Monday, May 26, 2008

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.

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Memorial Day 2008

Blockhouse #1, Central Park

Remember those that lost their lives in battle.
Memorial Day 2008.


Saturday, May 10, 2008

Globe At Night results

Click here to go to NOAO press release.

If you didn't know (like me), the Office of Public Affairs and Educational Outreach of the National Optical Astronomy Observatory published results of the recent Globe At Night (GAN) event. This was the multi-night event where observers around the world assessed the darkness of their skies using charts and training provided by GAN organizers.

Myself and members of NYSkies conducted observations and guided others to perform an assessment. We captured the results of all and then filed the separate reports at the GAN website.

As an experienced observer, I measured an estimated 1 magnitude difference from the corner of 56th & Broadway looking above Times Square to the usual observing spot at the Great Lawn in Central Park.

Thursday, May 08, 2008

When is Manhattanhenge 2008?

Manhattanhenge occurs at sunset, 8:18PM EDT, on the 28 May at an azimuth of nearly 300°. By definition, sunset occurs when the Sun's trailing edge descends below our horizon , so one wants to arrive prior to 8:18PM to watch it entirety. 300° azimuth is 30° greater, or more northern, than cardinal point west, yet it corresponds to orientation of the cross streets of the Manhattan grid. Cross streets align along azimuths 120° on the east and 300° on the west, as depicted in the illustration below.

The Sun has an angular measurement around a half of a degree. The angular measurement of the street canyon from where I observed that sunset is slightly greater than my pinky held at arm's length, about a degree to a degree and one half ( 1° ~ 1.5°). In the schematic below the solar is disk is larger and brighter because of glare, the actual solar disk when observed through a solar filter is smaller, where nearly 3 solar disks could fit between the buildings.

At this time of the year the Sun lies on the ecliptic within the boundaries of the constellation Taurus. This is a section of the ecliptic where its angle with respect to the horizon is nearly perpendicular. In other words, the Sun sets on a steep angle so one can watch the sun set with more of a vertical drop rather than being carried across a shallow path.

If you miss the event or weather is afoul, one can still observe this on days leading up to or just past with the same effect. A list of the days , time of sunset and azimuth is provided below. Choose a cross street where you there is an unobstructed view to the western horizon. Any of the major cross streets work, like 23rd, 34th, 42nd, and 57th.

Don't forget to look behind you, your shadow is at its longest length, like the cone of night.

26 May, 8:16PM EDT --- 299° 29'
27 May, 8:17PM EDT --- 299° 43'
28 May, 8:18PM EDT --- 299° 56'
29 May, 8:19PM EDT --- 300° 09'
30 May, 8:19PM EDT --- 300° 21'

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Astronomy in NYC

The beginning of agrowing list that outlines astronomy resources in and around the city.

Amateur Astronomers Association (AAA)
NYC’s oldest astronomy organization with a diverse program of special interests.

NYSkies Astronomy Inc.
The premiere support group for home astronomy in New York.

Public Outreach
AAA - Observing
The AAA described above conducts regularly scheduled public observing events across the boroughs of NYC. A fine gorup of people sharing optics and knowledge to gain an appreciation for observing the celestial objects in the sky..

Columbia University Observatory
Columbuia U’s service to the general public with lectures and open dome nights. Sign up for email alerts.

Top of the Lawn
Informal group of dedicated amateur observers from the Great Lawn in Central Park. Most clear weekend nights around the northern perimeter.

Astronomical Observations
A NYC amateur observer that takes to the street often - day & night - and records his observations with a analytical eye.

Hayden Planetarium
A beloved institution that operates within the new Rose Center for Earth and Space of the American Museum of Natural History (AMNH). Regularly scheduled programs and special events. In general, AMNH regular exhibits spans many science disciplines.

A retailer that has earned my trust, confidence, and loyalty. The Astronomy dept on the fifth floor is operated by Mike Peoples, an amateur astronomer friendly to amateur astronomers and enthusiasts. Seasoned or new - a first stop before any other.

B&H Photo
A large retailer that many use for astronomy and photography supplies. If you know what you want you'll find great value. If you prefer one-n-one and some attention, look to Adorama.

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36 hour Crescent Moon

Session name: 20080506.1915

Another image of the recent crescent Moon, age 35h 55m, taken handheld through 7x50 binoculars. The vertical line doesn't look like a good thing.
How does one clean up the noise? I use gimp for cropping but haven't done any type of clean up.
The Moon sets toward the 5:00~5:30 direction and is approximately Lunar East. Lunar North is near the cusp on the right side.

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Wednesday, May 07, 2008

Crescent Moon and Bright Nights

Session name: 20080506.1915

Photo: 36hr Crescent MoonThis evening was much more fruitful. A teaspoon of the lunar disk, accompanied by ruddy-colored Mercury, settled into the trees on the western horizon after sunset. When the sky darkened during twilight and the mostly cloudy sky cleared to partly cloudy, a graceful, silvery curve appeared among the clouds.

Young Sasha, around 6 years old, walked to the tripod and peered through binoculars for the first time at the Moon . I asked her what shape saw and she replied, tracing her finger along her chin, "a smile".

I couldn't make out any specific details of the crescent Moon. Mostly because I didn't look at any references. I looked for librated maria but didn't see anything. The cusps were beautiful as slender illuminated horns that held whispered light and dark at the extreme tips. I doubt it was M. Crisium but I did see a notch in that general area of the moon.

Maybe a dozen or more people would pass by. Ken the Pilot, stopped and chatted for a while, not having seen him for many months. When he arrived I remember how forbidding the western sky looked. Dark and opaque, low clouds wore rain skirts that fell away. Our persistence proved that Mother Nature is fickle. The clouds moved to the east with a steady pace leaving fairly clear skies after sunset.

