Neptune at Opposition
September 2019 :
With Mars and Venus lost in the glare of the Sun, our attention this summer has been focused on Jupiter and Saturn. By late evening in September, our two large gas giants sink low in the southwest, giving way to a seemingly planetless void as the autumn constellations fill the sky.
Looking beyond Saturn, our solar system’s fourth largest planet is the next to grace the sky. Throughout 2019, Neptune is located near the border of Aquarius and Pisces. Normally, star-hopping to targets in this devoid-of-bright-stars area of sky can be a challenge. However, this year Neptune’s position makes it somewhat easier, notably because it spends the next several weeks within a degree of 4th magnitude Phi Aquarii.
To begin your journey to Neptune, begin at the Circlet asterism in Pisces. You can locate the Circlet below the Great Square of Pegasus. From the westernmost star in the Circlet, go south, about one-and-a-half Circlet diameters (roughly a binocular or finder field of view) to find Phi. Once you’ve located Phi, you’re there! Neptune should already be in your low power field of view.
Phi Aquarii is an M giant, and its orange hue will be in striking contrast to blue Neptune, especially in larger telescopes. Be sure to look for Neptune on September 5-6, when it will be within 40 arcseconds of Phi Aquarii. The close separation combined with the contrasting colors should give the pair an almost Albireo-like appearance.
The full Harvest Moon lies just over 5 degrees to the southeast of Neptune on the 13th.
