The Partial Lunar Eclipse – 19 November 2021

For the second time in 2021, the full moon will drift into the path of Earth’s shadow causing the bright lunar surface to darken and change to a dark reddy-orange colour.  On 19 November, we will see a partial lunar eclipse, however it will be one of the deepest such events for centuries, only narrowly missing out on achieving totality.  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 Partial Lunar Eclipse?

The alignment of the Sun, Earth, Moon system is such that the Moon is partially covered by the Earth’s shadow.  Any direct sunlight is blocked by the Earth.  Refracted sunlight, passing through the Earth’s atmosphere, is bent towards the surface of the Moon.  This indirect light is what allows us to see the Moon during the totality phase.

What causes the red colour?

Typically, a partial eclipse is seen as a dark shadow falling across part of the lunar surface, while the rest of the surface maintains its typically bright appearance.  This time however, during the peak of the eclipse, 99% of the moon’s surface will lie in shadow so even though it’s not quite total, we should still see the red tones associated with a total lunar eclipse with just a narrow edge of the moon in bright sunlight.  The beautiful, mysterious red colour is due to the scattering effect of sunlight passing through the Earth’s atmosphere – blue wavelengths of that light are scattered (that’s how we get a blue sky during daytime) while red wavelengths are “bent” (refracted) by the atmosphere and turn the Earth’s shadow a dark red colour which then falls across the lunar surface during the phases of the eclipse.

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.
  • Maximum eclipse.  This is the middle of the eclipse and occurs when the Moon is deepest into the Earth’s 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.

Eclipse Timings

The following timings are for Christchurch, New Zealand for the Partial Lunar Eclipse starting on Friday 19 November 2021.  Technically, the eclipse finishes just after midnight though the penumbral stages are difficult to observe with the naked eye.  Timings for your own specific location can be easily referenced at timeanddate.com

Phase NZDT Direction Altitude
Penumbral eclipse begins (below horizon) 7:02 pm
Partial eclipse begins (below horizon) 8:18 pm
Moonrise 8:29 pm 063° ENE
Maximum eclipse 10:02 pm 046° NE 13°
Partial eclipse ends 11:47 pm 023° NNE 23°
Penumbral eclipse ends 12:03 am 004° N 26°

Viewing the Eclipse

For New Zealand observers, the eclipse will already be underway as the Moon rises on the eastern horizon.  Altitude is measured in degrees with the horizon being 0° and directly overhead (ie the zenith) at 90°.  Anyone with clear skies to the North/Northeast should be able to view the eclipse through its various phases.  For the best views during maximum eclipse, it is recommended to seek out darker skies so that you have a better view of the stars which will also be visible during totality.  This particular eclipse happens with the Moon just a few degrees from the star cluster Matariki (the Pleiades)!  Remember that the timing of the eclipse for NZ viewers means the sky will gradually darken after sunset but there will still be quite a bit of lingering twilight about.

Photographic Equipment

The equipment required will vary depending on the type of image you wish to shoot.  As the Moon will be low in the sky, incorporating landscape elements in the foreground may be possible.  As most of the eclipse occurs during blue hour, typical landscape settings can probably be used as a starting point to good effect.

The following guidance assumes the photographer would like to make close-up images of the Moon, capturing the progress of the eclipse including the red moon near-totality.

Minimum equipment:
  • 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
  • Intervalometer
  • Headlamp
Recommended equipment:
  • DSLR or MILC
  • Telephoto lens (min. 300mm for a full-frame camera or 200mm on a crop sensor)
  • Tracking mount
  • Intervalometer
  • Headlamp

Photography Considerations

  • 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 give 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.  Frame your view so that you can photograph the rising Moon in the east and watch as it rises higher into the sky, moving left through your frame as it does.
  • 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!

Camera Settings

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.

Exposure Settings

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

 

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 nearing maximum eclipse 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.  This is where the advantage of using a star tracker, or telescope tracking mount, comes into play.  You’ll have a few minutes around the time of maximum eclipse 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.

Phase Aperture Shutter Speed ISO
Penumbral Eclipse f/8 1/1000s 400
Partial eclipse
0% f/8 1/1000 400
30% f/8 1/500 400
60% f/8 1/250 400
80% f/8 1/125 400
90% f/8 1/60 400
95% f/8 1/30 400
Maximum eclipse f/8 1/30 - 1s 400
Full Moon f/8 1/500 100

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)

Summary

The timing of this week’s eclipse (from a New Zealand perspective) means you’ll need to have your gear set-up before moonrise and sunset.  Take some test shots of the rising Full Moon (noticing the Earth’s shadow has already started taking a “bite” out of it), ensure your focus is pin sharp and that your other camera settings are ready to go.  Even better, practice your set-up and techniques tonight 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.

Clear skies!

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