Документ взят из кэша поисковой машины. Адрес оригинального документа : http://star.arm.ac.uk/~meb/ras_leaflets2012/Infrared.2012.pdf Дата изменения: Tue Mar 6 03:05:44 2012 Дата индексирования: Tue Oct 2 06:46:15 2012 Кодировка: Поисковые слова: california nebula

What is
wavelength (in metres) size of a wavelength common name of wave
longer

Infrared?
102 101 1 10­1 10­2 10­3 10­4 10­5 10­6 10­7 10­8 10­9 10­1
0

103

10­1

shorter
1

10­1

2

.
stadium house radio waves microwaves cricket ball full stop cell infrared bacteria virus protein water molecule `hard' X-rays gamma rays ultraviolet `soft' X-rays

T

The electromagnetic spectrum.

(TAKEN FrOm FIGUrE By ALS BErKELEy LABS)

he visible spectrum stretching from red to violet is only a small part of the electromagnetic spectrum. The whole spectrum extends from the shortest wavelength gamma rays to the longest wavelength radio waves. Just beyond the red, at slightly longer wavelengths, is the infrared. Astronomers measure infrared wavelengths in millionths of a metre (micrometres). Violet light has a wavelength of 0.4 micrometres and red light a wavelength of 0.7 micrometres. The invisible infrared region stretches from about 1 micrometre to around 400 micrometres. All objects emit a broad range of thermal radiation, with a spectrum that is characteristic of their temperature. Very hot objects are brightest at wavelengths shorter than visible wavelengths (in the ultraviolet or in the X-ray region). By contrast, an ice cube at 273 K (0 єC) is brightest at a wavelength of 19 micrometres. Interstellar dust at a temperature of 30 K (­243 єC) is brightest at 100 micrometres. So observations in the infrared tell us about the coldest parts of the universe, the space between the stars, where the temperature is only a few degrees Some infrared telescopes and satellites above absolute zero. AFGL ­ Air Force Geophysics Laboratory Objects can also emit and absorb radiation sounding rockets ­ 1976 catalogue at specific wavelengths, particularly in the infrared. This is how we can tell that molecules, UKIRT ­ United Kingdom Infrared Telescope such as water vapour, are present in space. (in Hawaii, USA) ­ opened 1979 Detecting infrared radiation The water vapour present in the Earth's atmosphere can absorb the faint infrared signals from space. To overcome this problem, infrared telescopes must be put on high, dry mountain tops, in balloons, in aircraft, or in space. Infrared detectors must be cooled (usually with liquid helium) and sometimes the whole telescope is cooled, so that the infrared radiation from the equipment does not mask the faint astronomical signals. IRAS ­ Infrared Astronomy Satellite (NL/USA/UK) ­ launched 1983 HST ­ Hubble Space Telescope (visible and near-infrared) (NASA/ESA) ­ launched 1990 ISO ­ Infrared Space Observatory (ESA) ­ launched 1995 SPITZER ­ Space Infrared Telescope Facility (NASA) ­ launched 2003 HERSCHEL ­ Far-infrared and sub-millimetre telescope (ESA) ­ launched 2009


Different

Infrared

Visible

Views

and

ust as fog and clouds can block out sunlight, so dust in space can hide visible light from distant stars. Longer wavelength infrared radiation can penetrate the "fog" and provide another view of familiar objects. The dark pillars in the Eagle nebula are regions of gas and dust in the constellation of Serpens. The visible image shows only the outline of the gas clouds and the bright foreground stars. We cannot see inside the gas and dust clouds. The infrared light penetrates the clouds, The Eagle nebula in visible light. (HST, NASA, HESTEr ANd SCOWEN) allowing us to see new stars forming within them. These are the whitish patches in the infrared image.

J

The Eagle nebula in infrared.
(ESA/ISO/ISOCAm)

When we look at galaxies in infrared light we find a wealth of detail about the stars that are forming in them. Here we see the Antennae galaxies, two galaxies that have collided. In the infrared, the warm dust clouds where new stars are The Antennae galaxies in visible The Antennae galaxies in infrared. light. (HST, NASA ANd WHITmOrE) forming show up as the (ESA/ISO/ISOCAm ANd VIGOUX et al.) brightest parts of the image. In the large white region, where the two galaxies overlap, there is an enormous burst of star formation, with millions of new stars being born. When we look at the galaxies in visible light, these regions appear as dark and reddish patches which are difficult to recognize.


