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Today we are going to be looking at the penumbral lunar eclipse happening later this month. For us here in Ireland, we are only going to see the first half or so of this eclipse. We will see the Moon move into the edge of the Earths just before it sets, so we won’t get to see it move out of our shadow. As we are seeing it at moonset, that means that we are seeing it very early in the morning, just before sunrise. So although we will see the Full Moon rising on the evening of the 24th, it is the morning of the 25th when we will see part of this eclipse. This of course means looking over towards the West, and clearer your horizon the more of the eclipse you will see. As with so many things, it will also look a little bit better in the countryside, the change in brightness should be a little more obvious.

A penumbral lunar eclipse is when the Moon moves through the edge of the Earth’s shadow. Thanks to the massive size of the Earth and the Sun, there is a large, partially shadowed, ring around our true shadow or umbra. While our umbra blocks out all of the Suns light, the penumbra is the region where only some light is blocked. The ring of the penumbra is pretty narrow, so usually penumbral eclipses are partial eclipses, with some of the Moon staying outside of the Earth’s shadow altogether, or they are partial eclipses where some of the Moon touches the really dark umbra. The Earths umbra is directly in line with the Sun, meaning that the Moon is almost directly behind us when it is in our penumbra. Thanks to the nature of the Moons orbit, it must line up with the ecliptic twice a month. If the Moon lines up with the Earth, or almost does, when it is behind us, then that means it is likely to line up again in front of us. This often leads to solar and lunar eclipses happening together as a pair. The eclipse that we’re seeing at the end of March is connected or related to the solar eclipse occurring on the 8th of April.

The relationship between solar and lunar eclipses can be complicated. Similar kinds of eclipses tend to occur following a certain pattern, repeating about once every 18 years. This 18 year cycle is the Saros cycle, and many of them can be running at the same time, matching up different eclipses. Usually, similar eclipses will reoccur every Saros. In between there will be other eclipses, usually of different types, on their own Saros cycle. A Saros series is a collection of these Saros cycles, following the changing types of eclipses, from penumbral to total, partial to annular, over thousands of years. The locations where these eclipses will be visible will also shift across the globe as these eclipses occur. These cycles can help, not only to calculate when an eclipse will occur, but what it will look like and where it will be visible from.

Looking at this eclipse under pretty bad conditions, viewing it near the horizon, at sunrise, with light pollution, it is still absolutely possible to see one side of the Moon beginning to darken. Without light pollution to worry about it should be even easier to see. Taking a look at the Moon with no atmosphere in the way would also remove the glow of sunrise, helping us to see the eclipse for longer, but it also has the effect of changing the apparent position of the Moon. Our atmosphere refracts light just like water, and this bending of the light changes the apparent position of objects in our sky. For example, we get to see the Sun in the morning a bit before it is truly above the horizon because the air bends the Sun’s light, making it appear higher in the sky. This is similar to why straws or pencils appear to be bent if they are resting in water. This is also one of the reasons spear fishing is so hard, you need to aim for where the fish really is, accounting for the refraction of the light. Removing the atmosphere should make the Moon appear to set a little earlier than it other wise would, but of course if the Earth really lost its atmosphere then that would be the least of our worries.

For most lunar eclipses, being close to the equator is going to give you a good view, especially close to the equinox as we are right now, as the Moon will appear to pass almost directly over head. Solar eclipses can be a little more finicky, as the Moon may block the Sun better on certain hemispheres, the shadow of the Moon won’t necessarily follow the subsolar point. This means that sometimes a solar eclipse will be occurring on your longitude but not on your latitude. Lunar eclipses are usually visible all along the longitude that they are occurring at, but of course the Moon will appear much lower in the sky from higher latitudes and this can make it a bit trickier to observe. We want to get the best possible view so we will be heading to the equator. The peak of this eclipse will occur when the Moon is over about 100 degrees West, but with the Moon being so high above us, it will be visible across a broad span of the planet. The Peak of the eclipse will be visible as the Moon sets for Eastern Brazil and rises for Western Alaska. Right in the middle at the equator is pretty close to the Galapagos Islands so that is where we will go.

Here I am calling it the peak of the eclipse, what would be the totality for a total solar eclipse. Totality can be used for total lunar eclipses as well, and this penumbral eclipse will reach close to 95% covered by our penumbra. This moment of totality should be right overhead if you are at the right longitude, where as those of us in the wrong places will see the Moon set or rise just after this point. For locations right in the center of the eclipse, you will see the shadow of the Earth slide on to the Moon, almost completely cover it, and then slide off the other side as the Moon moves out of our shadow. That is the view we will get from the Galapagos, and the Moon will be almost directly over head at the moment that it is almost fully covered. Looking at the Moon from the equator, or just south of the equator as it is in the video, does make the Moon appear a little different. It will look almost upside down and will appear to twist as it progresses across the sky, but of course this is just an illusion caused by the change in our viewing position.

Thanks to our observation of the eclipse from Ireland, we can see when the Moon is shadowed by the same amount in this new location, giving us an idea of when the Moon would be setting in Ireland. We can then continue to watch the eclipse without worrying about the Moon setting. As the eclipse is only penumbral, the Moon will look a little dimmer, but not red. The lovely red colour of a total lunar eclipse is really only visible when the Moon is in our umbra, and even then it is most obvious for total eclipses. Penumbral eclipses are a little harder to notice, even under ideal conditions. Penumbral eclipses do also have a solar equivalent, but these are usually just referred to as partial solar eclipses. If there is a total solar eclipse happening near you, but from your location it only looks like a partial, then you are in the penumbra of the total solar eclipse. If there is no total eclipse, only a partial, then anybody seeing it is in the penumbra, but these are usually just called partial solar eclipses.

A total solar eclipse only looks like one if you are under the umbra, and this is where the sky will look like night time in the middle of the day. It doesn’t just look like night time, it often feels like night time as well, thanks to a drop in temperature. Animals often feel like it is suddenly night time as well, which can lead to some strange behavior such as nocturnal creatures emerging by accident. It is usually the umbra of the Sun that people who chase eclipses are usually looking to see, and some people really do chase it. Travelling across your home country to catch an eclipse is one thing, but many people will travel hundreds of miles. Occasionally, an eclipse will occur in the Antarctic or the middle of the Pacific Ocean, and dedicated eclipse hunters will follow the umbra even there. People who truly love the shadow are known as umbraphiles, just like book lovers can be called bibliophiles. With enough effort and time, some people have seen numerous eclipses during their lifetimes, mostly thanks to the modern transportation network that they can avail of in the modern day. Before international travel, total solar eclipses were much more likely to be seen only once in a lifetime, even if many occurred scattered around the globe.

I will talk more about solar eclipses once we get closer to April 8th and the solar eclipse that will be visible from North America on that date. Unlike this one, it won’t just look better elsewhere, it will be completely unobservable from Ireland. With this partial penumbral lunar eclipse, at least we have a chance to see some of it. Of course, if you keep up to date with my articles and videos, I will give us a perfect view of the upcoming eclipse, no matter where you are. If you’d like to be kept up to date, then you can subscribe to this website or the Caoimhín’s Content YouTube channel to be notified when I post, and hopefully you’ll be back here for those upcoming events.