This is a delightful time to find the ever elusive Mercury because through the first two weeks of June it puts on its best show of the year for those in the Northern Hemisphere and it’s relatively easy to find because brilliant Venus points the way.
Special June 2013 dates for viewing Mercury, Venus, Jupiter and the Moon:
- 1 – Mercury at its brightest and Jupiter still in view.
- 9 – A very thin crescent Moon little more than one day old will be roughly 10 degrees – one fist – beneath the pair of planets – Venus and Mercury.
- 10 – A much easier to see – and quite pleasing – will be a 2-day lunar crescent beside the pair (just south) and almost fitting in the same binocular field of view.
- 11 – The 3-day crescent Moon will have climbed well past the pair, but still make a nice show.
- 18 – Mercury has reached its peak and started back down and on this date drawing within a couple degrees of Venus – just south. The two will be quite high – about 11 degrees half an hour after sunset, but Mercury will have faded to magnitude 1.1 making it a challenge to pick out in the twilight.
Also this month:
- Saturn should be easy to find any evening in June – look due south an hour after sunset
- The Sun marches itself to a northern standstill
- Oh – and the Moon will be at its biggest for the year – though I’m afraid just knowing that will muddy the observational waters a bit
But let’s start with Mercury because the speedy little planet is always a challenge to see. Why? First, because it is very fast. Earth chugs along at a “mere” 66,000 miles an hour in its annual journey around our star, the Sun. (Doesn’t feel like we’re going that fast, does it?) But Mercury, being closer to the Sun, moves much faster – it covers a much smaller orbit at a blazing 107,000 miles an hour. So that means when it is well placed for observing it doesn’t stay that way long and it’s easy for the weather and the rest of life to get in the way of seeing it.
What’s more, because it is so near the Sun we only see it as it pulls out to one side or the other of the Sun and it does that for relatively brief intervals.
And even these quick glimpses vary considerably because it’s orbit is much more lopsided than most. At one point it can be as much as 43.6 million miles from the Sun – and at another it may be as little as 28.6 million miles. (In comparison, Earth can vary from roughly 94.5 million miles from the Sun to 91.4 million miles.)
How far it is from the Sun impacts how easy it is for us to see. If close to the Sun it either rises or sets in strong twilight – and since it seldom gets much brighter than magnitude -1, it can be quite difficult to pick out in the twilight. And even when it gets pretty far away from the Sun, it’s so small that it never becomes as bright as Venus – in fact, in June it will be easily outshone by Jupiter and Venus. This June, Mercury will reach a maximum brightness of -0.4 and that on the first day – it grows a bit dimmer each night thereafter, though this will be hard to judge because it also puts more distance between it and the Sun, so that means we see it against a darker background each night.
Cool, huh? I mean it moves a little bit more into darker sky each night – but at the same time it dims a little each night – doesn’t want to make things too easy for us! 😉
But sometimes several factors combine to give us an especially good look at Mercury and this June is such a case – with the added bonus that the much brighter Venus will be near it and thus point the way to finding Mercury. The basic routine is simple. You want to start looking about 30 minutes after sunset and when you spot Venus, turn your binoculars on it – about any binoculars will do – and for much of the month Mercury will fit in the same field of view looking like a significantly dimmer star. As it gets darker you should be able to pick it out with your naked eye – though if you wait too long it will be too close to the Western horizon – so timing really counts.
As the month progresses Mercury will be a bit higher each night 30 minutes after sunset and Venus will appear to chase it – but Jupiter will drop out of view in just a few days.
Your first challenge, of course,is to merely find the planets in your evening sky and that require an unobstructed western horizon, good clear skies, and appropriate timing – and binoculars sure help, but aren’t absolutely necessary.
But what are you really seeing?
Or maybe the better question is: Why do you see the planets this way?
For the answer we turn to an Orrery – and there’s one online that can be found here. I used it – and modified the view with labels and arrows – to produce the two images that follow. Essentially this is a view from overhead showing the counter-clockwise motion of the planets around the Sun. It is only very roughly proportional and your challenge is to look at the Orrery view, then mentally place yourself on the Earth and imagine what your view at sunset would look like. Remember – now you’re getting down in the plane of the solar system and looking outward and what you see is a two-dimensional view that cancels out the huge distances between the planets.
