Archive for the ‘Imaging’ Category

Near and far

Posted: February 23, 2013 in Deepsky, Imaging, Minor Planets, Observing

I’m a little late posting this but I did manage to get a picture of asteroid 2012 DA14 during last weeks close approach.

The evening started clear but clouded over just as me and few other friends from NASTRO were arriving at Hauxley Nature Reserve.  I got polar aligned with the 80mm refractor through occasional gaps in the cloud so that when the sky did begin to clear at around 8.30pm I was able to find the asteroid fairly quickly.

A point of light drifting through the stars in the eyepiece.  It was easily discernible motion at low magnification.  I put the camera in place and took this one minute exposure:

2012DA14

The moving asteroid shows up as a line because of the long exposure.  Then the clouds returned so I felt very happy to have seen anything at all!

2012DA14 ranks as one of the closest astronomical objects I’ve taken pictures of….only spaceweather like the aurora, noctilucent clouds or ISS are closer.  Later that evening I had a go at imaging something much more distant….in fact, it’s the furthest object I’ve ever tried to take a picture of!  Here it is:

3C273

It looks like a star but is really a quasar (and that’s why these objects were initially named Quasi-Stellar Objects) but it is actually the active nucleus of a very distant galaxy.  3C-273 is a mind crushing 2.4 billion light-years away in the constellation Virgo.  That’s about 1,000 times further away than the Andromeda Galaxy.  This quasar is the brightest in the entire sky and one of the nearest to us.  Quasars were more prevalent in the early universe and are an indication how violent the processes at work in the centres of galaxies can be!  Material is falling into a supermassive blackhole and getting shredded and heated in the surrounding accretion disk.  The energy released, in the form of light and other radiation is beamed outwards and we happen to be looking down the beam. Rather like seeing a lighthouse beam sweeping past us.

Checking on my astronomy software…I noticed that another asteroid, called Hera, was also in the frame.  Hera is a foreground object – just under 200 million miles away in the asteroid belt between Mars and Jupiter.

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Capturing a comet

Posted: January 7, 2013 in Comets, Imaging

I’ve been out of touch with astronomy for various reasons in the past few weeks.  But a brief message from a friend alerted me to a comet in the sky.  A quick check on SkyTools revealed the comet to be C/2012 K5 LINEAR – a small object passing relatively close to Earth at the moment.  Although this comet is too faint to be seen without good binoculars or a telescope I thought it would be worth trying to get some images.

The orbit of the comet around the Sun is tilted to more than 90 degrees to the plane of the Earth’s orbit.  This basically means that K5 LINEAR is moving from celestial north to south in the sky.  The following chart shows the rapid motion of the comet during the next week or so.

LINEAR_Finder

K5 LINEAR is tracking south through a busy region between the constellations Orion and Taurus.  I set up the 80mm Skywatcher refractor on the HEQ5 Pro mount without much hope of getting a great picture.  It was overcast and raining at one point so me and Malcolm had to throw a cover over the whole setup.  But the cloud was quick moving and eventually I got a clear spell lasting more than half an hour.

C2012K5Linear_050113

This image is a composite of 10 one-minute subexposures taken with the Nikon D80 at prime focus of the Skywatcher telescope.  The processing was carried out in DeepSky Stacker and GIMP.

The green colour of the comet is from jets spewing cyanogen (CN) and diatomic carbon (C2) into space.  Both have a distinctive green glow under the action of sunlight in space.

The sub-exposures actually show the rapid motion of the comet across the field of view.  Here is an animation showing the comet as it tracks across the sky at a rate of 10 arcseconds per minute.

K5 was about 0.3 astronomical units away (about 28 million miles) when the pictures were taken.  That rapid motion corresponds to an orbital speed of about 80,000 miles per hour!  (Since the comet is passing through the plane of our orbit, the radial component is almost zero).

Comet K5 LINEAR is already fading as it heads south and away from the Sun.  But 2013 looks like it will be a spectacular year for other comets!  In late February we’ll have a naked eye comet called PANSTARRS in our sky and towards the end of the year – a more dramatic visitor called ISON might give the moon a good run for it’s money.

Two views of the Sun

Posted: June 28, 2012 in Imaging, Sun
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What a great lightning storm in Newcastle today! And a really eventful drive home which at one point involved navigating through a small lake of drifting traffic cones, in much the same way as I used to navigate a spaceship to avoid hitting asteroids in my youth.

The last thing you’d expect on a day like this is to be setting up the telescope to grab some images.  By 8pm the Sun was beginning to peek through the clouds.  I abandoned the Italy-Germany match and got set up in the bedroom because the Sun was too low to see from the garden.

Here is the view in Hydrogen Alpha:

Image

The Sun has been almost blank in white-light in recent days – barely a sunspot to shake a stick at.  That’s all changed now as the next image shows:

Image

Now it’s getting dark and the sky is completely clear.  Now what….bed or noctilucent cloud hunting?  The night is still young and the camera battery is charged.

