Astronomical Observing and Photography - Joseph Cali


Total Lunar Eclipse
Wednesday May 26th, 2021
A total eclipse of the Moon occurs on Wednesday May 26th.  Unlike the past couple of total lunar eclipses back in 2018, this one occurs at very civilised hours.

The penumbral phase of the eclipse begins at 18:48 but is barely perceptible to the human eye. If you were standing on the Moon, you would see the Sun partially eclipsed. Consequently, the lunar disc is fully illuminated, albeit at an ever-lowering intensity. Because our eyes adapt to different light levels, this cancels out our ability to detect the lower illumination. At the end of the first penumbral phase as the Moon approaches the Earth's umbra or hard shadow, some darkening will be visible on the east limb of the Moon.

The partial eclipse begins at 19:44, totality at 21:11. The Moon only has a shallow passage into the Earth's umbra (shadow) and because of this, totality lasts just 14 minutes finishing at 21:26.  You can probably keep the kids up to watch this one! The partial eclipse ends at 22:52 so you can get to bed early enough to be up for work the next day.

Lunar eclipse contact times courtesy of Fred Espenak http://mreclipse.com
Reproduced by permission, converted from UTC to local Australian Eastern Standard time by Joe Cali

At totality, the Moon will be at 50 degrees altitude. This makes nightscape photography difficult unless you juxtapose a nearby tall object with the eclipsed Moon. Otherwise, you need a very wide-angle lens which in turn will make the lunar disc very small in the frame.

Below are my estimates for exposures required at mid-totality.

Find the combination corresponding to your gear but then bracket several stops around that value. This exposure recommendation is only a guess on my part. The brightness of lunar eclipses varies greatly with many factors including the highly variable atmospheric conditions on Earth. The light you see on the Moon at totality is red because it passes through the Earth's atmosphere.  Varying weather and atmospheric conditions change the absorption greatly from one eclipse to the next. I expect this eclipse to be very bright but use my recommendation as a starting point, review your image and bracket and adjust accordingly.

The above recommendations are just for exposure values, they don't take account of the movement of the Moon during longer exposures.
If you don't have a tracking mounting, don't expose longer than the maximum exposure before movement can be seen. 

For an image viewed on a 2000 pixel wide laptop screen: -
The diagram below shows the size of the lunar disk compared to the uncropped image frame for full frame and APS-C sensors.

Clear skies!

Kind regards

Nightscape Astrophotography & Workshops


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