April 17, 2008

9pm-12am

A truly clear night, almost warm.  The moon, however, is high in the sky and three quarters full, its brilliance nearly drowning out the fainter DSO's.  In a few days, it will be full and I will need to wait until it wanes before resume imaging sessions.

The scope was first polar aligned – but not too well, I'm afraid – using Polaris and Arcturus, and the realigned using Arcturus and Regalus. The tracking was okay, and delivered object to the FOV most of the time in GOTO, but I could only expose for 15 seconds before getting movement in the image.

M65

With the bright moon so close by, this galaxy was almost lost in the glare.

60, 15 second sub-exposures were stacked to create this image.

M97

I continue to try and capture the Owl, but 15 second sub-exposures just aren't cutting it – and the bright moon didn't make it any easier. 

This image is composed of 86, 15-second sub-exposures. 

M99

For once, a decent image. 

Compared to the image I took a couple of weeks back, this stack of 100, 15-second sub-exposures shows an incredible amount of detail in the spiral arms – despite the moon's interference.  The difference between this photo and the previous one is a much finer focus. 

M91

Discovered by Charles Messier in 1781, M91 is a barred-spiral galaxy.  While it possesses a relatively bright core, the spiral arms and the “bar” connecting them are quite faint and difficult to record. 

This image is a stack of 86, 15-second sub-exposures.  Obviously, longer and more subs will be needed to capture the spiral arms in any detail.

M104

I always wait too long before getting around to the Sombrero.  By the time I swung the scope toward Virgo, this galaxy was already headed for occlusion by the treeline.  So I didn't have enough time to image it properly – as usual.

Still, the central dust lane is remarkably visible.  The trick will be to capture detail within the dust lane itself.  In order to do that I will need to increase the magnification.  This photo, like all the others, is taken with the LXD75 at f/5.  Barlow lenses would increase the f-ratio to f/10, but I don't know how well that would work with the DSI.

60, 15-second sub-exposures were stacked to create this image.

M13

The largest and brightest globular cluster in the northern sky.

This is almost certainly the best image I have ever obtained of M13 and shows just what the DSI Pro is capable of – if it has a good focus.

M13 was first discovered by Edmund Halley – the discoverer of Halley's Comet – in 1714 and was added to Messier's catalog in 1764. It is thought to have a diameter of about 145 light years, into which are squeezed several hundred thousand stars. Astronomers place its distance from Earth at about 25,100 light years.

April 14, 2008

9pm-12am

The sky was mostly clear for a good part of the night before finally clouding over completely.

M106

Another attempt.  Unfortunately, my tracking and alignment wasn't as good as it should have been, resulting in skewed stars.

This picture is a stack of 50, 21.2 second sub-exposures.  The galaxy's central disk stands out well, offering some detail of the star clouds swirling around the bright core. A dimmer halo of material surrounds the galaxy, just barely visible in this image. Longer and more sub-exposures should bring that detail out.

M109

I will not let the season pass without obtaining a good shot of this galaxy.  But if I am to do that, I will need considerably longer sub-exposures than I am using. 

While this stack of 80, 15-second sub-exposures shows the shape of the galaxy's spiral arms well enough, if fails to bring out any detail.  With M109 now reaching zenith just as the sky darkens at night, I won't have much longer to capture this galaxy unless I resort to moving the telescope out onto the front lawn, which is more effort than I'd like to put into getting the image.

M104 

Another galaxy that I really want to capture in detail before the season passes.  Yet, as with the others, I haven't yet applied long enough sub-exposures, or stacked nearly enough to reveal the fully amount of detail that the DSI Pro can capture.  

The poor tracking and alignment is quite visible here.  

April 12, 2008

9pm – 10pm

Desperate for a clear night to image, I was suckered out by a break in the cloud cover that left the entire sky clear just long enough for me to get the telescope set up and aligned and the camera ready.  By the time I had all that done, the clouds began moving back in and very soon covered the entire sky.  There was time to capture only one image, so I opted for the brightest object then convenient situated in the sky – one that would require a short exposure time.

M3

This image is comprised of about 20, 15-second sub-exposures, for a total five minute exposure. It is one of the better images of M3 that I have obtained.

