Download Intro

Observational Astronomy Laboratory
PHSC 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 Site
http://cosmos.atu.edu/observatory
Astronomical Resources
• Magazines
– Sky & Telescope
http://www.skypub.com
– Astronomy
http://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
Excerpt from SkyWatchers Diary
Tuesday, 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. Onethird of the way from Arcturus toward Vega look for a semi-circular
pattern of faint stars, reminiscent of a laurel wreath crown.
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
Celestial Navigation
• Constellation Atlas
http://www.slivoski.com/astronomy/
• Creating Star Charts 101
http://skyview.gsfc.nasa.gov/skyview.html
• The Star Finder
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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
Celestron C8’s
• Celestron 101 http://www.celestron.com/tb-2ref.htm
• Celestron 8 inch reflectors
– C8 Schmidt-Cassegrain
Meade LX 200 12-inch
• Meade 12 inch reflector
– LX200 Schmidt-Cassegrain
James Clarke Telescope
• Custom Telescope
– 16 inch newtonian or cassegrain reflector
Optica Reflectors
• Optica Telescopes
– 6 inch newtonian reflectors
Newtonian 8-inch
• Custom Telescope
– 8 inch newtonian reflector
Refracting and Reflecting Telescopes
Refractor Focal Length
Chromatic Aberration
Reflector Focal Length
Telescope Configurations
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 X
bigger 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 configuration
has a focal length of 64 inches (16 x 4).
Magnification
Magnification depends on the ratio of the focal lengths
for 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 telescope
with the longest focal length can achieve the greater
magnification.
Magnification Isn’t Everything
Magnifying something spreads the light out into a larger
and 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 by
changing eyepieces.
What do you want in a telescope?
Bigger Light Bucket
Light Gathering Power
Light Gathering Power
Telescope diameter (D)
Light Gathering Power (LGP) is proportional to area.
LGP = p (D/2)2
D = diameter
Light Gathering Power
Light Gathering Power
Telescope diameter (D)
Light Gathering Power (LGP) is proportional to area.
LGP = p (D/2)2
D = diameter
A 16 inch telescope has 4 X the LGP of an 8 inch.
LGP 16 inch = p (16/2)2
LGP 8 inch = p (8/2)2
LGP16/LGP8 = 4
A 16 inch telescope has 2800 X the LGP of the eye.
LGP 16 inch/LGP eye (0.3inch) = (16/0.3)2 = 2844
Size Does Matter
Same magnification,
different telescope
primary apertures.
Which telescope
is bigger?
Resolution
Resolving Power
Telescope diameter = D (cm)
Resolution = a (arcminutes)
a = 11.6/D
Larger D = smaller angular sizes resolved
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.
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.
Sensitivity Curve
For 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.
Photopigments
Our 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.
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?!
Microspectrophotometry
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.
RGB and Grey Photopigments
The 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.
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!
Advanced Red Flashlight Project
Red LED Flashlight Project
RadioShack 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
Averted Vision
Rods 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.
Blind Spot
Note 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.
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.
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.