Originally posted on Dark Sky Diary as “Perseids Meteor Shower 2011” by Steve Owens @darkskyman on twitter
This month sees the most reliable meteor shower of the year; the Perseids. You can begin watching for Perseid meteors now, and the shower will last until mid-August, but the peak of the shower occurs in the small hours of Saturday 13 August 2011.
Perseus under dark skies
Perseus under moonlit skies
Unfortunately this year’s shower will be obscured by the full Moon which occurs on the same day, and so it won’t present its usual excellent display.
The number of meteors that you will observe every hour depends on a number of factors:
the density of the cloud of dust that the Earth is moving through, that is causing the shower in the first place;
the height above the horizon of the radiant of the shower, the point from which the meteors appear to radiate;
the fraction of your sky that is obscured by cloud;
the naked-eye limiting magnitude of the sky, that is a measure of the faintest object you can see.
Please visit Dark Sky Diary for the rest of this article………..
Everyone is welcome to join in, whether they are an astronomer, have a slight interest in the night sky or just wonder?
As well as looking up, enjoying the night sky with us and seeing meteors, maybe for the first time? You will have the opportunity to contribute for fun with images and online, or to Scienceif you wish, by tweeting and seeing your results on a map, or by submitting Observing Forms if you are a more serious observer.
This event follows on from the popular Twitter Meteorwatchheld in August and December of 2009 and 2010 “Meteorwatch 2009”
Use the hash tag: #Meteorwatch and get involved, ask questions, do some science, follow the event and enjoy the wonders of the night sky with us. Images and other information will be tweeted as it happens. Live!
The highlight of the summer meteor showers: The Perseids reach maximum around the 12th/ 13th of August and may put on a display of approximately 80 to 100 meteors per hour under ideal viewing conditions.
Conditions this year aren’t ideal due to there being a full moon, but the brighter meteors will be seen. Let’s hope the skies stay clear.
Perseid meteors are often bright with persistent trails which can linger for a while after the meteor has burned up. Further information on the Perseid meteor shower and how to view it, can be found here.
While you are looking formeteors, there will be other objects to look out for such as the Planet Jupiter late in the evening, the Milky Way, Summer Triangle, manmade Satellites and more.
The Twitter Meteorwatch will start at 21.00 BST on the 11th of August and will continue through to the evening of the 13th. Amateur and professional astronomers and stargazers from the US and other countries are invited to join in and take over from the UK, when the sun comes up here, helping make the event run continuously and be truly international.
Star Count Week (Monday 31 January – Sunday 06 February 2011) aims to get you outside and looking up, specifically to assess how dark – or light – your sky is.
The technique is simple. 1. Find Orion. 2. Count all the stars you can see within the main rectangle formed by Betelgeuse, Bellatrix, Rigel and Saiph, the four stars that make up Orion’s shoulders and feet. (Don’t count the three bright belt stars). 3. Tell the CPRE.
That’s it. By counting how many you can see, astronomers can calculate your sky’s limiting magnitude, or the brightness of the faintest stars you can see. It’s a very simple – and rewarding – project to take part in.
At 1900 GMT on 3 January 2011 the Earth will be at perihelion, its closest approach to the Sun this year.
If that sounds confusing to you, and has you wondering why it’s so cold given that the Earth is at its closest to the Sun, then this belies (a) a northern-hemisphere-centric attitude (in the Southern Hemisphere it’s summer right now), and (b) a misunderstanding of what causes the seasons.
The Earth orbits the sun in a nearly circular orbit called an ellipse. The degree by which an orbit differs from a perfect circle is called the eccentricity, e. If e = 0 then the orbit is circular; if e = 1 then the orbit is parabolic, and therefore not gravitationally bound to the Sun. The Earth’s orbital eccentricity is 0.0167, meaning that it is very nearly circular, with the short axis of the ellipse being around 96% the length of the long axis.
Thus, during perihelion Earth is 0.983AU from the Sun, while during aphelion (its furthest distance from the Sun, occurring this year on 4 July) Earth is 1.017AU from the Sun. (1AU = 1 astronomical unit = the average distance between the Earth and the Sun = 150 million km). The seasons on Earth have really nothing to do with how close the Earth is to the Sun at different times of year. Indeed how could they, given that the difference in distance between closest and furthest approach is only a few per cent?
The seasonal differences we experience are of course caused by the tilt of the Earth’s axis, which is inclined by 23.5 degrees from the vertical. This tilt means that, as Earth orbits the Sun, for six months of the year one hemisphere tips towards the Sun, so that it experiences longer days than nights, becoming most pronounced at midsummer, at which point the Sun reaches its highest in the sky at noon. Simultaneously the other hemisphere tips away from the Sun, and experiences shorter days than nights, becoming most pronounced at midwinter, on which day the Sun is at its lowest noontime altitude.
