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| Astronomy Essentials on Jul 28, 2013

Everything you need to know: Delta Aquarid meteor shower

The moon will drown some Delta Aquarids from view tonight, during the predawn peak. But this shower keeps going and will combine with the Perseid meteor peak on August 11-13.

The long, rambling Delta Aquarid meteor shower can be seen across the entire Earth, and sky watchers in the Southern Hemisphere and northern tropics have an especially good view. This shower is officially active from about July 12 to August 23 each year. It overlaps with the more famous Perseid meteor shower in August, and those who observe the Perseids are sure to see Delta Aquarid meteors flying on the same nights. Best time to look for both the Perseids and the Delta Aquarids is between midnight and dawn.

Does this shower have a peak? It does have a nominal peak in late July. This year, 2013 is not particularly favorable for watching this shower in late July, as moonlight will be washing the predawn meteors from the blackboard of night. In years when the moon is out of the way, the broad maximum of this shower can be expected to produce 15 to 20 meteors per hour in the predawn hours around July 29. Don’t worry about moonlight spoiling the show in 2013. Last quarter moon falls on July 29, and after that the moon will be waning, casting less and less light in the sky. By the time the 2013 Perseids roll around (August 11-13), you’ll definitely be seeing many Delta Aquarids as well!

Skat: Radiant for the Delta Aquarid meteors

Radiant point of Delta Aquarid meteor shower

Radiant point for Delta Aquarid shower is near star Skat, or Delta Aquarii. This star is near in the sky to a much brighter star, Fomalhaut, which can be found roughly on a line drawn southward through the stars on the west side of the Great Square.

From mid-northern latitudes, the constellation Aquarius and the bright star Fomalhaut – with the star Skat above it – rise into the southeast sky by around midnight in late July and early August. Image via AlltheSky.com

Notice the radiant point of the Delta Aquarids. How can you tell which meteors are Delta Aquarids and which are Perseids? That’s where the concept of a radiant point comes in handy. If you trace all the Delta Aquarid meteors backward, they appear to radiate from a certain point in front of the constellation Aquarius the Water Bearer, which, as viewed from the Northern Hemisphere, arcs across the southern sky. The radiant point of the shower nearly aligns with the star Skat (Delta Aquarii). The meteor shower is named in the honor of this star.

Meanwhile, the Perseids radiate from the constellation Perseus, in the northeast to high in the north between midnight and dawn. So if you are watching the Perseids, and you see meteors coming from the northeast or north … they are Perseids. If you see them coming from the south … they are Delta Aquarids. In a particularly rich year for meteors, if you have a dark sky, you might even see them cross paths! It can be an awesome display.

The Delta Aquarid meteors may tend to be a bit fainter than the Perseids and meteors seen in other major showers. That makes a dark sky free of moonlight even more imperative for watching the annual Delta Aquarid shower. About five to ten percent of the Delta Aquarid meteors leave persistent trains – glowing ionized gas trails that last a second or two after the meteor has passed. The meteors burn up in the upper atmosphere about 100 kilometers (60 miles) above the Earth’s surface.

Rememeber, you never have to locate a shower’s radiant point to enjoy the meteors. However, it does help to have a dark night without moonlight. Next year – in 2014 – the prospects for watching the Delta Aquarids in late July will be much better, as there will be no moonlight to ruin the show.

Comet 96P Machholz, the possible parent of the Delta Aquarid meteor shower, was discoverd on May 12, 1986, by Donald Machholz. Photo: Wikimedia Commons

Delta Aquarid meteors may come from Comet 96P Machholz. Meteor showers happen when our planet Earth crosses the orbital path of a comet. When a comet nears the sun and warms up, it sheds bits and pieces that spread out into that comet’s orbital stream. This comet debris slams into the Earth’s upper atmosphere at about 150,000 kilometers (90,000 miles) per hour, vaporizing – burning up – as meteors or shooting stars.

The parent body of the Delta Aquarid meteor is not known with certainty. It was once thought to have originated from the breakup of what are now the Marsden and Kracht sungrazing comets. More recently, the Comet 96P Machholz has loomed as the primary candidate for being the Delta Aquarids’ parent body.

Donald Machholz discovered this comet in 1986. It’s a short-period comet whose orbit carries it around the sun once in a little over five years. At aphelion – its greatest distance from the sun – this comet goes out beyond the orbit of Jupiter. At perihelion – its closest point to the sun – Comet 96P Machholz swings well inside Mercury’s orbit. Comet 96P/Machholz last came to perihelion on July 14, 2012 and will next come to perihelion on October 27, 2017.

Bottom line: The Delta Aquarid meteor shower lacks a very definite peak. It rambles along pretty steadily in late July and August, coinciding with the Perseids. The nominal peak in 2013 is the morning of July 29, but there will be a last quarter moon in the sky that morning. From any time zone, the best viewing window on July 29 lasts for several hours, centered on roughly 2 a.m. (3 a.m. daylight-saving time). Find an open sky away from artificial lights, lie down on a reclining lawn chair and look upward. If you’re disappointed in late July, try again around August 12 when the Perseids are peaking!

Everything you need to know: Perseid meteor shower