The Total Solar Eclipse of 18 March 1988. The dark blue region is the path of totality (also known as the umbra).
The umbra shadow travels from west to east (left to right on the map). At the point of greatest eclipse, totality is at local midday. The duration of totality at greatest eclipse is 3 minutes 46 seconds. This occurs in the Pacific Ocean. On either side of that point, the duration is less. To the West of greatest eclipse the eclipse will be total before local noon; to the east, the eclipse will be total after local noon. The umbra is widest around the time of greatest eclipse as the Earth is bulging out towards the Moon in that region.
The blue circlular regions are the positions of the umbra at ten minute intervals. The umbra becomes more circular around the region of greatest eclipse as the meeting between the surface of the Earth and the umbra becomes more perpendicular. The sub-solar point is the location where the Sun is overhead at the time of greatest eclipse. In March this point is close to the equator.
The red regions are the areas where the eclipse occurs during sunrise (left) or sunset (right). The area on either side of the path of totality (in pale blue) provides a partial eclipse, the magnitude decreasing with distance from the path of totality.
The path of totality begins in the Indian Ocean, crossing the islands of Sumatra and Borneo (in Indonesia) and Mindanao (in the Philippines). It then passes into the Pacific Ocean leaving the Earth south of Alaska. The umbra takes 3 hours 7 minutes to traverse its entire path.
Our eclipse site was on the island of Mindanao where the eclipse occured in the late morning.
| Location | General Santos City, Mindanao, Philippines |
| Altitude | 5 m |
| Latitude | 6° 06' 47" N |
| Longitude | 125° 10' 18" W |
| Distance from Centre Line | < 10 km |
| 1st Contact (UT + 8) | 07:51 |
| 2nd Contact | 09:03:30 |
| 3rd Contact | 09:06:48 |
| 4th Contact | 10:26 |
| Duration | 3m 18s |
| Path Width | 171 km |
| Umbral Velocity | 0.8 km/s |
| Solar Altitude | 49° |
| Solar Azimuth | 98° |
| Saros Details | 139 (28 / 71) |
| Gamma | 0.4187 |
| Diameter Ratio | 1.0435 |
The Distance from Centre Line was estimated using a good quality aeronautical map with the path of totality and the centre line plotted from Fred Espenak data.
First Contact is the beginning of the eclipse when the first "bite" appears on the Sun's disk; it is the beginning of the partial phase. Second Contact is the beginning of totality. Third Contact is the end of totality. Fourth Contact is the end of the partial eclipse; we had packed up and moved on by then. The times are in local time which, for this eclipse, is UT + 8 (GMT plus eight hours).
The Duration of the eclipse at the observation site was 3 minutes 18 seconds.
The Path Width is the width of the path of totality. This was 171km, a reasonably large figure that produced a dark eclipse.
The Umbral Velocity is the speed of the Moon's shadow, 800 metres per second. This and the path width determined the duration of the total eclipse.
The Sun's Altitude is measured from the horizon; the Azimuth is the direction of the Sun measured clockwise from North. The figures are for mid-eclipse.
The Saros is a collection of eclipses belonging to a series. Each member of the series is followed by a similar eclipse approximately 18 years, 11 days and 8 hours later. This eclipse is a member of Saros number 139. It is the 28th eclipse out of a total of 71 in the series.
Of these 71 eclipses, 16 are partial, 43 are total and 12 are the normally rare hybrid eclipses.
The series began on 17 May 1501 with a small partial eclipse in the Arctic regions. After six more partial eclipses of increasing magnitude, a series of 12 hybrid eclipses occurred in the northern hemisphere, the first one being less than a second long on 11 August 1627. Hybrid eclipses are both total and annular along section of the central path. The eclipses became purely total on 21 December 1843 with the 20th eclipse of the series. The duration was 1m 43s.
The next eclipse of this series occurred on 29 March 2006 and I saw it in Turkey.
The 39th eclipse of the series will occur on 16 July 2186 and will have the very long duration of 7 minutes 29 seconds, just two seconds short of the theoretical maximum. The final total eclipse of Saros 139 will occur on 26 March 2601 (the 62nd eclipse) and its duratiuon will be 0m 35s. The series will end with nine partial eclipses, the final one being on 3 July 2763 in the Antarctic. The entire series will last for 1262 years.
Gamma determines how the Moon's shadow, if extended, would pass through the Earth. A Gamma of zero implies that the shadow would pass through the exact centre of the Earth. A Gamma of greater than 1 misses the Earth and no total eclipse would occur. A positive Gamma passes North of the Earth's centre; a negative Gamma passes South of the Earth's centre. The value of Gamma for this eclipse is 0.4187. This means that the shadow passes North of the Earth's centre, about four tenths of the way to the edge of the Earth. This, combined with the fact that in march, neither hemisphere is tilted towards the Sun, produces an eclipse mainly in the Northern Tropical and Temperate Regions.
The Diameter Ratio determines how much bigger the Moon's apparent radius is than the Sun's. In this case, the Moon's radius is 1.0435 that of the Sun's. A total eclipse can only occur if this figure is greater than 1. The Moon would then appear larger than the Sun and could cover it completely. If this figure was less than one a total eclipse could not occur because the Moon would appear smaller than the Sun.
