Astronomy at Ston̈ehen̈ge for the 2010 Summer Solstice

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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.

One thought on “Astronomy at Ston̈ehen̈ge for the 2010 Summer Solstice

  1. eccles

    I was on the verge of print­ing this out last night when I real­ised it was upside down for me :-) Sadly I didn’t see any­thing as easy to read & fol­low for the south­ern hemisphere.

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