The best opportunity to see Mercury is when the planet is at greatest ‘eastern’ or ‘western’ elongation. You need a clear horizon, because this inner planet does not appear high in the sky at night, nor far from the Sun’s glare. Remember when we tried to find Mercury just after sunset in March 2012? Millstone Night Sky News – (Mar 2012, in search of Mercury after sunset) Recall that it was difficult to get to a clear sky and clear horizon at sunset in the Mississippi Mills’ neck of the woods. You may also recall that Jupiter appeared in the sky at that time,… (This explains why the Greeks named our solar system neighbours, the ‘wanderers’ – as they appear at different times of the year over the years, and bunch up together as seen from our Earthly perspective).
This image shows the closest alignment of the 2 planets which occurred Jan 10 (less than 1 degree apart)… So close that the labels collide!
Now we have a helper! Venus shining at magnitude -3.9, it is very close to planet Mercury magnitude -0.4. (Smaller numbers for magnitudes mean brighter luminosity (again thanks to the Greeks))… So if you can find Venus, just look a bit west or nudge your binoculars towards the right, since you’re facing South, and you may spot the elusive, inner-most planet of the Solar System, Mercury.
So Mercury is relatively easy to find this January because:
- It reached ‘greatest elongation’ from the Sun, mid January 2015, and so stays away from the Sun’s glare long enough for us to try and find it. For Mercury to appear in the evening sky after sunset, it reaches greatest Eastern elongation because it’s east of the Sun and stays up after the sun sets on the western horizon.
2. The line of site proximity to Venus’ orbit provides a marker to help find Mercury. As you can see from the ‘blow-up’ of the inner planets and Mars, Venus and Mercury (and Mars) line up with respect to Earth’s orbit in January 2015.
For more information on observing planets, and understanding their orbital motions see: https://millstonenews.com/2014/04/night-sky-course-planets-earth-and-orbits-around-the-sun.html If you get hooked on chasing Mercury, and another apparition occurs without a nearby marker, you can always use this aid to help you find it: http://www.fourmilab.ch/images/3planets/elongation.html
So, during the next few weeks in January 2015, the next time it’s clear and you’re near an unobstructed horizon, remember to look West after sunset, and enjoy the glorious light of Venus and its fainter companion Mercury!