Throughout the month of August there is a lot in store for us to observe here in Ireland. At the beginning of the month we will see sunset just at around 9.20 PM and sunrise at 6 AM. By the end of the month sunset will be at 9.20 PM and sunrise at 6.45 AM. 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 and we have plenty of planets to observe. 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 August 12th, 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 asteroid, comet, or meteor it can all get very confusing, so let’s do a brief rundown of 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 relatively 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 threat to Earth due to the possibility of collisions.
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, 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 approximately 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.
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
Saturn will be visible every night throughout August. Look to the East at around midnight at the start of August to find it. Saturn will enter our sky earlier every night and by the end of the month it will rise at 9.30 PM. Saturn will be up all night long travelling across the southern sky until sunrise.
Venus 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, Venus will rise at around 3 AM in the east, followed about 20 minutes later by Jupiter. Throughout the start of the month, it will seem as though Jupiter is chasing Venus until the 12th of August when Jupiter will take the lead and we see them pass each other in the sky in what’s known as a conjunction. The gap between them will continue to grow and by the end of August Jupiter will rise around 2 AM, with Venus following at 3.45 AM. Venus is the closest planet to us, and Jupiter is the largest planet in our Solar System, so they both appear very brighter than any star in the night sky.
If you are willing to get up just before sunrise, you may be able to spot Mercury too. Mercury has a very short orbit and is the closest planet to the Sun. This makes it very hard to spot as it is often shielded from our view on Earth by the Sun itself. Towards the end of August however, Mercury will be visible from a short time before sunrise in the east. On August 19th it will rise 2 hours before the Sun.
If you happen to capture any images while you are stargazing, tag us on social media. Wishing you starry skies!
Blog post written by Jane Dooley