Venus’ brilliant evening showing for the rest of the year

Venus and an old crescent Moon are a spectacular sight on the pre-dawn of 12 September. This is the view at about 5.30am BST. AN graphics by Greg Smye-Rumsby.

Venus is now a brilliant ‘morning star’ seen for a short time in the pre-dawn eastern sky. The planet has raced west of the Sun following inferior conjunction on 13 August and is on the cusp of another superb apparition. The memory of Venus’ splendid, long-lived showing in the evening sky, which ended in July for UK observers, is still fresh. 

At its best during the late-spring, observers across the UK were treated to its sheer brilliance seen against the backdrop of an astronomically dark sky. As far as single planet showings goes it doesn’t get better. Happily, by the end of this month and through to November we are in for a repeat performance, except this time in the pre-dawn sky. It pulls out to greatest elongation west of the Sun on 23 October.

Presently, Venus rises at about 4am BST from London and climbs to an elevation of around 10° by 5am. It burns blazingly bright, at magnitude –4.5, and across an eaten horizon free from major obstructions, can be seen to climb to an altitude over 20° by sunrise. 

As the month progresses Venus makes rapid progress away from the morning horizon, enough for the planet to be set against a darkish sky (astronomical twilight in force) for a time. The pre-dawn of 12 September is picturesque, with Venus being joined by an old crescent Moon situated around 11° to the left (west).

At the end of September Venus, still shinning at magnitude –4.5, rises at 3am and achieves the observationally-important 30° altitude mark, lying just short of 35° up by sunrise (at about 7am from London). Across a flat horizon it’s possible to view Venus in an astronomically-dark sky for perhaps an hour or so, until the start of astronomical twilight at about 5am.

Throughout the month you can observe Venus’ changing phase through a small telescope; a 15 per cent-illuminated crescent fattens into a 36 per cent crescent. 

Venus crescent phase evolves from 15 per cent on 5 September to 36 per cent by the end of the month.