Seeing Dust with the Infrared

I

The Ophiuchus region.

(dATA AT 7 mICrONS ArE SHOWN IN BLUE, dATA AT 15 mICrONS IN rEd; ISO ImAGE, ESA/ISO/ISOCAm)

nterstellar space (the space between the stars) is cold, and the dust and gas there has a temperature around 20 to 30 K (­253 єC to ­243 єC). In some areas of the Milky Way where this material becomes concentrated, clouds of gas and dust collapse under their own gravity to form new stars. We see this process happening in the Orion Nebula as shown on the front of the leaflet. Above is the Ophiuchus region of the sky,

another region where new stars are forming. Each small bright smudge and point in the image shows where a new star like the Sun is forming. The large white patch near the centre may well become a star 100 times as massive as the Sun. There are more than 400 new stars in this image (less than 1 degree by 1 degree ­ an area not much larger than the full moon) and none of them can be seen in visible light.


Molecules with
the

Seeing

Infrared

M

any molecules have important features in their infrared spectrum. Hydrogen (H2) is the simplest molecule, composed of two hydrogen atoms. The two atoms can move in a variety of ways: in and out, and they can spin around one another. These movements result in the absorption or emission of radiation in the infrared. Each A molecule of hydrogen, demonstrating the type of molecule has a unique set of absorption different types of motion. or emission features which makes it easy to identify when it is present deep in space. The existence of molecules in space indicates the presence of cold, dense clouds of gas and dust. Without the protection of the clouds, the molecules would be split into atoms by the light from any nearby stars. This dramatic infrared image shows the formation of a new star. (The star is at the bottom of the image.) "Bullets" of dense gas have been shot out of the star. As they pass through the surrounding gas cloud the "bullets" excite molecules in it, leaving V-shaped trails of emission. This image records the emission of excited hydrogen molecules in the cloud.
The formation of a new star.
(UKIrT ANd ANTONIO CHrySOSTOmOU)


Infrared Astronomy
Betelgeuse

Seeing the Invisible:

The infrared image (left) and the visible light image (right) show the same region of sky but reveal very different details. (IrAS ImAGE IPAC,
USA, OPErATEd JOINTLy By CALTECH ANd JPL, UNdEr CONTrACT TO NASA)

I

Orion Nebula

n 1800, the astronomer William Herschel discovered the presence of invisible radiation from the Sun. He measured it using thermometers, beyond the position of the visible red light in the Sun's spectrum. This radiation, which had a wavelength longer than that of visible light, he called infrared ­ "beyond the red". Although we cannot see infrared radiation, we can feel it as heat emitted from warm objects. Our own bodies generate heat that can be seen at night by infrared-sensitive security cameras, or in a smoke-filled room by a fireman wearing special goggles.

In space, objects look very different in the infrared compared with our normal (visible) view. The vast clouds of gas and dust in the constellation of Orion dominate the infrared sky because they are heated by the new stars forming there. They appear as the yellow and red regions in this infrared image, which uses "false colour" to show the brightness at different wavelengths. Astronomers show longer wavelength (cooler) emission as red and shorter wavelength (hotter) emission as blue or white. The star Betelgeuse is colourcoded white because it is hotter than the dust clouds.

Advancing Astronomy and Geophysics

This is one in a series of leaflets prepared by the Education Committee of the Royal Astronomical Society. It may be copied for educational use. It was written by dr Helen Walker (CCLrC rutherford Appleton Laboratory) with help from Peter Hingley (rAS Librarian), dr margaret Penston and dr Betty Lanchester. designed by Paul Johnson (www. higgs-boson.com). © rAS 2004. Published by the rAS, Burlington House, Piccadilly, London W1J 0BQ, UK. +44 (0)20 7734 3307. reprinted 2012 by Armagh Observatory with funding from the Northern Ireland department of Culture, Arts and Leisure (dCAL). www.ras.org.uk


Planetary Atmospheres
in

Molecules

T

hese four images of Jupiter show a visible image, and three images in the infrared. At 3 micrometres (top right), the infrared view is similar to the visible one. We see the Great Red Spot near the centre, which is brighter because it is warmer than the surrounding cloud tops. At 3.3 micrometres (bottom left) Jupiter appears dark, because the methane in its upper atmosphere absorbs the light. At 7.6 micrometres we can see down to a different layer in Jupiter's atmosphere, where water vapour has been detected. Water has also been detected in the upper atmospheres of mars, Saturn, Saturn's moon Titan, Uranus and Neptune.

visible

3.0 micrometres

3.3 micrometres

7.6 micrometres

Jupiter in visible and infrared light. (In the infrared, black is faintest and white is brightest, with red used for intermediate intensities.)
(VISIBLE ImAGE NASA, ISO ImAGES ESA/ISO/ISOCAm ANd THErESE ENCrENAz et al.)


