We are all familiar with total solar eclipses and perhaps less so with total lunar eclipses. The latter is when the Moon passes into the shadow cast by the Earth and so it grows dimmer from our view than usual.
The Earth’s shadow, due to the way the light is blocked by our planet, falls into two parts. The darkest part of the shadow is called the umbra and therefore, when the Moon occasionally passes through this, we see a total lunar eclipse. However, unlike you would expect, the Moon does not go completely dark, but instead glows a deep orange colour due to some light being bent and passed through the Earth’s atmosphere.
A penumbral eclipse however, is much harder to see, as this part of the Earth’s shadow is much fainter. The Earth blocks some of the Sunlight reaching the Moon but not all of it. This can make it hard to tell with the naked eye that it is even happening, but you can record the eclipse with a camera. This will show you when the Moon is in the Earth’s penumbral shadow and when it isn’t.
Eclipses, both umbral and penumbral, only occur at the full Moon phase, when the Sun, Earth and the Moon are almost exactly in alignment. Penumbral events occur when the alignment is almost exact but not quite, otherwise we would see a total or umbral lunar eclipse.
This evening, the eclipse will start at 16:54 UTC (add one hour for BST), although it will not be visible in western Europe at this time, as the Moon will not be above the horizon.
However, mid-eclipse will occur at 18:54 UTC and so will be visible from western Europe at this time. The eclipse will end at 20:53 UTC. To see the full effect of the penumbral eclipse, it is worth taking a series of photographs with your DSLR camera. It’s best to space out your exposures at intervals of, say, 20 minutes throughout the course of the eclipse.
If you don’t want to take a series of photographs, then you can just take two images: one at mid-eclipse and another once the eclipse is over. This will show the difference in brightness of the lunar surface during and after the eclipse. A series of shots though will show the progress of the eclipse across the face of the Moon.
Shoot a penumbral lunar eclipse
To ensure that you get really good images at the time of the eclipse, take some test images with your camera on the evening before the event. This will give you an idea as to what settings to use regarding exposure time and the focal length of the lens or the setting on your zoom lens. Good focus is really important, so use your view screen at maximum magnification to make sure that your focus is as sharp as it can be. Don’t make the image too bright. It’s better to slightly under-expose than overdo it!
Step 1: Pick your observing site
Check the time of Moonrise as well as the maximum eclipse. It’s also important to know when the eclipse finishes for your observing site.
Step 2: Be aware of exposures
Work out the number of exposures you want to take during the penumbral eclipse. One every 20 minutes can work really well.
Step 3: Stay in focus with high magnification
Make sure that you have good focus. Use the high magnification on the camera’s view screen to help keep your focus sharp.
Step 4: Be consistent
The Moon will get brighter as it climbs in altitude. Do allow for this, but keep your exposure time the same throughout the eclipse.
Step 5: Image every 20 minutes
Take a series of exposures every 20 minutes to show the progress of the eclipse. Be sure to keep a note of the time of each shot.
Step 6: Enhance in Photoshop
If you process the images in software such as Photoshop, be sure to apply the same processes to every image to ensure consistency.