Wednesday, October 31, 2007

20071030 - 17P/ Holmes Observing Report

Prior to a brief session, I attended the monthly planetarium show, Celestial Highlights, at New York's Hayden Planetarium. Comet Holmes was given some time both as an object in Perseus and in a series of slides given at the end of the sky tour.

The presenter described Comet Holmes as difficult from the city with unaided eye but revealing in binoculars and scopes. I wanted to disagree but it was his show. He followed up with three images of the comet (one by Pete Lawrence) and for contrast, showed Comet Hale-Bopp with two tails trailing long and high into the sky.

After the show, I went for a brief session to TotL to take in the comet naked eye and with the 22x60 binoculars. I carried the Tele Vue Ranger to get tighter shots of the comet but it wasn't unpacked.

On my way around the Great Lawn I ran into Mark the Literary Agent. He stayed and we observed the comet and the passing people watching the two guys watching a comet. I didn't invite people to the bins nor did anyone ask but a few. One was Ken the Pilot who stopped to say, "Hello." He peeked in the bins and said, "Oh that's the comet. Not that impressive." I described the same features to look or that I described to Mark earlier.

My observation is that comet 17P/Holmes appears to be dimming. I compare to delta Per which is celestial-South, or around 9:00PM EDT, directly to the right naked eye. Their brightness looks nearly equal. The pedestrians that stopped to observe it naked eye agreed. They added the description that it looked fuzzy compared to the other stars (naked eye). Same observation to me. Late last week, the comet's brightness was almost midway between the brightness of delta Per and Mirfak, alpha Per. The comet's size is obviously growing.

Location in field of view
There are two ways that I help the pedestrians look for the comet, one from the direction of Cassiopeia and the other from Capella in Auriga. Around 9:00PM EDT, Capella has risen almost 25­° above the horizon due manhattan-north. The brightest star in the area is unmistakable and difficult to miss. With an extended, open right hand put your thumb on Capella and rotate your pinky up to about a one o'oclock direction. You'll notice another bright star, Mirfak. Consider Mirfak the apex of a tall, isosceles triangle. Two fainter stars are seen below Mirfak. Relax, give it a moment or two for your eyes to adjust to see the triangle. The base star to your left, may appear fuzzy, since this is the comet. Easily seen from the city as many pedestrians made it out with a little coaching.

In the binocular 2 degree field of view, the comet appears near the inside right corner of a right triangle. These three stars: mag 6.18-HIP17772; mag 7.72-HIP17713; and, mag7.55-HIP17476. In my mental image 17772 & 17713 are the base of the right triangle.

The separation between the two base stars is 23'15". I estimate that separation to be 2 1/4 ~ 2 1/2 comets yielding a size of 9.3' ~ 10.3' for the head of comet.

I didn't perform an in-out test for brightness. That is choosing stars of similar magnitude and bring them out of focus so that the star's size increases to s large as the diameter of the comet. If the comet's brightness appears equal to the star's de-focused brightness then the comet's brightness is assigned a value of the star used for testing.

The outer coma exhibits an uneven brightness, a darkening can be seen on the leading edge side. It is arcuate and extends almost halfway around the central condensation (what I have been calling the nucleus.)

As the comet grows larger its surface brightness decreases. The brightness is distributed across a greater surface area of the comet. (Consider the brightness and the appearance of M33.) This results in less contrast with the background sky and appears dimmer to the eye.
With unaided eye, compared to delta Per, 17P/Holmes' brightness is approaching delta's brightness, Late last week it was almost midway between alpha Per (Mirfak) and delta Per. Over the past few days I feel it is dimming, due to the explanation above.

The comet appears round with three sections of varying brightness. The coma appears with a bright central core which is about two-fifths of the comet's diameter and off-center relative to the outer coma ring. It is south of the leading (drift) direction. Within that brighter central condensation on its trailing side, a stellar condensation is evident. Its obvious in most photographs of the comet. I did not see any evidence of a tail.

This message posted with nBlog.

