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Simultaneous Multiple Wavelength Astronomical Observation.

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Presentation on theme: "Simultaneous Multiple Wavelength Astronomical Observation."— Presentation transcript:

1 Simultaneous Multiple Wavelength Astronomical Observation

2 A Short Quiz optical ultraviolet X-ray infrared radio wave

3 Electromagnetic Waves All EM waves travel at the speed of light of approximately 3x10 8 ms -1 in vacuum. All EM waves travel at the speed of light of approximately 3x10 8 ms -1 in vacuum. Different EM waves have different wavelengths and hence different frequencies. Different EM waves have different wavelengths and hence different frequencies. eg.Red light : wavelength of about 700 nm (nm, nanometer or m). Blue light : wavelength of about 400 nm. Radio waves : wavelength ranges from several centimeters to several meters. X-rays : wavelengths of about m. Light sensitive cells in our retina are only sensitive to EM waves in a small wavelength window between about 400 nm to 700 nm, it is known as “the optical window”. Light sensitive cells in our retina are only sensitive to EM waves in a small wavelength window between about 400 nm to 700 nm, it is known as “the optical window”.

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5 Can we investigate astronomical objects with EM waves spectrum? All objects are continuously emitting and absorbing EM radiation. The same object looks so different at different wavelengths simply because the object emits, reflects or absorbs light differently at different wavelengths. All objects are continuously emitting and absorbing EM radiation. The same object looks so different at different wavelengths simply because the object emits, reflects or absorbs light differently at different wavelengths. In an astronomical object, many different physical processes are going on. These processes may lead to production of “light” at different wavelengths. In an astronomical object, many different physical processes are going on. These processes may lead to production of “light” at different wavelengths.

6 Spectrum of a hot object, such as the surface of our Sun, depends on its temperature. Spectrum of a hot object, such as the surface of our Sun, depends on its temperature. A hot iron bar at 3000 K appears dull red. A 6000 K object such as the surface of our Sun emits most of its radiation in the form of yellow light. The hotter the object, the emitted radiation will be of higher frequency. The hotter the object, the emitted radiation will be of higher frequency.

7 Many other factors could also affect the emission and absorption of EM waves. Many other factors could also affect the emission and absorption of EM waves. For example, electrical charges moving under the influence of a strong magnetic field may lead to the emission of radio waves. Since most astronomical objects are so far away from us, it is difficult, if not impossible, to make measurements on the objects by actually taking samples from the object. Since most astronomical objects are so far away from us, it is difficult, if not impossible, to make measurements on the objects by actually taking samples from the object. Therefore, analyzing their EM waves spectrum is by far the most important way of investigating distant objects.

8 Simultaneous Multiple Wavelength Astronomical Observation It is a technique which observe an object in different windows of wavelengths at the same time. It is a technique which observe an object in different windows of wavelengths at the same time. Astronomers are able to deduce the sequence of physical processes or events in or near the astronomical object. Thus, they put themselves in a better position to infer the behaviour of the observed object and the underlying physics. Astronomers are able to deduce the sequence of physical processes or events in or near the astronomical object. Thus, they put themselves in a better position to infer the behaviour of the observed object and the underlying physics.

9 Gamma-ray Burst Gamma-rays are EM waves of wavelengths shorter than m. Gamma-rays are EM waves of wavelengths shorter than m. Gamma-ray bursts are sudden bursts of gamma-ray coming from the sky. It was first discovered in the cold war era (1960's to mid-80's) by gamma-ray detector satellites. Gamma-ray bursts are sudden bursts of gamma-ray coming from the sky. It was first discovered in the cold war era (1960's to mid-80's) by gamma-ray detector satellites. These bursts are found at a rate of about once every day and they do not seem to repeat. In other words, it is seldom to find a direction in the sky that bursts more than once. These bursts are found at a rate of about once every day and they do not seem to repeat. In other words, it is seldom to find a direction in the sky that bursts more than once. In a gamma-ray burst known as GRB at 28th February 1997, astronomers confirmed that the bursts are coming from a cosmological distance. In a gamma-ray burst known as GRB at 28th February 1997, astronomers confirmed that the bursts are coming from a cosmological distance.

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