Southern African Solar Eclipse of September 13, 2015

Partial solar eclipse seen from New Zealand in 2008. (Credit: Greg Hewgill)

Observers in southern Africa will enjoy a partial solar eclipse this weekend on September 13, 2015. This eclipse will be visible from all parts of South Africa, southern parts of Madagascar, Mozambique, Zambia, and Zimbabwe. It will also be visible for the very few observers over a wide area of the Indian Ocean and Antarctica. This is a partial eclipse– not total– so sky and Earth will not darken completely, and you will need proper solar filtering to enjoy this event.

The further south you are, the more you will see the Sun’s face covered by the Moon. On the coast of Antarctica, at the point of maximum eclipse, about 78% of the Sun’s face will be covered at 6:54 UT. In Cape Town, about 43% of the Sun will be covered at 5:43 UT. In Johannesburg, about 25% of the Sun at roughly the same time. The eclipse will begin about an hour before these times, just as the Sun and Moon are rising, and end about an hour after maximum coverage.

Visibility of the solar eclipse of September 13, 2015 (NASA/Fred Espenak).

The folks at GreatAmericanEclipse.com also have a good map to show you where the eclipse is visible in southern Africa.

During this entire event, the Sun will be far too bright to observe with your eyes, so don’t try! You will need a proper solar filter. A piece of #14 welder’s glass will work if you are just watching with your eyes. A white-light solar filter will do the job with a telescope.

If you don’t have a solar filter or a telescope, you can poke a pin hole in a piece of paper and let the Sun shine through the hole onto another piece of paper. This makes a small and faint image, but it works in a pinch. Again, don’t look directly at the Sun if you use this projection method.

With the Sun covered by 10% to 45% during this eclipse, you’d think the land and sky would become darker. But most people do not detect such darkening because the human eye adapts to the changing illumination. In my experience, you don’t really notice much darkening until the Sun gets 85% to 90% eclipsed. But you may notice the sky becomes a darker and purer blue.

If you see the eclipse through a properly filtered telescope, have a look at the sunspots. You may notice they appear greyish-black rather than pure black compared to the Moon. That’s because sunspots appear dark because they are cooler than the visible face of the Sun, about 4,000 K compared to the Sun’s average temperature of 5,700 K. Also look along the limb of the Moon for the slightly jagged outline of lunar mountain ranges silhouetted against the Sun.

If you find yourself in a location where the Sun sets during the eclipse, find a good location to try grab an image if the Sun is well attenuated by clouds or if you have a solar filter for your camera lens. It makes for a great photo-op… but make sure the Sun is not too bright when you try an image because it can damage the camera sensor.

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