When people think of meteor showers, they often picture themselves reclining under a star-filled sky and watching fleeting streaks of light paint the heavens. Most meteor showers, such as the Perseids, Orionids, Leonids and Geminids, reach their peak in the late-night hours, when darkness enhances their brilliance.
But a few perform their celestial dance during daylight, their beauty largely drowned in the sun鈥檚 overpowering glow. The most active of these is the Arietid Meteor Shower, and it is set to peak on the morning of June 7.
Like most meteor showers, the Arietids derive their name from the constellation from which they appear to radiate, in this case Aries (the Ram). The Arietid Meteor Shower is active for several weeks starting in late May. During its peak of activity on June 7, it will produce an estimated 60 meteors per hour. However, since the peak time is after the sun has risen, most meteors will be lost in the glare of the sun. The best opportunity to catch a glimpse is during the dark, pre-dawn hours when the sun has yet to rise.
Meteors are often called shooting stars or falling stars but have nothing to do with stars. These misnomers go back to the days when skywatchers did not understand the true nature of meteors and believed them to be the remnants of stars. In fact, people have used the term meteor to describe a variety of objects in the sky, including not only 鈥渟hooting stars鈥� but also clouds, raindrops (the term hydrometeor described a raindrop) and more. A holdover of this concept is our modern term 鈥渕eteorology,鈥� which is not the study of 鈥渟hooting stars鈥� but rather the study of the weather.
Astronomers at the Jodrell Bank Observatory discovered the Arietid Meteor Shower in 1947. As with the detection of other daytime meteor showers, the scientists used radio antennas to detect bursts of radio waves associated with plasma created in the upper atmosphere when meteors vaporized. (If humans could see at radio wavelengths, these daytime showers would be just as apparent -- or maybe more so -- as their nighttime, optical counterparts.)
The source of the Arietid Meteor Shower remains uncertain. Some scientists link it to Comet 96P/Machholz while others suggest an affinity to the asteroid 1566 Icarus. 96P is a short-period comet, meaning it takes less than 200 years to orbit the sun. In the case of 96P, it has an orbital period of only 5.27 years鈥搊ne the shortest of any known comet. Scientists also classify it as a sungrazing comet because it passes remarkably close to the sun (almost three times closer to the sun than Mercury gets).
1566 Icarus is a type of near-Earth asteroid, meaning its orbit crosses that of Earth and it could thus theoretically impact Earth. This is true of any candidate meteor shower parent body, including 96P; by definition, these objects must pass through Earth's orbit to produce a meteor shower. Scientists have yet to observe any signs of comet-like activity in Icarus and it thus remains a mystery as to how particles could depart their surface to generate a meteor stream. Its near proximity to the sun and resulting elevated temperature could indicate that the surface is essentially getting baked, perhaps causing particles to liberate from its surface, every 1.12 years when it gets closest to the sun.
Regardless of its origin, the Arietid Meteor Shower stands out for its high meteor count 鈥� even if its spectacle remains hidden in daylight. It is an unusual, little-known celestial phenomenon whose elusiveness sparks the imagination.