latest-images

Spring Comet C/2007 N3 Lulin in Leo

Mon, 16 Mar 2009 11:34:47 +0100

Comet C/2007 N3 Lulin became a fine Spring comet in February and March for UK observers. At around magnitude 6, perhaps a touch brighter, Lulin is not a true naked eye comet, but it is large and bright in any telescope or binoculars. Following solar conjunction at the end of 2008, Lulin has raced from Scorpio, through Libra, Virgo and then into Leo, skirting just south of Saturn around 23rd/24th February. Its orbit is very close to the ecliptic, which is why it has traced its path through the Zodiacal constellations.

Here is a sequence showing Lulin on the early evening of 3rd March as it edged towards the western boundaries of Leo at around 5° per day. The sequence comprises 25 two-minute exposures, taken with my LX90 @ f/3.3 using a Starlight Xpress SXV-M7C (giving a field of view of 34'x26'). You can see a satellite streak across the field midway through the sequence.

Here's the same data, but stacked in AstroArt 4 to reveal the large coma and tail. Can't really see much of the anti-tail unfortunately.

There's lots more info about this comet on the web, but in particular I found this Gary Kronk's site useful. As I post this, Lulin is now well on its way through Gemini, fading by the day.

Comet 144P Kushida in Taurus

Sat, 31 Jan 2009 08:17:14 +0100

At the start of the year, Comet 144P Kushida had just glided eastwards from Aries into Taurus. At magnitude 10.7 and no discernible tail, it glows eerily to the north west of the mag 7.4 star GSC 1234-545, which by comparisonshines brightly towards the bottom of the picture.

This picture 'freezes' the motion of the comet against the background stars by using some image processing trickery. First of all I used AstroArt to stack the images in AstroArt so as to correlate the stars, which results in sharp background stars and a trailed comet image. I then repeat the stacking process, this time to use the comet as the correlation reference point, which results in a good comet image with blurred background stars.

The second phase uses Adobe Photoshop: I created a layer with the crisp background stars and erased the trailed comet (using the healing brush and clone stamp tool). I then added a second layer using the image of the comet and trailed stars. After aligning the two layers, I used a layer mask on the second layer to hide everything on that layer. By then erasing the mask around the comet I could allow the image of the comet to show through against the background of field stars. A little Gaussian blur of the mask allows a smooth blending of the comet onto its background with the result you see above.

Pristine craters Messier and Messier A

Fri, 30 Jan 2009 07:12:50 +0100

Lying within Mare Fedunditatis (Sea of Fertility), the two craters Messier and Messier A can be seen at the centre of this image (Messier is the left one). Taken around midnight on 13th January 2009, with the moon around 16 days old, the characteristic ejecta plume shows well emanating towards the south west of the pair.

They are referred to as pristine craters because they exhibit none of the usual signs of deterioration, such as slumping crater walls, other crater impacts or basaltic lava flows. They are also rather elliptical in shape, although not along the same axis. It is believed they were created by two separate impact objects, both striking at an oblique incidence angle (around 5°).

Unfortunately the detail within the craters is not visible in the f/10 image, but instead there are some good views of the dorsa (wrinkle ridges) towards the east of the Messier pair. Dorsa are formed as compression artefacts caused by ancient tectonic movements disturbing the otherwise smooth basalt lava plains.

Saturn edge-on in the Winter Sky

Wed, 21 Jan 2009 00:19:35 +0100

If you look towards the east late at night at the moment you'll see Leo rising with Saturn some 10° below Leo's hindquarters. Around magnitude 0.8, Saturn is nowhere near its brightest, all because the rings are presented almost edge on to us. Twice every 29.5 years Saturn's rings appear edge on to the Earth due to the inclination of Saturn's orbit relative to the Earth. On 13th January I caught my first images of Saturn this season, combining some short exposure sequences of the planet with some longer exposures to capture some of the satellites. The seeing was pretty poor and - I later discovered - my telescope was not well collimated, so I'm not too happy with the image. It'll do as a starter for ten!

If you click on the image you'll get an annotated version showing which satellites are which. Mimas and Enceladus are hidden in the eastern edge of the rings but, given the seeing and poor collimation they're not visible in this image.

When I get a better image, I'll add it to my montage of Saturn's rings over the years, shown here.

Near and far

Sat, 10 Jan 2009 18:47:13 +0100

My main interests in astro-imaging are deep-sky objects, particularly galaxies. You obviously need a dark sky for this, and the moon is usually a nuisance to me. However, with the moon high in the sky on these recent freezing nights, I felt the urge do some lunar imaging. I've not used my webcam for some months now, and with Saturn also rising earlier each night, I decided it was high time to dust off the webcam (an old Philips ToUcam Pro).