Labels: , , , ,

Tuesday, October 30, 2007

Autumn Sky sans Milky Way

Mars is seen moving eastward against the background stars. It is growing in size and brightness as Earth is catching up to it on our tracks around the Sun. Our closest approach this year, about 6/10 astronomical unit, occurs on 18 December where Mars appears as a ~15.9" diameter disk. On the 24 December, Mars is at its brightest of magnitude -1.6 when opposition occurs. Mars will still be with in the constellation Gemini. The alignment is Sun, Earth, and Moon. This means that Mars is rising as the Sun sets, just like a Full Moon.

Labels: , , , , , , ,

20071029 - Brief Observation of 17/Holmes

20071029 - Brief Observation of 17/Holmes

A very short session looking through the living room window with Fujinon 7 x50 binoculars hanging from my neck and hands cupped to my eyes. Unaided I see the familiar tall right triangle with comet 17/P Holmes at its lower left base star. delta Per is the right angle to the west and Mirfak, at tip of the hypotenuse, is the northwestern acute angle.

The comet appears dimmer than delta Per. Like most we have watched it brightness increase Over the past few days but now it looks as if it is past peak and its brilliance diminishes gradually. The fainter appearance can be attributed to its growing size which could result in a lower surface brightness if its absolute magnitude doesn't change (if could say this for a non-stellar object such that it doesn't produce its own light)

In the 7x50 the comet head is large enough to easily discern a nucleus within the Coma. I don't see the off-centering of nucleus to the leading edge like I saw the night before. Nor can I see that tiny stellar point (or two) on the leading edge of the nucleus. On past observations, I felt that the nucleus had a fan-shape to its brightness with the stellar point just interior to a snub-nose point. Could be optical illusion but I can see the same detail in pictures. In the hand held bins I could not see this detail.

Still a remarkable sight to see. And as you're looking at it realize that it is Cosmic sibling of the Solar System.

posting with nblog

Labels: , ,

Sunday, October 28, 2007

With the gang - 17P/Holmes

Session name: 20071027.1935

Larger images: Marked up | Unmarked
Compare with this Perseus image from this post, where Comet Holmes is obviously unseen in the general area.

The comet continued to capture out attention and interest. Under other circumstances a disappointing lunar occultation of the Pleiades past midway on our moonrise would have been center stage. But not. Not with the comet of 2007 juicing up Perseus. Tycho had SN1572 in Cassiopeia and we have comet Holmes. Different as they are in nature is as great as the excitement of this new temporal light in the sky.

I arrived at TotL to see Ben already set up with his Tele Vue 76 aimed at Comet Holmes. He invited me to the scope asking if I saw any peculiar features. After getting eyepiece-adapted, a bright stellar point was visible on the interior, southwest edge of the nucleus. This larger nucleus continued to appear off center towards the east-southeast direction (towards the trailing side in the refractor's field of view) within the coma. The coma's circumference had a bright, consistent brightness, however, its interior was uneven with some dark patches. This was most pronounced on the leading edge, like a backward "C". This was the greater side of the coma as mentioned earlier that the nucleus was slightly displaced to the trailing side. AAA'er Bruce Kamiat (report) pointed out this feature which Ben & I agreed to seeing.

Ben & I disagreed on sizes. At first, I grossly over-estimated the size with a wrong mental image of Jupiter. I suggested the size of the nucleus to be something four jovian diameters, the overall sie of the head to about 6 jovian disks. Ben's estimate was more reserved as one jovian disk. Mars had cleared the trees so we used the ~12 arc second martian diameter to measure the components of the comet's head. I estimated the nucleus to be 3~4 martian diameters across, if I remember Ben's was less. On the leading edge, the coma was about 2 nucleus diameters and on the trailing edge about 1 1/2 nucleus diameters.

Down to our south, an area we call Turtle Pond Observatory (TPO) another crowd of astronomers had naked eye and optics turned to the sky to show the passing public. Turns out it was Kentaurian with some of the AAA'ers: Rich Rosenberg, Bruce Kamiat, and Joe; Rik Davis joined shortly after. They came up to TotL to join in on the cheer. Hawaiian George came by and so did Team Totl'er Kin riding in with a small group of TIME'S UP! riders led by Rich. Debbie, a dog owner, who used to observe with us appeared tonight. We had a thin regular flow of pedestrians passing through as we were eager to share sights with pointed fingers and optics.

