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.