Delta Aquariids and Alpha Capricornids

Southern Delta Aquariids:  A good meteor shower that suffers from a lowish radiant altitude from the UK.

Shower details – Radiant: 22:40 -16.4° – ZHR: 25 – Velocity: medium – 41km/sec – Parent Object:96P/Machholz?

Main Activity Dates July 12–August 23
Peak Rates July 30
Peak ZHR 25
Best Observed Rates Around the middle of the night
Visibility each night (UK) Visible all night
Moonlight issues at maximum 2 days old

Alpha Capricornids:  A lowish active meteor shower that can produce slow moving colourful bright meteors.

Shower details – Radiant: 20:28 -10.2° – ZHR: 5 – Velocity: slow – 24km/sec – Parent Object:169P/NEAT

Main Activity Dates July 5–August 15
Peak Rates Aug 2–3
Peak ZHR 5
Best Observed Rates Around the middle of the night
Visibility each night (UK) Visible all night
Moonlight issues at maximum Waxing Crescent

The naming of meteor showers can cause some confusion at this time of the year, with different meteor groups using different names for the same meteor shower. For example, the name Capricornids is used by some groups for a shower producing low activity throughout most of the month, whilst others use it as an alternative name for the Alpha Capricornid meteor shower that peaks during the transition from July to August.

The proximity of many (mostly) low activity meteor shower radiants within Aquarius and Capricornus can also be a problem. Visually it can be difficult to decide which of these radiants a particular meteor came from, especially from the UK as the radiants are generally low in the sky and the star patterns may be difficult to make out in hazy/light-polluted skies. Consequently, the International Meteor Organisation (IMO) groups most of them together as part of the Antihelion Source (ANT – see chart below). Only the southern Delta Aquarids (SDA, peak July 28-29) and Alpha Capricornids (CAP, peak Aug 2–3), with their higher rates, are listed separately by the IMO. Older listings sometimes include a northern Delta Aquarid shower peaking around Aug 7, with a radiant near the Aquarius–Pisces border.

The Delta Aquarids-S produce medium speed meteors whereas those of the Alpha Capricornids are rather slow (a difference that can assist in correctly assigning meteors between these two showers). The Delta Aquarids-S are rich in faint meteors, while the Alpha Capricornids can produce a good percentage of slow moving bright meteors.

The richness of the Delta Aquarids-S in faint meteors (produced by smaller particles) leads to the shower being particularly strong for radio observers. Indeed, they continue to outperform the Perseids at radio wavelengths almost up to Perseid maximum.

Alongside these showers, early activity may also be seen from the Perseids, whose radiant in late July lies below the “W” of Cassiopeia (see  here  for more info)

The charts which follow show the location of the radiants of the Alpha Capricornids and Southern Delta Aquarids, with the UK horizon shown for the early hours of the morning.

Alpha Capricornid radiant
Alpha Capricornid radiant
Delta Aquarids South radiant
Delta Aquarids South radiant