Marked up image of Moon & MercuryLooking manhattan-west from TotL image of Moon & Mercury.
Same image but unmarked of Mercury & Moon & Mercury setting.

Ken and I hosted others stopping and asking for what we were looking. I described how this crescent moon just passed alignment with the sun some 36 hours ago. (I mentioned the 12 hour crescent of yesterday but that may have fallen on deaf ears.) For those that arrived after the sunset, we observed the crescent, Mercury, and Saturn naked eye and through the 22x powered binoculars.

On crescent moons I like to remind the passersby of that we refer to near side and far side of the moon and that both sides receive sunlight. The crescent is just portion of the illuminated hemisphere where the majority of sunlight is falling on the far side. The crescent- shaped line we see separates night an day, the morning terminator line.

The near side of the Moon never really experiences dark nights. A person standing on the near side during New Moon is looking out into their night sky. (The far side is experiencing day.) And on this crescent evening where a lunar observer situated on the center of the Moon, Earth would be in waning gibbous phase, just past Full Earth.

This lunar observer would see a huge 2° disk reflecting much light back on to the Moon. We refer to this light as Earthshine and allows earth observers to see the Moon outlined and dimly illuminated on the background sky. For the lunar-based observer, one would mostly likely see their shadow from this Earthshine. Over time the Earth's phase wanes to New Earth but the lunar morning terminator advances. When the phase is New Earth for the lunar-based observer, it is Full Moon for the Earth-based observer.

This brief session provided more interaction than I expected. A birder and a photographer couple stopped and remarked of the sunset's beauty. At that time, I had just snapped some photos of a fan-shaped light - crepuscular rays - from the direction of the Sun. A man in a wheel chair described the sky in Argentina where he recently broke his foot. Later, the Columbia U. neuroscience student would ask after seeing Saturn & Titan if I return often to this spot. And others asked for looks and expressed delight and fascination with our solar system neighbors. Easily missed, otherwise unnoticed, but that wasn't going to happen from the Top of the Lawn.

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Tuesday, May 06, 2008

Chasing a very, very, young crescent moon

Session name: 20080505.1830

This crescent moon had all the makings for a record. A personal record and one that would rank in an area where few have succeeded. A 12 hour crescent moon set in the west with best of all conditions - except the weather.

The Moon is an Aries.
The angle of the ecliptic by Aries is nearly vertical to the horizon when setting.
The Moon is north of the ecliptic, increasing the angle to the horizon and situauting the Moon more vertical to the Sun.
Elongation was 8°32'E with illumination at 0.6%.
Exceeds Danjon's Limit of 7° or 7°30'.
Moon's age at sunset was 11h37m; age at the the time of predicted sighting 11h58m when the Sun was a little more than 4° below the horizon and the Moon at an altitude a little greater than 3°.

File a report or get details at I submitted one indicating crescent not seen.
If the weather agrees we can observe a 36 hour crescent Moon this evening. Still a splendid, magical sight of our sister world that laps the Sun with us. If you have binoculars or a telescope watch sunrise beginning in Mare Crisium and Mare Anguis.

A Method for Predicting the First Sighting of the New Crescent Moon (Yallop)
Calculating the length of crescent moon (cusp to cusp) (Sultan)
First Visibility: Beyond Danjon's Limit (Sultan)

Search for H. R. Blackwell

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Atmospheric Phenomena

On the way home to prepare for this evenings crescent moon chase, I looked up frequently to the sky. The sky was so milky with cirrostratus and some altostratus clouds when looking west. Through sunglasses I noticed a rainbow arc above the Sun. I stopped to investigate it further. A quick measurement with spread thumb and pinky held at arm's length confirmed a 22° separation between Sun and arc. A partial arc of a 22° halo was observed from about "10 o'clock to 1 o'clock" of a circle's circumference. At the 3 o'clock position, an isolated, rainbow-colored bright spot, detached from the arc, was observed (marked "a" in illustration). At the time, I didn't know that was a sun dog, a.k.a. mock sun or parhelia.

I observed the halo and the sun dog with and without polarized sunglasses. Had I not been wearing sunglasses I would not have detected them; however, after knowing these atmospheric treats were there I could sense there locations without sunglasses by the brightening of the sky in those areas, as a spot and arc. Without the sunglasses, I was unable to see the color.

Later when I arrived home, I looked out the living room to the west. Haze and clouds could be seen down to the horizon. Shadows weren't very sharp, yet the masked Sun was still too bright to look at directly. The sky was awash with grades of white. Above the Sun, with sunglasses, I could see the arc. It rose from a 9 o'clock position up to 1 o'clock where my building obstructed the view. As bright as it was I suspected that it was strong enough to make it to 3 o'clock to join the sun dog previously observed.

I thought the sun dog was a section of the halo, horizontal to the sun, but the observation showed it differently. During this second observation, a second sun dog was observed on the other side, appearing lower at an 8 ~ 8:30 position. Using a building rooftop and my pencil to create a horizontal reference line with the sun, this sun dog was below it. Lastly, the halo appeared to be inside of the sun dog. Since I wasn't seeing the green or blue portion of the arc at this location I thought the sun dog was part of it but it was clearly too far out; perhaps it is tangent if the entire colored spectrum were seen.

Concerning color, red was interior and yellow was the neighboring exterior color. From down on the street, the first observation, green and blue was not so apparent, except on the sun dog. The second observation, the rainbow effect was pronounced where there was evidence of blue on the outside. This is the same color sequence of a secondary rainbow.

Want to know more, visit Atmospheric Optics where most of the links above lead to for more information.

Illustration based on drawing in The Skywatcher's Handbook, edited by Colin Ronan & others.

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