The Sky Guide challenge
At opposition, on 4 March, Vesta will shine at mag. +5.9
4 Vesta has the potential to become brighter than any other asteroid. Like all asteroids, its brightness varies over the course of its orbit. Under favourable conditions it can reach mag. +5.1 ,which puts it within fairly easy naked-eye territory from a dark-sky site. At its dimmest, Vesta can drop down to mag. +8.4, necessitating at least binoculars or a telescope to see. This month, we’re challenging you to find and record Vesta with nothing more than your eyes.
Vesta reaches opposition on 4 March when it will shine at mag. +5.9, a fraction dimmer than Uranus at opposition. The naked-eye threshold magnitude is typically stated as mag. +6.0, a value which isn’t too hard to achieve as long as you live under good dark skies. Such skies will be required if you intend to look for Vesta close to opposition. Resources such as darksitefinder.com/map or www.lightpollutionmap.info are great tools for finding dark skies near you.
The Moon is in a waning gibbous phase at the start of March when Vesta is brightest, so plan any attempt before moonrise. On the evening of 1 March moonrise is at 20:54 UT, on 2 March it’s at 22:22 UT, on 3 March it’s at 23:48 UT and on 5 March at 01:14 UT. There is no moonrise on 4 March. As you can see, as opposition date approaches, the Moon moves conveniently out of the way.
The region where Vesta is located reaches highest altitude, due south, at 00:40 UT at the start of March; over 50º above the southern horizon from the UK. This moves the asteroid out of any low horizon murk. Located near the rear of Leo, the Lion, the Milky Way is also absent. This removes a lot of the fainter stars which could otherwise be confused for Vesta.
You will need to utilise all the tricks if you stand a chance of succeeding. Give your eyes at least 20 minutes in total darkness. Use the trick of averted vision – looking slightly away from the faint object you’re looking for, to place its dim light on a more sensitive part of your retina. We’d also recommend memorising the finder sequence we’ve prepared (below) so you don’t compromise your dark adaption by looking at the chart, even under a red light.
A chair or recliner will help you observe comfortably, an important and often overlooked aspect when looking for faint objects. Use our finder sequence and tick off the navigational stars one by one. If your eyes and sky are good enough, you may pull off what is, without question, one of the trickier challenges we’ve set.