Comet 17P/Holmes

Below are some recent sketches of Comet 17P/Holmes with brief notes below each. Notes are brief due to limited time. This blog has just been "cleared" so that I can once again make postings and I need to leave for my day-job in a few minutes . . .

Above is a sketch made from 1:58 until 2:10 UT on 26 October 2007. A 102mm SCT was used at 80x for this observation. North is up and west is to the left in this mirror-reversed view.

Note the tiny star-like pseudo-nucleus in the center of the larger glow and the broad, fan-shaped region south of center.

Above is a close-up of the visual appearance of the comet as seen with tripod-mounted 25x100 binoculars from 1:30 until 1:52 U.T. on 25 October 2007. North is up and west is to the right in this view.

Above is the full-field view of the comet on 25 October (1:30 until 1:52 U.T.) as seen with the 25x100 binoculars. The apparent size of the comet has been enlarged a little to better show the comet and its brightness relative to the stars in the field. Also shown is the observing form I now use for many of my sketches.

Jupiter 11 Sept. 2007 U.T.

Date: 11 September 2007 U.T.

Time: 1:35 - 1:47 U.T.

Telescope: 13cm refractor

Magnification: 138x

Seeing: Very Poor - Fair

NELM: Twilight

Temperature: +68 F (+20 C)

Shown above is my rough, at-the-telescope sketch of Jupiter. North is up. Preceding is to the right. As part of an experiment a 1.25 inch, 90-degree, erect-image diagonal was used. Also in use was a new filter wheel; but no filters were used during the making of the above sketch. The filter wheel was loaded with various filters for deepsky use; but the planned observing session was cut short due to clouds and high humidity.

Jupiter's North Equatorial Belt was the darkest feature on the planet. It had a subtle, somewhat rusty color. The other belts on the planet appeared to be blue-gray in color. The following limb of the planet was somewhat darker than the preceding limb due to the sun angle (a phase effect).

At times the seeing was very bad, leaving nothing more than the NEB visible on the planet. At other times the seeing was fair, approaching good. The seeing was both, worse at times and better at times than it was for my previous Jupiter observation; but for the most part it was better.

Jupiter & Lambda Ophiuchi

Date: 03 September 2007 U.T.
Time: 2:03 - 2:15 U.T. (Jupiter)
Telescope: 130mm refractor
Magnification: 138x (Jupiter)
Filter: Moon-SkyGlow (Jupiter)
Seeing: Poor to Fair
NELM: Twilight (Jupiter)
Temperature: +83 F (+28 C) (Jupiter)

The above rough (at the telescope) sketch of Jupiter has North up and Preceding to the left.

Due to poor seeing conditions small-scale, moving "ripples" were constantly visible around the limb of the planet. The "star" to the upper right of the planet is Io, one of Jupiter's moons. A little later in the evening Io was seen in transit across the planet's disk. The following limb of the planet was slightly darker than the preceding limb due to the sun angle (a slight phase effect). At times more detail was visible; but under the circumstances (poor seeing and a relatively quick observation and sketch) some of the details shown may not be particularly accurate.

The planet's North Equatorial Belt (the darkest belt on the planet) appeared brownish-red in color. Other features had colors that were too subtle to differentiate from shades of gray.



After completing the Jupiter observation I observed and sketched Lamda Ophiuchi A&B, a close double star. The above sketch (greatly enlarged from the telescopic view) shows this double with North up and West to the left. A #82A Light Blue filter sharpened the view a bit under the relatively poor seeing conditions. The "A" star appeared to have a yellow or yellow-orange color while the "B" component appeared bluish. A narrow gap was visible between the two stars during intervals of somewhat improved seeing conditions. A weak, broken, diffraction ring was also visible at times around the two stars. A magnification of 218x was used for this observation.

Venus - 13 July 2007

Date: 13 July 2007 U.T.

Time: 2:50 U.T.

