by VirtualAstro | Jun 2, 2011
Noctilucent Clouds
Noctilucent Clouds 2009 Panorama Credit: VirtualAstro
Soon you may see an eerie spectacle on clear summer nights if you are located at latitudes between 50° and 70° north and south of the equator: Noctilucent Clouds.
These ghostly apparitions are a delight to see and are quite rare. It is incredibly difficult to predict exactly when they will appear, but we do know they should begin to appear soon.
The season for Noctilucent Clouds (Noctilucent = Latin for “Night Shining”) starts early June and continues into late July. They are seen just after dusk, or before dawn and an apparition can last around an hour.
These mysterious clouds, with their bizarre tenuous wispy shapes reminiscent of ripples in sand or the changing surface of a pool of water, spread like a glowing web across the northern sky. Colours can range from brilliant whites, with tinges of blue, pink and orange.
Formed by tiny ice crystals, they are the highest clouds in the Earth’s atmosphere, located in the mesosphere at altitudes of around 76 to 85 kilometers (47 to 53 miles) almost at the edge of space.
They are normally too faint to be seen, and are visible only when illuminated by sunlight from below the horizon, while the lower layers of the atmosphere are in the Earth’s shadow. Noctilucent clouds are not fully understood and are a recently discovered meteorological phenomenon, only being recorded for about 120 years.
Noctilucent clouds can only form under very restrictive conditions, and their occurrence can be used as a guide to changes in the upper atmosphere. Since their relatively recent classification, the occurrence of noctilucent clouds appears to be increasing in frequency, brightness and extent.
There is evidence that the relatively recent appearance of noctilucent clouds and their gradual increase, may be linked to climate change. Another recent theory is that some of these bright displays come from particulates and water vapour in the atmosphere left over from Space Shuttle launches.
How can you see Noctilucent Clouds?
Over the next couple of months look north during dusk and dawn and try and spot this mysterious and elusive phenomenon. They are best seen when the sun is between 6 and 16 degrees below the horizon, and seem to occur more frequently in the Northern hemisphere than the Southern.
Good luck!
by VirtualAstro | May 18, 2011
23rd to 30th of October 2011
In celebration of its 5th year, the Salisbury Star Party will be hosting AstroParty with 7 days of Astronomy activities for people of all levels of interest and ability. All are welcome and those who attend will enjoy dark skies, a fantastic location, great company and lots and lots of fun. The organisers intend to make the Astro Party one of the biggest and best astronomy events in 2011 and beyond.
Venue:
The event will be held in a lovely and spacious campsite in the pretty village of Sixpenny Handley in the glorious Wiltshire countryside, (an area of outstanding natural beauty) with dark skies and excellent facilities including a large cafe/ conference area.
The site is located within 300m of the Village High Street. There are a variety of shops, including General Stores/Newsagents, Butchers, Post Office, Gift Shop and also a Public House. The village church backs on to the campsite, which adds a little more of that country atmosphere to the venue.
The historic City of Salisbury and the market towns of Blandford Forum, Wimborne Minster, Shaftesbury and Ringwood are all easily reached within 30 minutes drive.
If you aren’t keen on camping, there are local B&B’s and hotels etc in the surrounding area.
Activities:
Star Party – Running for all of the 7 nights with around 70 to 100 experienced astronomers at its core, the Star Party is the main part of the event, so bring your kit if you have any, join in and take advantage of observing and imaging with a large group, whatever your level of experience? You don't even need to bring a telescope, just use your eyes.
Imaging World Record – More info coming soon?
Inflatable Planetarium Shows – Big planetariums with big shows all topped off with what’s up guides.
Talks – A daily program of talks by famous and experienced people in the world of astronomy.
Tweetup – A social gathering of social media. Twitter and Facebook users meet and tweet with your online friends here.
Tours of the Sky – live and real tours of the sky by experienced astronomers.
Telescope and Equipment Workshops – Ask for advice or get help with astronomical equipment.
Trade Stands – More info and who is coming soon?
Competitions – A raffle for that nice telescope or piece of imaging kit?
Hospitality – There will be a hog roast on the final Saturday, and there is a cafe which is open through the week. We hope to have additional tents where you can warm up, tweetup, get a coffee, have some soup, or somewhere to chill and drink your beer. There is a licensed bar on site and a pub in the village.
More activities and services will be added to the program before the event starts.
A website will be launched shortly where you can look for additional information and book your tickets for the event.
Please book tickets here
Let’s Make AstroParty, hosted by the Salisbury Star Party one of the biggest and best astronomy events and we hope to see you all there.
by VirtualAstro | Mar 19, 2011
Originally posted on Dark Sky Diary by Steve Owens (@darkskyman)
Today, Friday 18 March 2011, it is the Spring Equilux throughout the UK (and possibly elsewhere too*) meaning that there are almost exactly 12 hours between sunrise and sunset.
Sunrise
This date differs from the Spring, or Vernal, Equinox (2321 GMT on Sunday 20 March 2011) for a variety of reasons, which I explain in a previous post but here is a list of sunrise / sunset times for a variety of towns and cities throughout the UK:
| Town / City |
Sunrise |
Sunset |
| Aberdeen |
0617 |
1817 |
| Glasgow |
0626 |
1826 |
| Belfast |
0632 |
1833 |
| Newcastle |
0615 |
1815 |
| Manchester |
0617 |
1818 |
| Birmingham |
0616 |
1817 |
| Cardiff |
0621 |
1822 |
| London |
0609 |
1809 |
As you can see the time between sunrise and sunset is not exactly 12 hours everywhere but this is the day of the year when that is closest to being true everywhere*. Yesterday the sun rose a couple of minutes later and set a couple of minutes earlier, and tomorrow the sun will rise a couple of minutes earlier and set a couple of minutes later, as the days lengthen.