Seeing was not the best and a light breeze caused scope shake when the magnification was increased to 117x on the Takahashi refractor. When the air calmed for a steady view the Moon was absolutely stunning along the terminator. Cruising along the line sunset it was difficult to ignore craters Langranus and Petavius. Rimae Petavius runs across the crater's floor. To the northeast, sunset begins where the far eastern walls of Mare Crisium try to repel blackness. Not for long.

A small diversion while near the comet was to spot NGC1528. A bright open cluster that I prefer with a darker sky without a nearby ~17d moon. Tonight only the brighter members stood out in a loose, sparse arrangement of crisscrossing arcs of stars. The same comments apply for M31 and M32 but for one pedestrian we gave here a small survey of the different heavenly objects.

During our observing session we placed a towel on one of the street lamps to block of the glare in our direction. The other lamp to our east spilled its light casting long thin shadows to the west. From high in the east, Moonlight competed casting darker, harder, shorter shadows. Crisp as bacon.

Lastly we visited Mars before packing up. It was still rising and seeing was not greatat even at an altitude of ~34°. I thought I may have seen some detail at magnification 117x but it didn't agree with Brian Tung's Mars Map. I thought I saw a dark band running central across the diameter of the disk, rather a large chord instead of an equatorial band. The trailing limb had a greater darkening on it.

Kin, Ben and I packed up for the evening a bit past 1AM. We pulled the towel from the street lamp to bring back the illumination and shadows leaning east.

Labels: , , , , , , , ,

Small Addition : Away from the Lawn

Small Addition

Small Addition : Away from the Lawn
Out of pure geekiness I have mounted an ancillary content repository - a web server on a Newton MessagePad. I have attempted in the past to mount a newton personal data sharing (npds) server but abandoned after a short while. I can't for say for certain how long this one will last.

For now the link above is to a Tracker server which my webserver registers and maintains state. Visit the other npds servers and then visit away from the lawn. While there browse and drop a message. not much today but likely to grow.

posted with nBlog

Labels: , ,

Friday, October 26, 2007

Rainy Friday

Rainy Friday

Was fortunate to get a chance with the Comet. Now the rain has come in.Seems that everyone's talking about it today. The following cloud signs tells us about the weather:
Cirrostratus clouds usually mean rain is coming. And last night the Moon exhibited a halo, a sign of cirrostratus clouds high in the sky.
The Amateur Naturalist's Handbook by Vinson Brown.

Newton Messagepad 2100

17P/Holmes - Naked eye comet

Session name: 20071025.2105

A photograph of comet 17P/Holmes where a bright central nucleus outshines the surrounding ionized gases, the coma. The nucleus and the coma form the head of a comet. This comet lacks any tail.

Observed the bright 17P/Holmes, my guesstimate is magnitude 2.3 ~ 2.5. It is less bright than Mirfak, brighter than delta Per, cheating towards Mirfak. Comparing to the few other brighter stars that beat the clouds, only Mirfak and Capella were brighter. So bright it shone through the cirrus and cirrostratus clouds. With naked eye, the comet's size is visibly greater than nearby stars though no tail observed. In 7x50 binoculars it is obvious in brightness and dimension. In 22x60 binoculars, the nucleus resolves clearly off center from a round coma.

Effect pronounced because of the clouds?

Discovered in 1892, Comet Holmes takes 7.3 years to revolve about the Sun. No one can say for certain how long this brightness will last - a few days, weeks, or months. Either way get out soon and take it in as early as possible.

What makes it glow so brightly? Most likely cause is the result of an eruption, heated gases from within escaping violently through the comet's crust. Think in terms of volcano, common activity with Solar System objects. A comet's crust and surface consist of loose accumulation of ice and rock so it becomes susceptible as it approaches the Sun and heats. When the gases expire or cool down the volcanic-like activity ceases and the comet goes on its merry way.

