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Quadrantid Meteor Credit: nasa.org

2012 has begun and we are in for a welcome treat with the start of this years annual meteor showers and the Quadrantid meteorwatch, on the evening of the 3rd/ morning of the 4th of January.

The Quadrantids can be quite an impressive shower with rates (ZHR) of up to 120 meteors per hour at the showers peak (under perfect conditions) and can sometimes produce rates of up to 200 meteors per hour. The peak is quite narrow lasting only a few hours, however there will be plenty of meteors to look out for either side of the peak. Read the rest of this entry »

Originally based on Dark Sky Diary by Steve Owens www.twitter.com/darkskyman

The first meteor shower of 2012 is the Quadrantids, the peak of which falls on the night of the 03/04 January 2012. The Quadrantids shower has one of the highest predicted hourly rates of all meteor showers, comparable to the two great annual showers, the Perseids and the Geminids, occurring in August and December respectively. However unlike the Perseids and Geminids, the Quadrantids peak is very narrow, occurring over just a few short hours.

The predicted Zenith Hourly Rate (see my previous post about ZHR and what it actually means here) for the Quadrantids is around 120. The narrow peak is predicted to occur some time between 2100 UT on 3 January and 0700 UT on 4 January 2011, however the radiant of the shower – the now-defunct constellation Quadrans Muralis – is very low in the evening hours, rising higher towards dawn, and so the best viewing times are later in this run, just before dawn. Read the rest of this entry »

Meteor Detection

When a meteor strikes Earth’s atmosphere it decelerates rapidly. The friction created by the air causes the meteor to burn up at extremely high temperatures creating the white “shooting star” that we are all familiar with. This process also ionises the air along the trail making it possible to reflect radio waves.

Utilising a high powered VHF radar signal sent into the sky, we are able to detect reflected waves from these ionisation trails. Because the meteor is moving, the reflected signal is shifted in frequency from the original, by an amount according to it’s speed. This shift is also heard as an audible ping by the station operator.

Our system translates the reflected wave into three main parameters - Amplitude (strength), Frequency shift (Doppler shift) and decay time. This allows us to determine the relative size of the meteor strike (vertical scale) and the relative approximate speed and deceleration (amount of shift and width of the trace).

You can see the output from our system above in real time (approximately 1 minute delay on the Internet). During a meteor shower this trace will be full of strike traces, but it is also surprising how many meteors are striking Earth’s atmosphere all of the time.

Typical Meteor Strike

Here you can see what a typical meteor strike looks like. The trace starts high in frequency and rapidly drops to the radar carrier frequency as the meteor decelerates in the atmosphere, increasing in strength    (ionisation) as it burns up. This creates this typical triangular shape you can see here. The width, height and shape tell us a lot about the meteor strike. The blue is the baseline atmospheric noise.

N.L.O. Meteor Detection Live View is kindly donated by Meteorscan.com All data is collected and sent live to meteorwatch.org via the state of the art meteor detection system at the Norman Lockyer Observatory in Sidmouth, Devon.

Perseid Credit: science1.nasa.gov

A classic summer astronomical standby may be in trouble this year, but that shouldn’t stop you from looking. That’s right, we’re talking about the Perseids, that “old faithful” of meteor showers which sees northern hemisphere residents getting bundled up to camp out under the summer stars every mid-August.

Some of our earliest astronomical memories come from watching this very shower under the dark northern Maine skies of our 1970’s childhood… yes, the Perseids are public crowd-pleaser and even an occasional Yahoo-trending fave that can even knock the likes of Brittany & friends down to the number 2 slot for a 12 hour period… so, what’s this news of the Perseids being “troubled?” They haven’t been threatened by irate pop stars, have they?

Unfortunately, this year’s menace is a more inviolate force; the Full Moon. Yes, this year’s Perseid meteor shower peaks the morning of August 13^th, mere hours before the Moon reaches Full status on the same day at 14:57EDT/18:57UTC. Instead of the usual respectable zenithal hourly rate (ZHR) of around 100 meteors per hour, observers can only expect to see a paltry few of the very brightest fireballs…

But all is not lost. With a little planning, a few factors can work in YOUR favor this year. Keep in mind that the Perseids have a very broad peak, and the radiant near the head of the constellation Perseus lies above the horizon all night for observers north of 32° latitude. Plus, this month’s Full Moon (known as a Sturgeon Moon) has a southerly declination of about -11° degrees; your best bet for catching Perseids this year may lie with watching several mornings prior, in the window of time between the setting of the waxing gibbous Moon and the beginning of local twilight… and yes, you CAN still watch a meteor shower during a Full Moon and see an occasional Perseid.