Also, the reason that sunrise and sunset does not occur at the same time everywhere* is due mainly to the longitude of the town, the further east a town is the earlier it sees the sun in the morning, and the earlier it loses it again at night.
So happy Equilux everyone*!
* interestingly, the equilux does not occur on the same same day for everyone, it depends on your latitude. The closer you are to the equator the earlier the date of your equilux. For example the equilux in most US cities occurred yesterday, 17 March, and in cities near the equator there is never a day with exactly twelve hours between sunrise and sunset! Take Quito, the capital city of Ecuador (latitude 0 degrees 14 minutes south) for instance. The length of day there only ever varies between 12 hours and 6 minutes long and 12 hours and 8 minutes long!
by VirtualAstro | Mar 16, 2011
I am often asked or hear about bright fireballs in the sky, often reported by non astronomy minded people, so when you ask where was it and what direction it was travelling etc, you get very sketchy information back like: It was over my house and headed towards town, I think?
Only if you have many sightings of the same fireball can you interpolate where it was and what direction etc it was travelling? Things are going to be made a lot easier if you live in some parts of the United States.
NASA is building a network of "Meteor Cameras" in a few of States in the US called the "All-sky Fireball Network". This is a network of cameras set up by the NASA Meteoroid Environment Office (MEO) with the goal of observing meteors brighter than the planet Venus, which are called fireballs. The collected data will be used by the MEO in constructing models of the meteoroid environment, which are important to spacecraft designers.
The Network will eventually consist of up to 15 overlapping cameras in north Alabama, northwest Georgia, and southern Tennessee, placed on public buildings and schools. The network will use sensitive black and white cameras which are able to see the whole of the sky (All Sky).
Because the cameras have overlapping fields of view, more than one camera can see the same meteor at the same time, helping in getting data about its trajectory and with clever data collection software, ascertain if the meteor came from a comet or an asteroid.
NASA’s All-sky Fireball Network uses ASGARD (All Sky and Guided Automatic Realtime Detection). ASGARD not only handles all the data processing (which is considerable) it also automatically pushes the results to the web. See the results here: http://fireballs.ndc.nasa.gov
by Steve Owens | Mar 10, 2011
Originally posted on Dark Sky Diary by Sreve Owens @Darkskyman
I’ll make a prediction: on or around 19 March, when the so-called “Supermoon” occurs, at its closest approach to Earth in two decades, people will indeed report that the Moon looks much bigger than normal. But it won’t really be much bigger in the sky at all. It’s all in our heads!
"Wow, the Moon's even bigger than that tree!"
You’ve probably all seen it before, a huge Full Moon sitting on the horizon. Time and again I have had people ask me why the Moon is so much bigger some times than others, and the answer is: it isn’t, really.
The Moon orbits the Earth in an elliptical orbit, meaning that it is not always the same distance from the Earth. The closest the Moon ever gets to Earth (called apogee) is 364,000km, and the furthest is ever gets (perigee) is around 406,000km (these figures vary, and in fact this Full Moon on 19 March 2011 will see a slightly closer approach of 357,000km).
So the percentage difference in distance between the average perigee and the average apogee is ~10%. That is, if the Full Moon occurs at perigee it can be up to 10% closer (and therefore larger) than if it occurred at apogee.
This is quite a significant difference, and so it is worth pointing out that the Moon does appear to be different sizes at different times throughout the year.
But that’s NOT what causes the Moon to look huge on the horizon. Such a measly 10% difference in size cannot account for the fact that people describe the Moon as “huge” when they see it low on the horizon.
What’s really causing the Moon to look huge on such occasions is the circuitry in your brain. It’s an optical illusion, so well known that it has its own name: the Moon Illusion.
If you measure the angular size of the Full Moon in the sky it varies between 36 arc minutes (0.6 degrees) at perigee, and 30 arc minutes (0.5 degrees) at apogee, but this difference will occur within a number of lunar orbits (months), not over the course of the night as the Moon rises. In fact if you measure the angular size of the Full Moon just after it rises, when it’s near the horizon, and then again hours later once it’s high in the sky, these two numbers are identical: it doesn’t change size at all.
So why does your brain think it has? There’s no clear consensus on this, but the two most reasonable explanations are as follows:
1. When the Moon is low on the horizon there are lots of objects (hills, houses, trees etc) against which you can compare its size. When it’s high in the sky it’s there in isolation. This might create something akin to the Ebbinghaus Illusion, where identically sized objects appear to be different sizes when placed in different surroundings.
Ebbinghaus Illusion – the two orange circles are exactly the same size
2. When seen against nearer foreground objects which we know to be far away from us, our brain thinks something like this: “wow, that Moon is even further than those trees, and they’re really far away. And despite how far away it is, it still looks pretty big. That must mean the Moon is huge!”.
These two factors combine to fool our brains into “seeing” a larger Moon when it’s near the horizon compared with when its overhead, even when our eyes – and our instruments – see it as exactly the same size.