Earth's tilted axis
The further you are from the equator the more pronounced the seasonal effects. In fact equatorial countries don’t experience seasonal variations, while the poles experience extremes with six-month-long winters and summers.
The timing of perihelion and aphelion relative to our seasons is entirely random. The fact the southern hemisphere midsummer (21 Dec) almost coincides with perihelion (3 Jan) is simply that; a coincidence. Given that fact, there is no reason to be surprised that perihelion occurs so close to northern hemisphere midwinter. it has to happen some time and it’s coincidence that it happens to occur within two weeks of midwinter / midsummer.
To take this explanation even further, we can calculate how much variation in incident sunlight (called the flux) there would be in two scenarios:
1. an imaginary scenario where the seasonal varioations in temperature are due to the tilt of the Earth’s axis but where the Earth goes round the Sun in a perfectly circular orbit
and
2. an imaginary scenario where the Earth’s axis isn’t tilted, but where it’s orbit is elliptical in the same degree as ours actually is.
1. The Sun appears at its highest point in our sky each day at noon. The highest it ever gets is at noon on midsummer. The lowest noontime altitude occurs at noon on midwinter.
In Scotland the Sun is around 55 degrees above the horizon at noon on midsummer, and only 10 degrees above it at noon on midwinter.
The amount of energy from the Sun radiant on a fixed area is proportional to the sine of the altitude, so the ratio of the solar energy radiant on a square metre of Glasgow between midsummer and midwinter is
sin(55) / sin(10) = 1.84
So here in Scotland we get 84% more energy from the Sun in summer than we do in winter, due to the tilt of the Earth’s axis.
2. If the Earth’s axis was not tilted, then we would only experience temperature differences from the Sun depending on how far or near we are from it. In this case, the amount of energy from the Sun radian of a fixed area is proportional to the square of the distance from the Sun, so the ration of the solar energy radiant on a square metre of Glasgow between perihelion and aphelion is
(1.017/0.983)^2 = 1.07
So we get 7% more energy from the Sun at perihelion than we do at aphelion., due to the differing distances to the Sun.
From this you can see that, while the distance to the Sun has some effect on how much heat we receive, it is a very small effect compared to that produced by our axial tilt.
A round-the-world wave to the humans aboard the International Space Station by their fellow humans on the Earth – choreographed by a grassroots Twitter campaign (@ISSwave).
24-31 DECEMBER, 2010
A celebration of human solidarity during the holiday season
For one week beginning Friday, 24 December, humans around the world will show their solidarity with their fellow humans in space (and on Earth) by waving at the International Space Station (ISS) as she passes overhead at 17,500 mph (28,000 kmph).
Participants, recruited through Twitter, are encouraged to share their waves — either alone or as part of an ISSwave tweetup (a physical gathering of twitterers, or tweeps) — by tweeting their zip/postal code and the hashtag “#ISSwave” along with photos and videos of their waves, thoughts, holiday wishes for the astronauts and cosmonauts, etc. Participants’ waves will be registered in real-time at www.isswave.org.
Astronauts and cosmonauts aboard the International Space Station may even film themselves waving back at ISSwave participants. At least two astronauts, including Ron Garan, have voiced their support for ISSwave in emails and tweets.
The idea for the wave emerged through a serendipitous twitter exchange among Twitter acquaintances and regular ISS watchers Lucy Rogers (@DrLucyRogers), Richard P. Grant (@rpg7twit) and Karen James (@kejames). They discovered that watching ISS passes is even more exciting when done together with other humans, whether they are standing right next to you or watching from afar. To know that you are not the only one looking up in awe at this spectacle of human ingenuity and cooperation speeding across the night sky creates a special connection between us.
“The first time I watched an ISS pass I was surprised by how much it affected me,” said Karen James. “‘We made that’, I thought, ‘there are humans up there!’ All of my worries just seemed so tiny in the face of this symbol of human achievement and cooperation. I want to share that experience with other humans and also show my support to the ones living and working aboard the station.”
‘“I’d always wave up at the ISS if I saw it pass overhead,” says Lucy Rogers. “Someone laughed and said the astronauts wouldn’t see me.” So she asked on Twitter if anyone else waved – a lot of people did – and the communal ISS waving began. “When Karen moved to the USA she saw the ISS at a different time to us in Europe – which prompted the idea of a round-the-world wave,” she says.
We see the ISS because it is lit by the Sun. Sunlight reflects off it’s solar panels in the same way it glints off windows here on Earth. As the ISS travels round the world, the reflection can be seen in a broad sweep across the Earth. Due to the angles involved between the Sun, ISS and our location on Earth, sometimes we see bright, high passes and sometimes we can’t see it at all. During the week 24th – 31st December, most places on the Earth should get a good view of it at some point.
