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