of the Moon (with distances in km)
	- eclipses of the Sun and Moon (with eclipse type and magnitude)
	- greatest elongation, inferior and superior conjunction (Mercury and Venus)
	- opposition and solar conjunction (Mars through Pluto)
	- close conjunctions/occultations of planets by the Moon (Mercury through Saturn)
		(for solar elongation's > 30 š)

TYPE will be distributed to all planetary scientists who are AAS/DPS members as of September 1994. In addition, TYPE will be mailed to several hundred observatories, libraries, planetariums, and science centers. A limited number of additional copies are available by contacting the author. Electronic versions of the tables are also available via Email. All calculations presented in this publication are those of the author and he assumes full responsibility for their accuracy.

This publication may be ordered in hard copy form.

1 Division of Planetary Sciences of the American Astronomical Society.
2 Jet Propulsion Laboratory Developmental Ephemeris 200 and Lunar Ephemeris 200. This is a numerical integration ephemeris based on optical, radar, and spacecraft observations of the planets.
3 Unless noted otherwise, all position angles are measured eastwards (counter-clockwise) from the celestial north point of the solar, lunar, or planetary disk.

Return to Twelve Year Planetary Ephemeris Directory

Webmaster: Fred Espenak Planteary Systems Laboratory - Code 693 Email: espenak@lepvax.gsfc.nasa.gov NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA