Last night was clear. Contrails and pollution make this less usual. So my sister's husband, Fred, and I went out to observe. (I am visiting; they live near Oswego, NY.)
Fred has a new `goto' equatorial mount for his 6 inch (150 mm) F/8 achromatic reflector. We experimented with it for the first time.
An equatorial mount moves the telescope along the paths of stars in the sky. This is different from an alt-azimuth mount in which the telescope moves up and down, left and right.
At dusk, we carefully leveled the mount and aligned the telescope on the celestial pole. The mount has a level in it, as well as a small telescope that goes through its polar axis. With the latter, we could see Polaris, which is 44 arc-minutes away from the pole — about one and a half times the diameter of the moon — at a right ascension of 2.5 hours.
A `goto' mount has electronics in it so that after alignment both on the polar axis and then on several widely separated stars, you can ask the mount to point the telescope at an object and it will. We aligned the telescope on Castor in Gemini, Denebola in the tail of Leo, and Arcturus in Bootes.
Because the new moon is in a few days, on 19 May, there was no natural sky glare. Light pollution from Syracuse prevented viewing a portion of the southern sky.
We looked first at M81 and M82, which are two galaxies in Ursa Major. Through the telescope, they look like smudges. As an astronomer once told me, `all interesting objects are smudges'. He used a telescope with a 1000 times the light gathering power of Fred's refractor; his point was that professional astronomers look mostly at objects that are hard to make out. By the time telescopes are invented that make the object easy to see, astronomers have figured out what it is.
The key to amateur observing is to recognize and understand what you are seeing.
In the constellation of Virgo, we saw M84 and M86, and between Corvus and Virgo, we saw M104, the `Sombrero Galaxy'. Had I planned the effort better, and concentrated on one object rather than several, I would have tried to draw M104. I could see its elongated shape easily, along with the `peak' part of the hat. However, I do not remember its dark `band', which appears so vividly in photographs. I have made out the band before, but not this time.
Observing is hard: even with the biggest amateur telescopes, galaxies are too faint for human eyes to register color. They are fuzzy white patches against a not-quite-black background. The background is not black because in regions like the north eastern US, artificial lights illuminate the sky, even clear skies. Dark and transparent skies are vanishing, an expensive and wasteful side effect of economic change.
Moreover, we look at astronomical objects through an atmosphere. Images move and change. They lack contrast.
Because astronomical images are so faint, we must often use `averted vision', which means viewing with the rods of our eyes rather than the cones. The rods pick up fainter images, but without either the color or the detail of the cones.
When we spend more time looking at a object such as the `Sombrero Galaxy', we get a chance to see the occasional detail from when the sky stops moving momentarily. In addition, we get a chance to figure out what we see with averted vision.
Besides galaxies, we looked at the `Ring Nebula', M57, in Lyra. The Ring looks like a donut with a somewhat filled-in center. (The center glows, but less so than the `Ring' itself.) The `goto' mount aimed the telescope a half degree or so away from the nebula. I found it, looking very small, towards the edge of the view from the 40 mm eyepiece. That eyepiece provides a 30 power magnification for the 1200 mm long telescopic focal length.
Fred just purchased a Televue 8 – 24 mm zoom eyepiece. A few years ago, this kind of eyepiece was rare and expensive. It is still not common and somewhat expensive, but optical machinery has so improved that people can now find them. We centered the Ring in the view of the 40 mm eyepiece. Then we could see it in the Televue at 24 mm (50x) and then twist the Televue eyepiece so its focal length decreases to 8 mm, tripling the magnification.
The Ring expanded, became dimmer. It looked even more like a partially filled-in donut. We tried looking at it with an eyepiece of even shorter focal length. The Ring looked bigger; so did the sky motions. Also the image showed even less contrast between the dim Ring and the background. I think 5 mm (240x) was too high a power for the seeing conditions.
Using the Televue eyepiece, we looked at M13, a famous cluster of stars in Hercules. I enjoyed changing the magnification, zooming in and out.
Also, we saw Jupiter. Near midnight, it looked that Jupiter was coming out of an occultation with HD 92993, a 9.5 magnitude star of spectral type F8. If the occultation occured, and I did not misidentify the speck of light, it did Fred and me no good. But with the proper equipment, an occultation can be used to determine the contents of and pressure changes within Jupiter's atmosphere, and how big objects within it are.
Also, we studied Comet C/2001 Q4 (NEAT), which is near the Beehive Cluster, M44, in Cancer. The comet seemed to me to have an integrated magnitude of 4 or 4.5. I compared the comet to an out-of-focus star. I often seem to see comets as fainter than others. Possibly this is because I live in an area with more light polluted skies; possibly I do a poor job of estimating magnitude. But I am consistent.
The comet showed a central condensation, a coma, and a short tail. With 12x50 binoculars, I could see a 1 – 1.5 degree long tail.
We looked at other galaxies and clusters, but this is enough for the moment.
The sky initially had a limiting magnitude no better than about 3.5 at the zenith, meaning we could not see any stars dimmer than that with the naked eye. But it improved over a two hour period to nearly 5.5 by about midnight.
Go to: Notions
Or return to: Rattlesnake Home Page