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

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

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.

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 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

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 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).

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.

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?

Bigger Light Bucket

Light Gathering PowerTelescope diameter (D)Light Gathering Power (LGP) is proportional to area.

LGP = (D/2)2 D = diameter

Light Gathering Power

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

Size Does Matter

Same magnification,different telescopeprimary apertures.

Which telescopeis bigger?

Resolution

Telescope diameter = D (cm)

Resolution = (arcminutes)

= 11.6/D

Larger D = smaller angular sizes resolved

Resolving Power

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 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.

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.

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?!

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

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.

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 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

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.

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.

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.