Zeta Aurigids

Observing

This minor meteor shower is visible during the period of December 11 to January 21, and reaches its maximum activity during December 31 (λ=279°), from an average radiant of RA=77°, DECL=+35°. Though the greatest activity seems to be detectable only by means of radar or telescopes, numerous visual radiants and photographic meteors indicate some activity is visible with the naked eye. A northern branch is also present during December 11 to January 15. Its maximum comes on January 2 (λ=281°), from RA=65°, DECL=+57°. The meteors of both showers are generally slow moving.

History

First detection of this shower was made by W. F. Denning during December 24-31, 1885-1886, when a radiant at RA=77°, DECL=+32° was noted producing slow meteors. On December 27, 1863, Alexander S. Herschel was one of several people who observed a fireball from RA=75°, DECL=+30°. Calculations revealed Herschel's fireball possessed a velocity of 32 km/s, which is identical to results obtained by Denning after analyzing observations of a bright meteor observed from RA=77°, DECL=+30° on December 28, 1886.

The true magnitude of this stream seems hard to determine, but some sense has been made out of the data after studying Z. Sekanina's radar data secured during the two phases of the Radio Meteor Project. The results seem to indicate a definite stream producing a shower during the period of December 14 to January 16; however, as can be viewed in the "Orbit" section below, the 1961-1965 survey possessed a smaller orbital inclination of nearly 7°, while the 1968-1969 survey indicated an inclination of about 11 deg. A possible explanation might involve the fact that the 1968-1969 session possessed a gap in the observational records that extended from December 21, 1968 to January 12, 1969. As a result, the period of maximum activity was missed and while the 1961-1965 survey revealed the stream to have crossed the ecliptic on December 30.9 (almost exactly at the time of the shower's expected maximum), the 1968-1969 survey showed the stream to have crossed the ecliptic on January 13.9.2 Thus, it seems this gap not only reduced the number of meteors being observed, but also influenced the shower's apparent distribution of meteor activity.

A notable feature among records of meteor activity for the first half of January is that radiants are frequently present in Auriga, but, when the positions are plotted, it seems activity is likely to occur in a region whose dimensions are about 10 degx30 deg. It should be kept in mind that this is based on radiants observed during the last 100 years. For any particular year the radiant seems to be less than 10 deg across. Examples of some of these observed radiants and fireballs are as follows:

Zeta Aurigid Radiants and Fireballs

YearDateα (°)δ (°)Source
1863Dec. 2775+30D1899
1885-86Dec. 24-3177+32D1899
1886Dec. 2877+30D1899
1888Dec. 24-2988+61D1899
1891Jan. 6-985+61D1899
1913Jan. 2.8275+30D1916
1921Jan. 14.586+42H1948
1932Jan. 182+36O1934

Interestingly, although most of these visual radiants originated from what might be considered as the "southern branch" of this stream, consulted lists of photographic meteors reveal a fairly well-defined "northern branch" consisting of 11 meteors detected during the Harvard Meteor Project conducted during 1952 to 1954. Eight meteors gathered from American and Russian sources form a fairly diffuse "southern branch."

The photographic northern branch seems to persist from December 11 to January 15, but may be active as early as December 1 and as late as January 21. Maximum activity seems to occur between December 28 and January 2, from an average radiant of RA=65°, DECL=+57°.

From the accumulated data, the Author sees the Zeta Aurigids as a split stream, with most photographic and visual data indicating the northern branch possesses a greater population of large particles. Most of the information gathered on the southern branch reveals it contains primarily small particles, which are easily detectable using radar equipment; however, this branch has produced several fireballs in the past, which is a feature not present in the northern branch.

Orbit

The radar orbits which were determined from the two phases of the Radio Meteor Project conducted by Sekanina at Havana, Illinois, during the 1960's are as follows:

1961-51968-9
Argument of Perihelion (ω) [J2000]235.8 deg.221.0 deg.
Ascending Node (Ω) [J2000]279.7 deg.293.9 deg.
Inclination (i) [J2000]6.7 deg.11.1 deg.
Perihelion Distance (q)0.816 AU0.901 AU
Eccentricity (e)0.6020.513
Semimajor axis (a)2.053 AU1.851 AU