Telescope: 80mm f/5 achromat

Magnification: 85x

Filter: #56 Light-Green

Seeing: Fair

NELM: Bright Twilight

Temperature: +80 F (+27 C)

The above (mirror-reversed) sketch has North up and Preceding to the left. It shows the basic appearance of Venus as seen in a small telescope.

As the planet's phase changes from full to quarter (half) to crescent to new the planet's disk appears larger and larger. When Venus's phase is near full the planet is on the far side of the Sun. When the planet is a crescent it's on the near side of the Sun. These changes have a dramatic effect on the apparent size of the planet as seen in a telescope.

Currently Venus is moving closer to Earth as it orbits the Sun. As a result it's appearing increasingly larger as seen in a telescope and its phase is becoming a thinner crescent.

Venus is currently visible in the evening sky in the west immediately following sunset. It's by far the brightest object in that area of sky and readily visible to the unaided eye.

Comet LINEAR - 12 July 2007

Date: 12 July 2007 U.T.

Time: 6:32 U.T.

Telescope: 30cm Newtonian

Magnification: 90x

Seeing: Fair

NELM: 6.5

Temperature: +58 F (+14 C)

After the previous night's look at C/2006VZ13 LINEAR with binoculars I decided to have a go at it with a telescope.

In the above sketch South is up and West is to the left. I experimented with magnifications from 60x to 120x before settling on 90x as my preferred magnification for this comet. I worked on the sketch for 20 minutes while observing the comet; but the comet's position was "frozen" (in relation to the stars) at 6:32 U.T.

For those unfamiliar with comets, the stars in the vicinity of the comet in the above sketch are different from those seen on the previous night's sketch. This is because comets are solar system objects that are moving in orbits around our central star (the Sun). They appear to slowly move against the background stars. It can take seconds, minutes, or hours before one notices the motion - depending on the comet, its distance from the Earth and Sun, and the solar system geometry of the line of sight.

This particular comet looks pretty much like a "generic" telescopic comet. There's no easily visible tail. The comet simply looks like a circular, fuzzy, disk of light with a brighter central region. This is what most telescopic (and binocular) comets look like.

Comet C/2006 VZ13 (LINEAR) & Aurora

Date: 11 July 2007 U.T.
Time: 5:50 U.T.
Instrument: 20x80 Binoculars
Seeing: Steady (for binoculars)
NELM: 6.5
Temperature: +55 F (+13 C)


The above sketch shows the basic appearance of Comet C/2006 VZ13 LINEAR as seen with hand-held 20x80 binoculars. Only a few of the many visible field stars appear in this sketch. South is up. West is to the left. The comet is the large, round, nebulous object with a brighter middle. The galaxy, NGC 6015 was visible in the 20x80 binoculars as a much smaller and fainter nebulous object to the west of the comet. The comet was easily visible with 8x42 binoculars as well as with the 20x80s.

The comet was in the constellation Draco. Its rough location at the time of this observation was RA 15hr 57min, Dec. +62 degrees 28min. I estimated the comet's coma to be about 0.2 degrees in diameter. The comet is currently well placed in the evening sky for observers at mid-northern latitudes.

An aurora was visible a few degrees above my northern horizon. The aurora was somewhat brighter (with a small amount of structure visible) around 5:20 U.T. than it was at the time of the comet observation (5:50 U.T.). The aurora never extended very much above my northern horizon and seemed to have little or no effect on the limiting magnitude higher in the sky.

Venus & Saturn - Together

Date: 2 July 2007 U.T.
Time: 2:40 - 3:40 U.T.
Telescope: 80mm f/5 (ST-80) refractor
Magnifications: 22x, 24x, 39x, 54x
Seeing: Fair
Transparency: Good
NELM: Bright Twilight
Temperature: +77 F (+25 C)

Venus and Saturn shared the same low to medium powered telescopic field this evening. Venus was a brilliant, white crescent while Saturn appeared roughly half as large and much fainter. At all of the listed magnifications it was possible to observe both planets simultaneously in the same field of view.

Venus was visible to the unaided eye prior to sunset; but Saturn proved difficult in the telescope until after the sun had set. Later, in a darker sky both planets became easily visible to the unaided eye in the western, evening sky.

