Saturday, September 27, 2008

Neptune - 162 years later

Session name: 20080923.2100

On 23 September 2008, 162 years passed since Neptune was first discovered in the telescope by Johnann Galle relying on predictions of mathematician Urbain Le Verrier.

At an average distance of 4.5 billion km, Neptune takes 164.79 years to complete one orbit. For the Neptunian inhabitant, on July 12, 2011 Neptune will have completed one lap around the Sun since it was first observed by Galle.

Today, Neptune is the most distant of the 8 planets, by revision of astronomical definitions. From 1979 to 1999, Neptune was the most distant of 9 planets, prior to the revision of astronomical definitions and because Pluto's highly eccentric orbit brought the ninth planet inside of Neptune's nearly circular orbit. This will occur again between 2216 and 2236.

From the city, the early Autumn Sky rising in the east may appear barren of stars. With a little patience, observing effort, and a knowledge of where to look, you'll find Neptune in no time. Even at the darkest sites, magnitude 7.9 Neptune requires optical aid to observe. Binoculars or telescopes are suitable to easily locate and identify the planet in the tail of Capricornus, the Sea Goat. Once the two tail stars of Capricornus are located then we can find Neptune about 2° from gamma Cap, Nashira.

To get your bearings, locate Deneb Algedi (delta Cap) & Nashira, the trailing pair of stars that appear nearly horizontal when Capricornus rises in the East. If you don't see them immediately look closer to the horizon where a bold star, Fomalhaut, shines brilliantly in soliloquy. Scan your bins in a one o'clock direction across 21° of the sky, there you'll see the pair of stars outshining any others in the area. In the field of view, note the trail of three mag 5 stars in a southeast to northwest line just north of Deneb Algedi. To the west of that line, I identify the triangle of fainter stars.

At a distance of 4.4 billion km (2.7 billion mi) from Earth, Neptune's size only subtends an angle of 2.3 arc seconds, an angular diameter the same size as Jupiter's moon Io. In binoculars the reward is finding and observing the most distant planet of the Solar System. In a telescope at 100x magnification there is no appreciable features to observe other than it may appear as a tiny disk rather than a star to the keen observer.

In Peter Grego's Solar System Observer's Guide, there is a brief description of Jupiter occulting Neptune during Galileo's time and how the immersion took more than a half hour to complete. One can easily appreciate this fact and the apparent size of Neptune in a telescope by observing the ingress of an Io transit across Jupiter. Away from the planet, Io looks like another bright star, but as it approaches and ingresses the planet one can absolutely see the diameter of this moon.

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Sunday, September 21, 2008

Autumnal Equinox 2008

Autumnal Equinox starts the clock to count off the next 89 days 18 hours to the Winter Solstice.

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Sunday, September 14, 2008

Description of Top of the Lawn

John P. of NYSkies offered to host a description of our group since we provide astronomy observing to the public. The following is a slightly modified version found at NYSkies. Ben, Charlie, John, Kin, & Tom reviewed and contributed to the description.

Top of the Lawn, more commonly called "TotL" (pronounced "total"), is a loose association of urban astronomy enthusiasts who gather on the northern perimeter path of Central Park's Great Lawn. The core group of sidewalk astronomers equipped with binoculars, telescopes, and a passion for sharing our skies. We are in the Park all year round to observe each season's sky, typically on clear weekend nights.

In addition to the TotL team, there are regular visitors that include dog walkers, cyclists, and pedestrians. These folks come by with such regularity that they learned the fundamental motions of the night sky and how to identify various targets in the sky. However, all visitors are welcome to stop by for peeks and chat.

Defying popular belief, there are many celestial delights to see with the eye and small optics. Many objects are challenged by high background sky brightness. Others, like the Milky Way, can be veiled from sight. Despite this impediment, TotL members help you find the brighter objects in the sky, by eye and optics, and provide some details about them.

In general, solar system bodies are easy to follow from the city, they include the Moon, planets, major comets, and larger asteroids. Man-made objects can be easy to observe, like International Space Station, Space Shuttle, Iridium flares, and large space capsules from other countries.

