1 Radiasi Elektromagnetik AS3100 Lab. Astronomi Dasar I Prodi Astronomi 2007/2008 B. Dermawan

2 Spektrum Elektromagnetik Nick Strobel’s Astronomy

3 Informasi Astrofisika (1) Tujuan astrofisika: Menggambarkan, memahami dan memprediksi fenomena fisis yang terjadi di alam semesta –Materi alam semesta: rapat/renggang, panas/dingin, stabil/tidak stabil –Informasi yg diterima pengamat ditransformasikan menjadi sinyal sbg basis klasifikasi ini

4 Informasi Astrofisika (2) Tujuan observasi: Strategi dalam rangka mengumpulkan informasi astrofisika –Menyusun variabel/parameter fisis yang diukur; menganalisis informasi agar tidak over-interpreted atau terbuang; menyimpan informasi guna telaah di masa datang –Tiap teknik observasi  filter informasi yg menghasilkan citra, spektrum, kurva cahaya, dll. pada suatu daerah panjang gelombang

5 Kurir Informasi Astrofisika (1) Radiasi elektromagnetik berkaitan dengan kondisi fisis sumber Keadaan dan gerak partikel, atom, molekul atau bulir debu: temperatur, tekanan, medan magnet Nick Strobel’s Astronomy

6 Perambatan radiasi e.m. dipengaruhi oleh kondisi sepanjang lintasan: kurvatur lokal alam semesta, distribusi lokal materi (lensa gravitasi), serapan dan hamburan selektif (ekstingsi) materi antar bintang dan atmosfer bumi Nick Strobel’s Astronomy

7 Materi Berkas kosmis (cosmic-rays) –Terdiri atas elektron, inti atom dari proton hingga inti berat –Berasal dari proses energi tinggi di galaksi (ledakan supernova). –Partikel bermuatan ini berinteraksi dgn medan magnet galaksi  distribusi spasial sangat isotropik Kurir Informasi Astrofisika (2) Kelimpahan elemen relatif thd Silikon (Si=100) berkas kosmik energi rendah ( MeV per inti) Kelimpahan elemen di tata surya Léna et al. 1996

8 Malasan, priv. com

9 Meteorit (meteorites) –Ukuran : mikroskopik  berat beberapa ton –Saat dihasilkan: Kini : oleh angin matahari Masa lalu: –pembentukan tata surya –reaksi energi tinggi di permukaan bintang (ledakan nukleosintesis) –Awal alam semesta (kelimpahan helium dlm berkas kosmik)

10 Neutrino –Interaksi lemah –Interaksi kuat e  :elektron, e + :positron n : neutron, p: proton e :neutrino elektron e : anti neutrino elektron  +,  ,  0 : pions/pi-mesons dg muatan +1,-1,0  +,  : muons/mu-mesons dg muatan +1,-1,  : neutrino muon  : anti-neutrino muon Kurir Informasi Astrofisika (3) Léna et al. 1996

11 Pengaruh pada Pencitraan Astronomis

12 Gravitational Waves –As the black holes, stars, or galaxies orbit each other, they send out waves of “gravitational radiation" that reach the Earth –A more massive moving object will produce more powerful waves, and objects that move very quickly will produce more waves over a certain time period NASA Kurir Informasi Astrofisika (4)

13 Kurir Informasi Astrofisika (5) Observation in situ Allows local measurements To experiment in the same way as a physicist, a chemist, or a biologist

14 Apakah Cahaya Itu? Sifat gelombang & partikel Interferensi Polarisasi Sifat partikel dominanSifat gelombang dominan Malasan, priv. com

15 Cahaya Kasat Mata Radiometri/Fotometri bertautan dg pengukuran radiasi kasat mata CIE 1931 Standard Observer: Acuan berdasar pd respons rata-rata mata di bawah iluminasi normal dan medan pandang 2  Tiga komponen model warna: Lightness: Transformasi hitam  putih Hue ; Transformasi putih  hitam Saturation: jarak dari sumbu lightness Malasan, priv. com

16 UV-A UV-A : Disebut juga ‘cahaya hitam’ Paling tak berbahaya Menyebabkan material fluoresensi berpendar kalau diradiasi Aplikasi dalam fototerapi (medis) UV-B UV-B : Bentuk radiasi yg paling destruktif Penyebab kanker kulit Penapis alamiah: Lapisan Ozon UV-C UV-C : Diserap sempurna oleh atmosfer Foton UV-C menumbuk Oksigen  Ozon Aplikasi dalam purifikasi air dan udara (dg lampu UV-C) Radiasi Ultraviolet Malasan, priv. com

17 Radiasi Inframerah Radiasi dengan muatan energi foton ter-rendah Umumnya dideteksi dengan detektor termal Malasan, priv. com