A sketch was made of the relative sizes and orientations of the two planets, but in order to show both together, as they appeared in the telescope it would be necessary to render the planets as very tiny objects.

The small, portable telescope was set up on my north porch for this evening's observation.

Venus - 19 June 2007

Date: 19 June 2007 U.T.
Time: 22:40 - 22:50 U.T.
Telescope: 102mm SCT
Magnification: 72x
Seeing: Poor - Fair
Transparency: Partly Cloudy (thin clouds)
NELM: Daytime observation
Temperature: +86 F (+30 C)

The above is my rough, at-the-telescope sketch. North is up. Preceding is toward the left. Disk details are questionable under the seeing conditions; but the south cusp was suspected to be somewhat brighter than the north. The limb was brighter than the terminator. The planet appeared white against the blue daytime sky.

I went outside around 4:00 pm local time, looked up, saw the Moon, looked a few degrees west of the Moon and spotted Venus with the unaided eye. Afterwards I set up the telescope and made the above observation.

Observational Slow-Down:
Lately a combination of factors have slowed down the frequency of my astronomical observations. Among those factors is increased activity in my other (long neglected) hobby - chess. If my renewed interest in chess continues long enough I may start an additional blog devoted to that interest.

Sunspot - 03 June 2007

Date: 03 June 2007 U.T.
Time: 16:53 - 17:22 U.T.
Telescope: 102mm SCT
Magnifications: 40x, 90x
Filter: Baader, white light
Seeing: Fair
Transparency: Scattered Clouds

The above sketch shows the sunspot group (Sunspot 960) that has recently rotated to the earth-facing side of the Sun. Preceding is up and south is to the left in this mirror-reversed view. At times during this session clouds blocked the Sun from view.

For most of the observation the telescope was used at 90x. Later 40x was used for the faculae portion of the sketch.

After completing this observation the view was shared with a guest.

Sharing the View

Date: 3 June 2007 U.T.
Time: 3:00 - 5:00 U.T.
Telescope: 13cm refractor
Magnifications: 35x, 90x, 170x, 240x
Filters: #56 and #58 Green (for Venus only)
Seeing: Good
Transparency: Bright and darkening twilight

After many cloudy or otherwise missed nights everything fell into place for a good evening. The telescope was set up on on an equatorial mount with an electric RA drive. The motorized tracking simplified sharing the view with two guests.

Venus was our first target, and for a long while our only target. The seeing was very steady with the refractor -- one of the benefits to using a relatively small telescope. The planet's sharply defined quarter (or 'half-moon') phase was easily visible to everyone present.

The green filters helped cut down the brightness of the brilliant, white planet to a more tolerable level. We took turns studying the planet at 90x. Through the use of questions and answers, it looked like the guests may have been able to perceive some of the subtle markings in the Venusian atmosphere.

Eventually the sky darkened enough for the younger guest to spot Saturn in the twilight sky. We shared views at 35x and gradually worked our way up to 240x. Titan was immediately noticed near the ringed planet. After the sky had darkened a bit more we saw three more of Saturn's moons. The two moons between Titan and the planet, one above the other, were later identified as Tethys (to the north) and Rhea (south of Tethys). Just off the north-following limb of the planet was Dione.

At the higher magnifications the ring was visible in front of the planet. The guests also noticed Saturn's South Equatorial Belt (SEB). Cassini's Division presented a challenge for the guests, but they eventually succeeded in seeing this division between Saturn's A and B rings -- at least on one side of the ring system. The shadow of the planet on the ring system proved to be a bit more of a challenge for the guests.

After Saturn we took a look at the globular cluster, M13 in Hercules. Next was the Ring Nebula (M57) in Lyra. The final object was Albireo (Beta Cygni) -- one of the northern hemisphere's "showpiece" double stars.

Twilight had still not quite ended by the sessions end. Nevertheless, part of the summer Milky Way was seen. We also saw at least one meteor, an airplane and at least one satellite.