Infrared

Pioneers

Sir William Herschel (1738­1822) William Herschel was inspired to study the heating effect of different wavelengths of light after his attempts to observe the Transit of mercury (the passage of mercury across the visible disc of the Sun) on 7 may 1799. He wanted to observe what was then called "our great central luminary" (the Sun) in safety and comfort, so he undertook a lengthy series of experiments using different materials as filters. His notebooks record some 881 distinct experiments between 1800 and 1805. Herschel placed a thermometer as a "control", outside the range of the Sun's visible rays, to measure the temperature of the room. At first he thought that the sunshine was heating up the room, but he later William Herschel. realized that the rise in temperature had been caused by invisible (IPAC USA) (infrared) rays from the Sun falling on the thermometer. Samuel Pierpoint Langley (1834­1906) Samuel Langley is mainly remembered as one of the people who worked towards heavier-than-air flight (aeroplanes), and he is commemorated on a US Post Office stamp. He invented an instrument called a bolometer, completed in 1881. It used the change of the electrical resistance of metals, in this case platinum, to measure temperature. He studied the solar constant (the average amount of energy per unit area received by the Earth from the Sun), the absorption of the Earth's atmosphere, and the atmosphere of the Sun. One of Langley's students penned the following "immortal" lines in commemoration of his achievement: Prof. Langley devised a Bolometer It's really a sort of Thermometer It'll detect the heat Of a Polar Bear's feet At a distance of Half-a-Kilometre! Thomas Alva Edison (1847­1931) Thomas Edison invented many things, including the phonograph, the telephone and the incandescent light bulb. relatively few people know of his invention the tasimeter, in which he focused infrared light onto a rod made of vulcanite (an early plastic). The rod expanded and pressed on a carbon button, changing its resistance. This was an adaptation of his carbonbutton microphone for telephones. during the total solar eclipse of 29 July 1878, in Wyoming, he used the tasimeter to measure the temperature of the solar corona. His equipment was so sensitive that he was also able to detect the star Arcturus.


I

Stars

Rin

s arou g

nd nd
(IPAC USA [OPErATEd JOINTLy By CALTECH ANd JPL (JCmT [GrEAVES et al.]) (JAC/UCLA)

nfrared emission can show the presence of even small amounts of dust around stars. Vega is a normal star, only about 20 light years away from the Sun. Infrared radiation reveals that there is a thin ring of material around the star, and the artist's impression here shows what the dust ring would look like from close to Vega. There is too little material in this dust ring to make a planet.
Vega.

UNdEr CONTrACT TO NASA])

The star Epsilon Eridani, which is only about half the age of the Sun, has a rather more massive dust ring. Since the star is one of the closest to the Sun (only 10 light years away), the dust ring can be imaged at a wavelength of just less than a millimetre, and we see an almost complete ring of emission around the star. The position of Epsilon Eridani is indicated by the asterisk in the middle of the image.
Epsilon Eridani.

The artist's impression of the Solar System shows how similar it is to the Epsilon Eridani system, with its ring of material which could be small rocks and comets, and a central void which might contain planets.

Artist's impression of the Solar System.


M

any galaxies are very bright in the infrared, showing that millions of new stars are forming there.

Dust

in other Galaxies

The Andromeda Galaxy (m31) is the spiral galaxy nearest to our own milky Way Galaxy, and the two galaxies are thought to be very similar. The visible light image of this galaxy shows its central bright nucleus and many stars in its spiral arms. It also shows the two small satellite galaxies (m32 and m110) near m31.

The Andromeda Galaxy in visible light.
(UNIVErSITy OF OrEGON)

This image shows the Andromeda Galaxy at a wavelength of 60 micrometres. The orange, red and white patches represent areas of "warm" dust at a temperature of around 40 K (­233 єC). The dust is heated by new or relatively young stars.

