Sky Matters: It's August so it's time to look out for Perseids

This month the most famous meteor shower — the Perseids — will peak on the evening of August 12

Sat, 02 Aug, 2025 - 17:05

Niall Smith

We are very fortunate to live at a time in human history when we have a comprehensive understanding of many of the objects in the night sky; how they came into being and how — and when — they will cease to exist.

Much of what we know, we have learned only in the last 150–200 years. The path to this knowledge has been far from straightforward. It is littered with theories that failed to stand up to close scrutiny, with observations that only told part of the story and indeed sometimes led us on the celestial equivalent of a wild goose chase. Nevertheless, through the fundamental self-correcting approach that is the very essence of the scientific method, only the best theories, supported by the best observations, have survived and brought us to where we are today.

There is absolutely nothing truly complete in our understanding of even the most common objects in the universe, such as stars or planets, and there will surely be twists and turns ahead as new theories and new observations challenge aspects of understanding which we feel confident about today. That is exciting! It is a characteristic of the scientific method, not a bug.

During August the most famous meteor shower — the Perseids — will peak on the evening of 12th.

We know meteors are caused by small particles, typically of the size of a grain of sand, as they burn up in the Earth's atmosphere in a second or two. We know that those which show colours do so because they cause molecules of oxygen and nitrogen in our atmosphere, primarily, to glow momentarily. Or sometimes because of the vaporisation of the material in the meteors themselves.

We know the particles from the Perseids come from the tail of a comet called 109P/Swift-Tuttle which takes 133 years to orbit the sun once — a discovery made in 1865 by the Italian astronomer Giovanni Schiaparelli. So you’d be right to think we actually know quite a lot about them.

Perseid meteor trail. Time exposure showing a trail of a Perseid meteor against a starry sky at dusk. The Perseids are meteors seen around August 12 each year, and which appear to originate from the direction of the constellation Perseus. These meteors are small dust particles from an orbiting dust belt known as the meteor stream. As the Earth passes through the stream, a large number of dust particles enter the atmosphere and burn up, creating a bright trail. At its peak, the Perseid shower has about one meteor per minute. This photograph was taken in British Columbia, Canada.

Yet there remains a thrill in simply going outside and looking up expectantly until a Perseid flashes across your vision. Observing the death of a grain of sand that may have been wandering the solar system for more than 4 billion years may not advance our scientific knowledge, but it has a way of connecting us as humans to the greater cosmos with minimal preparation on our part.

To paraphrase the great astronomer-communicator Carl Sagan, it does nothing to the romance of the Perseids to know a little bit about them.

Roll the clock back a few hundred years and those same Perseids had no scientific explanation. Yet they were just as visible to our ancestors as they are to us today.

Alongside comets and other meteor showers, Perseids were recorded in mythology, including Irish mythology. Medieval Irish annals such as the Annals of Ulster, Four Masters, and Annals of Tigernach recorded comets — “long-haired stars” and associated them as omens heralding disasters, famine, wars or death. Irish medieval monks who copied and preserved ancient texts recorded “wonders in the sky” as signs from God — noting flaming swords, burning stars, or falling fire. Some of these may well refer to brighter, rare meteors of a centimeter or more in size, though we can’t be sure.

'Falling stars' were considered a curse or a blessing depending on local traditions. In some cases they may have been linked to archaeological sites such as ring forts or dolmens. In other cases they were associated with a soul going to heaven, or perhaps a visit from a divine being from the 'otherworld' — rarely considered a good thing! More latterly, a meteor was an opportunity to make a wish.

Far from a momentary flash of light in the night sky, meteors are a reminder of the advancement of human thought and the power of celestial phenomena to brighten up our lives — quite literally.