Observational Astronomy Laboratory PHSC 1051/3051
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Transcript of Observational Astronomy Laboratory PHSC 1051/3051
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Observational Astronomy LaboratoryPHSC 1051/3051
• #4 McEver Hall (across from the BIG fish tank)
• Course Information and Lecture Notes can be found at http://cosmos.atu.edu/bigjay
– Then Go To ATU Courses (PHSC1051/3051)
http://pls.atu.edu/physci/physics/people/psjr/courses/
• Find and Browse the ATU Observatory Web Sitehttp://cosmos.atu.edu/observatory
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Astronomical Resources• Magazines
– Sky & Telescopehttp://www.skypub.com
– Astronomyhttp://www.kalmbach.com/astro/astronomy.com
• Observing Books– Norton’s Sky Atlas ISBN 0-582-31283-3
– Burnham’s Celestial Handbook ISBN 0-486-24064-9
– 365 Starry Nights ISBN 0-13-920570-5
• Sky Calendars and Events– Star Date http://stardate.utexas.edu
– Abram’s Planetarium http://www.pa.msu.edu/abrams/– http://www.skypub.com/sights/skyevents/skyevents.shtml
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Excerpt from SkyWatchers DiaryTuesday, August 29
A small, faint constellation in this evening's sky is Corona Borealis, the
Northern Crown. One and a half hours after sunset find two bright stars:
Arcturus, a third of the way up in the west, and Vega, overhead. One-
third of the way from Arcturus toward Vega look for a semi-circular
pattern of faint stars, reminiscent of a laurel wreath crown.
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Star Atlases• Norton’s 2000 Star Atlas and Reference Handbook
• Uranometria Vol. 1, 2 & Deep Sky
• Sky Atlas 2000 http://www.skypub.com/store/sa2000polakis.html
http://www.icstars.com/HTML/AmazonBooks/books_staratlas.html
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Celestial Navigation• Constellation Atlashttp://www.slivoski.com/astronomy/
• Creating Star Charts 101http://skyview.gsfc.nasa.gov/skyview.html
• The Star Finder– match current time with the date
– face south
– place south on the map at your belly
– look down at the map
– now swing the map overhead
– look up at the map
– the map is the sky in 360o
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Celestron C8’s• Celestron 101 http://www.celestron.com/tb-2ref.htm
• Celestron 8 inch reflectors– C8 Schmidt-Cassegrain
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James Clarke Telescope• Custom Telescope
– 16 inch newtonian or cassegrain reflector
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Optica Reflectors• Optica Telescopes
– 6 inch newtonian reflectors
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Newtonian 8-inch• Custom Telescope
– 8 inch newtonian reflector
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Refracting and Reflecting Telescopes
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Refractor Focal Length
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Chromatic Aberration
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Reflector Focal Length
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Telescope Configurations
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f-number (f/#)The f/# refers to the ratio of the focal length to the diameter.
An f/10 optical system would have a focal length 10 Xbigger than its diameter.
The f/10 celestron C8 has a focal length of 80 inches.(8 inch aperture times 10)
Our 16 inch telescope in the newtonian f/4 configurationhas a focal length of 64 inches (16 x 4).
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MagnificationMagnification depends on the ratio of the focal lengthsfor the primary aperture to the eyepiece.
M = focal length of objective / focal length of eyepiece = fo/fe
Therefore for the same eyepiece, in general, the telescopewith the longest focal length can achieve the greater magnification.
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Magnification Isn’t EverythingMagnifying something spreads the light out into a largerand larger area. An object is only so bright and magnifying an image too much causes it to become so diffuse that it ceases to be visible.
Magnifying power for a telescope is not what you are looking for. Besides, increased magnification can be achieved bychanging eyepieces.
What do you want in a telescope?
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Bigger Light Bucket
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Light Gathering PowerTelescope diameter (D)Light Gathering Power (LGP) is proportional to area.
LGP = (D/2)2 D = diameter
Light Gathering Power
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Light Gathering PowerTelescope diameter (D)Light Gathering Power (LGP) is proportional to area.
LGP = (D/2)2 D = diameter
A 16 inch telescope has 4 X the LGP of an 8 inch.
LGP 16 inch = (16/2)2 LGP16/LGP8 = 4LGP 8 inch = (8/2)2
A 16 inch telescope has 2800 X the LGP of the eye.LGP 16 inch/LGP eye (0.3inch) = (16/0.3)2 = 2844
Light Gathering Power
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Size Does Matter
Same magnification,different telescopeprimary apertures.
