A total lunar eclipse is sometimes called a blood moon, because of the reddish tinge the Full Moon takes on when fully eclipsed. The term blood moon is also frequently used to describe four total lunar eclipses that occur in a row. It happens in the span of two years, a phenomenon astronomers call a lunar tetrad. The eclipses in a tetrad occur about six months apart with five uneclipsed Full Moons between them.
Usually, only about one in three lunar eclipses are total, and about four to five total eclipses can be seen from any single location on Earth in a decade. This means that lunar tetrads are rare occurrences, leading some to attach special, even religious, significance to these events.
Lunar eclipses or blood moon can only happen during a full moon, when the sun fully illuminates the surface. Usually, a full moon has no eclipse because the moon orbits in a slightly different plane than the Earth and the sun. However, at times the planes coincide. Earth passes in between the moon and the sun and cuts off the sunlight, causing an eclipse.
A partial lunar eclipse occurs when the Earth moves between the Sun and Moon but the three celestial bodies do not form a straight line in space. When that happens, a small part of the Moon’s surface is covered by the darkest, central part of the Earth’s shadow, called the umbra. The rest of the Moon is covered by the outer part of the Earth’s shadow called the penumbra.
You will see a black shadow taking a bite out of the moon. Sometimes, the moon passes through the lighter part of Earth’s shadow, causing a penumbral eclipse. Only seasoned skywatchers will be able to tell the difference because the moon only darkens very slightly. For a partial lunar eclipse to occur, two celestial events must happen at the same time: A Full Moon and Sun, Earth, Moon must be aligned in almost a straight line.
During a full eclipse, however, something spectacular happens. The moon is fully in Earth’s shadow. At the same time, a little bit of light from Earth’s sunrises and sunsets (on the disk of the planet) falls on the surface of the moon. Because the light waves are stretched out, they look red. When this red light strikes the moon’s surface, it also appears red.
The colloquial term for a total lunar eclipse, it’s something that’s visible from most places on Earth every few years. Totally safe to observe with the naked eye and to photograph, it’s a slow-burning celestial spectacle that most people wait to come to them, though at its peak it’s a dramatic sight as a full Moon shines red, orange and pink. It’s typically the highlight of the astronomical calendar.
Make sure you have all the equipment you need ready to photograph the blood moon. Practice with your setup in advance so you’re prepared when the moment comes. Although there are a few dedicated pieces of kit that you’ll need, most of your equipment should hopefully already be in your camera bag.
To successfully photograph the blood moon up close, you’ll need a DSLR or mirrorless camera that allows full manual control of all settings. Use a sturdy tripod. You’ll need a telephoto lens with a focal length of a minimum of 300mm, but preferably over 600m.
Consider using a teleconverter to extend the effective focal length of the longest lens you have. Entry-level cameras like crop-sensor APS-Cs and Micro Four Thirds cameras have an advantage over more expensive, professional 35mm full-frame cameras in that their smaller sensors produce an effectively longer focal length.
That means a lens’ focal length is up to 1.5x longer than when placed on a 35mm body, making the blood moon larger in the frame. That’s because the smaller sensors only use a portion of the lens’ full diameter when shooting, giving the effect of a longer focal length.
Now find the clear sky. If you have ever seen a night sky picture where there is a lot of orange and gross brown colors near the horizon, then you have seen light pollution. Light pollution can really mess with any image taken of the night sky.
It should be avoided if you are looking for the “cleanest” sky possible. The only way around it is to find a location near to you with little light pollution and go there for the shoot. There are many great tools for finding dark sky near to you.
A shutter release cable will let you take photos without introducing vibrations. If you don’t have one then look for a self-timer or shutter delay mode on your camera so that it opens the shutter a few seconds after you’ve pressed the shutter button. The longer your lens is, the more critical it will be to have zero vibrations in the camera.
The eclipse will begin with a penumbral phase, during which the full Moon will begin to dull. In itself, it’s not exactly an exciting shot, but it is one of the easiest times to photograph the Moon. As a guide, you’ll need a lens at about f/4 and then set your camera to ISO 100 and a shutter speed of about 1/500 seconds.
Though as the blood moon enters, more of the Earth’s shadow you’ll have to up the ISO and increase the shutter speed. Once the Moon begins to enter the Earth’s umbra you’ll see an almost straight line on the lunar surface that divides a darker, browny-orange side of the Moon from a brighter grey side. That’s the curve of Earth!
Autofocus is notoriously unreliable in super dark conditions. While it may work just fine if you are shooting just the bright moon, if you are trying for any sort of artistic composition, your AF can fail you.
What you want to do is manual focus, and you also want to pre-focus on the moon while it is still bright. Once the eclipse starts, the blood moon will become harder to focus on. Do it early so you can focus on other parts of shooting. Another good tip is to focus and shoot using live view.