SUNSET: 
5Mercury has a fine evening apparition in February 2013, featuring an extraordinarily close conjunction with Mars on the 7th and 8t. Mercury should become visible in the first few evenings of February, and it will be highest from the 11th to the 21st.
This is one of two good evening Mercury apparitions in 2013 for observers at mid-northern latitudes, the other being from late May to mid-June. From the Southern Hemisphere, this is Mercury's worst evening apparition, and the best is in September and October.
Mercury peaks in the early evening sky from February 11th to 21st, while much fainter Mars appears lower each evening. The two planets pass spectacularly close to each other on February 7th and 8th. Their disks are shown in their correct shapes and orientations, but their sizes are exaggerated hugely, roughly matching their appearance through a telescope at high magnification.
Sky & Telescope diagram
The keys to locating Mercury are clear air, a location with an unobstructed view of the western horizon, and a bit of persistence. Binoculars are also a huge help.
A half hour after sunset, start scanning the horizon where the Sun's glow is strongest. Mercury should already be visible as a faint pinprick of light through binoculars, and it's likely to become more prominent as the sky grows darker.
During the first half of the month, you should also be able to see Mars near Mercury, as shown in our chart. But you might need binoculars, because Mars is about one-tenth as bright as Mercury. Mars and Mercury are spectacularly close on February 7th and 8th.
You may see an extremely thin crescent Moon to the lower right of the planets on February 10th. And a thicker but still delicate Moon floats above them on the 11th.
Mercury is at its highest from the 11th through the 21st. During this period it's still well above the horizon an hour after sunset, when the sky is growing dark even in the west. However, it fades significantly, from magnitude -0.9 on the 11th to +0.5 on the 21st.
After that, Mercury fades rapidly and appears nearly 1° lower each evening, soon disappearing from naked-eye view. However, this is also the period when it becomes most interesting through a telescope, becoming a long, thin crescent as it starts to come between Earth and the Sun.
Following Mercury with a telescope through an entire apparition is surprisingly rewarding. The key is to catch it as early as possible, while it's relatively high above the horizon. A bright sky is no obstacle to telescopic viewing; in fact it tames Mercury's otherwise overwhelming brilliance.
Comments
Joe Stieber
February 1, 2013 at 5:41 am
That's a great idea. I've spotted Mercury at each of its 13 elongations for the past two years (2011 and 2012), mostly with binoculars, but naked-eye when possible and occasionally through a scope. However, followimng Mercury with a scope for an entire apparition will add a new dimension to my effort. I was going to start last night, but it turned cloudy after sunset. The Clear Sky Chart for this evening (01-Feb-2013) looks promising, so I plan on taking my 80 mm refractor up to the local baseball field complex where there's a good western horizon. It will also be neat to watch Mercury and Mars converge in the coming days. Now we just have to hope for a spell of decent weather.
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Joe Stieber
February 5, 2013 at 9:40 am
I had my 80 mm, f/6 apo refractor out on 01-Feb-2013 for a look. I was able to see both Mercury and Mars in the scope (separate field of view), but the seeing was too dreadful to see any disk-like structure. 02 & 03-Feb were cloudy, but the sky was clear on 04-Feb, so I was out again to the local baseball field with the 80 mm scope. On arrival at 5:48 pm EST (25 minutes after sunset), I first spotted Mercury with 16x70 binoculars, and a few minutes later, both planets were seen with the scope. They were now close enough (about 3.5 deg apart) that they fit in the same field of view with a 40 mm eyepiece (12x, 5.2 deg field). Seeing was much better, so both planets showed a disc at 80x. Mars was a general ruddy color, while Mercury was whitish with some atmospheric chromatic aberration. The phase of Mercury (89% illuminated) was not yet evident. At 5:58 pm, I was able to spot Mercury naked-eye (but not Mars).
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Joe Stieber
February 18, 2013 at 6:57 pm
Since February 1st, I've seen Mercury on nine (9) evenings after sunset, basically every clear night. Using my 80 mm apo refractor at 160x, Mercury looked oblate on the 12th, the first time it clearly didn't look like a complete disc (it was 67% illuminated). On the 14th, a convex ternminator was apparent (59% illuminated). This evening, Feb 18th, the terminator looked concave, i.e., a crescent (Mercury was 41% illuminated). Following the phases of Mercury as Tony recommended has indeed been a worthwhile project. I look forward to seeing the crescent become even narrower in the coming days. However, nearby Mars is now difficult to find as it sinks lower in the twilight; the last time I could spot it was on the 12th.
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WIll
February 24, 2013 at 6:06 pm
I'd like to know if anyone has tried siting Mercury when on the east bank of the Mississippi river, a bit south of StL. I have tried a number of times, even with binoculars and wonder if there's simply to much vapor coming up off the river. I must admit I didn't start looking for it this year til well after it's highest point on the 16th. But I should have been able to see it the last few nights. It always seems there is this haze off towards the river. Simply curious if anyone else has any comments.
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Joe Stieber
March 3, 2013 at 3:49 pm
Now that February 2013 is complete, I can report that I saw Mercury with my 80 mm refractor on each evening of the month that had clear skies on the western horizon after sunset, a total of thirteen (13)dates. After my report on the 18th (when the terminator looked concave, as it would be for a beginning crescent), it was seen four more times in the scope, but the seeing did not allow much improvement in the appearance of the crescent shape (at best, it was a roiling, horizontal "banana"). My last sighting was on February 25th; the remaing February evenings were cloudy. Regardless, it was an interesting project, and I will try it again when there's a favorable elongation, hopefuly with better seeing.
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