As darkness falls on the evening of Monday, 21 March, observers in the British Isles should look low to the east-southeast to see the 13-day-old waxing gibbous Moon just four degrees to the right of planet Jupiter. The pair lie in southern Leo and will easily fit within the same field of view of most binoculars. For scale, this view is about 40 degrees wide, or twice the span of an outstretched hand at arm’s length. The Moon’s size has been slightly enlarged for clarity. AN graphic by Ade Ashford.Jupiter reached opposition almost a fortnight ago, so the largest planet in the solar system is still very much centre stage in the March night sky. Currently shining at a conspicuous magnitude -2.5, Jupiter is therefore more than twice as bright as the brightest nighttime star, Sirius, sparkling low in the south as night falls.
In the telescope, Jupiter’s mighty equator presently spans 44.2 arcseconds in angular measure. This means that as seen through a telescope, a magnification of little more than 40x is required to enlarge it to the same size as the adjacent Moon appears to the unaided eye. At higher magnifications, and with good seeing, you will also see the planet’s Great Red Spot (GRS) tonight as it passes Jupiter’s meridian close to 8pm GMT.
All four of Jupiter’s large Galilean moons — Io, Europa, Ganymede and Callisto — are also well presented tonight. While you’re looking for the GRS, note that moons Io and Europa pass each other at 8:09pm GMT, separated by just three arcseconds. The changing relative positions of the moons will be fascinating to watch at high powers — if seeing permits, naturally.The configuration of Jupiter and its Galilean moons at the instant Io passes close to Europa. The view is north up and east to the left — as one would see with a high-power terrestrial telescope. Users of Newtonian/Dobsonian reflectors should invert the graphic to match the eyepiece view, while owners of refractors, Maksutov- and Schmidt-Cassegrain telescopes using a star diagonal need to mirror the graphic left-right to match their view. AN illustration by Ade Ashford / SkySafari Pro.If you consult our interactive Almanac, you can obtain predictions of when the Galilean moons will pass in front of Jupiter (termed a transit), or when their inky-black shadows drift across the face of their parent planet — events called shadow transits; the latter are easier to view. For a summary of Jovian phenomena to see during the remainder of March, see this article.
As the night moves on, the angular separation of Jupiter and the Moon actually decreases owing to the latter’s rapid west-east orbit motion. As Tuesday arrives at midnight, the pair will be just three degrees apart as seen from the UK. By the time Jupiter and the Moon fade into the growing dawn twilight low in the west around 5am GMT for the centre of the British Isles, they will be closer still. If you’re an early riser Tuesday, when’s the latest that you can still see Jupiter with the naked eye?
Inside the magazine
Find out everything you need to know about observing Jupiter at its best and the other planets in the night sky in the March 2016 edition of Astronomy Now.
A team of scientists has documented atmospheric changes on Io, Jupiter’s volcanically active satellite, as the giant planet casts its shadow over the moon during daily eclipses. Io’s thin atmosphere collapses as the sulfur dioxide gas emitted from volcanoes freezes when shaded by Jupiter. The atmosphere reforms when Io moves out of eclipse and the ice sublimates.
A partial eclipse of the Sun is set to wow North Americans this afternoon (23 October) as the Moon’s silhouette will be seen to cover as much as 50 percent of the Sun from the USA, and up to 80 percent of the Sun in northern Canada.
We may be losing Jupiter in the west at dusk, but two other planets are well placed in the late evening. Skywatchers in the UK and Western Europe should look low in the southern sky around 12am local time on 17, 18 and 19 June to see the waxing gibbous Moon in the vicinity of planets Mars and Saturn, plus first-magnitude star Antares in the constellation of Scorpius.
