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ASTR_2011 Introduction to Observational Astronomy

ASTR_2011 Introduction to Observational Astronomy. Day-4. Announcements. Dark Observing Night tomorrow night Start time will be 8:30pm Start set-up at ~7:15pm at Observatory This is subject to weather cancellation If the weather is good, use this time for extra observing.

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ASTR_2011 Introduction to Observational Astronomy

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  1. ASTR_2011Introduction to Observational Astronomy Day-4

  2. Announcements • Dark Observing Night tomorrow night Start time will be 8:30pm Start set-up at ~7:15pm at Observatory This is subject to weather cancellation • If the weather is good, use this time for extra observing.

  3. Light is an Electromagnetic Wave

  4. Basic Properties of Waves Wavelength = l in metersFrequency = nin cycles per second or Hertz (Hz)Speed = c in meters per second

  5. Each “color” is characterized by its wavelength Using c = lnwe can see that the frequency of visible light is in the 1014 Hz range

  6. Visible light is only a very small part of the Electromagnetic Spectrum

  7. Magnitude Originally devised by Hipparchus around 140 BC. Based on when stars become visible after sunset. Sunset to astronomical twilight (complete dark) is divided into six equal time periods 1stmag…visible in first 2ndmag…visible in second 3rdmag…visible in third 4thmag…visible in fourth 5thmag…visible in fifth 6thmag…visible in sixth

  8. Modern definition of magnitude is based on light flux Note that this compares two stars. If a “zero point” is defined then where C is the zero point offset

  9. Zero Points N.R. Pogson, originator of the modern magnitude definition, proposed an average of the sixth magnitude stars in certain star catalogues . Result: mSirius = -1.6 North Polar Sequence…system of “standard stars” with known magnitudes to compare against mVega≡ 0.0 but problems with variability and dust leads modern values to mVega = 0.03 Most common systems now are standard star systems

  10. Absolute magnitude Defined as the magnitude of the object if it was located at a distance of 10 parsecs. This gives a distance (d) relationship between apparent magnitude (m) and absolute magnitude (M). Distance is measured in parsecs

  11. Types of Magnitude • Visual Magnitude (mv)…measured over the visible spectrum • Monochromatic magnitude(ml)…measured over a narrow wavelength range • Bolometric magnitude (mbol)…measured over the entire E/M spectrum • Photographic magnitude (mpg)…magnitude measured with photographic plate

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