The Delta Aquariid meteor shower rambles along steadily from about July 12 to August 23 each year. In 2018, a full moon will drown out these meteors at the nominal peak night of the shower on the night of July 27 (before dawn July 28). Although it’s a micro-moon – the most distant and smallest full moon of the year – it’ll still be difficult to spot these rather dim meteors on the night of their nominal peak. Still, July 27 is a big night. If you live in the world’s Eastern Hemisphere – Europe, Africa, Asia and Australia – July 27-28 could provide the incredible experience of seeing a Delta Aquariid meteor streak past a fully eclipsed moon. It’s the longest total lunar eclipse of this century, after all. Plus Mars reaches opposition on July 27 and will be near the moon that night. It’s not just any Martian opposition, but a special one that explains why Mars is now brightest in our sky since 2003. And you might also see some meteors in moonlight.
All in all, July 27 is a great night for watching for meteors, and more.
And here’s even more good news. Meteor numbers for this shower don’t bump up significantly at this shower’s peak; in fact, they’ll continue on into August and overlap with the famous Perseid meteor shower. The moon will turn new on August 11, 2018, providing dark skies for both the Perseids and the Delta Aquariids around then. The Perseids radiate from the constellation Perseus. The Delta Aquariids radiate from the constellation Aquarius. That means those August meteors will be flying from two different directions in the sky. Lots of fun to watch!
Want to learn more details about the Delta Aquariids? Keep reading …
What if I can’t watch on the night of July 27? This shower is long and rambling. Although its nominal peak is late July – and although the peak is mostly drowned in bright moonlight – you’ll have plenty of chances to see Delta Aquariid meteors even if you don’t watch around the peak.
Generally speaking, as with many meteor showers, the best meteor-viewing hours are after midnight and before dawn. For the Delta Aquariids, the best time is centered around 2 a.m. (3 a.m. Daylight Saving Time) for all time zones around the world. That’s when the radiant point is high in the sky.
If you want to wait until the moon leaves the morning sky (or at least wanes down to a fairly narrow crescent phase), you might try waiting until, say, around the morning of August 8, 2018. The moon will be rising increasingly later each morning that whole week, interfering less and less with the meteors until new moon (no moon up at night) on August 11. 2018’s moon-free and very convenient Perseids peak on the weekend of August 11-12.
The Delta Aquariid meteors tend to appear a bit fainter than the Perseids and meteors seen in other major showers. You’ll know they are Delta Aquariids, not Perseids, because you’ll see them radiating from a different part of the sky. More about that below.
The Delta Aquariid shower is said to favor the Southern Hemisphere. But viewers at mid-northern latitudes can see these meteors as well. In years when the moon is out of the way, the broad maximum of this shower can be expected to produce 10 to 20 meteors per hour, under a dark country sky.
About five to ten percent of the Delta Aquariid meteors leave persistent meteor 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 the Earth’s surface. Watch for their lingering trains!
How to tell Perseid meteors from Delta Aquariid meteors. This is where the concept of a radiant point comes in handy. You never have to locate a shower’s radiant point to enjoy the meteors. But … 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. As viewed from the Northern Hemisphere, this point – the Delta Aquariids’ radiant point – arcs across the southern sky. It’s overhead for Southern Hemisphere viewers (which is why the shower is best from that part of the world).
The radiant point of the Delta Aquariid 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, as seen from the Northern Hemisphere. So if you’re in this hemisphere, and you’re out watching for meteors, 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.
If you’re in the Southern Hemisphere, your Delta Aquariids will be radiating from nearly overhead. Your Perseids will be shooting up from somewhere along your northern horizon.
In a particularly rich year for meteors, if you have a dark sky, you might even see Perseid meteors cross paths with Delta Aquariid meteors! It can be an awesome display.
Delta Aquariid 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 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.
Bottom line: The Delta Aquariid meteor shower rambles along pretty steadily in late July and August, coinciding with the Perseids.
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.