The session was not without frustration. I chose to observe from Artists' Gate, the south Central park entrance used to refer to as The Statues. I really couldn't find a spot without interference from the street lamps and I didn't want to venture too far into the park in this area alone. Many places are off the beaten path. I ended up on the rock smaller in stature than Drip Rock. I left the SD card of one camera in the computer at home and the other camera simply misbehaved with the dreaded remote control. In the end I was able to capture a few photos and scratch a sketch or two.

A young guy, Jesus, who drives the Hansom Cab driver, stopped by. He reminded me that we've met before and that he hadn't picked up a scope yet. He asked some questions about the wonders of the sky. With naked eye and mounted Tak bins, we observed 17P/Holmes, rising Mars, and the Moon. We spoke of how rising stars appear to twinkle with rainbow effect as we look through more atmosphere due to our our angle. Castor was a shining example.

View of the sky from a tucked away spot on the rock inside of Artists' Gate. The sky improved and was clear for a period of time but the cameras were not cooperative. Naked eye limiting magnitude from this area under these conditions was around magnitude 3.5

Skychart of area around alpha Perseus and the Fishhook.

Marked up version of skychart of area around alpha Perseus and the Fishhook.

Labels: , ,

Full Moon at Perigee

Session name: 20071025.2105

ImageDescription - Full Moon at Perigee
Camera - NIKON CP995
DateTime - 2007:10:25 23:10:02
Weather - Broken Cirrus clouds, light breeze, cool temps

Looked at the Moon through the cirrus clouds in Tak bins. Beautifully large! Felt as if she filled the whole field of view (but really not at all). The south pole offered spectacular relief along the southern limb below Tycho. Looked like it would be a few more hours until Full Moon as a small crescent of night time remained in an area from 5:30 to 9 o'clock along the limb.

The full Moon do not stand in the way of 17P/Holmes. Saw it naked eye with ease all night long even through the cirrostratus and cirrus clouds.

And the rhythm continues ...

Labels: , , , ,

Sunday, October 21, 2007

Venus from Drip Rock

Session name: 20071021.1145

A warm Saturday afternoon at Drip Rock. Skies were clear and a light air, temp around 70° F. As has become custom, I was welcomed to the rock by a homeless women whom I have seen on recent sessions. Yards away down the slope of the rock before me were two young girls, one of them unclothed to her underwear to catch the rays of Sol. Unfortunately, she attracted the queer, perverted type of human nature. I made it clear he was not welcome in these parts but he remained. I thought this guy's a pro, definitely not a first-timer. I mentioned to one of the girls about the freak but she looked back and then shrugged him off.

The sky blue background were very clear that once I got my bearings where to look Venus glistened like a shard of glass wanting to be discovered.

When I arrived Venus was already began her descent being at altitude/azimuth ~ 235°/43°. Venus at magnitude -4.4 is in Leo one can expect to see the planet high in the sky as the early Spring ecliptic is still north of the celestial Equator. The sun is 46° east in Virgo.

Seeing was moderate but the light air was enough to shake the scope and the image when observing at 117x. It made it difficult to snap pictures using a 2x barlow with the Plossl 20mm eyepiece. With a size of 26.3" I could see the phase to be just shy of first quarter, slight horns still visible at the waxing tips. Along the sunrise terminator shows a softness in contrast to the crisp hard edge of the limb. In this phase it easy to draw a circle with the mind's eye completing the arc of the bright limb. Planetarium for the Palm reports the venetian phase at 93°44'. Next Saturday, Venus will be at first quarter and almost 2" smaller, and becoming smaller and smaller as she waxes to Full Venus.

Medium camera shot demonstrating how easy Venus is to see. Foreground objects can be of help to orient oneself in the sky, however, it is important to relax the eyes and let them focus to infinity and not the leaves.

A snapshot of Venus with a 35mm equivalent focal length of 3452mm = ( Focal length in 35mm * magnification) = (42.1mm * 82x).

Labels: , , ,

Wednesday, October 17, 2007

Manhattan's cardinal points

The New York City skyline appears when looking south from the Top of of the Lawn. The GE Building, formerly the RCA Building, sits squarely south of us. Get to the roof and you are on Top of the Rock.

