Late in the evening of Wednesday 26 May 2021, the full moon will drift into the path of Earth’s shadow causing the bright lunar surface to darken and change to a reddy-orange colour. This is a total lunar eclipse, otherwise known as a “blood moon”. It doesn’t happen during every full moon phase as the orbital plane of the Moon is tilted compared to the plane of the Earth’s orbit around the Sun. However, we can predict when these alignments will take place allowing those on the night side of Earth to view a lunar eclipse.
What causes a Total Lunar Eclipse?
What causes the red colour?
Phases of the Lunar Eclipse
- Penumbral eclipse begins. The Moon enters the outer regions of Earth’s shadow known as the penumbra. To the casual observer, there is little change in the visible appearance of the Moon. In reality, the Moon is a little dimmer during these phases than during a typical Full Moon.
- Partial eclipse begins. The Moon is entering the central, darker part of Earth’s shadow known as the Umbra. To the observer, the Earth’s shadow appears to be “taking a bite” out of the Moon. This is the partial lunar eclipse phase.
- Total lunar eclipse begins. The Moon is completely covered by the Earth’s umbral shadow. The length of totality will vary depending on how deep the Moon travels through the Earth’s shadow. The Moon will have a red-orange appearance.
- Maximum eclipse. This is the middle of the eclipse and occurs when the Moon is deepest into the Earth’s umbral shadow.
- Total lunar eclipse ends: The Moon starts to exit the umbral shadow.
- Partial eclipse ends. The Moon is clear of the Earth’s umbral shadow. To the naked eye observer, there is little distinction between the end of this phase and the full moon.
- Penumbral eclipse ends. The Moon is completely clear of the Earth’s shadow and is once again fully illuminated by direct sunlight.
The following timings are for Christchurch, New Zealand for the Total Lunar Eclipse starting on Wednesday 26 May 2021. As the eclipse spans midnight, it doesn’t finish until the morning of 27 May 2021. Timings for your own specific location can be easily referenced at timeanddate.com
|Penumbral eclipse begins||8:47 pm||079°||39°|
|Partial eclipse begins||9:44 pm||067°||49°|
|Total eclipse begins||11:11 pm||040°||62°|
|Maximum eclipse||11:18 pm||037°||63°|
|Total eclipse ends||11:25 pm||034°||63°|
|Partial eclipse ends||12:52 am||347°||67°|
|Penumbral eclipse ends||1:49 am||318°||62°|
Viewing the Eclipse
For New Zealand observers, the eclipse will take place with the Moon high in the northern sky. Altitude is measured in degrees with the horizon being 0° and directly overhead (ie the zenith) at 90°. Anyone with clear skies overhead should be able to view the eclipse through its various phases. For the best views during totality, it is recommended to seek out darker skies so that you have a great view of the stars which will also be visible during totality. This particular eclipse happens with the Moon near the constellation of Scorpio which lies near the centre of the Milky Way galaxy – so there should be plenty of stars surrounding the eclipsed moon!
The equipment required will vary depending on the type of image you wish to shoot. As the Moon will be so high in the sky, particularly during totality, incorporating landscape elements in the foreground may be difficult. Therefore the following recommendations assume the photographer would like to make close-up images of the Moon, capturing the progress of the eclipse including the “blood moon” phase at totality.
- DSLR or MILC (or bridge camera with long telephoto capability)
- Telephoto lens (the diagram below compares images of the full moon at various focal lengths for both full frame and crop sensors)
- Sturdy tripod
- DSLR or MILC
- Telephoto lens (min. 300mm for a full-frame camera or 200mm on a crop sensor)
- Tracking mount
- Exposure values will change significantly throughout each of the phases. Short, fast exposures are required to correctly expose for the Full Moon. Increasingly longer exposures are required as the Earth’s shadow darkens the Moon’s surface.
- The Moon will move through your frame if your camera is mounted to a fixed tripod. The longer the focal length, the faster the apparent motion. Periodically re-centre your composition as the sharpest results will be achieved using the centre of your lens. (Be careful not to bump your focus when doing so!)
- Bracket exposures to capture the full dynamic range available. For example, the colour of the Earth’s shadow can be revealed in longer exposures during the partial phases of the eclipse (though highlight details will be overexposed). Taking bracketed exposures will be you full flexibility when processing your images.
- Take exposures at regular intervals to record the progress of the eclipse. If you’re looking to blend images later as a multiple exposure, remember the Moon moves its own diameter across the sky every two minutes. This could be a great way to image the eclipse if you don’t have access to a telephoto lens. A 50mm lens (or wider) would be ideal for this sort of project.
- Use live view at maximum magnification to watch the eclipse in progress. Take your exposures when the Moon is still on the screen – it’s amazing how much even a gentle breeze can cause your lens to move!
Like any other astrophotography, best results will likely be obtained by using your camera in MANUAL mode.
- Manual exposure mode
- Manual focus
- Lens and in-camera image stabilisation OFF (assuming your camera is on a tripod or tracking mount).
- Image format: RAW
- White balance: Daylight (5500K)
- Metering mode: Spot metering (or refer to histogram)
- Bracketed exposures (to increase dynamic range).
- Cable release or intervalometer to operate shutter. Alternatively use the built-in time delay. You want to minimise any camera movement to ensure sharp results.
If this is your first time photographing a lunar eclipse, I’ve outlined a set of base exposure settings that should achieve reasonable exposures. As always, you should vary the settings as required to obtain the best results with your equipment. But these values should give you a good place to start! These figures are referenced from data provided by Fred Espenak at https://www.mreclipse.com/LEphoto/LEphoto.html
|Total eclipse||f/8||1s – 1m||400|
These values are based on setting a fixed aperture and ISO making shutter speed the only variable to manage during the shoot. Please note these won’t necessarily provide the best results though – particularly during totality where you may wish to open your aperture and increase your ISO to reduce shutter speeds in order to prevent trailing of the moon in your image. Depending on how dark the moon gets during totality, you may need an exposure of several seconds, or longer, to record sufficient detail. This is where the advantage of using a star tracker, or telescope tracking mount, comes into play. You’ll have 14 mins of totality to experiment with different settings to get that perfect shot.
Don’t forget to check your histogram periodically to ensure you are preserving highlight detail where necessary.
If you are using a wider angle lens, then longer exposure times will be less of an issue.
Partial Lunar Eclipse through clouds.
An HDR blend of two frames at 300mm, f/5.6, 1/60-0.4s, ISO 400.
Note the red tones visible in the earth’s shadow. (28 July 2018)
The timing of this week’s eclipse (from a New Zealand perspective) means you’ll have plenty of time after sunset to get your gear set-up and dialled in before the main event begins. Take some test shots of the rising Full Moon, ensure your focus is pin sharp and that your other camera settings are ready to go. Even better, practice your set-up and techniques over the next couple of nights so that you can relax a little on the night.
Enjoy the photographic challenges of recording the eclipse but don’t forget to look up and check it out with the naked eye too – it should be a spectacular sight.