The 11st-largest asteroid, 3 Juno, reaches opposition this month
Minor planet 3 Juno reaches opposition on 8 September, a time when it appears to the southwest of the faint, yet surprisingly distinctive, Circlet asterism in Pisces. On 1 September, 3 Juno is in Pisces, around 5˚ below the midpoint of a line between the Circlet and another famous asterism further to the west, the Water Jar. Shining at mag. +8.1, Juno crosses the border from Pisces into Aquarius on 3 September.
Juno brightens to mag. +7.8, the same as the planet Neptune, on 7 September, holding this brightness until 9 September after which it slowly begins to dim once more. By the end of September, Juno will have dimmed to mag. +8.4. This means it’s a viable binocular target throughout the month, and eminently suitable for tracking through a small telescope.
The comparison in brightness to Neptune is particularly apt as this distant main planet sits about 10˚ to the east of 3 Juno when both worlds share a similar brightness. The brightest guide star in the area is mag. +3.7 Lambda (λ)
Aquarii, Juno appearing around 7˚ to its northeast on 1 September. It then tracks southwest, appearing 1˚ northwest of Lambda (λ) Aquarii on 21–23 September. Between 10 and 13 September, 3 Juno appears to cross a roughly 3˚-long, bent line of faint stars formed from mag. +6.7 TYC-5245- 586-1, mag. +5.8 TYC-5245-1215-1, mag. +6.3 TYC-5238-1235-1 and mag. +5.8 BU 178. These provide a good location aid.
Juno is the 11th largest asteroid and the second largest stony (siliceous or S-type) asteroid, with an estimated 1% of the entire mass of the asteroid belt. Its elliptical orbit is highly eccentric and takes it out to 3.35 AU (Astronomical Units) from the Sun at aphelion and as close as 1.99
AU at perihelion. The entire orbit takes 4.36 years to complete and is inclined with a tilt of 12˚ to the ecliptic.