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APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 4:54 am
by APOD Robot
Hong Kong Sky
Explanation: This remarkable scene combines multiple exposures recorded on the evening of January 18th from a waterside perspective in
Hong Kong, China. It follows a
young crescent Moon, with brilliant planet
Jupiter to its left, as they set together in the western sky. Their two luminous trails are faintly paralleled by
trails of background stars. But easier to pick out are the short, bright airplane trails converging toward the horizon and the Hong Kong International Airport that seem to offer a frenzied imitation of the
celestial tracks. Of course, the reflection of city lights and boat traffic follows the water's surface.
Streaking car lights define the span of the cable-stayed Ting Kau bridge.
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Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 5:37 am
by al dumont
being an amatuer I will simply say that I believe the photo is looking east at a rising moon and planet.
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 6:17 am
by Case
On January 18 2010, the moon rises and sets later than the sun. (Hong Kong local times: Sunrise: 07:06, Moonrise: 08:44, Sunset: 18:02, Moonset: 20:35) Thus, to see the moon in a dark sky, you have to look west after sunset.
Jupiter being on the left side of the moon is another clue for the western horizon.
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 9:15 am
by soupphysics
I don't like it that much. It's messy and there isn't really anything fascinating in it.
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 11:46 am
by geckzilla
Such is city life, soup.
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 1:39 pm
by neufer
Case wrote:On January 18 2010, the moon rises and sets later than the sun. (Hong Kong local times: Sunrise: 07:06, Moonrise: 08:44, Sunset: 18:02, Moonset: 20:35) Thus, to see the moon in a dark sky, you have to look west after sunset.
Jupiter being on the left side of the moon is another clue for the western horizon.
Besides which, Hong Kong International Airport is WSW of the Ting Kau bridge.
Why a duck?
Posted: Sat Feb 06, 2010 4:12 pm
by neufer
http://www.tsingma.com.hk/Web_pages/Intro_tmca/ting_kau_bridge_e.htm wrote:
<<
The 1,177m long Ting Kau Bridge and the 500m long dual Approach Viaduct form a vital link in Hong Kong's new Route 3, connecting Hong Kong Island, Kowloon and the new airport at Chek Lap Kok to the New Territories and the mainland. Two main ramps connect to the Tuen Mun Highway and the Western New Territories.
The outstanding features of this unique cable stayed bridge are the 3 towers with heights of 170m, 194m, and 158m, located on the Ting Kau headland, on a reclaimed island in Rambler Channel and on the north-west Tsing Yi shoreline respectively. The arrangement of separate decks on both sides of the 3 towers contributes to the slender appearance of the bridge while acting favourably under heavy wind and typhoon loads. Each deck carries 3 traffic lanes and a hard shoulder. Spanning the 900m wide Rambler Channel, the Ting Kau Bridge ranks amongst one of the longest cable stayed bridges in the world.>>
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 9:50 pm
by antn_e
Surely planes have the white lights at the front, so the trails must be taking off and diverging not converging (unless they were flying backwards!)
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Sat Feb 06, 2010 11:12 pm
by neufer
antn_e wrote:Surely planes have the white lights at the front, so the trails must be taking off and diverging not converging (unless they were flying backwards!)
The planes themselves are taking off and diverging
but they are leaving behind trails which converge back toward the horizon.
(And don't call me Shirley.
)
http://www.youtube.com/watch?v=lqrllkAO1uA
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Tue Feb 09, 2010 12:44 pm
by statman
Why aren't the Jupiter and Moon paths parallel as the "movement" is nearly all due to the earth's motion?
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Tue Feb 09, 2010 1:12 pm
by neufer
statman wrote:Why aren't the Jupiter and Moon paths parallel as the "movement" is nearly all due to the earth's motion?
Only straight lines can be parallel.
These paths can only be straight lines if they are exactly on the celestial equator.
See:
http://apod.nasa.gov/apod/ap090314.html
--------------------------------------------------------
1) A simple lens or pinhole camera produces a
gnomonic map projection of the celestial sphere.
2) The gnomonic map projection displays
all great circles as straight lines.
3)
Right ascension lines and the celestial equator are great circles
. and, therefore, always appear as straight lines a gnomonic map projection:
4)
All other celestial declination lines are curved in a gnomonic map projection
--------------------------------------------------------
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Tue Feb 09, 2010 4:07 pm
by statman
I meant - why are the paths not parallel - as in, the same apparent distance apart on the image: meaure with a ruler and you will see they are different distances apart between top annd bottom.
Re: APOD: Hong Kong Sky (2010 Feb 06)
Posted: Tue Feb 09, 2010 5:32 pm
by neufer
statman wrote:I meant - why are the paths not parallel - as in, the same apparent distance apart on the image: measure with a ruler and you will see they are different distances apart between top and bottom.
http://apod.nasa.gov/apod/ap090314.html
Measure with a ruler and you will see these paths
are different distances apart between bottom & top.
The circular path of Ursa Minor around Polaris
is NOT parallel to anything because it is not a straight line.
