telescopes, observatories, data...

Intro to Galaxies Telescopes 1

Telescopes, Observatories,

Data Collection


Astronomy : observational science

only input is the light received

• different telescopes, different wavelengths

of light

• lab experiments with spectroscopy,

properties of matter and radiation

• space probes to measure conditions in

our own solar neighborhood

• use technology to ‘tweak’ the models,

simulations, graphics


VISIBLE ASTRONOMY (Optical)

visible wavelengths - 4000 A - 7000 A

detectable with human eye

optics : science of controlling the direction

of light

Light travels in space in a straight line,

a light ray - particles of light (photons) moving

in a straight line.

Change the direction using lenses, mirrors,

prisms.


Refraction

Light crosses one boundary to another,

it changes direction - it is bent.

The amount that light is bent is dependent

on what color it is, i.e., what wavelength.

Blue is bent more than red - the shorter

the wavelength, the more it is bent.


Reflection

Light bounces off a surface and rebounds

at the same angle it had when coming in.

Reflection does NOT depend on the

wavelength of the light.

Science of optics uses refraction and

reflection to make images.


image : gather light rays into the same

alignment they had when they

left the object

visual representation of the object

lens : smoothly curved surface, rays

are bent, and converge to a point

a lens brings light rays to a focus


extended object : something more than

a point source of light

a lens brings rays from an

extended object to a focus where

an image is formed - usually

upside-down and smaller

focal length : distance from lens to image


Hubble Space Telescope - Deep Field


mirror : a polished surface that reflects

light - if flat, image is not distorted;

if curved, image is distorted

smoothly curved mirror will bring

all light to a focus

f-ratio : important property that describes

a lens or mirror

f-ratio = focal length

diameter


Large diameter => small f-ratio

=> brighter the image

telescope : instrument to gather light &

allow you to examine an image

objective : lens or mirror that brings light

to a focus

eyepiece : allows you to examine the image


Refracting Telescope

objective is a lens (Galileo’s telescope)

problem: not all the colors in the light

come to focus at the same point

- chromatic aberration


Reflecting Telescope

objective is a mirror (Newton’s telescope)

light does not separate into colors, so no

problem with color haloes

cheaper to make

can be made much larger

have to figure out how to look at the image


Reflecting Telescopes

Newtonian - small mirror, tilted at 45 deg.

to the path of the light

Cassegrain - hole in the objective

secondary mirror in the light path

“fold” the path of light

cheaper to build


Functions of a Telescope

• Gather Light

“light bucket” - collect

photons, bring them to focus

objects seen in a telescope are brighter

than they appear to the naked eye


LGP (Light Gathering Power)

LGP is proportional to (diameter)2

amount of light depends on the area of

the objective

a mirror with 2 times the diameter will

have times the LGP 4


Some Comparisons

• human eye : diameter = 0.5 cm

telescope : diameter = 50 cm

How do the LGP’s compare ?

The telescope is 50/.05 = 100 times bigger

in diameter.

The telescope is (100)2 (=10,000) times

better for gathering light.


• Hale Telescope - 5 m (Mt. Palomar)

Mayall Telescope - 4 m (Kitt Peak)

How do the LGP’s compare ?

Hale is 5/4 times bigger than the Mayall

in diameter.

LGP is (1.25)2 = 1.563 times better in

gathering light.


• Resolve fine detail

resolution : ability to separate things

that appear close together

into separate images

resolution is measured in angular measure

example: 10 cm diameter telescope has a

resolution of 1.4 arc sec


If the separation is more than

1.4 arcsec, you’ll see them as

separate stars with this telescope.

If the separation is less than

1.4 arcsec, you’ll see them as

a big blob with this telescope.


Resolution is inversely proportional

to diameter

Resolution 1

diameter

Smaller resolution is better for learning

about details.

2 X the diameter means resolution

is twice as small (i.e. 2 times

better)


Human eye has a resolution of 1 arcmin.

Things that affect resolution :

seeing : turbulence in the atmosphere

distorts and blurs the image

measured in arcsec

Solution : put telescopes in space !

Resolution would be limited by the optics

of the telescope NOT by the Earth’s

atmosphere.


• Magnify the Image (least important) magnification : apparent increase in an

object’s size compared to

naked eye observation

MP = focal length of the objective

focal length of the eyepiece


What’s next?

very light materials

remote observing

very large mirrors in segments

adaptive optics

telescopes in space

telescopes on the moon?


Invisible Astronomy

wavelengths not seen by the human eye

wavelengths that are generated by very

different physical processes

allow us to discover astronomical objects

we wouldn’t ordinarily have seen


Milky Way in Radio

Vesta

VLA

Arecibo

Gamma Ray Moon

http://antwrp.gsfc.nasa.gov/apod/ap971214.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap971214.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970908.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970908.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970727.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970727.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970412.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970412.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970210.htmlhttp://antwrp.gsfc.nasa.gov/apod/ap970210.html


Earth’s Atmosphere

Radiation that has traveled for billions of

years to get here is blocked in the last 100 km

of the journey by our atmosphere !

IR - blocked by water vapor

UV and X-ray blocked by the ionosphere,

above 100 km


• ground-based (radio, IR)

• space-based - rockets, balloons,

airplanes, satellites, spacecraft

RADIO ASTRONOMY

Parabolic dish, focuses the EM rays (in

radio wavelengths) to a focal point


Radio Telescopes

detector (receiver) is placed at the focal

point, translates the radio signal to a voltage

which is then measured and recorded

computer then generates a map of these

intensities

can observe day or night, even on cloudy

days for the longer wavelengths


larger than optical telescopes (100 m!!!)

drawback is poor resolution

resolution also depends on wavelength

being observed

long wavelengths, poor resolution

SOLUTION : interferometers to create

effectively larger diameter telescopes


Two (or more) telescopes act like

parts of one big telescope.

Interferometer


VLA - Very Large Array, Socorro, NM


VLBA - Very Long Baseline Array

radio dishes from Hawaii to the

Virgin Islands

resolution of 2 x 10-4 arcsec

adding radio telescopes on the moon would

give a resolution of 10-6 arcsec

http://www.aoc.nrao.edu/vlba/html/thesites.html


IR Astronomy

• some wavelengths from the ground

• need high, dry climate

• optics are much the same as for optical

astronomy

• detectors must be different, cooled to 2 K

advantages:

less hindered by interstellar dust

cool objects can be detected

things not seen in visible can be detected


Space-Based IR

balloons, satellites

IRAS - international collaboration

mapped the sky - 200,000 IR sources

many related to the process of

starbirth

UV, X-Ray, Gamma Ray - done from space


IR Astronomy

• some wavelengths from the ground

• need high, dry climate

• optics are much the same as for optical

astronomy

• detectors must be different, cooled to 2 K

advantages:

less hindered by interstellar dust

cool objects can be detected

things not seen in visible can be detected


Space-Based IR

balloons, satellites

IRAS - international collaboration

mapped the sky - 200,000 IR sources

many related to the process of

starbirth

UV, X-Ray, Gamma Ray - done from space


Hubble Space Telescope (HST)

2.4 meter mirror

goal : faint objects with high resolution,

0.1 arcsec resolution

1200 A to 10,000 A

most expensive astronomical project to

date


Hubble

Space

Telescope


Image Collection

• images taken by detectors

photographic plates

CCD’s (charge coupled devices)

• computer visualizations, false-colors

• intensity maps


CCD = Charge Coupled Device

Each cell is

called a pixel. A

pixel captures

photons and

counts them

individually.

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