We can see many bright open clusters, double stars, planetary stars, some nebulae, and globular clusters. Their number and place in the sky vary with the season. Our city sky challenges most galaxies beyond the Milky Way, yet the great Andromeda Galaxy can be observed in optics as small as binoculars.

TotL members gather for the informal purpose of sharing our fascination for the night sky. Passersby are captivated by the vastness of space and distances to other worlds. They look into the eyepiece with awe and wonder. For our group, these reactions and expressed interest are reward enough to share with the public.

A visit to TotL, we can help with the following:

- getting started
- learn how to get your bearings in the sky
- how to use a planisphere
- identify constellations and asterisms
- how to find various deep sky objects
- what to consider when buying equipment
- how to use your binoculars or telescope
- tricks and tips with daytime observing

Just show up – with or without optics. Travel instructions and the map below detail our location in Central Park. We just ask that you respect our equipment and be considerate of others. No expert knowledge is required; an interest and positive attitude are helpful.

Look for us at the northern perimeter sidewalk of the Great Lawn, Central Park. That is approximately at 85th St. in the middle of the park. One can enter the park on the westside from Hunter's Gate at Central Park West (CPW) & 81st St. or Mariner's Gate at CPW & 85th St. at the north side of each entrance, follow the sidewalk straight into the park, crossing the road, West Drive, towards the Great Lawn.

The M10 bus stops nearby at 84th and CPW and the B & C subway stops at 86th and CPW.

If one enters the park from the east, use the entrances north or south (Miner's Gate) of the Metropolitan Museum of Art and walk westward along the path. From the southern entrance one crosses East Drive under the bridge. From the sidewalk north of the “Met”, one follows the sidewalk into the park and crosses East Drive when traffic and the light permit. The sidewalk continues, leading into the Great Lawn.

M1, M2, and other buses run south and stops around 84th & 5th Ave while the 4, 5, or 6 subway stops at 86th & Lexington.

Once you arrive, walk north on the perimeter sidewalk around the Great Lawn. We'll be at the top, or maybe a little further east.

This map indicates meeting places relative to the Great Lawn, Central Park. The red circle indicates our primary meeting place. There are some events where the horizon is more favorable when observed from the blue circles, for example lunar eclipses from Turtle Pond Observatory.

Map to TotL

A Google map

View Larger Map

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Monday, September 08, 2008

Urban Starfest 2008

Session name: 20080907.1915

Cheers to the Amateur Astronomers Association (AAA) and the Urban Park Rangers for hosting Urban Starfest 2008.

The New York City astronomy community and sidewalk naturalists assembled for our annual urban Star Party at Sheep Meadow in Central Park. A hearty turn out of optics that ranged from 12.5" reflectors to 3" refractors and tripod-mounted bins managed to satisfy the visiting public. I contributed eyepiece views from the Teleport scope and Takahashi binoculars. I was lucky to have George H. - another Teleport owner - give his time to guide the people with observing suggestions, encourage them to describe what they see, point out Callisto's shadow transit, describe how that is, react to their enthusiasm, and manage the scope by re-centering the object. All that began shirtly after arriving with Jupiter in the twilight to other objects like Albireo, M13, and the galactic nuclei of M31 & M32. Many of us saw two very different jovian shadow transits bookmarking the event from 7:30 ~ 10:00.

While George handled the scope I managed the Tak bins & tripod which offered a "lighter" view of the heavens. The intent was to contrast the big optics with small portable optics with a more convenient viewing experience: two eyes and objects appear the same with our without optics; and, to emphasize that a desore to look is more important than the big glass. Our first quarter Moon (missed another opporunity for Purbach Cross!), Neptune, and Double Cluster were featured in these eyepieces.

The convenience of the size, weight, and flexibility of the tripod and bins allows the setup to be custom fitted for the observer in seconds. With a little patience, children standing 3' tall to adults twice that size can equally stand at the eyepieces taking in sunlight refelected off the Moon or any other object that was in its sights.

