Astronomy Essentials

Delta Aquariid meteor shower 2021: All you need to know

Diagram of Earth's orbit crossing a wide arc of tiny dots representing cometary debris triggering the Delta Aquariid meteor shower.
Meteors in annual showers happen when Earth encounters debris left behind by a comet. Astronomers have investigated the various streams of debris in space left behind by comets in their passages near the sun. Image by AstroBob.

In 2021, wait for less moon

The Delta Aquariid meteor shower is long and rambling. You might catch a Delta Aquariid anytime from about July 12 to August 23 each year. The nominal peak falls on or near July 29. But don’t pay too much attention to that date; the shower typically provides a decent number of meteors for some days after and before it. In 2021, a bright waning gibbous moon will wash out a good number of Delta Aquariids in late July. As we move into early August, a much fainter waning crescent moon will be less intrusive. As always happens, when the Perseid meteor shower is rising to its peak (mornings of August 11, 12 and 13), the Delta Aquariids will still be flying, too.

And that’s always lots of fun, with meteors streaking across the sky from two different radiant points. Read more about the radiant points for both the Delta Aquariids and the Perseids, here. By the way, the Delta Aquariids are most numerous as seen from the Southern Hemisphere. But you’ll catch some of these meteors from mid-northern latitudes as well. Once the moon is out of the way, the broad maximum of this shower might be expected to produce 10 to 20 meteors per hour.

For the Delta Aquariids, as for most meteor showers, the best viewing hours are after midnight and before dawn for all time zones around the world.

Find out when morning dawn (astronomical twilight) begins in your sky via

Everything you need to know: Perseid meteor shower

Jupiter shines brightly in front of the constellation Aquarius, radiant of the Delta Aquariid meteor shower.
Aquarius, the radiant of the Delta Aquariid meteor shower, is highest up for the night around 2 hours after midnight (by midnight, we mean midway between sunset and sunrise). Aquarius is a relatively faint constellation. In late July 2021, dazzling Jupiter is on the western border of Aquarius, near the radiant point of the Delta Aquariid shower. So when you look toward Jupiter, you’re looking approximately toward this shower’s radiant.
Star chart showing the Great Square of Pegasus to Fomalhaut to the Delta Aquariid radiant point.
Note: this chart is for any year, and Jupiter doesn’t appear on it. In any year, you can find the radiant point for the Delta Aquariids using the bright star Fomalhaut as a guide. The radiant point for Delta Aquariid shower is near a faint star Skat, or Delta Aquarii. This star is near in the sky to Fomalhaut, which can be found roughly on a line drawn southward through the stars on the west side of the Great Square of Pegasus. This chart shows a wide area, from overhead to southward, as seen from the Northern Hemisphere. From the Southern Hemisphere, the radiant is closer to overhead. But don’t worry too much about radiant points. The meteors will appear in all parts of the sky.

How can I tell Perseids from Delta Aquariids?

This is where the concept of a radiant point comes in handy. If you trace all the Delta Aquariid 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 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 – assuming you’re in the Northern Hemisphere – if you’re 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 Aquariids. 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 Aquariid meteors 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 Aquariid shower. About 5% to 10% of the Delta Aquariid 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 60 miles (100 km) above Earth’s surface.

Remember, 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. This year – in 2021 – the Delta Aquariids at their peak will be marred by a waning gibbous moon. Fortunately, the waxing crescent moon won’t ruin the much-brighter August Perseids.

Starry background, largish bright dot with two fuzzy tails.
Comet 96P Machholz, the possible parent of the Delta Aquariid meteor shower, was discovered on May 12, 1986, by Donald Machholz. Image via Wikimedia Commons.

Comet 96P Machholz and the Delta Aquariid meteor shower

Comet 96P Machholz is thought to be the parent object of this meteor shower. As you may know, meteors in annual 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 cometary debris slams into the Earth’s upper atmosphere at about 90,000 miles (150,000 km) per hour, vaporizing – burning up – as meteors or shooting stars.

The parent body of the Delta Aquariid 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, Comet 96P Machholz has loomed as the primary candidate for being the Delta Aquariids’ 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 October 27, 2017, and will next come to perihelion on January 31, 2023.

Starry sky with Milky Way visible and fuzzy bright green dot with short glowing trail near horizon.
David S. Brown caught this meteor in late July 2014, in southwest Wyoming.
Long bright diagonal line streaking among clouds.
Kelly Dreller caught this meteor in late July 2016, in Lake Havasu City, Arizona.

Bottom line: The Delta Aquariid meteor shower lacks a very definite peak. It rambles along pretty steadily in late July and August, intermingling with the Perseids. The expected nominal peak happens in late July, and in 2021, coincides with a bright waning gibbous moon. From any time zone, the best viewing window 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.

Everything you need to know: Perseid meteor shower

July 26, 2021
Astronomy Essentials

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