May 2008 observations from Central Park

This month there were many opportunities at the Top of the Lawn where more than a hundred people would get views of our sky. Mercury, Mars, Saturn, and our Moon have been the dominant objects. Diversions to nearby doubles and bright deep sky objects offered variety to the pedestrians' visual palate.

Saturn continues to be the dominant object that stirs the general public. These past days, one looks high in the manhattan-southwest sky to see an obvious pair of stars; the upper, brighter "star" is Saturn. The star below and west of Saturn is the alpha star of Leo, Regulus. Most are just as surprised that one can see Saturn (or anything else for that matter) in the city sky without a telescope , as well as see the rings and moons in the telescope.

A Darker View describes people's reaction to observing Saturn. Anyone who has shared the eyepiece to offer peeks at Saturn will agree that there is a personal joy that you touched someone; their reaction is the immediate satisfaction. The reward actually belongs to that observer.

Mars has been another delight. Easy to locate as lone, reddish star, Mars sits almost halfway between Castor/Pollux pair and Saturn/Regulus pair. The red planet just passed through the heart of Cancer offering a splendid view of our neighbor superposed on M44, an open cluster some 577 light years distant. (On a separate observing session, I observed the motion of Mars against the background stars, an exciting first!)

Many who passed last night spoke of the Phoenix landing on the surface of Mars. (Bravo to the talent that makes these missions successful!) Through cirrus and alto stratus clouds we observed Mars at one side of the 2° field of view and the entire open cluster M44 on the other side. Since Mars is small and far from Earth in its orbit around the Sun, it appears as a small reddish disk at magnifications 63x & 12ox. Lately, I show to passersby a map of Mars on the Palm T3 using Brian Tung's Mars Map.

Placing the scope a little east of TotL proper, our western horizon improves where Mercury sets with Taurus. The tree line from this perspective offers convenient landmarks that are easy to describe and guide the pedestrians to locate Mercury relative to the crowns of the trees. Many saw Mercury for their time and just as many have forgotten - or didn't realize - that Messenger mission flew by Mercury earlier this year on its first pass of three before an orbital insertion around Mercury in 2011.

Earlier in the month many of us watched the beautiful crescent Moon set with Mercury attending by her side. I wonder how many would have noticed this spectacle if a telescope set up on the sidewalk didn't prompt their curiousity an ddesire to know what's up in the sky.

Look up after midnight to see the waxing moon rise. Recently, Jupiter, in Sagittarius, rose above our ciyy skyline about 8° west northwest of the Moon.

If it's a clear weekend night, stop by the Great Lawn to observe these and other fantastic objects.

Planets offer pleasing views

Session name: 20080224.1900

A cold session with a light breeze chilled exposed cheeks and shook the scope. Early in the session clear skies yielded slowly to accumulating clouds entering from the west. Thin, semi-transparent sheets gathered beneath Orion and ultimately coated a large part of the sky by 10PM EST. Over the course of the observing session a half dozen passersby and dog walkers stopped for breathtaking views of Saturn. Charlie and Kin were absent as well as familiar dog owners.



Mars still reveals some features in the eyepiece despite its size at 9.4", much smaller than the 15.6" of 08 DEC '07. First, it is obviously a pinkish-red disk compared with the nearby stellar pinpricks. It has area and with a sprinkle of imagination one can sense volume. Secondly, surface features of different albedo and tone were apparent. A light breeze caused the disk to dance in the field of view, but with firm scope and steady seeing I could see clearly Chryse Planitia, a martian basin with a high albedo. This circular white area contrasted with darker marial regions to the north and south. The southern marial region was larger and broader across the disk than the northern one which appeared more localized above Chryse. I was unable to detect the northern polar cap which I had seen in previous sessions. Magnifications used 90x, 120X and 240x, finally settling on the 7mm's 120x magnification for a bright, crisp view of the diminutive red disk.


Saturn was splendid this session. Passersby remarked the same. If you plan to consider sidewalk astronomy, this is an ideal season because Saturn is sure to delight all that see him. I can't think of any other object in the night sky that thrills the pedestrian observer with disbelief and astonishment.

When the air calmed, the scope would settle long enough to drink in long views of the ringed planet and its satellites. I heard gasps from those who took a look in the eyepiece. At 120x magnification, one could easily appreciate Saturn's characteristic parts and shape. With more scrutiny during the calm moments, many features were observed.

