July 24, 2010
Southern Delta Aquarids At Their Peak Next Week
The Southern Delta Aquarids are a meteor shower visible from mid July to mid August each year. Peak viewing times occur around July 28 or 29. The meteor shower originated from the breakup of the Marsden and Kracht Sungrazing comets.
The Delta Aquarids get their name from the area from which they appear to originate -- the constellation Aquarius, near one of the constellation's brightest stars, Delta Aquarii. There are two branches of the Delta Aquarids meteor shower, Southern and Northern. The Southern Delta Aquarids are the stronger of the two branches, with average meteor rates of 15 to 20 per hour, and a peak zenith hourly rate of 18. The Northern Delta Aquarids are weaker and peak later in mid August.
The first recorded observations of the Delta Aquarids came from G. L. Tupman in 1870, who plotted the paths of 65 meteors between July 27 and August 6. He plotted the radiant's apparent beginning and ending points, which were later corrected. Ronald A. McIntosh re-plotted the meteor's path, based on a greater number of observations made from 1926 to 1933.
Cuno Hoffmeister and a team of observers from Germany were the first to record the characteristics of a Northern Aquarid radiant within the stream around 1938. Canadian D.W.R. McKinley observed both branches in 1949, but did not associate the two radiants.
In 1952 astronomer Mary Almond determined both accurate velocity and orbit of the d Aquarids. She used a "Ëmore selective beamed aerial (echo radio) to identify probable member meteors and plotted an accurate orbital plane. Her paper reported it as a broad system of orbits that are "probably connected and produced by one extended stream."
The 1952-1954 Harvard Meteor Project confirmed her observations via photographic observation of orbits. The HMP also produced the first evidence that the stream's evolution was influenced by Jupiter.
The Delta Aquarids are best viewed in the pre-dawn hours, away from lighted areas such as towns and cities. Southern Hemisphere viewers will normally have better viewing because the radiant is higher in the sky during the peak times.
Since the radiant is above the southern horizon for Northern Hemisphere viewers, meteors will primarily fan out in all compass points -- east, north and west. Few meteors will be seen heading southward, unless they are short and near the radiant.
Image Caption: The constellation Aquarius as it can be seen by naked eye. AlltheSky.com