Another image of the Sun taken with the PST yesterday afternoon:

My best yet!  This was made possible by an interesting discovery about my Nikon camera.  The pictures I’ve been taking prior to this have been careful not to saturate the chip – typically using exposures of about 1/100s at ISO200.

Yesterday I tried to do some longer exposures to try and extract more signal from those prominences around the limb at the cost of overexposing the disk.  The PST only allows a specific colour of red light through to the camera so I was expecting to see a washed out red disk with more obvious prominences.  I began taking pictures with exposure times ranging from 1/20 to 1/5 of a second.

What I actually recorded was a glowing orange ball similar to the final image above!  How can you get orange when the only colour available is red?

The camera chip is an array of red, green and blue sensors.  At fast exposures those photons of red light were activating the red sensors on the chip.  At slower shutter speeds the red sensors become saturated and the signal leaked into the green sensors.  A lot of red plus a dash of green equals orange in this situation.

Splitting the raw image into its RGB components gives this:

 The “B” component was a black image – nothing had leaked into that channel.  The green channel contained a nicely exposed image of the disk, with all the detail around the edge contained in the red channel.  Presumably with an even longer exposure the signal may have leaked into the blue channel as well!  From what I can tell, the green channel contains a higher quality image than the equivalent red channel – it certainly seemed to stand up to the contrast enhancement and sharpening process that followed.

Ten minutes of Sun!

Posted: June 17, 2012 in Imaging, Sun

But that was just about enough to grab some more pictures through the solar telescope.  Here’s the result:

I found a great page on the Sky & Telescope website with tips for processing these images and I think it paid off with this one.  In particular I corrected the non-uniform illumination which seems to afflict these early images.  Also, I think I’ll try and blend the disk image and ‘edge’ image a bit more smoothly next time.

The Sun broke through the clouds late this afternoon and I was able to snap about a dozen images of the Sun through the PST before it disappeared.  Without further ado this is what I ended up with after processing several of the best images:

Here are some of my initial thoughts about the PST after one day of use. Well, about 30 minutes of use in total:

  • Focussing is a bit difficult – small image with the supplied eyepiece.  Trying to make the edge of the Sun as sharp as possible but small disk size makes it hard to tell when you’re there! Also, looking at a purely monochrome image takes getting used to.
  • First view through the eyepiece was startling: prominences all around the edge of the disk with one particularly large one.  Sunspots, prominences, filaments and plage visible on the disk.  A wealth of detail – more than is seen in the picture and very sharp when focus is perfect.
  • Disappointed that the PST couldn’t bring an image to focus in the Nikon D80 using the same adaptor/setup I have on my other telescopes.  In the end I dismantled a 2x barlow and plugged it into the T-adaptor.  That moved the focus far enough back and made the image bigger on the chip.
  • The pictures I took showed non-uniform illumination across the solar disk – depending on where the Sun was in the field of view.  Not so noticeable through the eyepiece but it means that several images (at least) with the Sun at different places in the FOV must be stacked to reduce the effect.

Again, I’m hoping for better weather tomorrow…

Summer astronomy

Posted: June 13, 2012 in Imaging, Planets, Sun

The summer solstice approaches and dark nights have all but vanished from Northumberland.  It seemed like I was just getting into deep sky imaging and now I’m waiting for the autumn to come so I can get back to it.  Realistically, I’ve got a couple of months before I’ll be doing that kind of imaging again.  With that in mind I’ve deferred getting an autoguider (and new finderscope) in order to get a solar telescope.  While I’m waiting for that to be delivered I took the chance to get some ‘white light’ images this afternoon.

Here is a composite of two images taken through the NexStar 102SLT (and 2x Barlow) filtered with Baader film.

Some very prominent groups of sunspots today.  I hope they’re still there when I get my PST in the next day or two!

After getting some solar images I had an attempt at finding Venus.  With the HEQ5 mount not accurately polar aligned it’s not that easy.  My method was to find the difference in altitude and azimuth from the Sun then slew the telescope to the approximate place.  Skymap Pro told me to move the telescope 9 degrees lower and 10 degrees right of the Sun.

Here’s a star chart showing the location of Venus this afternoon.  With an elongation nearly 12 degrees west of the Sun the planet was far enough to safely observe without taking steps to block out sunlight falling into the telescope tube.  Here’s a Stellarium rendition of the afternoon sky.

The real sky was much cloudier – lots of slow-moving patchy cloud.  After a gap appeared in the clouds Venus was easily visible in the camera field of view.  Venus is currently very narrow crescent – shimmering through what was obviously very unsteady air.  There followed a frustrating hour in which switching between eyepiece and camera was thwarted by the ever shifting clouds.  Eventually I had Venus in the field of view with the camera and 2x Barlow lens.  I began clicking away on the remote…

This is a stack of 33 images taken with the Nikon D80 through the NexStar 102SLT (and 2x Barlow) at ISO100 and 1/250s exposure.  Stacked in Registax 5 and post processed with GIMP.

Now that Venus is west of the Sun it will soon be a prominent morning sky object before sunrise.  As it recedes from Earth the angular size will grow smaller and the phase will increase.

It seems that you can do astronomy in the summer – you just have to change your targets, that’s all 🙂