Yesterday (the 9th January) around 4pm but already -2°C, the heavy gibbous moon was low in the north east with Venus high in the south. I quickly unscrewed the focal reducer I normally use to widen my field of view for those faint galaxies and fixed in place the eyepiece tube into which I can fix my webcam. It was still light, but started up the scope and slewed her to Venus. The difference in focal ratios between my f/3.3 reducer and the native f/10 is a lot of turns of the focus knob. Since I do this relatively infrequently, I found I needed to make a note of the 7 1/2 turns clockwise turns. Next, put in an eyepiece, make sure the target is dead centre and then replace the eyepiece with the webcam. K3CCDTools, my webcam capture software, showed a slightly out of focus Venus, nearly at "half-moon" phase. A quick tweak of the electric focuser fixed that and I grabbed 500 frames.

Not the most interesting target, perhaps, but I now was ready to swing round to the moon. Being a day or two from full moon, the terminator was very close to the western limb, highlighting some of the foreshortened craters on that coast of Oceanus Procellarum, the largest lava 'sea' on the moon. I picked the crater Hevelius, whost rugged crater walls contrasted beautifully with the smooth texture of the basalt lava flows to its east. Hevelius is some 106km in diameter and 1.8km deep. The crater to its north is the smaller, but prominent crater Cavalerius.

As soon as I'd captured this, though, some low cloud flooded in and prematurely stopped proceedings. I went indoors and processed what I'd got. Didn't take long - Registax is so good! So having done some solar system imaging I went through some recent deep-sky images I'd taken and found the huge spiral galaxy NGC 2403 in the constellation of Camelopardalis (the Giraffe). Its 12 million light years away, quite close, which helps to make it a large target around 18' by 11'.

Its outer spiral arms are faint and don't really show up too well here, despite over 4 hours of exposure, but you can glimpse emission nebulae in the inner arms.

So I started the evening on some near neighbours before drifting back to a far off galaxy where there are countless Suns, planets and moons.

New supernova SN2008in explodes in M61

Sat, 03 Jan 2009 10:06:57 +0100

Supernova 2008in was discovered on 26th December by Koichi Itagaki in the spiral galaxy M61 in Virgo. It is a type IIP supernova. Type II supernovae are formed from the core-collapse and explosion of massive stars (i.e. greater than 9 solar masses). Type IIP are designated as such because they reach maximum brightness, dim slightly, and then stay at almost the same brightness "plateau" for many days before fading (hence the name type IIP, i.e. II-Plateau). Other type II supernovae reach maximum brightness and then dim linearly and therefore classified as Type IIL (II-Linear).

This morning I managed to snatch 20 minutes of exposure in the pre-dawn sky. The supernova is relatively bright and clearly identifiable. Using AstroArt's photometry facilities I measured a magnitude of around 14.7 using the luminance data from my SXV-M7C camera.

Supernova SN2008in in M61 in Virgo

Mirach's Ghost

Thu, 01 Jan 2009 12:43:45 +0100

Most evenings when I start my imaging session, my set-up process involves selecting a bright star in my planetarium programme (Cartes du Ciel), slewing the scope to the star, ensuring it is centred and then 'syncing' the scope. The other evening, I subconsciously selected a star in Andromeda high in the south and started the guide camera. With the star bright and dead centre, I noticed a faint smudge some 7' north west in the autoguider window.

A quick glance at Cartes du Ciel and I saw I'd selected Mirach, Beta Andromeda and that the 'smudge' was the lenticular galaxy NGC 404, which lies some 10 million light years away. With Mirach blazing at magnitude 2.06, the 11.02 magnitude galaxy is rather difficult to see, hence the name of Mirach's Ghost. It was discovered by William Herschel in 1784.

This image is the result of only 15 minutes of imaging, but the ghost is clearly visible above-right of Mirach, in the centre of the frame.

Mirach's Ghost, NGC 404, 7' to the NW of Mirach

Projects for 2009

Thu, 01 Jan 2009 08:59:26 +0100

It was a cold but dull New Year's Eve, no chance of leaving my equipment imaging whilst we partied. So what do I want to have achieved this time next year? After a bit of thought, here's a list of 10 projects for 2009. Let's see how many I complete over the coming months. Happy New Year!

1. Capture Saturn's rings edge on

I've been constructing a montage of Saturn over the last few years as the rings close. In 2009 the rings finally close and I can add to that montage. In addition, as Saturn is - by definition - edge on to us, it affords opportunities to image Titan and maybe other moons as they transit Saturn, possibly even their shadows in transit.

2. Image a magnitude 20 object

Having recently imaged mag 18.7 dwarf planet Eris (see blog entry) I've rather got the bug for stretching my imaging setup to its limits. Having read an interesting article on the Starizona website I'm going to compile a list of faint quasars and possibly faint solar system objects (NEOs, asteroids, comets). I think I can reach magnitude 20 (based on no science at all) - still some distance off the amateur record of 24.7!

3. Image an Asteroid/Comet conjunction with a Deep-sky object

Comets can be attractive imaging targets. Less so asteroids. Whilst capturing sequences of either drifting through a star field is reasonably interesting, it would be a much more pleasing image to see such a body pass close to, or even across a deep sky object. I'm not sure if there's a list of such events published anywhere, in which case I need to resort to Cartes du Ciel, my planetarium programme, to try and spot some opportunities.