The Andromeda Galaxy at 60 micrometres.
(IrAS ImAGE, IPAC)

At longer wavelengths (175 micrometres), the Andromeda Galaxy shows cooler dust at a temperature of 12 K to 20 K (­261 єC to ­253 єC). The dark lanes in the visible light image (above, top) are the same features as the bright regions in the image on the right. The nucleus is almost invisible and new stars are forming in a ring of material far away from the centre (30 000 light years away).
The Andromeda Galaxy at 175 micrometres. (ISO ImAGE,

ESA/ISO/mPIA [HAAS, LEmKE et al.])


Using

Earth
on

Infrared

Observing Earth in the infrared Scientists use infrared wavelengths to study the Earth, measuring temperature changes that can indicate climate change and the effects of people on the environment.
Left: December 1995. Right: December 1997.
(ATSr PrOJECT)

This image of the world's sea surface temperatures in 1995 shows the normal winter pattern of ocean currents in the Pacific Ocean caused by the South Pacific trade-winds, with cooler water (the finger of yellow) on the sea surface stretching from near Australia (off the image on the left side) to South America. The cool water is rich in nutrients and so fish were plentiful off the coast of South America. In an El NiЯo year (for example 1997), this pattern of trade winds is disrupted and the warmer surface water moves eastward along the equatorial region from the western Pacific. This can cause storms around California, drought in Australia, and a lack of fish off the coast of South America since the warm water has fewer nutrients. Infrared images can also be used to track deforestation in the Amazon region and elsewhere. Domestic uses There are many everyday uses of infrared radiation. It is used in domestic objects such as TV remote controls. Some burglar alarms are triggered by the detection of heat from the human body, detected as infrared radiation. It is also used to transmit telephone and television signals along optical-fibre cables. Coastguards, police and firefighters use thermal (infrared) cameras to look for people when it is dark, or if smoke or fog makes it difficult to see.

Infrared at work in crime and accident prevention.
(IPAC USA)


the

Clouds

Above

Mountain tops This site at Mauna Kea in Hawaii is home to many telescopes including the United Kingdom Infrared Telescope (UKIrT). At 4200 metres above sea level, the telescopes are above much of the Earth's atmosphere. This minimizes the problem of absorption of the infrared radiation by the atmosphere. (PHOTOGrAPH GEmINI TEAm ANd PPArC)

Up, up and away In the 1980s, this European Space Agency (ESA) balloon was launched from Texas, USA. The balloon was filled with helium and its release from the truck carefully timed so that the truck did not take off as well! The spectrometer on the University College London (UCL) balloon platform operated at wavelengths between 40 and 100 micrometres. One of the experiments studied oxygen in Orion. (PHOTOGrAPH ESTEC/UCL ANd rOGEr EmEry)

Let the plane take the strain The Kuiper Airborne Observatory started flights in 1974. It had a 0.9 metre telescope which viewed the sky through an open hatch just behind the cockpit. Starting in 2010, a modified Boeing 747-SP called the Stratospheric Observatory For Infrared Astronomy (SOFIA) has carried a 2.5 metre infrared telescope for observations.
(ImAGE NASA AmES rESEArCH CENTEr CALIFOrNIA)


Space

Infrared

Astronomy

I

An image of infrared point sources in the entire sky as seen by IRAS. The plane of our galaxy runs horizontally across the image. The two black segments were areas not surveyed. (IPAC, USA)

n 1976 a landmark catalogue (the AFGL catalogue) was published from observations made using sounding rockets. It had just over 2000 objects in it, measured at wavelengths from 4 to 30 micrometres. The IRAS satellite was launched in 1983 to make an all-sky survey from 10 to 100 micrometres. In its first 12 hours of operation IrAS detected more objects than were in the whole AFGL catalogue. The IrAS catalogue contains almost 250 000 objects. IrAS also produced maps showing the warm and cool dust. The ISO satellite was launched by ESA in 1995, operating between 2 and 240

micrometres. The satellite was launched with over 2000 litres of liquid helium coolant on board. This lasted for 29 months, allowing ISO to make about 30 000 observations of astronomical objects, from planets and stars to distant galaxies. In 2003, NASA launched the SPITZER satellite to study infrared targets in great detail, and to look for faint galaxies in the early universe. In 2009, ESA launched a new infrared satellite called HERSCHEL (after William Herschel). It has studied faint galaxies as well as nearby star-forming regions in unprecedented detail.

The ISO satellite.

(ESA)