Table of Contents
- 1 Who realized the correct order of stellar spectral types?
- 2 What is the main reason that stellar spectra of different stars appear differently?
- 3 What are stellar spectral types based on?
- 4 Why are the spectral classes listed as Obafgkm?
- 5 What is the correct ordering of spectral classes in order of decreasing temperature?
- 6 What is the stellar spectrum?
- 7 How was the spectral sequence discovered and why does it have the order OBAFGKM?
- 8 In which spectral sequence are the hottest stars?
Who realized the correct order of stellar spectral types?
During the 1860s and 1870s, pioneering stellar spectroscopist Angelo Secchi created the Secchi classes in order to classify observed spectra. By 1866, he had developed three classes of stellar spectra, shown in the table below.
What is the main reason that stellar spectra of different stars appear differently?
The primary reason that stellar spectra look different is the stars have different temperatures. Most stars have compositions very similar to that of the Sun.
How are spectral types ordered?
From hot stars to cool, the order of stellar types is: O, B, A, F, G, K, M. (A traditional mnemonic for this sequence is “Oh Be A Fine Girl [or Guy], Kiss Me.”) Additional letters have been used to designate novas and less common types of stars.
What are stellar spectral types based on?
Classification of Stellar Spectra. Astronomers use the patterns of lines observed in stellar spectra to sort stars into a spectral class. Because a star’s temperature determines which absorption lines are present in its spectrum, these spectral classes are a measure of its surface temperature.
Why are the spectral classes listed as Obafgkm?
Description of the spectral types (the labels OBAFGKM are called “spectral types” because the way to measure hydrogen in stars is to look at their spectra, or emission lines).
Why do main sequence stars remain at about the same size throughout this stage of their life?
For most of its lifetime, a star is a main sequence star. It is stable, with balanced forces keeping it the same size all the time. During this period: radiation pressure from the fusion reactions tends to expand the star.
What is the correct ordering of spectral classes in order of decreasing temperature?
Most stars are grouped into a small number of spectral types. The Henry Draper Catalogue and the Bright Star Catalogue list spectral types from the hottest to the coolest stars (see stellar classification). These types are designated, in order of decreasing temperature, by the letters O, B, A, F, G, K, and M.
What is the stellar spectrum?
A star’s spectrum contains information about its temperature, chemical composition, and intrinsic luminosity. Spectrograms secured with a slit spectrograph consist of a sequence of images of the slit in the light of the star at successive wavelengths.
Who first developed the stellar spectral sequence?
The scheme in use today is the Harvard spectral classification scheme which was developed at Harvard college observatory in the late 1800s, and refined to its present incarnation by Annie Jump Cannon for publication in 1924.
How was the spectral sequence discovered and why does it have the order OBAFGKM?
The spectral types run OBAFGKM, where O stars are the hottest and M are the coolest. Hotter stars look bluer to us, and cooler stars look redder. The spectral sequence was discovered from work done by a large number of people.
In which spectral sequence are the hottest stars?
The spectral sequence of stars runs OBAFGKM.
- O stars are the hottest, with temperatures from about 20,000K up to more than 100,000K.
- B stars have temperatures between about 10,000 and 20,000K.
- A stars have strong absorption lines of Hydrogen.
- F stars are slightly hotter than the Sun.