Follow asteroid Pallas while at its best for 2021

Minor planet (2) Pallas reaches opposition on the night of 10/11 September (Friday night/Saturday morning) at 01:48h UT, when it lies at a distance of 321 million kilometres (2.146 astronomical units [AU]) from Earth and 471 million kilometres (3.149 AU) from the Sun. Pallas is the second asteroid discovered, on 28 March 1802 by German physicist and astronomer Heinrich Olbers (1758–1840). Just over two years earlier, on 1 January 1801, Italian Catholic priest and astronomer Giuseppe Piazzi (1746–1826) discovered the first asteroid (1) Ceres.

Asteroid (2) Pallas comes to opposition on 10/11 September and can be seen tracking through first Pisces and then Aquarius, where it stays for the remainder of 2021. AN Graphic by Greg Smye-Rumsby.

Pallas is one of the so-called ‘big four’ asteroids, together with Ceres, (3) Juno and (4) Vesta (Juno’s inclusion in this exclusive company is owing to its early discovery rather than its size; its the thirteenth-largest asteroid in terms of diameter). Pallas is a big body, being the third-most-massive asteroid, after (1) Ceres and (4) Vesta, with dimensions of 572 x 557 x 476 kilometres. Compositionally, Pallas looks like carbonaceous chondrite meteorites.

(2) Pallas is well placed for observation from UK shores at this opposition, tracking south-westwards through south-western Pisces and crossing into neighbouring Aquarius on 24/25 September. Pallas peaks in brightness at magnitude +8.6 at opposition, making it well out of naked-eye range and reasonably accessible to a pair of 10 x 50 binoculars, though you’ll find Pallas much quicker by searching for it through a small telescope. Pallas has an unusually wide brightness range; it can appear as bright as seventh-magnitude or as dim as eleventh-magnitude owing to its widely differing opposition distances, an effect of its moderately-eccentric (non-circular or elliptical) orbit around the Sun.

(2) Pallas is the third-largest asteroid after dwarf planet (1) Ceres, by far the largest asteroid, and (4) Vesta. AN graphic by Greg Smye-Rumsby.

Pallas also has an unusually high orbital inclination of over 38 degrees, despite it lying within the main concentration of minor planets in the asteroid belt. This means the track of Pallas can take it far from the ecliptic (the apparent path of the Sun across the sky to which the vast majority of Solar System bodies follow closely) at times.

Pallas lies just short of 40 degrees altitude when it crosses the southern meridian from London at 12.46am BST on 11 September. It lies at RA 23h 09m 25s, Dec –00° 14′ 29″, which places it among the stars of Pisces, 2.2 degrees east-south-east of magnitude +6.2 3 Piscium (HIP 113610) and five degrees above the ecliptic.

At around opposition, Pallas moves against the background stars at around 44 arcseconds an hour, speedy enough for high-resolution imagers to easily detect and for visual observers to pick up upon using high magnification over the course of a few hours or so. Why not have a go at creating a composite image showing Pallas’ path over the course of a night or every few days or so during the rest of September.