A total lunar eclipse following the so-called supermoon will occur on September 27 bringing the rare phenomenon of four consecutive total eclipses – known as a “tetrad” – to an end.
Late in the evening of September 27 the moon will venture very close by our planet and appear much brighter and bigger than usual. After that the supermoon will be completely eclipsed, since the Earth will stand directly between the moon and the sun. After about an hour and a half the celestial body will become visible again.
As a rule, total eclipses do not have a specific order of occurrence. However, when four total eclipses happen in a row in an approximately six month interval, it is called a lunar tetrad (from the Greek word for “four”). Astronomers have calculated that the number of such tetrads varies from century to century. The current century will have eight of them, which along with the 16th, ninth, and 26th centuries will be an absolute maximum.
The next lunar eclipse tetrad is scheduled for April 25, 2032.
©2015 NASA Science
Why do Total Lunar Eclipses happen?
During a total lunar eclipse, the Sun, Earth and Moon form a straight line. The Earth blocks any direct sunlight from reaching the Moon. The Sun is behind the Earth, so the Sun’s light casts the Earth’s shadow on the Moon. This shadow covers the entire Moon and causes a total lunar eclipse.
Sun, Earth and Moon Aligned
For a lunar eclipse to occur, the Sun, Earth and Moon must be roughly aligned in a straight line. If the Sun, Earth and Moon do not align, the Earth cannot cast a shadow on the Moon’s surface and an eclipse cannot happen.
When the Sun, Earth and Moon are not perfectly aligned, only the outer part of the Earth’s shadow covers the Moon. Such an eclipse is called a penumbral lunar eclipse. In a total lunar eclipse, the Earth’s umbra completely covers the Moon.
The Earth’s umbra is about 870,000 miles (1.4 million km) wide.
©2015 NASA Science
Only at Full Moon
Total lunar eclipses happen only when:
- The Sun, Earth and Moon are in a straight line.
- There is a full Moon.
This total lunar eclipse will be visible from most of North America, South America, Europe, west Asia and parts of Africa.
The eclipse will last for 3 hrs and 20 mins from beginning to end. The Moon will be totally eclipsed (totality) for about 1 hr and 12 mins.
When the eclipse happens
Lunar eclipses look approximately the same all over the world and happen at the same time.
| Event | UTC Time | Time in Halifax* |
|---|---|---|
| Penumbral Eclipse begins | Sep 28 at 12:11 AM | Sep 27 at 9:11 PM |
| Partial Eclipse begins | Sep 28 at 1:07 AM | Sep 27 at 10:07 PM |
| Full Eclipse begins | Sep 28 at 2:11 AM | Sep 27 at 11:11 PM |
| Maximum Eclipse | Sep 28 at 2:47 AM | Sep 27 at 11:47 PM |
| Full Eclipse ends | Sep 28 at 3:23 AM | Sep 28 at 12:23 AM |
| Partial Eclipse ends | Sep 28 at 4:27 AM | Sep 28 at 1:27 AM |
| Penumbral Eclipse ends | Sep 28 at 5:22 AM | Sep 28 at 2:22 AM |
* The Moon is above the horizon during this eclipse, so with good weather conditions in Nova Scotia, the entire eclipse is visible.
Note: most articles put this Total Lunar Eclipse on September 28th, 2015. This is because times are referred to in UTC (Universal Time Coordinated). For Nova Scotia with a time zone of UTC-3 (during DST) this event still occurs on September 27th.
[Feature image © Darrin Zammit Lupi/Reuters ]