Celestial-south is left of the tree on the left border of the skyline image above. The western edge (right) of the Citigroup Center its pitched roof pokes out from behind the tree is about 185° azimuth. Since we're talking of the Citigroup Center that building throws a javelin of light nearly reaching zenith. Can you guess where Time's Square is situated?

In spite of all the lights around us, the more visually acute will be able to detect magnitude 5 stars in the manhattan-north to manhattan-northeast direction. Other parts of the sky mid 4's and toward manhattan-south more like 3.7 Pedestrians stopping by may see magnitude 2 ~ 3. For example, this time of the year some point to Capella and ask which star is that. I'll follow up and ask if the can see the three ids. The higher up the better success but sometimes they'll onlyu catch one of them. On the clearest nights for us, we can count off three maybe four stars fo the Leaping Minnows.

On the island of Manhattan we are accustomed to speak of the compass points relative to the Cartesian grid we live in: Uptown is north and downtown is south. Avenues run north - south and Streets are east - west. It's no different when we look at the sky and describe where a particular star or object is located relative to our local horizon plane using the manhattan-cardinal points. I am not entirely consistent but I try most times to distinguish manhattan-south from celestial-South.

Looking east from the area at the Top of the Lawn, Great Lawn, Central Park. That foreground lamp next to the tree is sometimes cloaked with a light arresting adapter, a.k.a. a towel. The towel will cover half the lamp shielding the light in our direction. A very noticeable change to the local setting where we really use red torches.

On this session where we set up our shadows reached 55 feet to the east.

Looking west from TotL, Charlie consults Pocket Sky Atlas under the lamp. The same goes for this fixture when sometimes we limit the light our direction. Approaching us from west, that is from this direction, pedestrians see the lamp in full brightness and then a cutoff approximately where the shadow is in the photograph.

Closer to the light fixture Charlie's shadow is stunted to maybe 9 ~ 10 feet.

Returning to the tripod to look out over TotL's manhattan-south which translates to approximately 210°. It'll take a few moments for eyes to dark adapt.

Related is a study by the Grand Central Partnership (GCP) where they are experimenting with directional sidewalk compasses. Consideration is to place them at the street entrance of the subway and designed to orient pedestrians to their local surroundings. One doesn't have to be a subway passenger just disoriented. Another NYC fixture that reinforces ths microcosm's

If you're up for a trigonmetric exercise find recreation in Charles Petzold's article, How Far from True North are the Avenues of Manhattan?

Labels: , , ,

Monday, October 15, 2007

The Hero in Central Park

Perseus the Hero and NELM.

Rey's Perseus with less markup.
Perseus constellation with no markup.

Perseus is among my favorite constellations. The Hero.

He serves as a reminder of when I started and conjures emotions of my first discovery - Alpha Persei Association! From left field of a Heckscher diamond, I looked above the buildings lining Fifth Avenue out into the eastern sky. Off the beaten path in Central Park, this was a relatively dark sky spot. No lighting fixtures in my immediate area. They lit the walk that surrounded the baseball diamonds but I was well in.

On that seemingly black background sky Aries, Taurus, Cassiopeia, Perseus, and Andromeda twinkled before me. Yet I could see nothing. The sky was brand new to me and black is an absolute term not to be used in this circumstance. With persistence I returned to the field with Fujinon 7x50 binoculars and a Tele Vue Ranger, sometimes with Chet Raymo's An Intimate Look at the Night Sky or Peterson's Field Guide Stars and Planets, learning to identify the constellations.

How surprised was I when I "discovered" a waterfall of stars below Mirfak, the alpha star of Perseus. I thumbed through the books I had on hand to find no catalog number. The Pleiades, Andromeda Galaxy, and the Double Cluster were grabbing the headlines while this bright splash was waiting for announcement.

I am sure we all have similar stories.

Turns out this is well known as the Alpha Persei Association. It is cataloged as Melotte 20 and described as a stellar stream about 600 light years distant.