M3 is a massive globular cluster, one of the brightest in the skies over the northern hemisphere, eclipsed in beauty and fame only by the great globular cluster in the constellation Hercules, M13.  A globular cluster is a dense sphere-shaped cluster of stars, bound together by strong gravitational attraction. The stars in these clusters tend to be quite old and metal-poor, suggesting that most globular clusters are formed in a galaxy's early youth. Globular clusters are usually found in a galaxy's halo – outside the main plane of a spiral disk. The Milky Way is known to have 151 globular clusters, but it is estimated that there are probably 20-30 more that are occluded by the dust and gas of our galaxy's spiral arms and are thus not visible from Earth. Globular clusters have been spotted in many distant galaxies

M3 lies about 33,900 light years from Earth. Located in the constellation Bootes, it is easily glimpsed as a round, hazy patch with good binoculars; a telescope is needed to resolve it into a dense cloud of stars, concentrated at the center.  The cluster was first discovered by Charles Messier in 1764, but was not identified as a star cluster until William Herschel's superior telescope resolved it twenty years later.

April 8, 2008

9pm – 1am

The first clear night in almost a week!  I set up the scope and immediately took fresh darks.

The night sky wasn’t as dark as I'd have liked, and there was a faint pinkish tinge, but it was clear and dark enough for my purposes.  I spotted the crescent moon low on the western horizon, portending its eventual rise to blinding brilliance (and the ruin of any DSO imaging on those nights), but that is still a week or so ahead.  Unfortunately, NOAA predicts that only Thursday night will offer even a small chance of clear skies in the next five days.  

M81

This is a large spiral galaxy in Ursa Major (the Big Dipper) first discovered by German astronomer Johann Bode in 1774, and included in Messier's famous catalog in 1779.  Due to it's original discoverer, it is sometimes referred to as Bode's Galaxy.  M81 is the brightest of 34 galaxies in the M81 Group, located about 11.7 million light years away.  It is appears in the sky near the star Dubhe (Alpha Ursa Majoris) and can easily been spotted as a faint smudge of light with a good pair of binoculars in a reasonably dark sky.

As with many large spiral galaxies, obtaining detailed images of M81's spiral arms requires lengthy exposure times.  This is because the arms are so faint compared to the galaxy's core.  Indeed, when observing the galaxy visually through a small telescope or binoculars, it is the core that is seen, rather than the delicate spiral arms.  Large telescopes can reveal enough of the structure, visually, to suggest a spiral shape (as 19^th century astronomers like Lord Rosse were able to detect in several similar “spiral nebula”).  But only long exposure photography or digital imaging can reveal the breathtaking sweep and structure of a spiral galaxy.

 The above image comprised 100, 15-second sub-exposures. More and longer subs will be needed to truly draw out detail in the arms.

M97

 

This stack of 80, 15 second sub-exposures (20 minutes exposure time) still doesn't do the Owl Nebula justice, especially since a passing airplane streaked across the image, leaving a visual record of its passage. This is one of the hazards of letting Meade's Envisage software capture the final image without saving each individual sub-exposure.  If I had saved all the subs, I could have gone back and deleted the one taken while the plane was crossing the camera's FOV and thus removed the lines of its lights from the final image.  But, as I have said, I am lazy.

Clearly, I will have to come back again to this object.  The Owl Nebula is an object whose image would clearly be improved by color.  I am considering the purchase of a filter wheel.  (I found the filter slide that came with the DSI to be clumsy and unworkable.)

M51

After last week's ruined image, I felt I had to return to the Whirlpool Galaxy to get a better image.  The galaxy is perfectly positioned for imaging in the night sky at the moment.

 

This image comprises about 240, 15-second sub-exposures (60 minutes total exposure. I would like to try using longer sub-exposures – say 60 seconds – to see if that draws out any additional detail.  But I have the feeling that I have reached the limits of the DSI-Pro with this subject.

M104

The last image of the night.  I continue to hope to capture an image showing better detail of the Sombrero Galaxy's great disk of dust, gas and stars, but I haven't done it yet.  

40, 15-second sub-exposures were stacked to create this image.  Many more were needed, but the galaxy slipped behind some tall trees before they could be taken and stacked – the consequence of waiting too long to begin imaging this target and failing to consider what terrestrial objects would soon occlude it.

