Royal Astronomical Society of New Zealand Eclipses and Transits

Eclipses

A Solar eclipse takes place when the Moon passes in front of the Sun as seen from somewhere on the Earth.  The distance of the Moon from the Earth varies - the closer the Moon is, the larger it appears to be.  When the Moon is at its closest to the Earth (near perigee) it appears large enough to completely cover the Sun.  If this happens a total eclipse of the Sun can be seen - if you are at the right place on the Earth.  At times when the Moon is more distant from the Earth its apparent size is slightly less than that of the Sun.  In which case if an eclipse occurs there will be a ring of sunlight surrounding the dark silhouette of the Moon resulting in an annular eclipse.  Annular eclipses are more frequent than total eclipses, because even at its average distance from the Earth, the Moon is not quite large enough to completely cover the Sun's disk.

Solar eclipses can only occur at the time of New Moon.  However at most New Moons, the Moon either passes above or below the Sun as seen from the Earth, hence the Moon's shadow misses the Earth.

A Lunar eclipse takes place when the Moon moves through the shadow of the Earth cast by the Sun.  Since the Moon shines by reflecting Sunlight, it is darkened during the eclipse.  The Earth being nearly four times the diameter of the Moon, its shadow is also larger than the Moon's.  It is big enough for the entire Moon to be immersed in the shadow.  This contrasts with a the shadow of the Moon on the Earth causing a Solar eclipse, where the area where the Sun is completely hidden will only be of the order of 100 km across at the most, and during an annular eclipse it is reduced to nothing.

When a Lunar eclipse occurs, it is visible from half of the Earth at any moment.  This contrasts with a Solar eclipse where the area from which a total or annular eclipse is visible is only of the order of a hundred kilometres across, although a partial eclipse will be visible over a considerably larger area, although still much less than half the Earth's surface.  As a result from any one place on the Earth's surface you will see many more Lunar eclipses than Solar eclipses.  Despite this, taking the Earth as a whole, there are more Solar eclipses than Lunar eclipses: in effect the Earth is a larger "target" for the Moon's shadow, than the Moon is for the Earth's shadow.

Lunar eclipses can only occur at the time of Full Moon.  However, just as in the case of Solar Eclipses, at most Full Moons  the Moon passes either just above or below the Earth's shadow and so no eclipse occurs.

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To the west of Cairns, the Sun will rise already partly eclipsed. For observers in Arnhem land to the east of Darwin, across the Gulf of Carpentaria and the York Peninsula, the partly eclipsed sun will rise before totality. Further west still the Sun will also be partly eclipsed as it rises, but this will be after maximum eclipse.

Only near Cairns will the Sun rise just before the start of the eclipse so that all phases of the eclipse can be seen.

After Cairns the path of totality crosses the Tasman sea to the south of New Caledonia, just north of Norfolk Island, where the Sun will be 98% eclipsed at maximum. The path continues in a south-easterly direction passing between New Zealand and the Kermadecs, with North Cape New Zealand and the Kermadecs seeing a 91% eclipsed Sun.

The path continues in an easterly direction across the south Pacific but in no place will it again touch land. Cairns will be the only place on land to see full totality. Here the partial phase will start with the Sun about 1° up. Totality will last a second or two more than two minutes with the Sun at 13°.

The following year, 2013 May 10, a near sunrise annular eclipse will cross the York Peninsula a little to the north of Cairns.

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Next Total Solar Eclipse in New Zealand.

There are two further total eclipses for New Zealand within a decade, in 2037 and 2038. In addition nnular eclipses cross the country in 2035, 2042 and 2045. Solar eclipses in New Zealand to 2050.

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Total Lunar Eclipses Visible from New Zealand

The table shows a list of total eclipses of the Moon up to 2080 at which all or part of the totality is visible from New Zealand. Dates are as in New Zealand, most straddle local midnight, so a double date is shown. In a few cases where the Moon sets during the eclipse, the eclipse does not start until after midnight, so only the date of the morning is shown.

The length of totality gives a measure of the centrality of the eclipse. The longest in the list is the eclipse for 2000 which lasted 107 minutes.

Data obtained from David Herald's WinOccult program.

Conditions necessary for an Eclipse to Occur

Recurrence of Eclipses.  After 18 years (more accurately 6585 and a third days, i.e. 18 years and 11 and a third days) the Lunar nodes return to the same place and so similar eclipses occur.  This period of time is known as the Saros.  Because of the third of a day involved the positions of the eclipses on the Earth's surface move round by about 120° of longitude.  Thus similar eclipses recur at a similar position on the Earth after 3 Saros.  Even then there are changes to the latitude.

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