I cringe thinking that this is a once a year event. We have a great community of persons, thoughtful, caring, and giving. It's demonstrated in the way these good folks interact with people, like Craig building a human solar system or offering sky tour lectures at the tip of the green laser, while they wait to look through a telescope. To see the excitement and enthusiasm of the public is rewarding. It's nice to think that we ignited an an interest. That we made a difference. Let's do it more often.

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Monday, September 01, 2008

One of them nights

Session name: 20080831.1950

I'm easy to please. The ingredients of last night combined to make for a greater experience than the sum of its parts. There was proper mix of friendly interested people, clear skies, lube in my joints, and sky full of celestial gems. A fine recipe for joy.

I arrived at TotL shortly after sunset. As passersby looked on at the Teleport reflector with curiosity and amazement. Responding to questions of "What is it?", I anticipated the next question with a finger pointing to Jupiter, shining in civil twilight. I continued setting up the scope while people stopped and gathered round. I see others point to the sky and announce Jupiter is there in the southeast. Infectious!

In what seemed like moments we began to point out brighter stars appearing in the twilight sky, a sky brightness that pedestrians could mistake for daytime. As the number of stars increased so did the crowd of people standing around. As Earth rotated to the east the Sun continued descending below the horizon. The sky darkened. Antares appeared in our South, Vega cramped our necks when we looked to zenith, and Arcturus, the brightest star of early summer sky, sets to our west. To our good fortune, the night sky was clear and transparent.

There are scales that observers describe transparency, atmospheric clarity, however, I assess our night skies with a subjective test. I look to the south from TotL, a skyscape (the picture under the blog's title) punctuated with light pollution. If I see entire constellations culminating above the CitiGroup Building or just above Times Square and the obnoxious light cones from the usual suspects radiate dimly and sharply up the sky, then I judge the sky to be very, very good.

I didn't wait long for the scope cool down before offering views to the pedestrians. Unlike the visual acuity of experienced observers, casual observers do not require the fidelity of a perfectly tuned instrument. In just 10 minutes of setting up, the scope turned on Jupiter, we were fortunate to see in addition to the four moons of Jupiter and the two equatorial belts, Io's shadow transit on the edge on the northern equatorial belt. Not everyone was able to confidently detect it, but those that did see it stated so with confidence and certainty.

This evening Scorpius is entirely visible from the 3 vertical stars of its head through Antares to the east down along the curve of the body and tail to the Stingers. If your scope is pointed in this direction, have a look at one of my favorite open clusters, NGC6231, in the Table of Scorpius. For New Yorkers, it doesn't rise high in the sky because of its southern declination at -41.48°.

East of Scorpius, I see the entire Teapot and Teaspoon, asterisms found in Sagittarius. Jupiter is the bright drip falling from the Teaspoon. Later in the evening when their times arrive the fainter constellations, Capricornus harbors Neptune (very easy starhop!) and Aquarius hosts Uranus, rise above the trees challenged by the sky brightness. With moderate effort one can find the brighter stars and trace each constellation. Realize their size in the open sky and shrug off that NYC claustrophobic nag.

It's not an exaggeration to say that about 3 dozen people passed through, most in groups of 3 - 5 people. Of course, Jupiter was the highlight and both Tom & I offered views from bins and scope. For those that stayed for a while, like trio Sean, Jonas, & Carol, I showed other objects including Albireo, Ring Nebula, Andromeda Galaxy & M32, and a bunch of open clusters along the line of Perseus and Cassiopeia.

At the end of busy evening, I stand before a familiar sky filled with an overwhelming feeling of joy. I stood alone in the middle of the Central Park. Not afraid. Crickets' chirps mingle the constant hum of cicadas. I ignore the bright strret lamps around me the brilliant buildings to my back. The Fall sky rises from northern Manhattan. I flatter myself thinking of amazed pedestrians telling others of the worlds they saw. I remember how I would end evenings just like this with other Team TotL'ers. I remember that in a month I celebrate 5 years of observing from around the Great Lawn. Despite the absence of Ben, Charlie, and Kin, the night sky from TotL elicits a sense of unmatched joy.

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