A close-up view of the galaxy might be needed to show the dust lane in all it's glory

April 2, 2008

9pm – 12:30am

The sky was clear, the air was cold, the scope was nearly perfectly aligned and focused ... and I made a rookie mistake.  I was so eager to start imaging that I neglected to take fresh darks*, relying instead on darks taken a few nights before.  Problem was, those darks were taken during a much warmer night and contained a lot more noise.  Meade's Envisage software automatically subtracts darks from each image in a stack during the image process. Unfortunately, the effect of my error was only visible during post-session processing, not as the images piled up on the laptop's screen.  When I processed the raw images, I realized the error and wanted to kick myself for ruining what would have been some nice images. 

The following images are the highlights of the evening.  The graininess and drizzle-like noise obvious across each image is a result of using the wrong darks. 

*Dark frames, for those unacquainted with the term, are images taken with a CCD camera with the telescope tube closed.  With no light coming into the tube, the image should be perfectly dark (hence the name).  However, heat from the camera's chip produces a faint glow that registers on the chip's sensors (along with artifacts resulting from the heat or dead pixels). The object of taking darks is to subtract them from images taken with the telescope tube open, thus removing the glow from the camera's own heat from the final image (darks also help remove dead pixels and other noise from final images).  Because the extent to which the camera's internal heat will affect an image varies with the ambient heat around the camera – i.e., whether it is 5 degrees or 50 degrees outside – darks should be taken at the start of each imaging session to best mitigate camera noise in the final image.

M97

A planetary nebula in Ursa Major (the Big Dipper). A planetary nebula is a cloud of gas and dust created when a star blows off its outer layers in an explosion called a nova near the end of its life. The star's shrunken core remains as a white dwarf star, illuminating the nebula from within. Planetary nebulae are so named because they appear generally disk-shaped, and thus reminiscent of planets. Planetary nebulae can take a variety of other forms, including hourglass-like shapes, depending on their position when seen from Earth.

This image is composed of 206, 8-second sub-exposures for a total of 27 minutes of exposure. 

First discovered by Charles Messier's colleague Pierre Mechain in 1781, M97 was dubbed the “Owl Nebula” by Lord Rosse nearly seventy years later due to the two eye-like spots on the nebula's otherwise featureless disk. 

 M97 is brighter visually (at 9.9 magnitude) than photographically (12.0 magnitude) due to its spectral composition, and is believed to have a more cylindrical shape than is apparent from Earth. The two “eyes” that gave the nebula its name are actually the poles of the bulged cylinder that is the nebula; these appear as dark spots because matter in those places is less dense. It's distance has been estimated at about 7-10,000 light years.

M63

Another chance to image the Sunflower. Too bad the image is substantially degraded by the faulty darks. 

This image comprises 120, 15-second sub-exposures.

M63 was one of the earliest galaxies to be described as a “spiral nebula” by nineteenth century astronomers.  At that time, scientists thought that the stars and nebulae seen in the night sky was the entire universe. Spiral nebulae were assumed to be ordinary nebula – clouds of dust and gas – albeit with a curious spiral shape that piqued the interest of observers. It was not until the early 20^th century that spectrographic analysis reveal the spiral nebula for what they were: island universes of billions of suns far beyond the Milky Way.

M63 is part of the same galaxy group as M51 and lies about 37 million light years away in the constellation of Canes Venatici.

M51

Popularly known as the Whirlpool Galaxy because of its magnificent, sweeping spiral arms, M51 was discovered by Charles Messier in 1773. But Messier's telescope didn't have optics good enough to reveal anything more than dim fuzzy cloud.  It fell to Irish astronomer William Parsons (the third Earl of Rosse – usually noted as Lord Rosse) to first detect and sketch the “nebula's” spiral structure with his 36 inch reflector in 1845. 

This image comprises about 150, 21.2-second sub-exposures (roughly  53 minutes total exposure.

M61

One of the larger galaxies in the Virgo Cluster, M61 has a diameter estimated at 100,000 – similar to the Milky Way.  It is a spiral galaxy and astronomers put its distance at 60 million light years.

This image is composed of 80, 15-second sub-exposures.