C/1930 L1 (Forbes)

For other comet discoveries by Alexander Forbes, see 37P/Forbes and C/1932 Y1 (Dodwell–Forbes).

Comet Forbes, formally designated as C/1930 L1, is a parabolic comet that was only observed through optical telescopes in the year 1930.

C/1930 L1 (Forbes)

Discovery[1]
Discovered by	Alexander F. I. Forbes
Discovery site	Cape Town, South Africa
Discovery date	31 May 1930
Designations
Alternative designations	1930e[2] 1930 V
Orbital characteristics[3][4]
Epoch	6 June 1930 (JD 2426133.5)
Observation arc	49 days
Number of observations	54
Perihelion	1.1528 AU
Eccentricity	~1.000
Orbital period	<270,000 years (inbound)
Inclination	97.0912°
Longitude of ascending node	279.265°
Argument of periapsis	320.966°
Last perihelion	10 May 1930
Physical characteristics
Apparent magnitude	9.0 (1930 apparition)

Observational history

The comet was discovered by Alexander F. I. Forbes as a 9th-magnitude object on the early morning skies of 31 May 1930. It was the fifth new comet of the year and the second of three comets he discovered overall.^[5] He immediately informed the Union Observatory in Johannesburg after an exact position was determined about two days later.^[1][6]

The comet was already on its outbound flight since it reached perihelion on 10 May 1930, about three weeks before discovery, but was still approaching Earth at the time, allowing it to be regularly observed from Johannesburg until the end of June.^[7] It was only visible in the southern hemisphere until June 23, when first northern observations were recorded by the National Observatory in Athens, Greece.^[8]

George van Biesbroeck made his first observations of the comet from the Yerkes Observatory on June 21, with Georg von Struve following suit from the Berlin Observatory shortly afterwards,^[9] however by that time it rapidly faded away from magnitude 11 to 15 by the end of the month, though a short tail was reported.^[6] Van Biesbroeck continued his photographic observations of the comet until July 17, and its last known position was recorded on July 21.^[10]

Orbit

In 1952, Austrian astronomer Erich Senftl of the Vienna Observatory was able to calculate a retrograde parabolic orbit based from 54 observations over 49 days, which is inclined to 97 degrees from the ecliptic.^[11] It reached perihelion at a distance of 1.12 AU (168 million km) on 10 May 1930, and made its closest approach to Earth at a distance of 0.37 AU (55 million km) on June 21. Due to limited data acquired, it is unknown whether it remains bound to the Solar System or it was ejected into interstellar space.^[4]