Which telescopeis bigger?
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Resolution
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Telescope diameter = D (cm)
Resolution = (arcminutes)
= 11.6/D
Larger D = smaller angular sizes resolved
Resolving Power
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Clock Drive
Last but NOT least.
You and telescopes
are on the moving
observatory we call
earth.
A clock drive is
required to counter
earth’s rotation and
provide tracking
for telescopes and
cameras.
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Night Vision
It takes nearly 15 minutes for your eyes to make adjustments
to see in low light levels. WHY?
First, your pupil dilates. This allows more light to be collected
by your eye. When it is really dark out, your pupil opens up
and lets you see things that were too faint to see when you first
walked outside.
Even more important to night vision is a
chemical called rhodopsin. You've probably heard that human
eyes have rods and cones. The cones help you see color,
and the rods help you see when it gets dark.
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Sensitivity CurveFor approximately the
first 10 minutes in the
dark, the cones require
less light to reach a
threshold response than
do the rods. Thereafter,
the rods require less light.
The point at which the
rods become more
sensitive is called the
rod-cone break.
It is after this break where you can start to really see detail
well in the dark.
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PhotopigmentsOur visual system is most sensitive when the photopigments have not
absorbed any light for about 30 minutes. Under these conditions we say
that the photopigments are fully regenerated. When the rod
photopigments are exposed to light they undergo a process called
bleaching. It is called bleaching because the photopigment color actually
becomes almost transparent. In the dark they regenerate and regain
their pigmentation again.
In the rod receptors the unbleached photopigments appears purple. The
technical name for the rod photopigment is rhodopsin.
The photopigments in the cones also bleach when exposed to light.
There are three classes of cone photopigments (RGB).
Each class is photochemically a little different than the other and
therefore their spectral absorbencies are different.
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Bleaching (After Image) Demo
Concentrate on the black checkerboard for at least
20 seconds. Your pigments become bleached.
Afterwards you will see an inverse image
in the box at the right. And just what are those
illusionary gray dots at the white cross intersections?!
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Bowmaker & Dartnall (1980) projected a known amount of light directly
through the outer segments of photoreceptors and measured how much
light was absorbed by the photopigment molecules at each wavelength.
Microspectrophotometry
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RGB and Grey PhotopigmentsThe wavelength of maximum absorbance is indicated at the top of each
curve. The 420 nm curve is for the short wavelength cones,
the 498 nm curve is for the rods, and the 534 nm and 564 nm curves are
for the middle and long wavelength sensitive cones respectively.
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Night Vision
The rhodopsin is in the rods. It takes 15 minutes or more for
the rhodopsin to get back to a good level after you look at
white light. But, because this chemical is not as sensitive to
dim light, the good astronomer carries a dimmed or reddened
flashlight instead of a bright one. This allows them to look at
their star chart and find the next object. When they look back
up at the stars, their night vision is still good.
The smart astronomer doesn't have to wait after looking at the
chart. Why?
Because smart astronomers use dim red flashlights!
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Advanced Red Flashlight Project
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Red LED Flashlight ProjectRadioShack and ~ $7.00
• one project case
• bright LED and holder (LED1) another LED and holder (LED2)
• a 22 ohm resistor (R1)
• a 47 ohm resistor (R2)
• one AAA battery holder
• two AAA batteries
• two switches
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Averted VisionRods are actually densest outside the central 1-degree foveolar area.
Since the rods have a lower threshold than the cones,
they are much more sensitive at low light levels.
A person attempting to see in light dimmer than moonlight,
has to depend entirely on their rods.
To best detect small targets with the rods under such circumstances,
the individual must look approximately 15-20 degrees to one side,
above, or below an object to place the object of interest on the part of the
retina that possesses the highest density of rods.
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Blind SpotNote the almost
complete absence
of rods on the
fovea.
The fovea is that
position on the
retina where the
best focus of
the eye is located.
This and the optic
nerve bundle give humans
a day and night blind spot.
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Blind Spot Demo I
Close your right eye.
With your left eye look at the on the right.
At the correct distance the will disappear.
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Blind Spot Demo II
Close your right eye.
With your left eye look at the red dot
At the correct distance the gap in the
blue lines will disappear.