Each summer amateur astronomers from all over the world look forward to observing the famous Perseid Meteors, but they often overlook six lesser showers that peak between July 28 and Aug. 19.
This year, a waning gibbous Moon three days past full phase will seriously hamper Perseid watching, so why not take this opportunity to try and view the other six, all but one of which will enjoy dark skies?
Anyone gazing up on a clear night sky this time of year for even a short length of time is likely to spot a few "shooting stars" darting across the sky. In general, the Earth encounters richer meteoric activity during the second half of the year.
And you're more likely to see twice as many meteors per hour in the predawn hours as compared to the evening hours. This is due to the fact that during the pre-midnight hours we are on the "trailing" side of the Earth, due to our orbital motion through space. So any meteoric particle generally must have an orbital velocity greater than that of the Earth to "catch" us. However, after midnight when we are turned onto the Earth's "leading" side, any particle that lies along the Earth's orbital path will enter our atmosphere as a meteor.
So objects collide with our atmosphere at speeds of 7 to 45 miles per second, their energy of motion rapidly dissipates in the form of heat, light, and ionization, creating short-lived streaks of light popularly referred to as "shooting stars."
Summertime meteors, occasionally flitting across your line of sight are especially noticeable between mid-July and the third week of August. And between August 3 and 15, there are no fewer than six different minor displays that are active. These six are listed in the table below.
The only equipment you'll need is your eyes and a modest amount of patience. The actual number of meteors a single observer can see in an hour depends strongly on sky conditions.
The rates given in the table are based on a limited star magnitude of +6.5 (a really good sky!), an experienced observer, and an assumption that the radiant is directly overhead. The radiant is the place in the sky where the paths of shower members, if extended backward, would intersect when plotted on a star chart. Your clinched fist held at arm's length is equal to roughly 10-degrees on the sky. So if the radiant is 30-degrees ("three-fists") above the horizon, the hourly rate is halved; at 15-degrees it is a third.
While the hourly rates from these other meteor streams are but a fraction of the numbers produced by the Perseids, combined, overall they provide a wide variety of meteors of differing colors, speeds and trajectories. Among these are the Southern Delta Aquarids, which can produce faint, medium speed meteors; the Alpha Capricornids, described as "slow, bright, long trailed yellowish meteors" and the Kappa Cygnids which are classified as "slow moving and sometimes producing brilliant flaring fireballs." As such, if you stay out and watch long enough, you may be nicely rewarded for the time spent.
Shower | When | Peak | Rate | Remarks |
S. Delta Aquarids | July 12 - Aug. 19 | July 28 | 15 | Faint, medium speed. |
Alpha Capricornid | July 3 - Aug. 15 | July 30 | 4-5 | Slow, bright, a few fireballs. |
S. Iota Aquarids | July 25 - Aug. 15 | Aug. 4 | 1 - 2 | Faint, medium speed |
N. Delta Aquarids | July 15 - Aug. 25 | Aug. 8 | 1 - 4 | Faint, medium speed |
Kappa Cygnids | Aug. 3 - Aug. 25 | Aug. 18 | 1 - 3 | Slow moving, sometimes brilliant |
N. Iota Aquarids | Aug. 11 - 31 | Aug. 20 | 1 - 3 | Faint, medium speed |
Note that five of the six showers liste, come from the region around the constellations of Aquarius and Capricornus. These constellations are highest in the southern sky between roughly 1 and 3 a.m. local daylight time.
Only the Northern Delta Aquarids, peaking on the night of August 8, will be spoiled by the light of the Full Moon (which will reside in nearby Capricornus). But a week or so earlier, the Moon will have already set earlier in the evening, leaving the after-midnight skies dark for the Southern Delta Aquarids, Alpha Capricornids, and Southern Iota Aquarids.
Meanwhile, the Moon will have slimmed to a waning crescent by the time the Kappa Cygnids and Northern Iota Aquarids reach their peak. Of these six minor showers, the Kappa Cygnids are the most favorably placed for northern observers: the constellation of Cygnus lies high overhead at around midnight making it favorably placed for viewing all night long.
Basic Sky Guides
- Full Moon Fever
- Astrophotography 101
- Sky Calendar & Moon Phases
- 10 Steps to Rewarding Stargazing
- Understanding the Ecliptic and the Zodiac
- False Dawn: All about the Zodiacal Light
- Reading Weather in the Sun, Moon and Stars
- How and Why the Night Sky Changes with the Seasons
- Night Sky Main Page: More Skywatching News & Features
Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for The New York Times and other publications, and he is also an on-camera meteorologist for News 12 Westchester, New York.
| DEFINITIONS |
1 AU, or astronomical unit, is the distance from the Sun to Earth, or about 93 million miles. Magnitude is the standard by which astronomers measure the apparent brightness of objects that appear in the sky. The lower the number, the brighter the object. The brightest stars in the sky are categorized as zero or first magnitude. Negative magnitudes are reserved for the most brilliant objects: the brightest star is Sirius (-1.4); the full Moon is -12.7; the Sun is -26.7. The faintest stars visible under dark skies are around +6. Degrees measure apparent sizes of objects or distances in the sky, as seen from our vantage point. The Moon is one-half degree in width. The width of your fist held at arm's length is about 10 degrees. The distance from the horizon to the overhead point (called the zenith) is equal to 90 degrees. Declination is the angular distance measured in degrees, of a celestial body north or south of the celestial equator. If, for an example, a certain star is said to have a declination of +20 degrees, it is located 20 degrees north of the celestial equator. Declination is to a celestial globe as latitude is to a terrestrial globe. Arc seconds are sometimes used to define the measurement of a sky object's angular diameter. One degree is equal to 60 arc minutes. One arc minute is equal to 60 arc seconds. The Moon appears (on average), one half-degree across, or 30 arc minutes, or 1800 arc seconds. If the disk of Mars is 20 arc seconds across, we can also say that it is 1/90 the apparent width of the Moon (since 1800 divided by 20 equals 90). |
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