Will the moon ruin the Eta Aquarid meteor shower this week? Here’s what to know

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Just before dawn on Wednesday morning (May 6) is the peak of the annual Eta Aquarid meteor shower. This meteor display is active during the first week of May and produces long streaks whose trajectories are away from the “water pot” of Aquarius.

Their sequences are long for good reason, which we’ll explain in a moment.

THE Eta Aquarids have a most interesting lineage. Unlike some other annual meteor displays whose history dates back centuries, the Eta Aquarids were not “officially discovered” until the late 19th century. In 1870, while sailing in the Mediterranean Sea, Lt. Col. GL Tupman (1838-1922) saw 15 meteors on the morning of April 30, and 13 more a few mornings later. All the meteors seen by Tupman appeared to emanate from the zodiacal constellation of Aquarius the Water Bearer. Then in 1876, Professor Alexander Stewart Herschel (1836-1907) pointed out that the orbit of Halley’s Comet almost coincided with the Earth’s orbit during the first week of May and that if we encountered comet debris capable of producing meteors, these streaks of light would seem to spring from the surroundings of Aquarius.

Herschel immediately noticed that Tupman’s observations were very close to his prediction. In the years since, a growing number of other astronomers and observers have also noted similarities between the orbits of Halley’s Comet and those of the Eta Aquarid stream.

Like other comets, Halley’s is a cosmic bug; approximately every three-quarters of a century, when it comes closest to the the sunit leaves in its wake a “river of rubble” along its orbit. When Earth interacts with this river of rubble, these comet fragments travel through our atmosphere at high speed to produce the effect of “shooting stars”.

It turns out that Halley is responsible for not one, but two annual meteor displays:

The dusty material that the comet releases into space as it heads toward the sun produces the Orionid meteors in late October, as material released after the comet bypasses the sun and returns to the outer limits of space. solar system produced the Eta Aquarids at the beginning of May.

The muscles of the moon

But to curb your enthusiasm, we must also tell you that this year, the Eta Aquarids will be poorly seen, because of the glare of a waning gibbous moon, which became full on May 1st. Although not as bright (81% lit) as when full, it will still serve to significantly brighten the morning sky and likely prevent most of the fainter streaks from being visible. In other years – without a bright moon – the Eta Aquarids are typically the richest meteor display for observers in the Southern Hemisphere, producing up to 60 meteors. meteors per hour.

Too low

But moonlight is only one of two obstacles to observing this shower. The other problem is that if you live north of the equator, hourly meteor rates decrease quite quickly. This is especially true for northern temperate latitudes, because the Eta Aquarid radiant, from which meteors appear to burst, never reaches a high altitude above the southeastern horizon (it rises around 3 a.m. local time), so rates are therefore low. Since these meteors appear to radiate from a low position on the eastern horizon in mid-northern latitudes, observers in the tropics are best placed. Under the most favorable conditions, a dozen or more meteors per hour can be observed from the Eta Aquarid swarm. However, observers in northern mid-latitudes can see only about half of it.

Hope of a “grazer”

Always . . . even if you live in a very northern area, there is always a reason to go out and take a look, because it is possible that you will chance and spot a “Earth Grazer.” These are bright meteors emerging from the Aquarid radiant that will travel horizontally through the atmosphere – much like an insect brushing against the side window of an automobile. They also sometimes leave colorful and lasting traces.

Remember earlier when we said Aquarid meteor trails were long? GOOD . . . Earth-grazing meteors tend to be extremely long and generally appear to hug the horizon rather than shooting overhead on most cameras. “There are rarely many earthlings,” warns Bill Cooke, a member of the space environments team at Marshall Space Flight Center. “But even if you only see a few, you’ll probably remember them.”

Comet Crumbs

And if for nothing else, remember that if you spot an Aquarid meteor, you will have seen a piece of space debris that was shed by the famous Halley’s Comet in centuries past. They continue to travel more or less along the comet’s 75-year orbit around the sun. Each meteoroid collides with Earth’s upper atmosphere at a speed of 66 km per second, creating a glowing trail of ionized and shocked air. It’s this hot trail and not the small meteoroid itself that is what you see. These particles are not very large and likely range in size from grains of sand to pebbles, and they have the consistency and texture of cigar ash or copier toner – debris that astronomers believe is nearly five billion years old. birth of the solar system; primordial material that intersects Earth’s orbit around this time in early May each year.

And just in case you’re wondering, Halley’s Comet itself will return to the sun’s vicinity sometime in the summer of 2061. So, based on life expectancy statistics, if you were born after 1982, you have a better than 50-50 chance of seeing the comet itself. Until then, we will have to be content with seeing shooting stars which are in reality the traces of this famous visitor from the depths of space. . . and most likely the dawn of creation.

Joe Rao is an instructor and guest lecturer at New York University Hayden Planetarium. He writes on astronomy for Natural history review, Sky and telescope, The Old Farmer’s Almanac and other publications.