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I’ve been busy, recently and I’m likely to stay that way for a while, hence the lack of posts. Still, I’m hoping to be able to take a trip to Stonehenge this year to see the solstice. That’s why my prediction is that it will be cold and wet and thick cloud will prevent anything interesting making an appearance. However, if there are clear skies, there could be plenty to see over Stonehenge this solstice.

Natural Astronomy

There’ll be plenty to see in the evening sky after sunset at 9.26pm. To the west Venus will be extremely bright at magnitude -4.0 (the lower the number the brighter something is). When you see it you won’t be able to mistake it for anything else. That will be setting at a quarter to midnight, so there’ll be plenty of time to see it.

Stonehenge astronomical chart for sunset solstice 2010

Position of the planets at sunset. Click for full size.

Moving to the left, are Mars, Saturn and the Moon. Mars will be magnitude 1.3 so it won’t be the brightest thing in the sky, Arcturus and Vega will be brighter but it’ll still be easy to find. If you’re struggling find the Plough. The two pointer stars that point up to the Pole Star will be more or less also pointing down to Mars this evening. Mars sets at a quarter to one, but if you want to see it realistically you’ll have to be looking before midnight. If you’re lucky it’ll have a slight ruddy glow. Saturn will be the only bright object between Mars and the Moon. In fact it’ll be slightly brighter than Mars in perfect atmospheric conditions, but I doubt my eyes will be good enough to measure that.

The Moon will be in Virgo, near the star Spica, which was thought to be a sheaf of corn in the hand of Ceres, if you’re Roman, or Demeter, if you’re Greek. Fans of mythology will be keenly aware that Demeter/Ceres had a daughter with Zeus which makes her not technically a virgin, but the Greeks called her Parthenos and that usually gets translated as virgin. To find Spica usually you’d follow the arc of the handle of the Plough to Arcturus, and then Spica is the next bright star down. This night it’ll be the closest bright star to the Moon. It could be hard to spot because the Moon will be bright. It’ll be 69% lit, nine days old and waxing gibbous. It’ll be more or less low in the sky to the south at sunset and set around 1am, which is astronomical midnight. It’s not the same as civil midnight because these days Stonehenge is on Daylight Saving Time, like the rest of the UK.

Stonehenge astronomical chart for midnight solstice 2010

Stars at 1am over Stonehenge. Click for full size.

Around 1.20am Jupiter rises. It’s likely that you’ll need to wait till 2am to get a good view. It’ll be shining in silver at magnitude -2.4 and, because Venus will have set, it’ll be the brightest planet on the sky. Jupiter will have a partner, but it’s highly unlikely you’ll see it at Stonehenge. Uranus will be close to Jupiter. If you hold out your hand at arm’s length then Uranus will be five or six little fingernail widths to the right of Jupiter. Normally there’s no chance at all of seeing Uranus, but at the moment it’s at magnitude 5.8 which puts it right on the limit of human vision. If you have very good eyesight and the atmospheric conditions are perfect you’ll see what looks like a very faint star next to Jupiter, and that’s Uranus. But even if we have that, I still doubt you’ll see it.

The reason is that it takes time for your eyes to adapt to the dark. Ian Musgrave says it takes a few minutes to see down to magnitude 5 or 6. Your eyes need to build up chemicals to make them more sensitive. Every time you see a bright light, like car headlights from the nearby roads, torches from other visitors who – quite reasonably – don’t want to break their necks walking around and any lighting from English Heritage this adaptation will be lost. On top of this there’s light pollution. We don’t just use energy lighting streets. A lot of energy is used to light up the sky, for no obvious reason. This reflects from any water droplets in the atmosphere and gives a sodium glow to the sky. Even cities over the horizon will be visible by their light pollution and this will prevent you from seeing some of the stars. You’ll stand a better chance of seeing Uranus if you use binoculars.

There is another difficult-to-spot object in the sky. To the north near Capella is Comet McNaught. Searching on the web for this is no help. There’s a lot of Comet McNaughts because Robert McNaught has found over fifty of them. This one is Comet McNaught 2009 R1. The current figures I have are that it will be between magnitudes 5 and 6. If that’s the case then you might not see much without dark-adapted eyes and it’s a binocular object. This figure is uncertain though because the comet is getting closer to the Sun. Around June 30-ish it’s predicted to be as bright as magnitude 2. Capella is not too hard to find. It’s the only bright star above the northern horizon, and it will be due north around half-past midnight. The comet will be a couple of degrees above it. Look for a fuzzy star.

The Sun is due to return a few seconds before 4.52am. Again, daylight saving explains why the Sun sets less than three hours before midnight, but doesn’t rise till almost five hours after.

IFOs

Or, if you don’t tell your friends what they are, UFOs.

The big events will be the passes of the International Space Station. There’ll be two and half over Stonehenge. The first will be at 1.08am till 1.10am. You’ll be able to see the ISS dropping from 38º up in the sky to the southeast down to the horizon. It’ll be bright (magnitude -2.7) but it will also be fast. This is the half appearance and you may not see it. You best chance is to be looking at Aquila, the brightest star in the southeast at this time, and it should appear near there.

The next appearance is the best. At 2.40am it will rise in the west and pass overhead before setting in the east at 2.46am. It will look like Venus did, but it will visibly be moving across the sky. It could look like an aeroplane and if anyone else says that you might want to agree before pointing out that there’s no visible flashing lights like there would be on an aeroplane. It will also be travelling too fast. Get your friends to rule out other obvious causes like Chinese lanterns, reflections of headlights, planets and so on so that you sound like you’ve been reluctantly convinced that whatever you saw was not of this world.

Then at 4.15am you can make everyone jump out of their skin by yelling “They’re BACK!” when the ISS makes another pass from the west again. This time it will set 4.23am in the eastsoutheast.

For extra UFO points you can also try pointing out an Iridium flare. This is a sudden bright reflection from one of the Iridium communications satellites. There are two during the course of the night. At 10.52:44pm on June 20 there’s a magnitude -1 flare westnorthwest above a handspan above the horizon. At 3.22:06am there’s a brighter magnitude -4 flare in the eastsoutheast. These will be fast; they’ll last for just a few seconds.

Flare Simulation. Source: Wikimedia Commons

Heavens Above, where I got these details from for the ISS and Iridium also has some transit times for fainter satellites, but the night sky is littered with satellites. If you see anything that looks star-like moving across the sky over six-eight minutes then it’s quite possibly a satellite. Some of these could be mistaken for aeroplanes. Registering on the site will enable you to print off your own star charts for ISS and satellite passes. If you’re on twitter @twisst can tell you when the ISS is passing over your location and send you alerts.

If you’re interested in visiting Stonehenge for the solstice this year and want more practical advice, like remembering to pack toilet roll, you’ll find Heritage Key helpful. And if there are clouds, it might not all be bad news.