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?

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