Generally speaking, the farther north in latitude you are located, the more likely you’ll be able to take advantage of these twin factors. Finding as dark a site as possible and putting something physically between yourself and the bright Moon is the key. A building or a hill makes an excellent “Moon-block.” Perseids are swift movers with an atmospheric entry velocity of about 61 km/sec.

The meteors are tiny grain-like debris shed by the comet Swift-Tuttle, and the shower occurs as the Earth intersects the path of the comet every mid-August. The Perseids are also famously known as the “Tears of Saint Lawrence” who was martyred on August 10^th, and are probably the most well known of all meteor showers because of their annual dependability and their timely occurrence with the northern hemisphere summer vacation and holiday season.

Historic ZHR rates have always hovered around 60, but the past several years have seen an enhanced ZHR of +100. This shower is also infamous for sparking “Meteor Shower of the Millennium!” headlines annually, Although I have yet to see the same occur this year… a shower that MAY be a contender for said headline is the Giacobinids (or do you say Draconid?) meteors in early October 2011, an obscure shower that may dazzle this year… more on this to come in October.

Wonder what that the above graphic has to do with anything astronomical? You are looking at what is known as a nomogram, a graphical device that is a neat way to show interrelationships between factors. (Hey, how do you spend your weekend?) The graphic above was adapted from a nomogram featured in the November 2002 issue of Sky & Telescope; it shows the interrelationship between the two biggest factors that affect the zenithal hourly rate; namely, the radiant’s elevation above the horizon, and the limiting magnitude of your sky. (For a way “math-y-ier” dissertation on nomograms and the ZHR, click here).

This device will be your indispensible friend and secret weapon as you plot your meteor observing adventures for this or any shower. The ZHR is a theoretical limit; it assumes that you have absolutely perfect skies with a radiant directly overhead and an unwavering 360°degree view. Unrealistic, right? Well, it’s something to strive for. As you can see after playing around with the graphic a bit, the biggest killer of how many meteors you’ll see is how dark a sky you are under.

Even when the Perseid radiant is half way (45° degrees) in altitude towards the zenith, a limiting magnitude of +4 (as is typical around a Full Moon) means you’ll see roughly 10% of the zenithal hourly rate, i.e. 6-10 meteors per hour instead of 60-100. Yes, light pollution, both natural and manmade, is a real meteor shower buzz-kill. And keep in mind, other factors can conspire to lower that rate even further, such as obstructions on the horizon and the fact that a sole observer can only cover a limited swath of the sky visually. Still, the sight of a well placed fireball can be unforgettable and just plain pure magic to witness.

Do get out there on days leading up to this week’s Perseid meteors, and be sure to follow and report the magic via #meteorwatch on Twitter; they’re worth setting an early alarm for!

David Dickinsen

www.astroguyz.com

http://twitter.com/Astroguyz

Thursday 11th to Sunday 14th of August 2011

From Thursday 11th to Saturday 13th of August 2011 @VirtualAstro on Twitter with the help of The National Trust, Universe Today, Royal Astronomical Society and many more, will be holding a Twitter Meteorwatch for 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 for fun with images and online, or to Science if 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 Meteorwatch held 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!

Join in on Twitter, Facebook and Google+

The highlight of the summer meteor showers: The Perseids reach maximum around the 12^th/ 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 for meteors, 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.

Watch the awesome new trailer here….

This evening I decided to try some iPhone astrophotography. This blog post will let you see how I got on, and give you the info you need to get started yourself.

While the iPhone 4 camera is far from ideal for astrophotography (the sensor is small compared with a DSLR; in fact it’s not even as good as most point and shoot cameras) it does have one distinct advantage – it’s usually very much to hand, just in my pocket in fact.

There are two kinds of astrophotography you can do with an iPhone: with and without a telescope. The former is called afocal astrophotography, but it is the latter that I tried out tonight: just using the iPhone camera, some extra hardware, a 59p app, and a clear sky.

Afocal Astrophotography. Simply hold the camera to the eyepiece of a telescope (or binoculars) and snap a picture of whatever is in the field of view. For this you can just use the standard camera app on the phone to snap a picture, and it’ll use software to ensure that the image is exposed correctly (although this might not always work). I’ve tried this once before, using the Moon as my target, with decent enough results:

You can also buy several apps that claim to allow you to take longer exposures, even letting you use a bulb setting (this isn’t actually possible with the iPhone shutter hardware – each of these apps is actually using a clever software work around, but you’re not getting a true 60 second exposure when you set your “shutter speed’ for 60 seconds).

The apps that I use are:

Slow Shutter Cam: has shutter speeds of 0.5, 1, 2, 4, 8, 15? and a B (bulb) setting, plus a crucial self timer delay to prevent wobble when pushing the “button” to take the shot (£0.59 on iTunes App Store)

Magic Shutter: has shutter speeds of 1, 2, 4, 8, 15, 30 and 60? and a B (bulb) setting, but no self timer (£1.79 on iTunes App Store)

Both of these apps have a variety of software setting to allow you to get the best picture; tonight I used Magic Shutter with a 60s shutter speed.

