All attempts to detect stellar parallax failed until the 1830s because people believed that the
brightest stars in the sky were the nearest stars to the Earth.
He announced that the stars have their own unique motions across the sky, but because the stars
are so distant, their motion appears so tiny that we can't easily perceive it.
The stars move in their own direction with different speed.
Stellar parallax was finally seen in the nearest stars, now chosen for their brightness and large
motion- Instead of assuming the brightest star are the nearby stars, the brightness requirement
was combined with the requirement that the stars had large motion. REASON: if a star has no
noticeably motion after a century of tracking it then this star is probably very far away.
Alpha Centauri is the nearest star
Distance of 270,000AU [4.4 ly (light years) or 1.3 pc (parsecs)]
The definition of a light year is the distance that light travels in one year. Aparsec is the distance
of an object with a parallax of 1 arcsecond. Aparsec is bigger than a light year.Aparsec is
roughly 206,000AU (31 billion km) and a light year is about 63,000AU (9.5 billion km).
All light waves travel like waves; they are waves of oscillating electric and magnetic fields.
6. Describe how a wave from a bright blue light source is different from a wave from a
faint red light source.
Abright blue light source will have a high amplitude and a small wavelength. Afaint red light
source will have a small amplitude and a high wavelength.
Blue light is the shortest in wavelength. Red light is the longest in wavelength. Blue light has the
highest frequency; red light has the lowest frequency.
Gamma waves have the shortest wavelength, but have the highest frequency. Radio waves have
the longest wavelength, but have the smallest frequency.
9. What is a spectroscope?
Aspectroscope is a scientific instrument that splits light into its different wavelengths,
which humans see as different colors. Violet has the shortest wavelength that people can see and
red the longest. This instrument can also identify wavelengths that humans cannot see, such as
infrared and ultraviolet radiation. Invented in 1814 by Joseph von Fraunhofer. 10.
Fraunhofer passed sunlight through glass and observed the spectrum through a telescope. He saw
roughly 600 thin dark lines and labeled them with letters to designate their wavelength. It
contained absorption lines.
Through Spectroscopy: which is the analysis of the spectrum of a light source for the purpose of
determining its chemical composition (the study of light spectrum in order to determine the
chemical composition of a light source).
The unique spectra of known substances could be used to identify the spectra of an unknown
substance- e.g. unknown substance- meteoroid u want to know what its composed of, you would
have to heat up a sample of it and disburse the light from its flame and examine the pattern of
coloured lines in the flames spectrum then you can match the wavelengths of the coloured lines
that you see with the wavelengths of lines in known substances.
We can collect a stars light.
They found the darker lines got thicker. They concluded, the Sun’s core, which produced the full
spectrum of light, is surrounded by a gas layer (an atmosphere). Molecules in the Sun’s
atmosphere absorb light at their signature wavelengths, producing the dark lines (absorption
lines). During the solar eclipse, the spectrum of the Sun’s atmosphere was produced, revealing the
“emission lines” predicted by Bunsen and Kirchhoff.
Norman Lockyer discovered an absorption line that had never been detected before. He suggested
that it must be produced by a new element. He named it ‘helium’, after ‘Helios’the greek god of
In a graphical spectrum, emission lines appear as peaks in the graph.Absorption lines appear as
The spectra of a gas cloud is made up of emission lines.Astar cluster is made up of continuum
emission and absorption lines. Gas/star systems are made up of continuum emission, emission
lines and absorption lines.
Huggins produces the spectrum of a planetary nebula and found unidentified emission lines.
These emission lines were for the element Oxygen, but because he found them within planetary
nebula, he named it Nebulium.
17. OnAugust 29, 1864, Huggins was the first to analyze the spectrum of a planetary
nebula. His observations of stars showed that their spectra consisted of a continuum of
radiation with many dark lines superimposed on them. He later found that many nebulous
objects had spectra that were quite similar. Planetary nebulae are usually identified by
their emission-line spectrum. These nebulae were later shown to be galaxies.
Radial motion is the approaching or receding motion. If I am giving out light waves as I move
towards you, the light waves are going to get compressed, as I move away from you the light
waves are going to get stretched. This i