4. High resolution moon montage

I've created on moon montage, an f/20 image of the crater chain Alphonsus, Arzachel and Ptolemaeus. I've seen some beautiful images of showpiece craters such as Clavius and the south pole region and would like to find some new targets, perhaps the same target through the lunar month. I don't image the moon as much as I should, mainly because of the hassle of switching imaging setups. As Saturn approaches opposition I will have the webcam set up more often and this should provide more opportunities.

5. Capture a good comet image

Well I'm rather reliant on what nature serves up here, but assuming a suitable target - perhaps Comet C/2007 N3 (Lulin) - I'd like to produce one of 'those' images with a comet nucleus, coma and tail frozen against a background of field stars. Maybe I'll even understand how to use the Larson-Sekanina filter!

6. Get a monochrome camera

I'm pleased with my Starlight Xpress SXV-M7C one-shot camera but want to move to a larger format CCD. So I thought I might as well take the plunge and move to a monochrome camera. I'll need a filter wheel, ideally one I can remotely control from AstroArt with an ASCOM driver. I'll try and get one off Astromart or UK Astronomy Buy & Sell, failing which Atik have launched the 314 range of CCDs which look attractively priced.

7. Start higher-resolution deep-sky imaging

Following advice taken when I started imaging, I've tended to do my deep-sky imaging at low focal ratios (f/3.3) using a focal reducer on my f/10 natiive LX90. The main reasons for the advice are that the lower f/ratio allows you to use shorter exposures over wider fields, which is more forgiving on tracking errors introduced from poor polar alignment, poor tracking or poor guiding.

Whilst the LX90 mount is not renowned as a 'benchmark' imaging mount, I think I can squeeze some higher f/ratios out to provide some more detailed images of smaller galaxies. f/5 ought to be eminently achievable, perhaps even f/8 or f/10.

8. Start narrowband imaging

If I do upgrade to a monochrome CCD I want to start using specialised narrowband filters (H-a, OIII, etc). I already own an OIII filter and tried to use it on some OIII-emitting nebulae in the summer. Trouble is, on a one-shot camera like mine, the Bayer matrix filters out so much light I never reached usable S/N ratios.

9. Get a picture printed in a magazine

Perhaps a little vain I know, but successfully getting an image published will mean I've improved my image capturing and processing skills beyond where they are today! It might also mean I've captured something noteworthy and unusual, not the run-of-the-mill.

10. Construct an all-sky camera

If and when I upgrade my camera, my current guidescope CCD - a Meade DSI-C - will be going spare. I've seen how people have used them plus a suitable wide-angle lens to create an "all-sky cam". This can be used to monitor the sky for approaching cloud (which, if your setup permits, enables the observatory to be shut down) or for wide-area images of the sky, constellations, meteors, star trails, aurorae. Not sure I'd so this if I didn't have a spare CCD, but might prove an interesting project.

How did Messier miss this?

Wed, 31 Dec 2008 09:01:35 +0100

There are, I'm sure, plenty of contenders for the biggest and brightest object not included by Charles Messier in his famous catalogue of faint fuzzy objects which might have been mistaken for comets. Lying around 4° west of the nose of Leo, NGC 2903 must surely be near the top of the list. At around magnitude 10 (according to SEDS) and 13.3' along its major axis, this is a large and bright Sb+ spiral galaxy some 20.5 million light years from us.

Despite NGC 2903 being missed by Messier, Giangi Caglieris has pointed out that three of his comets came quite close to this object: Messier;s second comet of 1760 passed it during the night of March 11-12, 1760 at only 1°40', and the comets of 1762 and 1771 also passed close by.

This image was taken on 30th December, a cold (-6°) frosty evening as 2008 draws to an end.

NGC 2903 in Leo on 30th December 2008

136199 Eris - definitely located this time!

Tue, 30 Dec 2008 08:23:52 +0100

In late November and early December I imaged the dwarf planet Eris on several nights. Using Cartes du Ciel to help me pinpoint where she should be and the apparent movement of a faint object over the different nights I was fairly confident I had located the magnitude 18.7 dwarf planet. Here's my earlier post.

On the 28th December I tried again. With clearer skies I was able to image for longer to improve the signal-to-noise ratio. I'd also downloaded the Hubble Guide Star Catalogue to allow Cartes du Ciel to show fainter field stars to aid identification. The result is shown below.

Faint (mag 18.7) Eris located near the centre of this 13' field

Eris is very clearly shown, and with a S/N ratio of 7.8 and the finder chart below there is no doubt this time. For comparison the two small stars close to each other to the left and slightly below Eris are mag 15.08 GSC 4687-1542 (top) and mag 14.81 GSC 4687-1841; the 'bright' star near the left hand edge is mag 10.92 GSC 4687-2132.

Cartes du Ciel finder chart for Eris