On the disk of the planet, a salmon-pinkish toned belt ran parallel across the disk beneath (south) the ring. Of the ring system, Cassini Division on each side was a challenge but discernible. The A-ring offered a translucent glow which contrasted with the Division and whiter, opaque B-ring. Perhaps a shadow provides the darker lineal feature on the south side of the ring that crosses the planet. I am confused because tonight Saturn is at opposition and no shadows should be displayed. Like a full Moon, the Sun is shining directly on the planet from our point of view on Earth offering no shades of relie


Saturnian moons Titan, Rhea, Tethys were clearly visible, pinpoints of light created by sunlight reflected off their surface. I suspected a prick of light inside Rhea's orbit but had wavering confidence. Checking planetarium software StarryNight at home, those pings of photons turned out to be Dione.
Lastly, I suspected a point of faint light about 5 Titan-Saturn-separations distant on the same side as Titan. Field notes agreed with the planetarium program indicating this unusal moon at magnitude 10.92. There is not much room for the limiting magnitude in this scope under these skies. (Magnitude 11.6 with previous measurements using NGC225 and NGC1647.)

I finished of this session with a practice run for GAN'08. I was able to detect stars as faint as 4.7 above Times Square. I don't propose that NYC has dark skies but that my observation skills, visual acuity, and confidence allow me to see pinpoints of light, even if more contrats is desired.

Mars observation

Session name: 20071217.1645

This session about a dozen passersby stopped for views of an 8-day First Quarter Moon in Pisces and the little Mars at the foot of the Twin Castor. A light breeze, sometimes gusting to a moderate wind, rustled and darted dry leaves along the sidewalk. In the northeast sky and zenith, naked eye limiting magnitude was around magnitude 5 using my personal candlesticks in Cassiopeia and Perseus. Ahhh... it was was cold.

Despite its size, surface features can be discerned. The thin, dark necklace of Mare Boreum delineated the northern polar cap from the greater fields of reddish tint. Syrtis Major obviously rose from the southern hemisphere jutting up past the equator into the reddish fields, appearing to point one's eye toward the north polar ice cap. Leading in the eyepiece drift, Mare Tyrrhenum was not as bold and great in size as Mare Erythraeum which was situated on the trailing side. Over the course of the session features on the trailing side turned on to the disk. Beneath Syrtis Major, Iapygia completed the dark band across the disk joining the maria and capped Hellas near the south pole.

Trapezium & Mars form Central Park

Session name:20071208.1945

On this short session, Kin and I observed and shared the views of Mars to about a dozen pedestrians and dog owners. Most of the evening the sky background appeared bright to our south and up to zenith, a little haze seemed to fill the air diffusing the lights of CitiGroup building and Times Square. We commented that seeing was not so good and transparency was significantly better in the celestial northeast with a naked eye limiting magnitude around magnitude 5.0.

Trapezium
At magnification to 121x, I could resolve the E & F star of the Trapezium. (Stan was able to see them and I can't recall if Kin separate them.) Below are two diagrams I created for use on the Palm. One is based on information in Burnham's Handbook for the reflector where it is inverted and mirror reversed. The Garfinkle-based diagram has north at top and adds a few extra measurements to stars beyond the reach of this 4" in city skies.

What makes resolving the magnitude 11 E & F stars challenging is the brightness of the nearby A & C stars, respectively. My experience has been that the E star is easier to detect than the F star because of A's brightness.

Trapezium Chart - Burnham

Trapezium Chart - Garfinkle

Mars
We could see surface features in the northern hemisphere with a white polar cap and contrasting maria: Mare Boreum formed a collar around the bright cap with Mare Acidalium adding some area in the center. In the southern hemisphere a large, dark smudgy area contrasted with the brightening around the limb and across the equatorial zone. It was difficult discern shape and extent since contrast was low with the surrounding surface. I suspect a great part of the darker albedo was Mare Erythraeum.

Most of the pedestrians were able to see the darker collar and obviously contrasting northern polar cap. I don't think they had as easy a time with the southern hemisphere or equatorial zone.

We disagreed on what we sensed across the equatorial region. Kin saw a brigher area extending across the entire disk, describing it as a contrast with the maria to north and south. I said I saw a crisp white disc that stood out above that bright equatorial band. The white spot is Chryse Planitia. I made this remark after consulting Brian Tung's terrific Palm application, Mars Map.
I felt that I saw it but lost confidence and considered that averted imagination miught be at play. That is why the sketch shows dots along the central region and doesn't include a small pea shape just east of center (opposite direction of drift).


References
Burnham's Celestial Handbook: An Observer's Guide to the Universe
Robert Burnham, Jr.

Star-Hopping: Your Visa to Viewing the Universe
Robert Garfinkle

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.