Posted on 08/17/2011 2:31:32 AM PDT by SunkenCiv
Explanation: Denizens of planet Earth watched this year's Perseid meteor shower by looking up into the moonlit night sky. But this remarkable view captured by astronaut Ron Garan looks down on a Perseid meteor. From Garan's perspective onboard the International Space Station orbiting at an altitude of about 380 kilometers, the Perseid meteors streak below, swept up dust left from comet Swift-Tuttle heated to incandescence. The glowing comet dust grains are traveling at about 60 kilometers per second through the denser atmosphere around 100 kilometers above Earth's surface. In this case, the foreshortened meteor flash is right of frame center, below the curving limb of the Earth and a layer of greenish airglow. Out of the frame, the Sun is on the horizon beyond one of the station's solar panel arrays at the upper right. Seen above the meteor near the horizon is bright star Arcturus and a star field that includes the constellations Bootes and Corona Borealis. The image was recorded on August 13 while the space station orbited above an area of China approximately 400 kilometers to the northwest of Beijing.
(Excerpt) Read more at 129.164.179.22 ...
[Credit: Ron Garan, ISS Expedition 28 Crew, NASA]
|
Nice shot .. What is that bright orange-ish spot on the earth’s surface?
It’s almost right below the fan like structure (aerial?) of the space station.
It’s city lights of some largely populated area. There’s another somewhat dimmer smudge of orange/yellow light to the right of the one you pointed out. It’s hard to tell but one or the other could be Japan or South Korea.
"South Korea is bright, North Korea is dark. This amazing image is included in the
standard US Department of Defense briefings on North Korea. It was mentioned
in a news briefing on 23 December 2002 by Defense Secretary Rumsfeld, who
stated that "If you look at a picture from the sky of the Korean Peninsula at night,
South Korea is filled with lights and energy and vitality and a booming economy;
North Korea is dark."
http://www.globalsecurity.org/military/world/dprk/dprk-dark.htm
I find the 60 km/sec number a little hard to credit. The escape velocity from the sun at the distance of the earth is 42.1 km/s, while the earth's orbital velocity is about 29.8 km/sec. Meteors and the earth do not collide “head on”, the meteors tend to orbit the sun in same direction as the earth. The motion of the meteor prior entering the atmosphere is almost perpendicular to the orbit of the earth and vector sum of their velocities would be about 50 km/sec, or a little less.
Viewing meteors from above the atmosphere does give confirmation to the experiments of a couple of 19th German amateur astronomers, who observed a meteor shower from points about 100 kilometers apart and correlated their observations to show that meteors occur about 100 miles above the surface of the earth. They did this by comparing the angular distance between the centers of the trails to well know stars and noting the changes between the two stations. (Tycho had famously demolished the long held belief that comets were atmospheric phenomena by demonstrating that they exhibited far less diurnal parallax than the moon, and were, therefore, much further away.)
Since zero scrapped the shuttle, how does Garan get back home?
From jpl.nasa:
Perseids
Meteor Velocity: 61 kilometers (38 miles) per second
http://www.jpl.nasa.gov/news/news.cfm?release=2010-119
“you’re more likely to see twice as many meteors per hour in the predawn hours as compared to the evening hours. This is due to the fact that during the pre-midnight hours we are on the “trailing” side of the Earth, due to our orbital motion through space.
So any meteoric particle generally must have an orbital velocity greater than that of the Earth to “catch” us. However, after midnight when we are turned onto the Earth’s “leading” side, any particle that lies along the Earth’s orbital path will enter our atmosphere as a meteor.
As such, objects collide with our atmosphere at speeds of 7 to 45 miles (11 to 72 kilometers) per second, their energy of motion rapidly dissipates in the form of heat, light, and ionization, creating short-lived streaks of light popularly referred to as “shooting stars.””
http://www.space.com/12478-minor-meteor-showers-summer-skywatching-tips.html
the text says that the meteoroid filmed was north and west of Beijing China, probably the orange spot.
