Saturn: 25 February 2007

Date: 25 February 2007 U.T.
Time: 5:55 - 6:48 U.T.
Telescope: 30cm Newtonian
Magnifications: 250x and 300x
Filter: #80A and unfiltered
Seeing: Fair to Good
NELM: 5.3 (Moon in sky)
Temperature: +17 F (-8 C)

The above sketch shows the basic appearance of Saturn on this night. South is up. Preceding is to the left.

After initial collimation of the truss-tube telescope I pointed the scope at Polaris, increased the magnification to 400x, and used the de-focused star's Fresnel pattern for a final 'tweak' of the collimation.

The scope had been outside for a few hours prior to the session. At the beginning of the observation the seeing was Fair. The sketch was initially made at 250x with the #80A filter.

As the session progressed the seeing improved. I removed the filter and increased the magnification to 300x. At times of steadier seeing the image was quite sharp. Tethys, one of Saturn's moons is shown just south of (above) the preceding (left) portion of the ring system.

Initially, Cassini's Division was not visible all the way to the limb of the planet, but that changed after the seeing improved. Both the preceding and following limbs of the planet were darkened a little. The C-Ring was visible against the background sky as well as against the ball of the planet. The filter may have darkened (increased contrast) of the planet's southern hemisphere belts as well as the C-Ring against the planet. The outer portion of the A-Ring was darkened somewhat and some structure was hinted at. The inner portion of the B-Ring was darkened somewhat.

Some clouds came and went during the observation. The outside of the telescope had attracted a fair amount of frost during the session.

This was my first high magnification planetary observation with the 30cm Newtonian. It's not likely to be the last!

The Great Orion Nebula

Date: 20 February 2007 U.T.
Time: 4:20 - 4:50 U.T.
Telescope: 30cm Newtonian
Magnifications: 61x and 155x
NELM: 6.5
Seeing: Poor
Temperature: +24 F (-4 C)

The Great Orion Nebula, also known as M42 is one of the brightest and most beautiful nebulae in the night sky! This large nebula practically fills the field of view at 61x. In its brightest regions it's possible for some people to see color. I noted a weak greenish glow in the brightest parts of the nebula and a hint of red in some of the other areas.

Within the brightest part of M42 is a tight group of four stars known as the Trapezium. At 155x I was able to see a fifth star in the Trapezium without much difficulty. A sixth star was more difficult due to the poor seeing conditions; but it was occasionally suspected near the glow of the brightest member of the 'big four.' On a good night I've seen all six stars with ease while using a considerably smaller (13cm) telescope.

M42 is a very irregularly shaped nebula. It has many curves and regions of widely varying brightness. I used the low magnification of 61x in order to be able to see the entire nebula at once; but it's well worth the time to study individual parts under higher magnification.

M43 shares the field with M42. It's much smaller in size, has a semi-bright star within it, and has the shape of a fat comma. While having separate entrees in the Messier Catalog, M42 and M43 are parts of the same nebula complex.

Before ending the session I swung the scope around to Saturn for a quick look at one of our solar system's real show-pieces. Saturn is always a joy to behold!

Even if I weren't too tired to continue observing I would have had to quite soon due to increasing clouds. As I was bringing the scope, etc. back inside more and more stars were disappearing behind the thickening clouds.

Horsehead Nebula, etc.

Date: 20 February 2007 U.T.
Time: 4:10 U.T.
Telescope: 30cm Newtonian
Magnification: 61x
Filter: UltraBlock
NELM: 6.5
Seeing: Poor
Temperature: +25 F (-4 C)

I started out without using the above mentioned filter. NGC 2024 (also known as the Flame Nebula and Tank Track Nebula) was visible near Zeta Orionis. This nebula has a prominent dark lane running through it.

After shifting the telescope slightly to the south, Zeta Orionis left the field of view. The small, bright nebula NGC 2023 was now easily visible surrounding a star.

The next logical step was to look for IC 434 (a faint 'bright' nebula) and the dark notch within it known as B33 -- the Horsehead Nebula. These objects were visible with difficulty. IC 434 was only slightly brighter than the background sky. The Horsehead Nebula has a reputation for being a particularly difficult object to see visually without the use of a specialized (H-Beta) filter. In order to successfully see this object without a filter one must observe from a dark location that's free from the glow of city lights.

I don't have an H-Beta filter; but I do have an UltraBlock filter. The UltraBlock is a multi-layered, interference filter that selectively blocks the wavelengths of some of the more common man-made light sources (as well as some of the natural sky glow) while allowing other wavelengths to freely pass through. I screwed the UltraBlock filter into the eyepiece and took another look.

IC 434 and the Horsehead Nebula were suddenly significantly easier to see! The filter significantly darkened the background sky, but not the light from IC 434. As a result, the nebula became easier to see.

I should add that filters such as the UltraBlock do not improve the visibility of all objects in the night sky. Many objects become more difficult to see when such filters are used. Everything depends upon the wavelengths of light and their relative intensities as emitted by the various celestial objects. Furthermore, the effects of many such filters can vary significantly depending upon one's sky conditions and light pollution situation.

For more information on the Horsehead Nebula the curious reader is encouraged to visit Stephen Waldee's excellent Horsehead Nebula Main Page and associated links at:
http://home.earthlink.net/~astro-app/horsehead/index.html

Limiting Magnitudes, Plans, etc.

Date: 15 February 2007 U.T.
Time: 3:00 - 3:40 U.T.
NELM: 6.6
Temperature: -9 F (-23 C)

During the lengthy cloudy spell I revised observing projects, etc. A (new) home-made, square, eyepiece field stop was fabricated that includes a means to more accurately determine angular size as a fraction of the field of view. Refinements were made on a deep-sky project geared toward an all-sky, telescopic survey. Rough plans were drawn up for systematically sketching (mapping) the entire visible portion of Earth's moon.

I'll be as surprised as anyone if I actually manage to succeed in seeing these plans through to their natural conclusions! I'm easily distracted by a bright comet, a well positioned planet, other projects, etc.

I dug up some 'new' limiting magnitude charts that should allow me to make nightly estimates on the limiting magnitudes of my binoculars. I wore red goggles inside a dimly illuminated room for half an hour or so to aid in dark adaptation prior to going outside.

Once outside I used my new charts to determine my Naked-Eye Limiting Magnitude (NELM). Next I repeated the procedure using 8x42 and 20x80 binoculars, both hand-held. I have little doubt that a solid tripod would increase the binocular limiting magnitude. Eventually I'll need to check that out . . .

The limiting magnitude of the 8x42 binoculars was about 10.0. That of the 20x80 binoculars was about 11.4. All values, including the NELM were adjusted for the zenith -- one tenth of a magnitude was added from what was seen in the 45 degree altitude star fields. With practice these values should become more reliable. I hope to eventually correlate the various measurements with one another.

Later I may add telescopic limiting magnitudes figured for a specific exit pupil size (telescopic aperture divided by magnification) to the mix.

I also want to start making better use of filters for the Moon, planets, and deep sky objects; but I think I'm going to need multiple lifetimes in order to accomplish everything!

Happy Birthday Galileo! Galileo Galilei was born on 15 February 1564 in Pisa, Italy. He's known not only for his ground-breaking telescopic observations; but also for his experimental approach that led to the discovery of the pendulum's time-keeping potential, ballistic science, and much more.