Your guide to Ireland's skies

Throughout the month of August there is a lot in store for us to observe here in Ireland. Hopefully the summer weather will show itself a little more this month and allow us some cloudless nights to do some stargazing, because this month the Perseids meteor shower is coming around once again. Let’s talk about what this means and what else we can expect to see in August. 

Perseids Meteor Shower

The Perseids meteor shower is one of the most anticipated astronomical events of the year. The Perseids are ongoing now, they run from 17th of July to 24th of August, but the best time to view will be between August 12th and 13th, when it is at maximum. Look for the distinctive “W” of the constellation Cassiopeia in the north-eastern sky. The constellation Perseus can be found just below this. Perseus is the radiant of the Perseids, the point from which the meteors appear to originate. During this period, you can expect to see up to 100 meteors per hour if you observe away from city lights. This is one of the most active and spectacular meteor showers seen on Earth. 

But what is a meteor shower anyway? When you hear the terms comet, asteroid, or meteor it can all get very confusing, so let’s do a brief rundown of all these minor solar system objects and their differences.  

Asteroids

An asteroid is a small, rocky body that orbits the Sun, primarily found in the asteroid belt between Mars and Jupiter. Unlike planets, asteroids are much smaller and most do not have a spherical shape. They can be as small as 1 m or as large as 1000 km in diameter, like Ceres which is the largest asteroid in the belt and is also classified as a dwarf planet. Asteroids are remnants from the early solar system, 4.6 billion years ago, and are considered leftover building materials from the formation of the planets. The gravitational influence of Jupiter prevented these materials from forming into a planet within the asteroid belt and caused them to collide with one another, forming the numerous asteroids we see today. Asteroids have remained mostly unchanged since the formation of the solar system and studying them helps us understand the early conditions and processes that shaped our planetary neighborhood. Asteroids can also pose a potential threat to Earth due to the possibility of collisions. NASA’s DART (Double Asteroid Redirection Test) mission tested the ability to change the trajectory of an asteroid by deliberately crashing a spacecraft into it, specifically targeting the moonlet Dimorphos of the asteroid Didymos in September 2022. Listen to Episode 4 of the BCO Podcast to learn more about asteroids and the dangers they pose to us.  

Comets

Comets, sometimes referred to as dirty snowballs, are small solar system objects made of dust and ice that orbit the Sun. Best known for their long, streaming tails, these ancient objects are also leftovers from the formation of the solar system. Unlike asteroids, we believe comets formed beyond what we call the frost line, where it was cold enough for water and gases to freeze. This is why most comets are found in the far reaches of the solar system. When comets pass close to the Sun, they begin to release gases as they heat up, giving them their distinctive tail. Comets have a wide range of orbital periods, ranging from several years to potentially several millions of years. A comet may be seen from Earth without the aid of a telescope if it is close or bright enough and have been observed and recorded since ancient times by many cultures and religions. Ancient astronomers believed comets foretold the death of kings, or the outcomes of wars. Halley’s Comet is the most famous of the periodic comets we see and is visible from Earth every 76 years. The comet’s last visit occurred in 1986, and it is expected to return in 2061. 

Meteoroids

Lastly, we have meteoroids, which are small space rocks or particles, too small to be an asteroid or comet. These typically come from ejected material from impacts on planets/moons or from asteroids and comets. If a meteoroid enters Earth’s atmosphere it becomes a meteor and will begin to burn up as it falls to the ground.  This can appear brighter than our brightest planet, Venus, and these are what we also call shooting stars. If a meteor survives its fiery descent through the atmosphere and lands, it is then called a meteorite. These terms essentially describe the stages of a space rock’s journey from space to Earth. 

Meteor Showers

So then what happens when a meteor shower occurs? When Earth passes through the trail of debris left by a comet, the left behind meteoroids enter our atmosphere and thousands of shooting stars can be seen in the night sky. Meteor showers occur at roughly the same times each year, as the Earth crosses the same debris trails during its orbit around the Sun. So, despite it seeming as though the Perseids have arrived, it is us who have made our annual return to them. The Perseids come from the leftover debris of Comet Swift-Tuttle, a large comet with an orbital period of 133 years.  

Planets

Venus

Venus will be visible every evening throughout August for around half an hour. Look to the west as the Sun is setting to find it. At the start of the month, it will be visible from 9.30pm. It will stay close to the horizon and near the Sun all month long. We will see it appear earlier each evening as we head through August, but the Sun will be setting earlier every evening too. By August 31st Venus will be visible from around 8.30pm. Venus is often known by two nicknames, ‘The Evening Star’ or ‘The Morning Star’. This is because Venus is the closest planet to us and therefore the brightest object we can see from Earth at night, excluding the Moon. If there is nothing obscuring your view of the horizon, you should easily recognize it as it will become visible before any nearby stars.  

Saturn

If you stay up a little longer you will see Saturn rising in the east just before 11pm from the start of the month. Saturn will enter our sky earlier every night as we head through August, slowly becoming much easier for us to find. By the end of the month, you will see Saturn rising in the east just before 9pm. For any early birds, Saturn will be up all night long travelling across the southern sky and can still be seen in the early hours of the morning. At the start of August, it will fade from view in the southwest just after 5am, extending to 6am by the end of August.  

Mars and Jupiter

Mars and Jupiter are also in the sky, but you will need to stay up a little later to find them. From the beginning of August, they will be rising around 1.30am in the northeast. Throughout the start of the month, it will seem as though Jupiter is chasing Mars until the 14th of August when Jupiter will take the lead. The gap between them will continue to grow and by the end of August Jupiter will rise first, around midnight in the northeast, with Mars following just before 1am. Mars should look slightly red, due to iron oxide on its surface. Mars’s thin atmosphere is often filled with this iron oxide dust from storms on the planet’s surface which enhances its reddish appearance. Jupiter is one of the brightest objects in our night sky due to its size. Being the largest planet in the solar system, Jupiter can reflect much more of the Sun’s light and look even brighter than some of the planets nearer to us, like Mars.  

The planets are quite distinctive compared to stars because they do not twinkle. This is because stars are extremely far away and the light from a star is coming from a tiny source that human eyes are not strong enough to fully make out. Atmospheric turbulence as the light passes through our atmosphere will give the illusion of a star twinkling. Planets do not share this phenomenon because they are much closer to us and therefore appear larger in our sky, so the light reflected off a planet will appear static and unchanging.   

August Rare Moon

This month’s Full Moon on August 19th will be quite a rare event. Not only is this going to be the first Supermoon of the year, but it will also be this year’s first and only Blue Moon. A Supermoon occurs when a Full Moon is at its closest approach to Earth and therefore appears bigger and brighter in the sky. This distance varies throughout the year, and we will be in for a treat with four supermoons from now until the end of 2024. A Blue Moon has two definitions; It can either be the third of four Full Moons in an astronomical season, the seasonal Blue Moon, or the second Full Moon in a calendar month, the calendrical Blue Moon. The second definition for a Blue Moon comes from a misinterpretation of the original but is the more popular, despite being made up in 1946 and having no astronomical significance. The August Full Moon will be a seasonal full moon because we will have four Full Moons this season between the Summer Solstice and the equinox in September. The August Full Moon will be the third of these. The next seasonal Blue Moon will occur on May 20, 2027. 

This month we will be celebrating National Heritage Week across Ireland, from August 17th to 25th. Visit heritageweek.ie to find an event in your area or join us at Blackrock Castle Observatory on August 17th. For more details on this event check here.

If you happen to capture any images while you are stargazing, tag us on social media. Wishing you starry skies!