September 2023 offers a great opportunity to spot the planet Venus as a bright planet early in the dark autumnal morning sky.
Venus is intensely bright at present, currently shining brightly in the morning. You can see it rise in the east from about 4am onwards.
And as we approach the end of September we're going to get a wonderful chance to see bright Venus against a dark sky.
Read Patrick Moore's archive article on what makes Venus so special and find out more about Venus in September in our video below:
At the start of September, Venus was well-placed and couldn't be seen against a dark sky, as it rose only two hours before the Sun.
However, that's changing and by the end of September Venus will rise nearly four hours before sunrise.
This gives us an amazing chance to see this dazzling jewel of a planet against an astronomically dark sky.
What will Venus look like?
The light from Venus is intense and effectively a point source.
On 15 September, after rising, Venus remains against astronomically dark skies for around 80 minutes, reaching an altitude of 10° as astronomical darkness comes to an end.
By the end of the month, Venus is visible under astronomical darkness for two hours, reaching an altitude of 18° before true darkness ends.
Catch it from mid-month onwards, before the Moon interferes, and there will be an opportunity to see it casting a shadow.
The Venusian shadow is quite something, as the point-source nature of the planet creates razor-sharp shadow edges.
The only problem is that the shadow is very faint and easily lost.
Why Venus appears in the morning
You may have heard of Venus referred to as a morning or evening star.
So why does Venus sometimes appear as a bright point of light in the morning or evening sky?
It's to do with the fact that Venus is an inner planet, lying between Earth and the Sun.
Venus reached inferior conjunction on 13 August, a moment marking when the planet lined up with the Sun, technically moving from the evening to the morning sky.
As a result, by the end of September, Venus will be a bright morning star and look amazing against the dark morning sky.
Photograph a shadow cast by bright Venus
The planet’s re-emergence into the morning sky will be dramatic and as it will be visible against a dark sky there’s an opportunity to photograph the shadow it can cast.
Being nearer the Sun than Earth and enshrouded by a thick, reflective atmosphere, Venus appears very bright in our sky.
Around mid-September it reaches magnitude –4.5, and under dark skies towards the end of the month the effect will be striking.
This is the perfect opportunity to photograph the delicate shadow it can cast.
Don’t expect this to be easy though, as the Venusian shadow is – like the cloud markings on the planet itself – very subtle.
You can find out more about this in our pick of interesting ways to photograph Venus or our guide on how to photograph a shadow cast by Venus.
And if you do manage to photograph Venus, don't forget to send us your images.
This guide originally appeared in the September 2023 issue of BBC Sky at Night Magazine.
