The famous Eta Aquarid meteor shower – one of the year’s major meteor showers – peaks every year in early May. This shower is known to be richer as seen from Earth’s Southern Hemisphere than from the Northern Hemisphere. Why?
If you traced the paths of Eta Aquarid meteors backward on the sky’s dome, you’d find that these meteors appear to stream from an asterism, or recognizable pattern of stars, known as the Water Jar in the constellation Aquarius.
This spot in the sky is the radiant point of the Eta Aquarid meteor shower. The meteors seem to emanate from the vicinity of the Water Jar, before spreading out and appearing in all parts of the sky.
Because the Water Jar is on the celestial equator – an imaginary great circle directly above the Earth’s equator – the radiant of the Eta Aquarid shower rises due east as seen from all over the world. Moreover, the radiant rises at about the same time worldwide, around 1:40 a.m. local time (2:40 a.m. Daylight Saving Time) in early May, around the shower’s typical peak date.
So you’d think the shower would be about the same as seen from around the globe. But it’s not. Why?
It’s because sunrise comes later to the Southern Hemisphere (where it’s autumn in May) and earlier to the Northern Hemisphere during the month of May.
For that reason, the radiant point of the Eta Aquarid shower climbs higher into the predawn sky as seen from more southerly latitudes. That’s why the tropics and southern temperate latitudes tend to see more Eta Aquarid meteors than we do at mid-northern latitudes.
Cruise to a southerly latitude, anyone?
Bottom line: Everyone around the globe can enjoy the Eta Aquarid meteor shower in early May. But it’s better viewed from the Southern Hemisphere than the Northern Hemisphere. Why? Because of the later sunrises in the Southern Hemisphere at this time of year. Those later sunrises give the radiant point of this shower a chance to climb higher into the predawn sky, when most of the meteors will be visible.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.