While the Eta Aquariid meteor shower produces the strongest hourly rates seen from the southern hemisphere, it is the Delta Aquariids (SDA) that produces the most total activity during its entire activity period. The Delta Aquariids (aka Southern Delta Aquariids) can be successfully observed from the northern hemisphere but their numbers are reduced due to the lower radiant altitude.
This shower is active for more than a month stretching from July 21st through August 23rd. Some other studies have stretched this period from July 19th through September 3rd, but shower membership of possible SDA’s at these extremities are dubious at best. Peak rates occur on July 29 or 30 with stated ZHR’s of 15-20. I have personally seen hourly rates of 25 from latitude 33 N. and experienced observers have seen hourly rates as high as 40 from equatorial locations. Of course these rates were seen under near perfect skies where faint meteors made up a majority of the activity.
In 2014, the lunar conditions for viewing the Delta Aquariid maximum is extremely favorable. On July 30th (the predicted maximum date for this year) the moon will be a waxing crescent phase. It will set well before midnight allowing the prime morning viewing hours to be free of interfering moonlight. Moonlight will not encroach on viewing this activity until the second week of August, well past the time of maximum activity.
On the date of maximum activity the radiant for the Delta Aquariids lies at 22:42 -16. This position lies in southern Aquarius just a couple of degrees west of the 3rd magnitude star known as Skat (Delta Aquarii). This area of the sky rises in the east around 22:00 (10pm local daylight time). Serious observations should not begin until after midnight, allowing the radiant to gain sufficient altitude. The radiant lies on the meridian near 0300 LDT when it lies highest above the horizon. This is the best time to view the Delta Aquariids. As seen from latitude 40N the radiant will lie 34 degrees above the southern horizon. At this elevation above the horizon this will allow you to see slightly more than one-half of all the SDA activity. The other half of the SDA activity will occur beyond your line of sight. The best location to view the SDA activity is from latitude 16 S., where the radiant will pass directly overhead.
The Delta Aquariid meteors strike the atmosphere at a velocity of 26 miles per second (42km). This is an average velocity therefore few persistent trains are expected from these meteors. Unfortunately the SDA’s are not known for bright meteors and a majority of the activity is on the dim side. This fact, along with the low radiant altitude, makes it a challenge to view these meteors during the normally hazy July mornings.
A suggested strategy to view this activity would be to watch these meteors on or near the date of maximum activity from a rural site away from city lights. The best time lies between 0200 and 0400 local daylight time. Face southward with your field of view centered approximately one-half high in the sky. SDA meteors will shoot in all directions from the lower portion of your field of view. There will also be other weaker showers active at this time. Most notable will be the well known Perseids that will produce swift meteors entering your field of view from the upper left. The much slower Alpha Capricornids are also active with a radiant in the right portion of your field of view. Of course there will also be random activity with various velocities occurring at this time.
With the Perseids peaking near a full moon in August, the Delta Aquariids will offer the best opportunity to view meteor activity under favorable conditions this summer. Make an effort to see these meteors and be sure to let us know your results!