As I watch this wonderful dance of the planets from night to night – and the changes are especially obvious with the swiftly moving inner planets of Mercury and Venus – I try to get a picture in my minds eye of what’s really happening. Do this enough and when you look at a planet or the Moon in the sky, you can easily sense exactly where they are in their orbits around the Sun – and where you are in respect to them. I find this a very satisfying piece of mental gymnastics – that we little creatures on our tiny little spaceship Earth, whirling and hurtling about the Sun at incredible speeds, have been able to figure this out. Don’t get me wrong – I take no c edit for that – just one of those special moments when I feel proud to be one of the billions of homo sapiens here and feel maybe we have earned that name – sapiens indeed! 😉
One last piece of dynamics at work. As mentioned, Mercury is at its brightest at the start of the month. By the 14 it has dropped about one whole magnitude to 0.76, by the 21st it’s magnitude 1.5, and by the 28th magnitude 2.6. So it will be getting harder and harder to see as it drops more and more into the twilight zone and as it loses brightness. Why does it get dimmer? Look at the Orrery charts – it is moving to a position between us and the Sun and just like the Moon, as it gets between us and the Sun it goes through phases. By the 28th it is a thin crescent and so is reflecting very little light our direction. (These phases can be seen with a small telescope, but you will not detect them with binoculars.)
Mercury and Venus week by week
The following chart shows you the changing positions of Venus and Mercury during June 2013. All are for 30 minutes after sunset for mid-northern latitudes, and all are prepared from Starry Nights Pro screen shots with labels added. Venus never gets much higher than 10 degrees above the horizon – not only throughout June, but essentially for the rest of the year it will be a pretty constant western star – slipping southward somewhat and eventually, in late fall, rising some , before going off stage in January 2014. Mercury’s appearance int he West is strictly for June and as you can see, by the end of the month it’s heading quickly for the horizon and is quite faint.
Saturn – a southern star!
Wait until about an hour after sunset during June 2013, then look due south. Almost four fists above the horizon (from mid-northern latitudes) and about one fist apart are two bright “stars.” The slightly brighter one on the left (east) is Saturn. The other – which should appear bluer – is the first magnitude guidepost star Spica. Down to the lower left is another star of about the same brightness, Antares. Compare these three – they are roughly the same brightness, but Antares is tinted red, Saturn yellow, and Spica blue. They make a good introduction to noting star colors – which to my eye are more tints, but certainly detectable.
Who can resist the Solstice magic?
We’re fascinated with extremes and since the Sun is responsible for maintaining all life on Earth it’s rather natural to want to track its movements in our sky and mark its extremes. There’s no better time to do so than when it reaches it’s most northern point – the Summer solstice. And if you want to be really accurate that happens at 1:04 am EDT on the morning of June 21. So the time to greet the astronomical start of Summer is to mark the sunrise on June 21.
That said, this is more for those who are fond of records. Truth is you will be hard pressed to tell the difference of where exactly where the sun rises or sets a couple days before that date, or a couple days afterwards. The changes are just too small for us. So you have to take the word of those who track such things with sophisticated math and instruments – 1:04 am June 21 is the time and date when the Sun reaches its most northerly point. And the shortest night of the year is June 20-21.
All of this, of course, is for northern hemisphere observers. Our friends Down Under are marking the start of winter.
And speaking of special events . . .
On the night of June 22-23 we have a full Moon – the largest full Moon of the year.
Why is this larger than other full Moons? Because it is closer to us at this particular full Moon. How much larger is it? Significantly – but not so much that you really can tell the difference. To do that you need to see a larger full moon next to a small full Moon – and you can do that by going to this web site which gives a wonderfully detailed explanation.
Meanwhile, just sit back and enjoy it – and don’t confuse this with the Moon illusion phenomena – that is simply our eyes and brain playing tricks on us to make the Moon (or the Sun) look much larger when it is near the horizon, than when it is high in the sky.