Lunar Limb - Daylight Observation

Date: 24 August 2008

Time: 17:18 - 17:33 U.T.

Telescope: 80mm f/5 achromat

Magnification: 70x

Filter: Polarizing

Seeing: Fair - Good

NELM: Daylight

Temperature: +85F (+29C)

Wind: Calm

Transparency: Very Good (cloud-free sky


The above sketch shows two lunar mountains that were silhouetted against the darker sky background. North is up. Lunar East (preceding) is to the left in this mirror-reversed view. The sketched region is at 90 degrees west longitude and approximately 12 or 14 degrees south latitude. The moon was a fat, waning crescent at the time of the observation.

Not shown in the sketch is Lacus Aestatis which was seen as a dark patch to the left of the lower mountain peak beyond the sketched region. A very rough, larger scale sketch was made to facilitate finding this region on a lunar map. That sketch showed Lacus Aestatis, Cruger, Grimaldi, and Riccioli all as dark patches.

The sun was still spotless today. I used the 80mm refractor at 24x. A glass, white-light solar filter covered the front of the telescope. The filter gave the sun a soft, golden, peachy color. There was something aesthetically pleasing about observing a spotless sun through a telescope with one's own eyes.

Venus and Mercury in Evening Sky

For the past three evenings I've managed to see these two planets low in the western sky shortly after sunset. Brilliant Venus has been the easier planet to spot. Dimmer Mercury has been between one and two degrees to the lower right of Venus.

Binoculars seem to be better suited for catching these two planets than a telescope. The sky has been too bright at prime observing time for Mercury to be seen with the unaided eye.

This evening I set up a small, 80mm f/5 refractor on the porch. Venus was easily visible, but trees blocked Mercury from view. From nearly the same location I managed to see both planets with 20x80 binoculars. This was primarily because my eye level with the binoculars was a little higher than the telescope -- just enough to bring Mercury above the trees.

On the previous two evenings I viewed the two planets with 8x42 binoculars as well as with the 20x80s. Mercury was easier to see with the 20x80s. Venus showed up easily with either pair of binoculars. Once I knew where to look, Venus could also be seen with the unaided eye.

On all three evenings I had to look thru thin clouds when observing Venus and Mercury. The clouds appeared to have formed near the time of sunset low in my western sky. They showed up as horizontal bands of varying thickness, but not thick enough to block the planets from view with binoculars.

Meanwhile, Jupiter shines brightly in the south-southeast. Jupiter and its brightest moons are not difficult to see with either tripod-mounted or steadily held binoculars.

Our Spotless Star

The above photo of the sun was taken today, 12 August 2008. A DSLR camera was used at the prime focus of a 102mm (700mm focal length) Schmidt-Cassegrain telescope. A full-aperture, white-light solar filter covered the front of the telescope.

I knew the sun was without spots today - as it has been for quite some time now. Nevertheless, even a spotless sun can be of interest. Notice that the limb (edge) of the sun is darker than the center of the sun. This is called "limb darkening" and is due to much of the solar radiation originating deep within the interior (rather than the 'surface') of the sun.

The sun goes through a roughly 11-year sunspot cycle. Approximately 11 years pass between sunspot maximums. Sunspot minimums occur roughly midway between the maximums.

Shooting the Moon

Shown above is a 'snapshot' of this evening's gibbous moon. It was taken under poor seeing conditions with a DSLR camera attached to a 102mm Schmidt-Cassegrain telescope (about 700mm focal length). This was one of two experimental images I took of the moon. The telescope's tripod was set up on my south porch - not the most stable of platforms, but sufficient for experimental purposes.

The Perseid Meteor Shower should be near its peak after the moon sets later tonight. If you read this early enough (Monday night - very early Sunday morning), have adequate sky conditions, and can affort to lose the sleep (a lot of 'ifs') you might want to spend some time lying back, staring at the sky, and counting meteors.

What is a planet?

What is a planet? In my opinion any astronomical body that's essentially massive enough to maintain a spherical shape, but not massive enough to trigger a self-sustaining fusion reaction (becoming a star) should be considered a planet.

Looking over the known bodies in our solar system, it seems that a reasonable cut-off at the low end would be 10e20 (one with twenty zeros) kilograms. Some solar system bodies with a mass in the 10e19 range are reasonably spherical, others are not. Since it's desirable to have an unambiguous definition (based solely on mass - which is one of the most easily determined properties of solar system bodies) it seems reasonable to fix 10e20 kilograms as the lower limit for planetary status.

The upper limit would be more flexible (as far as mass goes). The primary criteria here is that the body in question is not a star - that is, it does not generate a self-sustaining fusion reaction. For objects otherwise similar to those in our solar system, this limit would likely lie within the 10e28 kilogram mass range.

Planet Classes can now be designated as:

Class 0 -- with masses in the 10e20 kilogram range

Class 1 -- with masses in the 10e21 kilogram range

Class 2

Class 3

Class 4

Class 5

Class 6

Class 7 -- with masses in the 10e27 kilogram range

Class 8 -- with masses in the 10e28 kilogram range

Jupiter would be a Class 7 planet. Earth would be a Class 4 planet. Pluto would be a Class 2 planet. Tethys (one of Saturn's moons) would be a Class 0 planet.

Bodies with masses less than 10e20 kilograms could be referred to as "subplanetary" and designated as lying within Subplanetary Class -1, Subplanetary Class -2, etc. for masses in the 10e19 and 10e18 kilogram ranges respectively.

Note that the location of an object is not relevant in this system. The object is classified the same regardless of whether it orbits a star or a planet. A Class 5 planet, for example, could even be adrift in interstellar space.

Jupiter's Family via 25x100 Binoculars

Shown above are two sketches of Jupiter and its brightest moons as observed on 1 August 2008 U.T. The uppermost sketch was made at 3:15 U.T. The lower sketch was made at 7:25 U.T. The lower star at the far left is an actual star, not one of Jupiter's moons. Europa was in transit across Jupiter's disk (and not visible in the large binoculars) at the time of the first sketch, but by the time I had started working on the second sketch it had reappeared off Jupiter's preceding (western) limb.

Jupiter's North and South Equatorial Belts (the dark bands running parallel to Jupiter's equator) were visible in the tripod-mount 25x100 binoculars. Seeing conditions were rather poor on this night. Jupiter's moons and the various field stars appeared to twinkle due to earth's unsteady atmosphere. A haze (most likely from forest fire smoke) seemed to fill much of the sky as well.

My First Star Field Photo

This is my first (and so far only) photograph of the night sky taken with my new camera. I attached the camera to a homemade equatorial wedge (built for a 102mm SCT) and set the assembly on my north porch. The "Little Dipper" asterism can be seen offset toward right center. Some nearby tree tops are silhouetted against the brighter night sky at the bottom of the photo.

Digital photography is certainly far more user friendly than film photography! One gets to see the results right away, and PCs make it easy to tweak the images as necessary. The above photo is a 30 second exposure at ISO 800 with an 18mm lens at f/3.5. It was taken at 11:59 pm local time on July 31, 2008.