How apt is that name: stellar stream? When describing the nature of open clusters to pedestrtians I often relate how leaves fall from the same tree into a stream. Over time the leaves part in their own direction yet retain the same proper motion of its siblings. Stars born from the same molecular cloud.

The Hero pulls up the late Fall and early Winter sky and provides a means to judge our naked eye limiting magnitude (NELM). Comfortable, cool temps that I prefer over summer's heat and humidity. This photo above is pretty close to what we see at TotL on transparent nights. All the stars labeled in this 8 second exposure captures the stars we use to measure NELM. The first star I look for is the magnitude 5.2 star, HIP14043, near the Steeple (labeled as "Cap"). Charlie, Kin and I count off the stars of the Fish Hook. The magnitude 5.4 star is difficult but doable on the clearest of nights. In the Alpha Persei Association we can count 4, rarely 5 stars, between Mirfak and delta Per. Even though we don't get a hint (never had a hint to date) of the Milky Way, we can resolve stars as dim as mag 5.4.

As John Bortle notes in his article, The Bortle Dark-Sky Scale, naked eye limiting magnitude is not a reliable descriptor of a site's transparency.

Amateur astronomers usually judge their skies by noting the magnitude of the
faintest star visible to the naked eye. However, naked-eye limiting magnitude is
a poor criterion. It depends too much on a person's visual acuity (sharpness of
eyesight), as well as on the time and effort expended to see the faintest
possible stars. One person's "5.5-magnitude sky" is another's "6.3-magnitude

Quoted from Sky&Telescope site

Labels: , , ,

Sunday, October 14, 2007

The Bull in Central Park

Session name: 20071013.2245

Click Taurus the Bull for a large version. Here for unmarked version.

When I arrived at nearly 11:00PM Charlie was already set up with bins pointing to a sky clouded with stratus and altostratus clouds. He remarked that the transparency was good in the cloud breaks. By 12:30AM ~ 1:00AM the sky cleared up nicely with not a cloud in the sky. Transparency appeared to be good but neither of us had any large optics to judge seeing. From the looks of stars rising in our horizon, I would say that seeing what fairly good even tough the clouds moved off rather quickly. I brought the coffee can scope again tonight but never unpacked it. Instead, we observed the sky naked eye and I snapped a lot of photos of our terrific skyline and constellations.

The photograph above is marked to present the constellation Taurus in the style of H.A. Rey from his book, The Stars, A New Way to See Them. Child or adult, one couldn't find a better book than this if one wants to get out and learn how to navigate in the sky. Forget that it looks like a children's book and the stick figures look corny throughout. Its simplicity and matter of fact is the magic of the book which gets one traveling across the sky in no time. Grab this book and step outside with someone familiar with the sky to get you started. If you're on your own, I suggest looking for Cassiopeia the Queen for use as an easy landmark. At this time of the year, one of the most recognizable and popular asterisms, the Big Dipper, is too low skimming the northern horizon.

Taurus is rather easy constellation in our early winter night sky. The bull's head is easier to see than its hind quarters but we can see rather easily from TotL. First the Pleiades, an open cluster about 370 light years distant, poke above our tree line to the northeast. The bright, ruddy star, Aldebaran, follows shortly afterward tagging an optical ride with an open cluster, Hyades, in the shape of a large arrowhead. Hyades (Melotte 25) is the second closest open cluster to our solar system, about 150 light years away. Only the Ursa Major Moving Cluster (Collinder 285) is closer to us at 76 light years.

[Check out this Pleiades observing report where Charlie and I counted 12 ~ 13 stars of or around the Pleiades. A picture of M45 taken last night can be used to compare the description of the report.]

As the clocked ticked past curfew, the sky racheted eastward bringing Mars higher above the tree line further east northeast of the Hyades. Charlie hunted for M35 in his bins but was unsuccessful. The sky was absolutely clear enough despite being low. We could see withe little effort Tejat (mu Gem), Propus (eta Gem), and 1 Gem at magnitude 4.1, the three stars of Castor's feet. He would have been rewarded with greater glow and resolution had he larger optics.

The police cruiser came through and stopped. We chatted about the night time sky and our schedules. Clear weekend nights are almost certainty we told them. They saw us off as they headed west and we exited to the east.

