This isn’t rare, but it isn’t really common either. This month (or at least this week) astronomical viewers can have a chance to see 5 planets in a single evening.
After sunset, Mercury will be visible just above the horizon in the West sky – and we do mean just. Trees and houses may block your view of Mercury. However Venus and Jupiter will be more visible right above them also right after sunset, nice and bright, along with Mars, which while still not in occultation is pretty bright, rising in the East just after sunset.
Later in the evening, Saturn will rise in the Eastern sky – this is the only planet you will need to wait for as it is not immediately visible after sundown.
Although Mercury may be blocked by buildings, all of these planets can be seen with the naked eye, even in light-polluted areas.
For your best viewing be sure to get an area with a clear horizon so that all the planets can be seen.
Mercury is the innermost planet in our Solar System, and until recently it was mostly considered to be unchanging. Scientists having sent a couple of probes towards it conclided that there wasn’t much changing on its surface. That is, until the MESSENGER mission started sending back images of the surface that showed some rather odd changes to Mercury’s surface:
These pock-marks, or hallows were found on Mercury’s surface and were as big as a mile across. The weren’t impact craters as they were not deep enough. While rockey planet surfaces are not uncommon in our Solar System (our own Moon and many of the outer planet’s moons).
The likely culprit would seem to be minerals brought to the surface by actual impacts – the dramaticly changing temperature of Mercury’s surface means some elements and chemicals might be ‘erupting’ in a chemical, rather than a geological volcano of sorts.
In any case, it sheds some interesting light on little Mercury. You can read more as the story develops on NASA’s webpage