Just to put this event into perspective - here is the layout of the solar system at the time of photo. It's a simulation of the planetary orbits from above.
Earth (blue), Mercury (green) and Venus (white) all lie on a straight line today. That's why we see Mercury and Venus in the same direction from Earth. If the alignment was exact then Venus would be eclipsed (or occulted) by Mercury. But the view from above doesn't tell the whole story. The orbits of the planets are not quite coplanar (meaning not exactly level with each other) and so exact alignments - where one planet passes directly in front of another - are extremely rare events.
Mercury is about as far from the Sun as it can appear to be from Earth but Venus will continue to climb higher into the evening sky over the coming months. For the next few days the two planets will remain close together in the sky.
The clouds cleared for a couple of hours yesterday afternoon and I got a chance to see Mercury catching up to Venus in the evening sky. This was the view from my garden in Red Row.
The distance between them was about half a degree; closer than your little finger at arms length! You can just about see my telescope in the foreground of the picture. When I put the camera on that I got this view:
Venus is much brighter than Mercury. Both planets are almost behind the Sun as seen from Earth but Mercury is nearest to us. However, Venus is much bigger and has very reflective clouds whilst Mercury has no atmosphere and a dark, dusty surface. The upshot is that Venus always outshines Mercury.
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Dr Adrian Jannetta. Amateur astronomer, maths teacher and science enthusiast.