When we exited the park we couldn't miss Orion. Huge. Awakening from the diurnal sleep, he rises into a night sky announcing that winter is nearby. Tracing Rigel at his feet to Aldebaran to Capella down towards Castor and Pollux, we could see the Winter Hexagon ascending the sky at 1AM. In no time, we'll be seeing high overhead in early chilly evenings.

Labels: , , ,

Saturday, October 13, 2007

Coulter CT-100

Session name: 20071012.2000
Weather: Cool temps at 46°F/7°C with gentle [3] to moderate breeze.

Telescope: Coulter CT-100, 4.25" f/4 (FL=432mm)
Mount & Tripod: Manfrotto/Bogen 410 on Manfrotto/Bogen 3221s
Eyepiece (magnification / fov): Kellner ~20mm (21.6x / 2°)

The Coulter CT-100 reflector is one of the scopes I occasionally use to observe. Charlie has the same scope and has dubbed his S.A.R. Mine is aptly called at CiTy-100 befitting an urban observer. It is a small richest field scope, packs handy in its own case, sets up in seconds. This scope was mentioned in Gary Seronik's Telescope Making column in Sky & Telescope, Dec 2003, page 126, including a copy of an old advertisement. I like this scope for its portability and ease of use.

This session's skies were one of the best recently with clear, dry skies. NELM was about magnitude 5 in zenith, counting 6 stars of Ursa Minor with Pherkad Minor making 7. eta UMi was not seen. Transparency was good across most of the sky, even in our gegenschein to the south. In the eyepiece of CT-100, the Milky Way glowed as the background sky beneath the brighter field stars while panning through Cygnus all the way down toward Albireo.

The CT-100 consists only of essential elements required for a telescope. The observer is provided an optical train whereby two assemblies mount on a single strut with beveled edges. The strut serves as a rail where the two assemblies, outfitted on the underside with teflon strips, slide to rough focus the telescope. The CT-100 front assembly houses the spider, secondary mirror and eyepiece chimney. The front assembly also has a surface-mounted slot to hold a finder scope, although I don't have one. The CT-100 rear assembly holds the mirror and its cell.

The advertisement copy shown in the S&T issue states that scope comes with a "27mm helical focusing eyepiece with 1 1/4" barrel provides 14x". The one I purchased came with a helical focusing eyepiece but I estimate it to be a Kellner 22mm with 40° field of view. This yields a magnification of 19.6x and a 2.04° true field of view. This agrees with a field measurement taken last night by placing stars of the Alpha Persei Association at the edge of the field stop. The magnification and field of view is similar to that of the Takahashi 22x60 binoculars. Telescope limiting magnitude was 9.06 using stars within the area of HIP 16118, -16210, and -16244 (34 Per).

The front assembly provides no relief extra tubing beyond the spider attachment points. It suffers from extraneous light intruding directly into the eyepiece but this could be corrected with a fold of paper. This scope was purchased without a shroud so I use black flocked paper and rubber bands. The same paper and bands have held up over three years, even on some dew-filled evenings. I store the flocked paper in an empty paper towel tube. Sometimes I'll attach this paper towel tube to use as a simple finder scope, otherwise I sight over the top of the tube.

Following are some daytime shots out the window. With camera zoomed out fully, one can see vignetting and the shadow of the secondary. Following that are shots zoomed in. Off axis is not so bad but in the field with stars coma is noticeable. The scope could have used tweaking to the focus to sharpen up the scene. Also the eyepiece adapter sat a little off center where I had to tug on the camera to center the shadow in the low power shot. In the higher power shots I let the camera rest naturally.
Zoomed out showing shadow of central obstruction. When observing low power on large, bright objects, like the Moon, one can see the shadow float in the middle of the image.
Same shot as above but zoomed in. And as in the field when looking at star fields and clusters the obstruction is not noticed. In practice, I use only two size of eyepieces: a Tele Vue Plossl 32mm or a Plossl 20mm/Kellner 22mm.

A shot across the Hudson River looking at the helical that feeds the Lincoln Tunnel from the New Jersey side.