The three formed the Twitter account@ISSwave to coordinate, promote and provide updates on the event. Their hope is that seasoned and novice ISS watchers alike will experience the startlingly emotional experience of an ISS pass, amplified by solidarity with thousands of others watching around the world.
Additionally, the team hopes the buzz around ISSwave will persuade those who have never watched an ISS pass to participate, marking an increase in awareness about the International Space Station and the existence of a community of space enthusiasts on Twitter (“spacetweeps”).
The wave also celebrates the 10th anniversary of continuous human presence in space (ISS10years) on 2 November 2010 and the 50th anniversary of Yuri Gagarin’s flight into space — the first human spaceflight — on April 12th 2011 (www.YuriGagarin50.org).
ISS Wave Info:
The International Space Station has been orbiting the Earth over 15 times a day for more than ten years.
Although it is about 390 km (~240 miles) high, we can still see it from the Earth, thanks to the Sun reflecting off the solar arrays. The solar array wingspan is 240 feet (73 meters). This is longer than that of a Boeing 777 model at 212 feet (65 meters).
Currently on the ISS are Oleg Skripochka, Alexander Kaleri, Dmitry Kndratyev, Paolo Nespoli, Catherine Coleman and Scott Kelly (Commander).
Photos of the ISS passing overhead are available at http://www.isswave.org/ISSWave/Media_Photos.html
There are various ways you can work out when it will be possible to see it from where you are, including Heavens Above, Twisst, NASA, ESA and Orbiting Frog.
As of 19 December, @ISSwave had over 600 followers from across all continents.
Dr Karen James (@kejames) is Director of Science for The HMS Beagle Trust, a UK charity aiming to rebuild the famous ship that carried Charles Darwin around the word on his seminal voyage of discovery. Through the Beagle Project she collaborates with NASA Astronaut Michael Barratt a long-duration spaceflight veteran and member of the crew of the upcoming STS-133 mission to the ISS aboard Space Shuttle Discovery. She is a former postdoctoral researcher at the Natural History Museum in London and has recently repatriated to the United States. For more information visit http://kejames.com/.
Dr Lucy Rogers (@DrLucyRogers) a Chartered Mechanical Engineer and Fellow of the Royal Astronomical Society, aims to infiltrate the public’s consciousness by writing scientific stuff in plain English. She has published a book about space flight, “It’s ONLY Rocket Science”, which doesn’t contain any equations. She lives on the Isle of Wight where she can see the Milky Way from her back garden. For more information visit http://lucyrogers.com.
Dr Richard P. Grant (@rpg7twit) is a biological scientist turned writer, editor and poet. He currently lives and works in London, and has a habit of taking on far too many projects. For more information visit http://rg-d.com/rpg, or his blog at Occam’s Typewriter.
From Wednesday 11th to Saturday 14th of August 2010 the Virtual Astronomer @VirtualAstro with the British Astronomical Association@britastro Beyond International Year of Astronomy and amateur astronomers, will be holding a Twitter Meteorwatchfor the Perseid Meteor Shower.
Everyone is welcome to join in, whether they are an astronomer, have a slight interest in the night sky or just wonder?
As well as looking up, enjoying the night sky with us and seeing meteors, maybe for the first time? You will have the opportunity to contribute to Science if you wish, by tweeting and seeing your results on a map, or by submitting Observing Formsif you are a more serious observer.
This event follows on from the popular Twitter Meteorwatchheld in August and December 2009 "Meteorwatch 2009"
Use the hash tag: #Meteorwatch and get involved, ask questions, do some science, follow the event and enjoy the wonders of the night sky with us. Images and other information will be tweeted as it happens. Live!
The highlight of the summer meteor showers: The Perseids, reach maximum around The 12th of August and may put on a display of aproximately 80 to 100 meteors per hour under ideal viewing conditions. Conditions this year are good due to there being no moon visible. Let’s hope the skies stay clear.
Perseid meteors are often bright with persistent trails which can linger for a while after the meteor has burned up. Further information on the Perseid meteor shower and how to view it, can be found in this site.
While you are looking for meteors, there will be other objects to look out for such as the Planet Jupiter, the Milky Way, Summer Triangle and manmade Satellites and more.
The Twitter Meteorwatch will start at 21.30 BST on the 11th of August and will continue through to the evening of the 14th of August. Amateur and professional astronomers from the US and other countries are invited to join in and take over from the UK, when the sun comes up here, helping make the event run continuously and be truly international. The event will close in the UK, in the early hours of the 15th of August 2010.
Perseus under dark skies
Perseus under moonlit skies
