Astronomy beyond the visible

Beatriz García, Ricardo Moreno

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International Astronomical Union

ITeDA and Universidad Tecnológica Nacional, Argentina

Colegio Retamar de Madrid, Spain

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Goals

• Show phenomena beyond the visible, e.g. the electromagnetic energy emitted by celestial bodies, but undetectable by the human eye.
• Perform several simple experiments for determining the existence of emission in the wavelength regions of radio waves, infrared, ultraviolet, microwave and X-ray.

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Presentation

• For centuries, the universe had been studied only with the light detected by the human eye.
• There is information that comes electromagnetic waves of other wavelengths that our eyes cannot see.
• Astronomers observe today in the radio, microwave, infrared, ultraviolet, X-rays and gamma rays as well as in visible rays.

Electromagnetic Spectrum

All wavelengths of electromagnetic radiation.

Blackbody Radiation

Any “black body” when heated emits light at many wavelengths.

There is λ_max at which the intensity of radiation is maximum. This λ_max depends on the temperatura T:

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Wien’s Law

By studying the radiation of a distant object, we can measure its temperature without having to go there. This applies for the stars, which are almost black bodies

Solar radiaton

Windows for different energy regions

The Earth’s atmosphere is opaque to most wavelengths of radiation. We can detect the hight energies from space and low energies require special detectors.

When the solar electomagnetic energy goes through the atmosphere, the “black body” radiation change, but the λ_max at which the irradiance is máximum remains almost without change

The night vision devices uses this λ_máx.

We know that there is λ_max at which the irradiance or emission is maximum depends on the temperature T, but it does not need to be in a visible region of the spectrum

For example, the human body has a temperature of T = 273+37 = 310 K.

Then, emits the maximun in λ_máx = 9300 nm.

Activity 1: Building a spectrometer

Depending what you use, a DVD part or a CD one, you cut the matching portions the template.

Activity 1: Building a spectrometer

Remove the metal layer of the CD using tape or scratching it.

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NB! The coating will not peel off white or commercial CDs.

Activity 1: Building a spectrometer

The black surface folded on the inside.

Compare the spectra from filament lamps, fluorescent lamps and streetlights.

Activity 1: Building a spectrometer

Activity 2: Decomposing sunlight with water drops

Children can split the sunlight and make a rainbow.

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They need a hose with a fine spray. They must have their back to the Sun.

Other regions of the spectrum

• There is a matter with a temperature much lower than that of the stars, for example, clouds of interstellar matter.
• They do not emit visible radiation, but emit infrared radiation, microwaves and radio waves.
• The type of radiation is associated with the processes that are occurring inside the object. E.g., details in the centre of our galaxy ...

The infrared radiaton

• William Herschel discovered the infrared using the prism and thermometers.
• It is a property of warm bodies, even those not hot enough to emit visible light.
• To highlight this radiation we establish an equivalence between temperature and colour.

Activity 3: Herschel Experiment

• In 1800, Herschel discovered the infrared in sunlight.

Activity 3: Herschel Experiment

SPECTRUM THERMOMETERS

PRISM

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PRISM

BOX

THERMOMETERS

In the spectrum

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A little beyond the red

RED

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YELLOW

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BLUE

SUN

Activity 3: Herschel Experiment

Activity 3: Herschel Experiment

Activity 4: IR detection with a phone

• Remote controls emit infrared signals but our eyes cannot see them.
• Many but not all mobile phones cameras are sensitive in IR.

The power of the infrared

• The interstellar dust absorbs visible light but not infrared so much.

Activity 5: Detection of IR light of a bulb

• Most of the energy emitted by an incandescent bulb is in the visible region, but it also emits infrared that can penetrate some fabrics that cannot be penetrated with visible radiation.
• The same happens with the galactic dust, which can be detected from its infrared emissions, but is opaque in the visible region.

Activity 6: Constellation with IR LEDs

Cassiopeia with IR LEDs.

Resistance between 100 and 500 Ω

Activity 7: Constellation with remote controls

Emission of radio waves

• EM radiation with wavelengths from metres to kilometres is called radio waves.
• They are used for commercial stations.
• Radio waves also come from space, and thus provide information that cannot be seen at other wavelengths.

Activity 8: Producing radio waves

Ultraviolet radiation

• UV photons have higher energies than those of visible light.
• UV destroys the chemical bonds between organic molecules.
• At high doses UV can be fatal for life.
• UV-C radiation is filtered by atmospheric ozone.

Johann Ritter discovered ultraviolet radiation in 1801

Ultraviolet radiation

• The Sun emits UV radiation, but most of it is filtered by the ozone layer at the top of our atmosphere; the amount that arrives on Earth is beneficial for life.
• This radiation is what makes our skin to tan.
• If the ozone layer decreased in thickness, the Earth would receive higher doses and skin cancers would proliferate.

Ultraviolet light

Andromeda Galaxy in visible light (Hubble)

Andromeda Galaxy in UV light (Swift)

Activity 9: Black light (UV)

• Counterfeit detector for bank notes and identity cards.

Activity 10: Filter UV radiation

• Black light bulbs are detectors for fake money .
• Fluorescent material (reacts to UV light).
• Common glass and glasses (no organics glasses, because they are plastic): the glass filters UV radiation, the plastic does not.

Fluorescent material and glasses, illuminated with white light.

The same material and glasses but illuminated with UV light.

Shadow of the glasses on the material

Activity 10: Filter UV radiation

• The ozone layer is created by UV (UV + O₂ = O₃) and at the same time ozone filters this radiation. There is the adequate equilibrium for life to survive.

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• The glass filters out UV radiation. For this reason it is impossible to tan your skin through a glass window! The plastics do not filter UV so well.

It is important to use special sunglasses to avoid retinal damage!

(with UV filter)

X-rays

• More energetic than UV is the X-ray radiation.

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• It is used for radiographs and other medical imaging techniques.

X-rays

• In the cosmos, X-ray radiation is acharacteristic of high-energy events and objects: black holes, star collisions, etc.

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• The mission of the Chandra Space Telescope is to detect and monitor these kinds of events and objects

More energetic than UV

Gamma rays

• It is the most energetic radiation.
• On the Earth these rays are emitted by most of radioactive elements.
• Like X-rays, both are used in medicine, in imaging tests and in therapies to cure diseases like cancer.

Gamma rays

• The occasional violent eruptions of gamma rays are not unusual in the sky.
• There are different types that last from seconds to hours. One problem is to define their exact location to help identify what objects are producing the radiation.
• Astronomers tend to associate them with the fusion of binary stars, which can result in a black hole being formed.

Fermi's Five-year View of the Gamma-ray Sky

Uses of EM radiation in Medicine

Use of X-rays

• Imaging tests and therapies to cure diseases like cancer. Used in positron emission tomography (PET scan)

Use of Gamma-rays

Use of Radio Waves

• Magnetic resonance, diagnosis of soft tissues

MRI Normal knee

MRI Human heart

CAT Normal knee

X-ray

• Radiographs and computed axial tomography (CAT scan)

Thank you very much �for your attention! �