An Inferior Planet is one that lies inside the Earths orbit, and therefore will never stray too far from the Sun. This means that both Mercury and Venus can be only seen in either on the morning or evening skies prior to sunrise or sunset. As such, both planets will also experience phases, whose shape is determined by the orbital positions as seen from the Earth, Sun and planet at any given time.

In these days of interplanetary spacecraft visiting the inner or outer regions of the solar system, the term inferior planet could be probably more properly considered as one which lies inside the orbit of the observer or spacecraft. So for example on Mars, the Earth would also be an inferior planet, exhibiting the characteristics seen with Venus from Earth.

The various alignment positions in the sky for inferior planets are termed either as Conjunctions or Greatest Elongations.

Conjunctions are termed as superior or inferior, being those more distant than the Sun, or closer than the Sun, respectively. At superior conjunction, such planets appear as small circular disks, whose full phase is never really seen because of the inferior planets proximity to the Sun. At inferior conjunction, the planet will lie between us and the Sun, and here the diameters are expectantly large. For Venus this may exceed 1 arc minute (1′) or 60 arcsec. Just before and after inferior conjunction, the phases of the disks can appear as thin crescents making attactive targets with this odd geometry.

Greatest elongations can be deemed either East or West of the Sun. If the planet appears East of the Sun, it so will appear in the evening sky. If the planet is West of the Sun, it will appear in the morning sky.

All greatest elongations are at the maximum separation between the sun and planetary centre for each apparition. These elevations can vary slightly for Venus, and significantly for Mercury. Differences are cause by the eccentricity or flatness of the planetary orbit around the Sun, which is expressed in the extremes of the orbital shape - being either aphelion (furthest from the Sun) or perihelion (closest to the Sun). In Mercurys case aphelion combined with the planets greatest elongation distance may mean significant difficulties in seeing the planet when near the eastern or western horizon, and more often than not, can only be seen during twilight.

As the orbits of the inferior planets are not perfectly aligned to the plane of the planets, the ecliptic, it becomes rare for transits across the disk at inferior conjunction to occur. In November 2006, Mercury will next transiting across the solar disk. Times between Mercurian transits are roughly 7 and 13 years. Similarly, on 8th June 2004, Venus produced a rare transit and will again do so on 6th June 2012. The next dual series will not be for another 120-odd years.


DATE : Month and Date (0h U.T.)
RA : Right Ascension (hour, minutes) in apparent geocentric co-ordinates. Epoch J2000
DEC : Declination (degrees, minutes) in apparent geocentric co-ordinates. Epoch J2000
Vis Mag(v) : Visual Magnitude of the planet at given distance
Diam. : Diameter of the planet measured in (″) seconds of arc
Phase : The amount of illumination of the planetary disk. The value of 1 minus the Phase can calculate the amount unilluminated disk.
Elong. : The angular distance in degrees between the sun and planet centres
Dist (AU) Geocentric distance at 1 Astronomical Unit between the Earth and planets centre.
Rise : Is the rise time of the planet from the given location. I.e. Sydney
Set : Is the set time of the planet from the given location. I.e. Sydney
Trans : Is the local transit time of the planet across the local meridian, and can be used to locate a inferior planet during the daytime.
Elev. : Is the height above the northern horizon of the planet at the local transit time, and can be used to locate a inferior planet during the daytime.
Elev. N : Is the elevation in degrees of the planet, along the local meridian, from the locations true horizon due north.
Elev. Z : Is the elevation in degrees of the planet, along the local meridian, from the locations true zenith.
Con : Is the constellation that the planet lies at the given date and time.


This table gives the general phenomena of Venus for the year. The time is expressed in hours and minutes for the given location I.e. Sydney in Australian East Standard Time (A.E.S.T.)


This table gives the calculated half-phase or dichotomy of Venus for the years 2003 to 2024. Pval is the time, expressed in decimal hours and minutes, for the given location I.e. Sydney in Australian East Standard Time (A.E.S.T.) It is the theoretical time of dichotomy, which may vary by several days when observed through a telescope.

TRANSITS of VENUS (1600 to 2400 AD)

This table gives the calculated transits that have or will occur in the specified time frame. It gives the date of the transit, predicted time of mid-transit in U.T., the length of the chord across the sun measured in arc seconds or ″, and the position angles on the Sun for both exterior ingress (start) and exterior egress (end). Most of these will be unseen by anyone alive to today, but it does show the long term changes occurring in Venusian transits.


The user applying this data for any purpose forgoes any liability against the author. None of the information should not be used for either legal or medical purposes. Although the data is accurate as possible some errors might be present. The onus of its use is place solely with the user.


Last Update : 1st December 2012

Southern Astronomical Delights © (2012)

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