Astronomy Essentials

Find Perseid and Delta Aquariid radiant points

Perseid and Delta Aquariid radiant points, and those of other meteor showers, are shown by streaks radiating from a single point. The point has a white circle around it.
Meteor showers have a radiant point, a point in the sky from which they appear to radiate. Image via Anton/ Wikimedia Commons.

The Delta Aquariid meteor shower has a broad maximum, as opposed to a sharp peak in activity, and produces meteors throughout late July and early August. It overlaps with the more famous Perseid meteor shower, which rises slowly to its peak each year around August 11, 12 and 13. The Perseids take their name from the constellation Perseus the Hero. And the Delta Aquariids take their name from the star Skat, aka Delta Aquarii, in the constellation Aquarius the Water Bearer. For both showers, if you trace the paths of the meteors backward, you’ll find the meteors’ radiant points. Keep reading to learn more about these sought-after points in the sky. Now here’s the good news. You don’t need to know a shower’s radiant point to enjoy the meteors. But these points in the sky are fun to find!

Find the radiant point for the Perseids

Perseus itself isn’t all that easy to find. But a nearby constellation – Cassiopeia the Queen – is. Look northward for Cassiopeia. It has a very distinctive shape of the letter W or the number 3. See it? Good. Perseus rises later than Cassiopeia on these summer evenings. By the wee hours, you’ll find Perseus below Cassiopeia in the northeastern sky.

As viewed from the Northern Hemisphere, the Perseids’ radiant point sits low in the northeast sky at evening and climbs upward throughout the night. The higher that the radiant is in your sky, the more Perseid meteors you’re likely to see. For the Perseids, the radiant is highest before dawn.

Chart of constellation Perseus with arrows pointing radially outward from spot near its top.
The radiant point for the Perseid meteor shower is in the constellation Perseus. The easy-to-find constellation Cassiopeia is nearby. Just remember, you don’t have to find a shower’s radiant point to see meteors. Instead, the meteors will be flying in all parts of the sky.

Do you have a dark country sky? Then look for the Double Cluster in Perseus. This dual cluster of stars almost exactly marks the radiant point of the Perseid meteor shower. You can find it by scanning with your binoculars between Perseus and Cassiopeia.

Although the Double Cluster can be seen with the unaided eye, its stars burst into view through binoculars. The clusters are more formally known as NGC 884 (Chi Persei) and NGC 869 (h Persei).

Looking for a dark sky? Check out EarthSky’s Best Places to Stargaze.

Starry field with outlined constellation Cassiopeia and an arrow pointing to 2 small smudges.
Here’s a cool binocular object to look for while you’re watching the meteors. The constellation Cassiopeia points out the famous Double Cluster in the northern tip of the constellation Perseus. Plus, the Double Cluster nearly marks the radiant of the Perseid meteor shower. Image via Flickr/ Mike Durkin.
The sky above an orange horizon, with Perseus constellation, stars, and Pleiades labeled.
Here’s more to see, as the night passes. From mid-northern latitudes, the constellation Perseus, the stars Capella and Aldebaran, and the Pleiades cluster light up the northeast sky in the wee hours after midnight on late July and early August nights. The meteors radiate from Perseus. Image via Till Credner/
Milky Way over observatory buildings with a meteor streak above a building on the left.
Some Perseid meteors will be visible in the Southern Hemisphere, although the numbers will not be as high. Photo from northern Chile, via the European Southern Observatory/ S. Guisard.

Find the radiant point for the Delta Aquariids

As mentioned above, the Delta Aquariids radiate from the constellation Aquarius, specifically from near its star Skat or Delta Aquarii. Skat isn’t a bright star. It ranks as only the third brightest in the dim constellation Aquarius the Water Bearer. Still, you can glimpse this constellation and this star if you go someplace dark. If you’re in the Northern Hemisphere, you’ll also need a good view to the south to see Aquarius. From mid-latitudes in the Southern Hemisphere, the star and constellation are northward and higher in the sky.

Skat appears only modestly bright. But as viewed on the sky’s dome it’s near to a very bright star, Fomalhaut in the constellation Piscis Austrinus the Southern Fish.

If you can see the Great Square of Pegasus and Fomalhaut, they can help you find Skat. See the 2nd chart down, below. Also, in 2021, Jupiter is near the Delta Aquariid radiant. See the chart directly below.

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.
Star chart of the region around constellation aquarius. A red circle marks the radiant of the Delta Aquariid meteor shower.
View larger. | Want to see the star Skat, radiant point of the Delta Aquariids? This chart can help. The radiant is circled in red. To see Skat, you need a dark sky. Chart via Wikimedia Commons.

Why do meteor showers have a radiant point?

Of course, in actuality, the Delta Aquariid meteors have nothing whatever to do with the star Skat. And the Perseid meteors have nothing to do with the Double Cluster in Perseus. Skat lies about 160 light-years away. The Double Cluster is thought to be over 7,000 light-years away from us, in the Perseus arm of the Milky Way galaxy. Meanwhile, meteors in annual showers start out close to Earth, as bits of debris left behind in space by comets. They encounter Earth’s atmosphere and begin to vaporize some 60 miles (100 km) above our world’s surface.

So why do meteor showers have radiant points? It’s because the meteors enter Earth’s atmosphere on parallel paths. Seeing them come from a radiant point in the sky is much the same illusion as standing on railroad tracks and seeing the tracks converge in the distance.

View of train tracks as if wide apart close to you and close together in the distance.
When you stand on a railroad track, you can see the illusion of tracks converging in the distance. Likewise, the paths of meteors in a single meteor shower appear to converge at a point – the radiant point – on the sky’s dome. Image via Shutterstock.

Bottom line: How to find the radiant points for the Delta Aquariid meteor shower and the Perseid meteor shower. Plus an explanation of why meteors in annual showers have radiant points.

Great Square of Pegasus: Easy to see

Read about all the major meteor showers: EarthSky’s meteor shower guide

July 26, 2021
Astronomy Essentials

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