2015 October 5

Planetary line-up in the morning sky

Stewart Moore

All astronomical action seems to be taking place in the morning sky at the moment: a close approach of Mars to Regulus on September 25, a beautiful total lunar eclipse on September 28, the occultation of HIP 14977 by 275 Sapientia on September 30 and now, over the next few days weather permitting, a spectacular morning line-up of Mercury, Venus, Mars and Jupiter. And on October 9 and 10 the waning crescent Moon joins them in the act. If you ever wanted to see a portion of the ecliptic delineated in the sky, now is the time. Although this means getting up early (or going to bed very late) the reward is often much steadier seeing – just what is needed for planetary observing.

The chart below shows the sky (for Colchester, Essex) at 05:00UT (06:00BST) on October 9 looking due east. Venus at mag -4.5 dominates the view at an altitude of 27 degrees with Jupiter at mag -1.7 below. Fainter Mars (mag +1.8) hides between these 2 brilliant guardians. Mercury (mag +0.9) brings up the rear and at an altitude of around only 3 degrees may be difficult (or impossible) to locate unless you have a very good horizon and one clear of morning mist – a common fearure of autumn mornings. By 06:00UT Mercury will have risen to an altitude of 11 degrees, but is likely to be lost in the ever brightening sky as sunrise takes place only a few minutes later. Hunting for Mercury with binoculars at this time, so close to sunrise, is dangerous and should not be attempted.

Mars and Jupiter continue to play cat and mouse with each other for the next few days after this event, and on October 18 pass within half a degree of each other making a wonderful observing or imaging opportunity. What better reason do you need for getting out of bed early!