(These apps might allow you to take better images while the camera is mounted to a telescope, but I haven’t tried this yet. Watch this space for test of this later in the year.)

Afocal Astrophotography Hardware

The main obstacle to taking long exposure shots with the iPhone (apart from the fact that the hardware won’t actually let you!) is that you need to make sure that the iPhone doesn’t move at all during the duration of the exposure, so holding it in place with your hand isn’t an option. Luckily there’s a great gadget available from a company call Magnilux. The device is called the Magnilux MX-1 Telescope Adaptor, which allows you to attach your iPhone to any telescope eyepiece. It also doubles as a tripod adaptor.

 

Magnilux MX-1 Telescope Adaptor

 

Magnilux MX-1 Telescope Adaptor with iPhone 4 attached (works with any iPhone model)

 

Magnilux MX-1 Telescope Adaptor configured as a tripod mount

Astrophotography Without a Telescope

Tonight I didn’t connect my iPhone to my telescope since my target, the International Space Station (ISS), moves so quickly and travels across such a large part of the sky that you need as wide a field as possible to catch it.

To capture the ISS you need a long exposure (use Magic Shutter app – see above). The pass tonight lasted 4’19?, and traveled 90° through the sky (from 254° WSW to 164° SSE). The iPhone 4 camera field of view is only 60.8° so I couldn’t capture the whole pass. Instead I decided to try to capture a 60s exposure as the ISS rose to its highest and brightest, at 206° (SSW).

With a 60? exposure, of course, I had to have my iPhone mounted to a tripod. I could have used the Magnilux MX-1 Adaptor set up for tripod mode (see above) but instead I opted to use my new Kungl iPhone case with built in tripod thread, which I attached directly to my tripod.

 

Kungl iPhone Case

This held the iPhone still, and using the Magic Shutter app set to 60? exposure I managed to get this image:

 

The ISS passing over, iPhone 4 Camera, Magic Shutter App set for 60″ exposure, 2344, 23 June 2011

Far from ideal, but not bad given (a) it was my first attempt, (b) I had one chance to take the image before the ISS faded from view, (c) the sky was very bright (this was taken at 2344 on 23 June 2011, just after midsummer, with the sky just out of civil twilight), (d)  cars kept driving past (note the light art in the foreground!).

Once the sky darkens again later in the year I hope to test this set up under a truly dark sky to see whether it can pick up sharp star images. I suspect that might be tricky!

If anyone else has tried iPhone Astrophotography please let me know in the comments.

I took this image of the Solstice Sunset near my home in West Berkshire UK last year, it was an amazing experience watching the sun sink below the horizon on the longest day.

Will we be lucky enough to be able to witness this wonder again this year and see some more great images?

Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)

Today, 13 June, is one of only four days in the year when the time as read on a sundial will be exactly correct.

Sundials usually tell the time using the shadow of the gnomon as cast by the Sun. This is possible as the Sun appears to move across the sky at an approximately constant speed, and so the shadow of the gnomon also moves at an approximately constant speed. The inconstancy of the Sun’s apparent motion in the sky – and therefore of the gnomon’s shadow on a sundial – is the subject of this article, and is calculated using the Equation of Time.

If you look at the shadow of a sundial’s gnomon it will fall onto a curve of numbers, along hour lines indicating local solar time. This is not equal to the official clock time until three important corrections are made:

Please read the rest of this article on Dark Sky Diary

Originally posted on Dark Sky Diary by Steve Owens (@darkskyman on twitter)

The first total eclipse of the Moon of 2011 occurs this Wednesday evening, 15 June 2011, and it will be the longest lunar eclipse in over a decade. However the views from the UK (and Europe) will be constrained by the fact that the Moon will be below the horizon for much of the eclipse, and will rise fully eclipsed, or in some cases even coming out of eclipse. It’s still worth having a look though: just try to find somewhere with a very low and clear SE horizon, as this will be the direction in which the Moon will rise, and it will be in eclipse only while it is VERY low (only a few degrees above the horizon).

A lunar eclipse occurs when the Moon, in its orbit around the Earth, passes into the Earth’s shadow, as cast by the Sun. You might imagine that this would happen once every lunar orbit, or once a month. That it does not is due to the fact that the Moon’s orbit around the Earth is tilted by around 5 degrees compared with the Earth’s orbit around the Sun. So in most orbits the Moon passes above or below the Earth’s shadow.

Please read the rest of this article on Dark Sky Diary

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 them? 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!