Periodically throughout the year, the sky lights up with meteor showers. A few of these attract attention, either for providing a relatively consistent supply of “shooting stars”, like the Perseids, rare breathtaking outbursts (Leonids), or unusually slow meteors (Geminids). Meanwhile, many other showers tend to be overlooked.
Moreover, some showers last for quite a long time but are usually only discussed around their peak. That's not so surprising when you consider most people willing to journey far from city lights to sit in a dark field want to be rewarded with lots of meteors, which means choosing the brighter showers’ maxima.
However, as Space.com first highlighted, not only are there many lesser-known showers, but the next week sees six of these coincide, albeit at low levels in most cases. The only other part of the year where so many showers overlap is in early December, usually when it is too cold for many people to go outside.
Overlapping showers increase the number of shooting stars one can hope to see. It also means the very observant may be able to identify which shower a meteor comes from, or if it is from no shower at all, and even compare the composition of each shower.
Some of these showers are also restricted in latitude so you’ll need to be in the right location and be blessed with dark skies.
What Is A Meteor Shower?
Meteors occur when bits of dust, grains of sand, or pieces of gravel enter Earth’s atmosphere. Occasionally something even larger makes for a really bright display. The speed of entry produces enormous friction with the atmosphere, leading to the incoming object burning up, releasing plenty of light (and sometimes smoke) in the process.
About half the meteors are “sporadics”, coming from random directions in the sky with unpredictable timing. The other half appear to come from specific points in the sky at certain times of the year. These are known as showers, other than very rare cases where they are so abundant they’re called meteor storms.
Showers are the product of comets or asteroids that broke up, leaving patches of material following a similar orbit. When the Earth’s orbit runs into one of these patches we get more meteors, which appear to come from a particular part of the sky – known as the radiant – determined by the patch’s location. Showers are named after the constellation from which they appear to come, for example, the Perseids appear to come from the direction of the constellation Perseus and occur every August. Some constellations have several showers at different times, in which case each is named after the nearest bright star.
Meteor numbers are measured by “Zenith Hourly Rate” (ZHR), the number someone with good eyesight would see under dark skies if the radiant was directly overhead. When the radiant is low, the number visible can be far below the ZHR.
Some patches are small and dense, meaning high ZHRs around the peak. Others, particularly older ones, are broader. These may never achieve high ZHRs but last a long time. Others, of course, are just weak, without many meteors at all.
Which Showers Are Occurring This Week?
The exact timing of when showers start and finish is not always precise. However, the following showers are considered to be underway August 3-10, even if some are nowhere near their peak.
One of the most famous, and consistently bright, meteor showers with a ZHR of 100 and many bright meteors. They started on July 17 and are slowly increasing towards their August 13 peak. Unfortunately, however, the Moon will also be full around the peak, making an argument for getting in early or it will outshine the shower. Radiant of 58 degrees North, so this one is only for people in the Northern Hemisphere or the southern tropics.
Southern Delta Aquariids
These peaked on July 30 and will run until August 23. The radiant is at latitude 16 degrees South, so only people near or above the Arctic Circle miss out. With a peak ZHR of 25 and many bright meteors, this is one of the best of the showers, even if the peak has passed.
A long but sparse shower, running from July 3 to August 15 and peaking on July 30. Peak ZHR of just 5, but often bright and slow, making them easy to point out when observing with friends. Radiant so close to the celestial equator these are visible from almost everywhere.
Although they peaked on July 28, the Piscis Austrinids last until August 10, having started on July 15. The radiant is 30 degrees South, so this one is not visible from Northern Europe or most of Canada. With a ZHR of just 5 even at the peak, and usually faint meteors, it’s also not such a bad one to miss.
Although sparse enough that Wikipedia doesn’t even list them, the Iota Aquarids have a peak ZHR of about 6. Also only viewable from southern latitudes, but for those that can see them, they peak on August 6.
Starting tonight and peaking on August 18 this has a ZHR of 3, but the meteors are considered of medium brightness. Radiant 59 North. Similar timing to the Perseids but radiant on the other side of the sky.
Space.com also refers to an additional shower, known as the Capricorids but separate from the Alpha Capricornids and peaking slightly earlier. The International Meteor Organization does not recognize the distinction but notes the Antehelion Source (ANT) is an area of the sky almost opposite the Sun, which has a number of patchy and hard-to-distinguish showers throughout the year. In August some of these may appear to come from Capricorn.
Most meteor showers are best seen between midnight and dawn, rather than in the evening. That’s particularly the case this week, with the waxing Moon obscuring observations earlier in the night.