Mercury and Venus – See them while you can
For the last week or so, and for the next few nights, Mercury and Venus are putting on a lovely display low in the western sky just after sunet. The closest two planets to the Sun, Mercury and Venus appear to move very quickly from night to night against the background stars, and so are never in the same place for very long.
Mercury is always difficult to spot as it is often quite faint and is so close to the Sun that it either sets very soon after sunset or rises only just before sunrise. For that reason it’s always good to have a brighter marker to locate Mercury by; for the next few days that marker is Venus.
Last week on April 3rd and 4th, Mercury and Venus were at their closest to one another, seperated by only a few degrees (or a bit more than a thumb’s width held at arm’s length), and Mercury was at its brightest.
- Mercury (faint) and Venus low in the west
As the month of April draws on, Mercury will set earlier and earlier, getting fainter and fainter, until by the middle of the month it will be all but lost in the western twilight.
So get out tonight (or the next time it’s clear over the following week) and have a look.
You can find out more about observing Mercury and Venus on the British Astronomical Association’s website
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So is Mercury the dim one to the right and slightly below the level of Venus in the pic. If so, why does it appear to be nearly the same diameter as Venus?
Yes, that’s right Mercury is the very dim dot to the right of Venus.
Basically they appear the same size due to seeing, the effect of atmospheric turbulence on their light.
The atmosphere was turbulent and so smeared out both of their images by the same amount. They differ in brightness and so the total amount of light on Mercury’s smudge is less, but smeared out over the same area.
Had seeing been perfect they’d still be smudged out due to the camera’s pixelation.
Add to that the fact that they’re not so different in angular size (Venus is 10″ and Mercury is 7″) since Venus is behind the Sun and Mercury in front, and there’s your answer.