Download JWST_eye - University of Arizona

OBSERVING LIST
60” (naked eye) & 12” (CCD) telescopes
Naked eye and small telescopes:
Mars, Jupiter, Saturn
Star clusters: h&chi Per, M45 (Pleiades), M44 (Praesepe)
FIRST OBJECTS
Rigel
Orion Nebula (M42)
Betelgeuse
Mars
Saturn
Jupiter
5.2h
5.5h
6h
6.3h
8.5
-8 deg
-5 deg
15h
408 lyr
15 lmin
1.3 lhr
-15 deg
37 lmin
Planetaries:
Eskimo nebula (NGC 2392)
Ghost of Jupiter (NGC 3242)
Owl nebula (NGC 3587)
7.5h
10.5h
11h
20 deg
-18 deg
55 deg
2.9 Klyr
2.9 Kly
Star formation:
M42 (Orion nebula)
5.5h
-5.5 deg
1.6 Klyr
9.5h
9.5h
11h
12.5h
13.5h
14h
12.7h
50 deg
21 deg
13 deg
25 deg
47 deg
54 deg
-11.6 deg
(Castor)
7.5h
13.3
32 deg
55 deg
52 lyr
78 lyr
(globular)
(globular)
(globular)
13.5h
13.7h
15h
-47 deg
28 deg
2 deg
30.6 Klyr
22.8 Klyr
Galaxies:
NGC 2841
(classic spiral)
M54
M65 (Blackeye)
NGC 4565
(edge-on!)
M51 (Whirpool)
M101 (Pinwheel)
M104 (Sombrero)
M63
Binary stars:
Alpha Gem
Mizar
Star clusters:
Omega Cen
M3
M5
Planets:
Mars
Saturn
Jupiter
7 deg
25 deg
20 deg
815 lyr
1.6 Klyr
6.3h
8.5
25 deg
20 deg
15h
83 Klyr
12 Mlyr
37 Mlyr
24 Mlyr
50 Mlyr
15 lmin
1.3 lhr
-15 deg
37 lmin
12” telescope with CCD:
M81, M82, M101
NGC 4038 (Antennae)
12h
-18deg
Relating to the James Webb Space Telescope
measure the performance of your eyes
Our eyes are like telescopes. Both have an opening to collect light and an optical element (lens or
mirror) to focus that light into an image.
Our eyes are also like the instruments attached to telescopes. Both have light sensors at the focus
to respond to the image and both produce data that the brain interprets.
--------------------I. “Light Gathering Power”
In daylight the opening in the human eye is about 1-2 millimeters across. At night the eye becomes “dark
adapted” and the opening enlarges to about 6 millimeters to collect more light. The opening of JWST is 6
meters across, about 1000 times larger, so it lets in more light than the naked eye. Since the eye and
JWST have circular openings, they collect light over the area of those openings, not just the width. For
this reason, JWST is one-million times (1000x1000) more light sensitive.
How sensitive is your eye? Use the attached star chart of the Orion constellation to measure the “limiting
magnitude” of your eye while you get dark adapted to the night sky. Fill in the blanks below to
characterize your eye.
My eye can see to a “limiting magnitude” of ___________.
It takes my eye about ________ minutes for my eye to get fully dark adapted.
II. “Exposure Time”
More light can also be collected during a long exposure. The human eye takes about 10 pictures every
second, one picture every 0.1 second. Instruments on JWST, like NIRCam, can take much longer time
exposures to collect even more light and record much fainter objects.
How much more light would be collected if your eye could take a one hour exposure instead of its normal
0.1 second?
____ (minutes per hour) times ____ (seconds per minute) times 10 (eye exposures per second) =
_________
So, JWST collects more light than the human eye for two reasons: larger area and longer time exposures.
Together these effects mean allow JWST to see __________________ times fainter than the human eye.
III. “Field-of-View”
The human eye is designed to see a wide angle all at once. It has a large “field-of-view” of about 180
degrees. In contrast, JWST is designed to study small regions in great detail so it has a small field-ofview, about 1/60th of a degree (one arc-minute).
The Orion constellation is about 20 degrees across between the stars Betelgeuse and Rigel. Go outdoors
to view Orion and try to estimate the angle between the three stars in Orion's belt. The angle between
Mintaka and Alnilam appears to be about __________. The angle between Alnitak and Alnilam appears
to be about __________.
IV. “Resolution”
The diameter of a telescope determines its ability to “resolve” small details in an object of interest. JWST is 1000
times wider than the human eye so JWST makes images about 1000 times sharper than the human eye.
You can compare the resolution of your eye to that of a telescope by examining the stars in the Pleiades star cluster.
The Pleiades cluster is about 2 degrees across. My eye can see stars in the Pleiades separated by about this angle
________ degrees.
The binoculars will also collect more light than your eye and reveal stars that are invisible to the eye.
How many Pleiades stars can you count using your eye alone?: ____________
How many Pleiades stars can you count using binoculars?: ____________
V. “Spectral Response”
The human eye has a “retina” to sense the presence of light. The retina has “rods” to sense the amount of
“visible” light and “cones” to sense particular color (blue, green, red).
If you have excellent color vision and light sensitivity, you may be able to see that the stars Betelgeuse
and Rigel in Orion have much different colors.
The color of Betelgeuse is ________. The color of Rigel is ________. The color of stars in the Pleiades
is ______.
JWST is designed to sense “infrared” colors of light about 3-30 times redder than the limit of the human
eye. Infrared light penetrates into the gas and dust of the Orion Nebula to reveal newly formed stars
emerging from their cocoons. If your eye could see radio wavelengths of light, the glowing gas clouds of
star formation in the Orion Nebula would appear more than 10 degrees across!!
VI. “Look Back Time”
Compared to our naked eyes, modern telescopes collect more light and reveal fainter objects. Celestial
objects are often fainter because they are farther away, so it takes their light some time to make the
journey to us. Thus, the light that reaches us is old, and we see objects as they appeared in the past.
JWST's near-infrared camera (NIRCam) is designed to see the first objects that began to shine in the
early Universe, some 13 billion years ago. How far back in time has your eye seen during various parts of
this Astronomy Camp?
A. What is the most distant object you have seen with your naked eye during the daytime?
__________________
What is its distance?:
__________________
B. What is the most distant object you have seen with your naked eye during twilight?
__________________
What is its distance?:
__________________
C. What is the most distant object you have seen with your naked eye at night?
What is its distance?:
__________________
__________________
D. What is the most distant object you have seen with your eye through the 60” telescope?
__________________
What is its distance?:
__________________
E. What is the most distant object you have seen with a CCD camera and the 12” telescope?
__________________
What is its distance?:
__________________
Limiting magnitude = 4th magnitude.
Limiting magnitude = 5th magnitude.
Limiting magnitude = 6th magnitude