Comet Swift–Tuttle (formally designated 109P/Swift–Tuttle)
It is the parent body of the Perseid meteor shower, perhaps the best known shower and among the most reliable in performance. [5]
An unusual aspect of its orbit is that it is presently captured into a 1:11 orbital resonance with Jupiter; it completes one orbit for every 11 of Jupiter.[6]
The ephemeris is available from NASA's Jet Propulsion Laboratory [1], although it is not listed in NASA Close Approach Tables [2] of Near Earth Objects
Potential threat to Earth:
"The comet is on an orbit which puts it close to the Earth and the Moon.[7] Upon its 1992 rediscovery, the comet's date of perihelion passage was off from the then-current prediction by 17 days. It was then noticed that, if its next perihelion passage (August 14, 2126) was also off by another 15 days, the comet would very likely strike the Earth or Moon. Given the size of the nucleus of Swift–Tuttle, this was of some concern. This prompted amateur astronomer and writer Gary W. Kronk to search for previous apparitions of this comet. He found the comet was most likely observed by the Chinese in 69 BC and AD 188, which was quickly confirmed by Brian G. Marsden.[8] This information and subsequent observations have led to recalculation of its orbit, which indicates the comet's orbit is very stable, and that there is absolutely no threat over the next two thousand years.[9] Astronomers believe that in the 2126 pass it will likely be a great naked-eye comet like Hale–Bopp.[3]
A close encounter with Earth is predicted for the comet's return to the inner solar system in the year 4479, around Sept. 15; the closest approach is estimated to be 0.03–0.05 AU, with a probability of impact of 1×10−6.[6] Subsequent to 4479, the orbital evolution of the comet is more difficult to predict; the probability of Earth impact per orbit is estimated as 2×10−8.[6] As the largest Solar System object that makes repeated close passes of Earth, and which does so at a relative velocity of 60 km/s,[4][10] leading to an estimated impact energy of ≈27 times that of the K–T impactor,[11] Comet Swift–Tuttle has been described as "the single most dangerous object known to humanity".[10]"
Thanks. You’re likely correct. From the pic I wasn’t sure which areas were land and which were clouds.
Thanks for input. I am a natural skeptic and I haven’t “done the math(s)”, though I’m perfectly capable of doing so. It just seems counter intuitive, especially if its in orbital resonance with Jupiter, it should be in a direct, rather than retrograde, orbit and the vector sum of the velocities should be smaller than if they were in quadrature, i.e., smaller than the sum of the squares.
I think what I am missing is the added energy obtained by falling from “infinity” to earth. There still doesn’t seem to be enough energy in the orbits, though.
"Based on their observations, and those of other astronomers who began tracking the comet's highly elongated orbit, it was calculated that Swift-Tuttle would make its next appearance during the 1980s. They were close. Japanese astronomer Tsuruhiko Kiuchi rediscovered the comet in 1992.
Aside from its unusual orbit, Swift-Tuttle is also significant as the host body of the Perseids meteor shower, one of the most prominent in the northern sky.
Oh, and there's one more thing.
Comets come and go, literally, but Swift-Tuttle's orbit is of particular interest to us earthlings since astronomers calculate that it is very likely to strike either the Earth or the moon on its next pass. They've even zeroed in on a date: Aug. 14, 2126."
http://www.wired.com/science/discoveries/news/2007/07/dayintech_0716
____________________________________________________________
109P/Swift-Tuttle:
http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=109p;orb=1;cov=0;log=0;cad=0#orb
I love it!
“...Since zero scrapped the shuttle, how does Garan get back home?...”
Aboard Soyuz TMA-21. Same way he got up there, but in reverse.
It works out if the meteor is deflected towards the earth such that the angle between it’s velocity vector and the earth’s orbital velocity vector is 24 degrees (or 156 degrees, depending on how you measure it), close to a head on collision. I was assuming that the meteor’s velocity vector is almost perpendicular to earth’s and was ignoring the added kinetic energy that the meteor gets from falling towards earth. The earth will deflect the meteor off its unperturbed orbit, so there is enough energy available to get up to 70 km/sec.
V = 42.1219*sqrt( 1/r - 1/(2*a)) km/sec
regardless of eccentricity.
r = distance from the sun in AU,
a = object's semimajor axis in AU
If you set a = 1.0 and r = 1.0, you get 29.8 km/sec, not surprisingly, earth's orbital velocity. If you set a = Inf and r = 1.0, you get 42.1219 km/sec, escape velocity from the sun at the distance of earth's orbit.
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.