Virgo Meteor Sky View
Some notes on meteor related topics
The Antihelion Source
In 2006, the International Meteor Organization (IMO) decided to summarize a number of well-known meteor showers under the term antihelion source [1, 2]. This is not a radical new concept but a term present since the first radiants have been named. Those of you reading Robert Lunsford's weekly outlook on meteor activity are used to the antihelion (anthelion) source for a long time.

The radiants of the replaced meteor showers have one thing in common: they all are located close to the ecliptic and were named after the constellations of the Zodiac:
  • delta-Cancrids (DCA)
  • Virginids (VIR)
  • Sagittarids (SAG)
  • Northern delta-Aquarids (NDA)
  • Southern iota-Aquarids (SIA),
  • Northern iota-Aquarids (NIA),
  • Piscids (SPI),
  • Northern Taurids (NTA),
  • Southern Taurids (STA),
  • Northern chi-Orionids (XOR).
These meteor showers are caused by particles associated with the main belt of minor planets and some short period comets. Their radiants are concentrated slightly east (12 degrees) of the so called antihelion direction. When you draw a line from the sun to the earth and extend this line through the earth to go beyond the earth's dark side, it will point into the antihelion region (see figure to the right) [2].

With their radiant lying opposite the sun, the antihelion meteors belong to the night sky and will never occur during daytime. The radiant rises near the end of the evening twilight in the east and reaches its culmination point shortly after local midnight. In the first sun light of the new day, the radiant will vanish in the west [3].

Over the year, there is no significant change in the ZHR of the antihelion source. The annual average amounts to approximately 2.5 meteors per hour (rounded to 3). One exception occurs through November, with the Northern and Southern Taurids (NTA and STA) slightly enhancing the ZHR up to 5 specimen per hour (see figure below) [2]. For the IMO, the Taurids' exception is of adequate importance to keep them in their working list of visual meteor showers replacing the uniform antihelion source for the duration of their peaking time [1, 2].

All figures from [2]

[1] Rainer Arlt, Jürgen Rendtel: Ongoing meteor work; A new Working List of meteor showers.
WGN, The Journal of the IMO 34:3 (2006) 34:3, pp. 77-84

[2] Jürgen Rendtel: Fundamentals of meteor science; Visual Sporadic Meteor Rates.
WGN, The Journal of the IMO 34:3 (2006), pp. 71-76

[3] Robert Lunsford: Fundamentals of meteor science: The anthelion radiant.
WGN, The Journal of the IMO 32:3 (2004), pp. 81-83

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Sabine, DL1DBC