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2163 - How far can our eyes see? -
With the newest backyard telescope it is possible for amateur
astronomers to see 2,000,000,000 years back in time and 11,760,000,000,000,000
miles distance. The human eye is an
amazing instrument and working together with modern telescopes our brains
perceive far back in time and far, far away.
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------------------ 2163
- How far can our eyes see?
-
- How far can
your eyes see? You may be
surprised. How far back in time can your
eyes see? With a 10-meter telescope you
can see quasars and galaxies that are 12 billion lightyears from Earth. These views are also 12 billion lightyears
back in time. What you see happened then
and that is what it looked like 12 billion years ago. These galaxies look totally different if you
could see them as they are today.
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- What you would
see is similar to what the Milky Way Galaxy probably looked like when it first
formed about 12 billion years ago. The
Earth in our Solar System first formed about 6 billion years ago.
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- In distance measured in miles 12 billion light
years is:
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70,560,000,000,000,000,000,000,000 miles (70.56*10^21 miles)
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- But, what may
surprise you is that you don't need to go to the Mauna Kea Telescope in
Hawaii. From your own backyard you can
see 17% of that distance.
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- Even with the
naked eye you can see a fuzzy ball in the night sky that is the Constellation
Andromeda. In the north east just above
the horizon. Use the corner of your eye,
that part of the back of the eye is more sensitive to dim light. The Andromeda Galaxy is 2,500,000 light years
away. (14.7 * 10^18 miles).
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- When we see
the Andromeda Galaxy we are seeing what it looked like when the Earth was
populated with only bacteria, Achaeans, algae, jellyfish, and worms. (the Proterozoic Eon). The Earth will become a snowball 200 million
years later after that era. The first
animal life will not appear on the Earth for another one billion years later.
-
- So, the
Hawaii telescope will let you see 4,800 times further. In effect the telescope is giving your eye a magnification
of 4,800 to one.
-
- Andromeda looks like a little cloud and is at
first disappointing to many astronomy buffs.
The Hubble Space Telescope will restore your wonder of this beautiful galaxy. Check the pictures out on the internet.
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- All the rest
of the stars you see with the naked eye are in the Milky Way galaxy. The Milky Way is 100,000 lightyears across.
We are located 30,000 lightyears out
from the center. So the stars we see are
no further than 70,000 lightyears away,
still that is 41.2 * 10^16 miles away.
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- The ancients
recorded 6,000 stars in the night sky and that was in 150 B.C. Their nights were darker and clearer than the
ones we live in today. Air pollution and
light pollution have decreased our seeing ability to about 3,000 stars in a
typical night sky. (See Review 535
"Hipparchus - sky maps in 150 B.C.)
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- The human eye
sees using four main properties of light.
Light photons are refracted, reflected, diffracted, and absorbed. Light enters the eye in parallel beams from
the distance of stars. Because the eye
has a limited aperture it is only able to collect a very small portion of the
rays coming from any one astronomical object.
The eye's collection area is about 38 square millimeters, when fully
dilated and darkness adapted. This means
you can see stars with a light intensity of magnitude 6. (See Review 535 for a full discussion of
light magnitude scales).
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- The eye is
limited by diffraction, light waves are bent when passing near an object's
gravity or through a hole. It is a form
of refraction where light is bent when passing through different mediums. Diffraction in the iris creates a diffusion
that allows photons to come only so close together. These characteristics of light limit our ability
to see in any greater detail. Things
tend to get fuzzy.
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- The eye uses
refraction to bend photons entering the cornea and the lens behind it. The cornea does 67% of the focusing of light
and the eye lens does the remaining 33%.
The lens can change its curvature to focus an image on the retina where
the tiny neurons convert light energy into nerve signals the brain can
interpret. It is the occipital lobes at
the back of the head that do the image processing. The brain gives coherence to the steady
stream of signals arriving from the eye's retina.
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- To detect the
light the retina uses absorption.
Photons landing on the neurons of the retina depolarize. Depolarization moves chemo-electrical signals
from axons to dendrites in the
brain. The retinal neurons are
made up of rods and cones. There are
about 220,000,000 of them in the back of your eyes.
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- The rods
detect light of any color and are more sensitive than the cones. The cones detect specific colors and are only
found along the main axis of the eye.
The rods on the other hand are mainly off - axis. This is the reason the averted eye can see stars
2.5 times fainter than if you are looking directly at the star.
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- To get from
the retina to the brain neural signals pass through the superior collicus. The collicus can detect even fainter sources
of light, but, only if it is in apparent motion. This is what causes a flinch response. You can actually flinch before the brain sees
what you are flinching about.
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- You can avoid the strike of the rattlesnake
before your brain realizes the snake is even there. To use this capability in night vision sweep
your eye across the night sky and you can see stars 4 times fainter than
straight on viewing.
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- The eyes
naturally adapt to night vision in about 30 minutes. First, the fine muscles retract the iris
located between the cornea and the eye lens to admit as much light as your eye
can allow. Second, the visual purple (rhodopsin) on the retina rods takes on a rosy red
color. This change increases the
sensitivity of the rods to the point where a single photon of visible light can
be detected. A single photon, amazing!
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- The neurons
in the eye can reside only so close together so the eye can only have a 1 x
magnification at 25 millimeters focal length.
Since the eye can only open to 7 millimeters, it becomes an effective
equivalent pair of binoculars of 1 x 7 millimeters.
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- With the eye's
1 x 7 millimeter binoculars you are limited to 8th magnitude star brightness. This is viewing under the best
conditions. The 8th magnitude brightness
is 1,500 times fainter than the brightest star Vega in the southern sky. Your eye is able to resolve binary pairs of
stars to about 2 arc minutes of angular separation. This is 1/15 the apparent size of the Moon
which is 30 arc minutes, or 1/2 a degree of arc.
-
- CCD, charge
coupled devices, offer telescopes a enormous advantage. CCD's can accumulate photons over a long
period of time, something the eye cannot do.
CCD's can look at the same image over a very long period of time,
months, and simply add up all the photons over that period of time. As long as nothing moves side to side
relatively, a clear image will
materialize. This is how the Hubble Deep
Field telescope gets its far away images.
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- Of course
telescopes can also have much larger apertures to capture light and they are
not limited to only collecting visible light.
They can collect images in the ultraviolet and in the infrared. In fact telescope detectors can see the
entire electromagnetic spectrum from radio waves to microwaves to gamma rays.
-
- With the
newest backyard telescope it is possible for amateur astronomers to see
2,000,000,000 years back in time and 11,760,000,000,000,000 miles
distance.
-
- The human eye
is an amazing instrument and working together with modern telescopes our brains
perceive far back in time and far, far away.
-
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- One light
year is 5.88 * 10^12 miles
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- 3C273 quasar
is 2 billion lightyears away. It has a
variable visual magnitude of 12.8 magnitude.
It can be seen with a 6 inch, 150 millimeter aperture telescope at 150
power. The night sky needs to be clear
enough for naked eye visibility to 5.5 magnitude.
-
- November 12, 2018. 536
from January 4, 2005 An
Index of recent Reviews is available.
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----- Comments appreciated and Pass it on to
whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for
copies or Index of all reviews
--- to:
------
jamesdetrick@comcast.net
------ “Jim Detrick” -----------
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--------------------- Monday, November 12, 2018 -------------------------
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