PLANETARY OCCULTATIONS : Part 8

PLANETARY OCCULTATIONS by STARS

By Andrew James

IOTA (International Occultation and Timing Centre) has made a useful world-wide table of Stellar Occultations by Planets (and their moons) ; Predictions

The following bright example of predictions have been made for future reference. These include;

Planetary Occultations by Stars

Planetary Occultations of First Magnitude Stars

Close Planetary Conjunctions of First Magnitude Stars

Close Grazes by Planet and Stars

MUTUAL PLANETARY OCCULTATIONS

Occultations of planets by other planets do occur. They are generally more frequent than occultations of the first magnitude stars — averaging in series once every forty years. A previous event occurred on the 03rd January 1818 AD by Venus and Jupiter, but to my knowledge was not observed. The next event will again be between Venus and Jupiter on the 22nd July 2065 AD, with an earlier Jovian occultation of Ganymede will take place an hour earlier. Needless to say, this event will be best seen in the southern hemisphere as the declination of both these planets will be fairly well south.

Between these years there is a veritable drought
of observable mutual planetary occultation events.

Events can be either transits or occultations, but common sense says that it depends on the planet being referred too. Clearly the fastest moving planet is likely to be the closest, so that Mercury and Venus will always transit across the disk of any superior planet. This is furthermore complicated with the inner inferior planets, which, depending on which side of the Sun they are, may either transit or be occultated. I.e. When Venus is closer than Mercury to us, Venus will transit across Mercury, whereas if Venus on the opposite side of the Sun, Mercury will be in transit. Events are more likely to take minutes (instead of hours) “ especially for Mercury or Venus, because they are usually moving rapidly against the background sky. It is possible for events to occur more slowly when the planets are near the points in the change of direction near the times beginning or ending their retrograde motion.

Observations of minor planets are possible. In this instance these are highly important as they can determine the size of the asteroid directly. Predictions of planetary occultations are infrequent often given with their stellar counterparts in an ephemeris or yearbook.

Like any of the transits of Venus and occultations of planets, there are four main Contact Points. The first two are called the ingress, while the last two are the egress. Each point of contact is made from the outer and inner parts of the transiting planetary disk, touching one edge then the other. Similarly when the disk leaves the planet, the reverse occurs. Seen from Earth, the times and general circumstances of the position angles (PA) of the four contact points will vary only by several minutes This is caused by the slight parallax shifts between different observe locations. Useful timings of each of the planetary limbs contacts could be used to determine planetary diameters, but as now and in the future, the sizes of the planets have been obtained with enough precision by many interplanetary satellites.

Between 1700 AD and 2200 AD, there are only eighteen (18) calculated mutual planetary transits and occultations.

MUTUAL PLANETARY EVENTS

NOTE: I have taken the above table directly from Jean Meeus, and checked each with the software program Voyager 4 and Red Shift 4.

Unfortunately, especially with mutual events with Mercury and Venus, many of the will only lie close to the Sun to be properly observed. (Most from my own location in Sydney either occur in daylight or are below the horizon.) For any particularly location to see an predicted evening or nighttime event you would have to be in the right place at the right time. In any case, most of these mutual occultation events will not happen in most of any readers lifetime. (Except if you are younger than about twenty years old!) Unfortunately, the next event will be mostly unobservable as both Venus and Jupiter will be less than 8°W from the Sun — too dangerous for visual observing. It will also not be visible in Australia, as the mutual planetary occultation will occur when it is below the horizon.

Only two events have received much notoriety in the literature. One of the first appeared in Chinese records where an event between Mars and Jupiter on the 12th September 1170 AD, however, this was only visible to the naked-eye and the observers would have no means of ascertaining if an true occultation occurred unless there was a slight but short increase or decrease in brightness. According to some sources, this same event was also made by a monk in Canterbury, England. (Though admittedly, I have never sighted the source document, myself.) Regardless, this 1170 AD event at the time would have more of an astrological significance than any astronomical one!

From various sources, the only other event I have read about was made by John Bevis at Greenwich Observatory on the 28th May 1737. This event was of Venus and Mercury, where there are some fairly detailed telescopic accounts. There has been some debate on the validity of these observations, by they remain perhaps the only event ever recorded.

Disclaimer : The user applying this data for any purpose forgoes any liability against the author. None of the information should be used for either legal or medical purposes. Although the data is accurate as possible some errors might be present. Onus of its use is placed solely with the user.

Last Update : 10th October 2012

Southern Astronomical Delights © (2012)

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