CA 6.02 Light Speed & Observation

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SPEED OF LIGHT & OBSERVATION

Cosmic Adventure 6.02 A & B


Cosmic Adventure 6.02A

SPEED TO CARRY IMAGES


The Greatness of being Constant

Why is the finiteness and constancy of the speed of light so important to us?

Being of constant speed, the various colours will come to our eyes simultaneously so there will be no mixing-up.

The images will also come to us in the proper chronological order, one after the other. The earlier events will come earlier and the later one will come after, otherwise the universe will look totally different.


Image CarriersThese visual phenomena are possible and natural because our vision of this universe depends on the finiteness and constancy of the speed of light in carrying images to us.


Emission or Reflection of Light

Every object in this universe either emits or reflects light.

Reflection

Emission


Light & Vision

We can see an object because its light brings the images to our eyes. This means that light is the visual image carrier in our lives.


Vison in classical optics

The visual appearance of an object is determined by the light from all points on the objects that arrives simultaneously at where the eye is.


. . . Remembering that the images are not transmitted by a single photon, but by trillions of them. The more they are, the higher resolution we’ll get.

Images – The Work of Multitude


Vision Science

Vision is a human perception. It is a very complex science and no one has figured out the full picture.


Automatic Interpretation

But we only need to know the simple fact that our eyes are there to automatically interpret the light coming to our eyes and into the images in our minds. So we don’t have to know the detail of the optical science and only concentrate on the simpler process of how images come into our eyes.


Our eyes intercept the light and interpret them as the images in our mind. This is how we can see.


In all scales

The process is universal. It takes place big and small, whether of material bodies or environment, from a microbe to a galaxy.


Image Carriers In such a way, light is serving as the carrier of images, bringing us the enjoyment of vision.


TIME DELAY IN IMAGE DELIVERY

Cosmic Adventure 6.02B


Speed of Light too Fast

Light travels at a speed of about 300,000,000 meters per second.

This is an astronomical figure. There is nothing in our daily life that comes anywhere close to it.

For example, the speed of sound is only 343.2 meters per second; even supersonic speeds of 5 or six times greater than the speed of sound are only about 1,500 meters per second.

300,000,000 meters per second

1,500 meters per second.


26.8

70

100

770

13,000

66,641

671,000,000

0.1 1 10 100 1000 10000 100000 1000000

Light

Earth

Jet

Sound

Baseball

Cheetah

FastestRunner

Speed in miles per hourSpeed in km per hour

109,870,000

107,244

20,921

1,239

161

113

43

Comparison of Some Speed Samples


Light Takes Time to Travel

But no matter how fast light travel, light still needs time to cover a distant, no matter how small the distance is. For an object one meter away, light from it takes 3.3 nanoseconds (10-9 second) to reach our eyes; for an object one kilometer away, light from it takes 3.3 microseconds to reach our eyes. (A microsecond is a unit of time equal to one millionth or 10-6 of a second.)


Delayed Vision

This means that by the time light from an object reaches our eye, some length of time must have elapsed. This is the universal delay of image delivery.

𝑇𝑖𝑚𝑒 = ∆𝑡


In the astronomical scale, the difference is more appreciable. Take for example, the moon is 384,400 km away from the earth and the speed of light is 299,799 km per second. The time taken for its light to reach earth is:

384,400 𝑘𝑚

299,799 𝑘𝑚/𝑠𝑒𝑐𝑜𝑛𝑑= 1.28 𝑠𝑒𝑐𝑜𝑛𝑑

About 1.28 𝑠𝑒𝑐𝑜𝑛𝑑


The light from the sun, which is about 3 × 1011

metres away, will take light to travel about 8 minutes in space before reaching earth. This means that if the sun were suddenly to go dark, it would take over eight minutes before we notice the darkening.

About 8 minutes


Another example: The galaxy of Andromeda is 2,538,000 light years away from the earth. A light year is the time taken for light to travel in one year – covering about 9 trillion kilometers (about 6 trillion miles). This 2,538,000 light years is the time needed for its light to reach earth.

2,538,000 𝐿𝑖𝑔ℎ𝑡 𝑦𝑒𝑎𝑟𝑠


Remember how Römer discovered the speed of light due to the delay in time obvious in astronomical observation?

Ole Römer Discovered the speed of Light

Jupiter

Io

Earth moving towards Jupiter

Io hides behind Jupiter and becomes invisible

Earth moving away from Jupiter


Distance Distance Speed of light in vacuum (c): 3 × 108 m/s

10-9 s 10-1+ m Objects a foot away are seen as they were a nanosecond in the past.

10-8 s 100+ m Light speed delay across a human is about 5 nanosec.

10-7 s - 10-2 s 101+ m - 106+ m

10-1 s 107+ m Circle the earth in 1/10 s. | Geosync communication satellites.

100 s 108+ m 1.25 sec from moon.

101 s to 102 s 109+ m to 1010+ m

103 s 1011+ m 8 minutes from sun.

104 s to 107 s 1012+ m to 1015+ m

108 s to 1011 s 1016+ m 9 years (0.3 Gigasecond) from Sirius (108×2.7 s)

109 s 1017+ m to 1019+ m

1012 s 1020+ m 100 kyr (3 Terasecond) across galactic disk (1012×3 s)

1013 s to 1017 s 1021+ m to 1025+ m

1018 s 1026+ m 1/2 Exasecond (~15 Gyr) from edge of visible universe (1018×~1/2)

1027 m Current distance to edge (of Universe)

Light-speed delay. Ref: Mitchell N Charity <[email protected]>


Findings from Australian Space Academy

“Distance communications are carried by electromagnetic radiation - commonly by radio waves, but increasingly by light. The speed of propagation of these carriers is about 300,000 kilometres per second - the speed of light (and all other electromagnetic radiation).

While this is an incredibly high speed, it already causes problems in some of our day to day communication, and as we begin to contemplate interplanetary travel, we find that the finite or limited speed of light imposes serious limitations on our activities.”

www.spaceacademy.net.au


Telephone Delay

The delay caused by the speed of light can even be noticed here on Earth in long distance telephone calls. These called may have been routed over one or more space satellites. So delay between the speaker and the listener may be as long as over half a second.


Circuit Distance Delay Time

HF link (UK-NZ) ~20,000 km 0.07 s (67 ms)

Submarine cable(UK-NZ) ~20,000 km 0.07 s (67 ms)

Geosat Link (US-Aus) ~80,000 km 0.25 s

Earth-Moon 384,000 km 1.3 s

Earth-Mars 55 - 378 million km 3 - 21 minutes

Earth-Jupiter 590 - 970 million km 33 - 53 minutes

Earth-Pluto ~5800 million km 5 hours

Earth-Nearest Star ~9.5 million million km 4 years

Communication Delaywww.spaceacademy.net.au/spacelink/commdly.htm


Time & Distance Gap

What we see are only images delivered to our eyes by light

coming from a source some time ago. In general, there is always a

time delay in messages which need light as a carrier, no matter

how short the distance is between the observer and the

observed.

Observer Observed


𝒄

So distant objects are all old ones at various times in the past.


TIME DELAY IN CLASSICAL PHYSICS & THE THEORY OF SPECIAL RELATIVITY

To be continued on Cosmic Adventure 6.03

CA 6.02 Light Speed & Observation

Science

Transcript of CA 6.02 Light Speed & Observation