18 Daya Radiasi EM Watt (W)  Satuan fundamental daya optik: laju energi 1 joule (J) per detik Malasan, priv. com

19 Light: spectrum and color Newton found that the white light from the Sun is composed of light of different color, or spectrum (1670) Zang 2006

20 Young’s Double-Slit Experiment indicated light behaved as a wave (1801) The alternating black and bright bands appearing on the screen is analogous to the water waves that pass through a barrier with two openings Light has wavelike property Zang 2006

21 The nature of light is electromagnetic radiation In the 1860s, James Clerk Maxwell succeeded in describing all the basic properties of electricity and magnetism in four equations: the Maxwell equations of electromagnetism. Light is Electromagnetic Radiation Zang 2006

22 A general rule: The higher an object’s temperature, the more intensely the object emits electromagnetic radiation and the shorter the wavelength at which emits most strongly Radiation depending on Temperature The example of heated iron bar. As the temperature increases –The bar glows more brightly –The color of the bar also changes Zang 2006

23 Hot and dense objects act like a blackbody Stars, which are opaque gas ball, closely approximate the behavior of blackbodies The Sun’s radiation is remarkably close to that from a blackbody at a temperature of 5800 K Blackbody Radiation The Sun as a Blackbody A human body at room temperature emits most strongly at infrared light Zang 2006

24 Blackbody Radiation: Wien’s Law Wien’s law states that the dominant wavelength at which a blackbody emits electromagnetic radiation is inversely proportional to the Kelvin temperature of the object For example –The Sun, λ max = 500 nm  T = 5800 K –Human body at 37 degrees Celcius, or 310 Kelvin  λ max = 9.35 μm = 9350 nm Zang 2006

25 Blackbody radiation: Stefan-Boltzmann Law The Stefan-Boltzmann law states that a blackbody radiates electromagnetic waves with a total energy flux F directly proportional to the fourth power of the Kelvin temperature T of the object: F =  T 4 F = energy flux, in joules per square meter of surface per second  = Stefan-Boltzmann constant = 5.67 X W m- 2 K -4 T = object’s temperature, in kelvins Zang 2006

26 Dual properties of Light: (1) waves and (2) particles Light is an electromagnetic radiation wave, e.g, Young’s double slit experiment Light is also a particle-like packet of energy - photon – Light particle is called photon –The energy of phone is related to the wavelength of light Light has a dual personality; it behaves as a stream of particle like photons, but each photon has wavelike properties Zang 2006

27 Planck’s law relates the energy of a photon to its wavelength or frequency –E = energy of a photon –h = Planck’s constant = x 10 –34 J s –c = speed of light –λ= wavelength of light Energy of photon is inversely proportional to the wavelength of light Example: 633-nm red-light photon –E = 3.14 x 10 –19 J –or E = 1.96 eV –eV: electron volt, a small energy unit = x 10 –19 J Dual properties of Light: Planck’s Law Zang 2006

28 Spectral Lines The Sun’s spectrum: in addition to the rainbow-colored continuous spectrum, it contains hundreds of fine dark lines, called spectral lines (Fraunhofer, 1814) A perfect blackbody would produce a smooth, continuous spectrum with no dark lines Zang 2006

29 Spectral Lines Bright spectrum lines can be seen when a chemical substance is heated and vaporized (Kirchhoff, ~1850) Zang 2006

30 Each chemical element has its own unique set of spectral lines. Zang 2006

31 Kirchhoff’s Laws on Spectrum Three different spectrum: continuous spectrum, emission-line spectrum, and absorption line spectrum Zang 2006

32 Bohr’s Model of Atom Absorption is produced when electron absorbs incoming photon and jumps from a lower orbit to a higher orbit Emission is produced when electron jumps from a higher orbit to a lower orbit and emits a photon of the same energy Zang 2006

33 Bohr’s Atomic Model for Hydrogen The strongest hydrogen spectral line from the Sun, Hα line at 656 nm, is caused by electron- transition between n = 3 orbit and n = 1orbit Lyman series lines: between n = 1 orbit and higher orbits (n = 2, n = 3, n = 4,…) Balmer series lines: between n-2 orbit and higher orbits (n = 3, 4, 5,…) Zang 2006

34 Doppler Effect Doppler effect: the wavelength of light is affected by motion between the light source and an observer Zang 2006

35 Red Shift: The object is moving away from the observer, the line is shifted toward the longer wavelength Blue Shift: The object is moving towards the observer, the line is shifted toward the shorter wavelength  / o = v/c  = wavelength shift, o = wavelength if source is not moving, v = velocity of source, c = speed of light Doppler Effect Zang 2006 Nick Strobel’s Astronomy 