Labels: , , ,

Saturday, October 06, 2007

Vallis Rheita

This photograph shows features along the sunset terminator in the southeastern quadrant of the Moon.

Click on image to study Vallis Rheita and nearby prominent overlapping and adjoining craters Janssen, Fabricius, & Metius. Vallis Rheita is the conspicuous gash just lower left of center inside the sunset terminator. It is a chain of craters that rips through the lunar landscape intruding on craters Young and Mallet. Vallis Snellius more northerly (bottom of the picture/south is up) is not favored in this lighting.

Janssen is the largest crater seen in this image. Crater Fabricius is interior to the rim and Metius appears tangent to both Fabricus and Janssen. On the larger image, one can see the brightened rille features, contrasting with the crater floor, forming a partial "X".

Click here for the marked up image with feature names on Southeastern lunar limb.

The Nectaris Basin and associated mare figure off the lower right corner. Crater Fracastorius is the darker, mare-colored crater on the picture's border in the lower right hand corner. Crater Piccolomini with a central peak sits south of Fracastorius, an 11:30~ish direction in the photograph (south is up). These craters help to identify the concentric rings of Nectaris Basin.

Consult the
Digital Lunar Orbiter Photographic Atlas of the Moon search tool at Lunar and Planetary Institute to search for these same features by name and observe pictures from the Lunar Orbiter 4 mission.

Additional references used to mark up photograph. (No affiliation with Amazon, convenience only.)

Charlie's report of our 20070928.2245 session.

Photograph taken from the top of the Great Lawn using a Nikon CoolPix 995 attached to a Takahashi FS102 refractor on the morning of 29 September 2007 at 00:31 EDT.

Chong, S. M., Albert Lim, & P. S. Ang. Photographic Atlas of the Moon. 1st Edition. Cambridge University Press, 2002.

Rukl, Antonin. Atlas of the Moon. Revised, updated edition. Sky Publishing Corp., 2004.

Rhythms I can count on

Individual birds fly silhouetted across the face of the moon at steady pace. Their frequency is such that I can step away from the scope to let others observe. It doesn't take long to see one of the birds fly across, little wings flapping laboriously to cross our field of view, sometimes two or three can be seen at once.

It isn't uncommon to see to objects cross the face of the Moon. Many have probably seen airplanes cross the lunar disk, their trailing exhaust undulates the light of the moon as if we were watching its reflection on a disturbed lake. The migrating birds evoke a different sensation than passing aircraft. It is a natural clock that ticks off a different time. On our recent lunar observing sessions, we see the birds fly south. Outside of the eyepiece with naked eye, occasionally we see thin black ribbons against the bright urban night sky. Intrigue and mystery remain even though we soon discover the source these oscillating, sinuous Vee formations. And in months ahead, we'll see them return though heading in the opposite direction. A clock that ticks by the rhythm of geese.

Another rhythm that resonates with me is one from the regularity of the TIME'S UP! cyclists. I look forward to these monthly occurrences. On their approach, like the geese their formation is a quivering line of small lights seen across Central Park's Great Lawn. Even for an astronomer, the headlamps and blinking safety lights do not cause distress. Eventually, bikes rest and lamps extinguished, the lively spirit of the crowd illuminates our area. The Central Park Moonlight Ride occurs on the first Friday of the month. Cyclist Richard leads a pack of riders, that grows and shrinks in size depending on the season and weather. If we're out with scopes, he makes a point to make a brief stop at the top of the lawn for chat and observing.

Alternately, on the last Saturday of the month, the Riverside Ride, the riders stop on a clear nights. On this evening, people share stories of their astronomical experience and some express their first time fascinations of observing in a telescope.

Lastly, I can count on Andy & Masha for a rhythm of greater frequency, more closely related to the day. Always nearing curfew, dog-owner Andy comes by with Masha. He too may pass with others or on his own. What's more important is that I rely on Andy, TIME'S UP, and the geese to free me from the ordinary tick tock of circadian rhythm .

Click to see the 18 day 21 hour moon on 30 Sept 2007.