Getting oriented in the night sky with Orion

Session Name: 20071229.1940

Click picture for larger image or here for unmarked image.
This image was taken at 12:40AM on 30 Dec 2007.

For a cold December evening and the last observing session for the year, it turned out to be okay in the sky and on the ground. More familiar faces stopped by then newcomers. Kin and I would observe with Hawaiian George, Stan & Gee, and Carol & Doggie. Later Time's Up stopped by. They left just as John and his dog Spencer stopped to spend the rest of the observing session. Mars was the highlight object for the evening, but some naked eye viewing of constellations and brighter open clusters were part of the program. Comet 8P/Tuttle was another primary object sought but ultimately went undetected.

Orion, The Hunter, is one of the most conspicuous constellations in the urban sky. When one locates Orion a host of interesting objects are nearby. These can be had with the naked eye (depending how keen), binoculars, and telescopes.

At this time of the year around 7:30 ~ 8:00, look toward manhattan-east spying for three equally bright and equally spaced stars that form Orion's belt. At the hour described Orion's belt will be almost vertical in the sky. On our Manhattan sky, one should be able to see the brighter members that figure Orion's body, an hour glass shape where the Orion's belt is the pinched center between the pair of bright stars, Saiph & Rigel, that make up his feet towards your left and the other pair of bright stars, Betelgeuse & Bellatrix, that make up his shoulders towards your right. A keen naked eye will detect two or three stars of the Orion's sword, the middle one appearing sort of fuzzy, unfocused.

When Orion is rising, he is leaning backward, where the Betelgeuse lies to the left & Rigel lies lower in the sky to the right of a vertically-oriented belt; at culmination, Orion stands straight up with horizontally-oriented belt, Betelgeuse to the upper left and Rigel lower right (similar to photograph above); lastly, when Orion sets he falls forward maintaining a horizontally-oriented belt, Rigel will fall below the western horizon first.

The marked up illustration describes Orion's Sword with a cartoon insert for detail. When Time's Up arrived this evening, Rich with 3 or 4 other riders, this was the first object shown in the scope at magnification 98x and a true field of view of ~50 arc minutes, about 8/10 of a degree. Using a Thousand Oaks Oxygen-3 (OIII) filter filter, the nebula was stunning. The central density was thick and texturized with undulating grades of brightness; averted vision extends the periphery out to greater distance and enhances the shape of an already interesting "bat" shape.

While some are waiting for a chance at the eyepiece, Mars is pointed out as the brightest object following a rough line from Orion's Belt through Betelguese into the territory of Taurus's constellation boundary. It wasn't too long ago that Mars was in Gemini and having just crossed the boundary. Earth had caught up to and now has passed this red planet in our laps around the Sun. In another 2 and half years, Earth and Mars will once again be nearby within their respective orbits.

Returning to Orion's Belt, our outstretched fingers arced upward to our right to the bright reddish star, Aldebaran. Letting our eyes adjust, the large open cluster shaped like an arrowhead begins to resolve. This is Hyades not too far from Orion's Shield. It is not cataloged as a Messier object, however, one will find as #25 in Melotte's catalog and #50 in Collinder's. Though Aldebaran appears to be a member of the cluster because of its visual proximity, in truth it is not. Aldebaran shines from a nearby 65 light years, whereas Hyades fills a volume of sky and share a common motion some 150 light years distant.

Continuing the line from Orion's Belt past the Hyades, a twinkling array of stars is seen. Some see 3 at first and others can pick out 6 fairly quickly. This is the open cluster, Messier 45 (M45) in Taurus. Legend has it that these are the seven sisters that Orion chases across the sky.

Observing Mars in the telescope at magnification 182x and a true field of view of ~46 arc minutes, a little shy of half of one degree, one could see surface details. Early in the session we could see a dark feature crossing the disk as a chord from an 11 o'clock - 3 o'clock line. Inverted by the scope, this corresponds to maria features above the southern polar cap: Mare Sirenum, Mare Cimmerium, Mare Tyrrhenum. Later in the session around when Mars rose substantially in the sky and the sky conditions improved, some phenomenal views were available. At this time, around 12:30, Syrtis Major had turned on to the disk. Above in the field of view, Hellas's form was observed, especially with the contrasting surrounding maria, Mare Hadriaticum to the west, Iapygia to the north and Mare Australe to the East. At the opposite side, Mare Boreum collared the northern polar cap. In contrast to nothing spotted at the south pole, one could easily see the whitish polar cap inside of the Mare Boreum. Lastly, a faint darkening feature was detected in an area corresponding to Elysium and Stymphalius Lacus. At this time, I am not certain what feature was observed.

For variety of character, the scope was turned from Mars to nearby M35, an open cluster at the feet of Gemini.

During the session, Kin and I looked for Comet 8P/Tuttle with no success. With the ephemerides we had on hand, we located the starfield but couldn't sense the comet in binoculars or with the telescope.

Comet Holmes shines above the street lamps

Session name: 20071106.2000

Skies cleared up after the rain where a naked eye limiting magnitude was in the neighborhood of magnitude 5. Comet Holmes continues to be seen naked eye from New York City, even from well lit spots in the city. Find some shade if you can and look toward Mirfak to see an obvious non-stellar object nearby.

Artists' Rock, an outcrop of Manhattan Schist behind Artists' Gate is not the ideal place to observe from (view of area) yet this photo shows a good likeness of the night sky with acute vision unaided. The four brighter stars of Alpha Persei Association show between Mirfak and delta Per.

The comet continues grow in size, my estimate based on ~7 comet diameters to in the 22x60 binoculars' 2.1° field of view is about 18'. The brightness profile consists of an evenly illuminated central condensation surrounded by a paler ring. The coma is about 3 central condensation diameters across. The psuedonucleus was not detected. In acsii it could appear like __/---\__

Its location has moved west, north of west, morphing the right triangle it created with Mirfak and delta Per last week to a flat isosceles.

I find the observation with 7x50 binoculars to be the most pleasing. It takes in the large, richer field of stars that contrast sharply with this dandelion interloper, ready for a breath of air to blow it apart.

Another pleasing view was the Double Cluster observed in the Tak bins. Framed nicely the clusters reveal the stardust that clings around some of the brighter stars; all the while sitting on a bed of uneven faint light.


Marked up photo || unmarked photo

20071030 - 17P/ Holmes Observing Report

Sketch in Moleskine notebook & astromick image on iPhone.

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.

Size
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.

Brightness
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.

Shape
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.

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.

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.

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
sky."

Quoted from Sky&Telescope site

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.