13 Exploring Starlight Flashcards
What is magnitude?
Magnitude is the measure of a brightness of a star
What is the scale of magnitude?
The magnitude difference of 1 corresponds to the fifth root of 100≈2.5
What is apparent magnitude?
Apparent magnitude is how bright a star seems from Earth
What factors affect apparent magnitude?
- The total energy by the star in the visible region
- The distance to the star
- The amount of interstellar gas and dust that reflects and absorbs light
- The amount of light absorbed and scattered by the Earth’s atmosphere
What is absolute magnitude?
Absolute magnitude is how bright a star would be if all stars are 10 parsecs away
How do you calculate absolute magnitude?
M=m+5- 5log(d)
M=absolute magnitude
m=apparent magnitude
How do astronomers find the chemical makeup of a star?
Spectroscopy
What is spectroscopy?
Spectroscopy is when you collect light with the aid of a telescope and then diffract it to create a spectrum.
How do you know what chemicals are in a star?
When you do a spectroscope, there are a set of darker lines. The spectral lines correspond to exact wavelengths at which atoms in the outer layers of stars absorb light; each element has its own unique set of wavelengths
What do astronomers classify stars in?
Spectral types
How do astronomers classify spectral types?
Astronomers examine the ratios of
hydrogen: helium: other elements
What are the different Spectral Types?
O B A F G K M
What is the H-R Diagram?
The H-R diagram is a scatter graph the classify’s stars in accordance to their luminosity, spectral type, colour, temperature and evolutionary stage
What is plotted against each other on a H-R Diagram?
A star’s luminosity or absolute magnitude is plotted against either spectral type or temperature
Where are the main sequence stars found on the H-R Diagram?
The main sequence stars lie in a band running from top left to bottom right
Where are Giants and Supergiants found on the H-R Diagram?
Giants and Supergiants stars lie above the main sequence band
Giant are what colour?
Red or Blue
Where are White dwarf stars found on the H-R diagram?
White dwarfs lie below the main sequence band towards the left
How long is one light year?
1 l.y = 9.5 × 10 ¹²
How long is one parsec?
1 pc = 3.1 × 10 ¹³
How long is one parsec in accordance to light years?
1 pc = 3.26 l.y
What are minutes of arc?
Minutes of Arc is one degree split into 60 minutes of arc. 1 arc minute is further split into arc seconds where one degree is 3600 arc seconds
What technique can we use to figure out the distance to a near star?
Heliocentric Parallax
What is Parallax?
Parallax is when the position of a near object differs greater in comparison to distant objects when viewed from different places
What are variable stars?
Variable stars are stars that vary in brightness
Why do stars appear to vary in brightness?
- Changing physical quantity such as size
- Changes in the light reaching Earth
What are light curves?
Graphs of apparent magnitude against time
What are the two types of variable stars?
Intrinsic and Extrinsic variables
What are Cephied Variables?
Cephied Variables are when the Star actually pulsates. When it’s larger, it has a greater magnitude, and therefore it’s brighter
What are binary stars?
Binary stars are when there is a bright primary star and a dimmer secondary star that orbit around their mutual centre of gravity
What happens when the secondary star eclipses (moves in front of) the primary star?
When the secondary eclipses the primary, there is a large drop in intensity
What happens when the primary star eclipses the secondary star?
When the primary star eclipses the secondary star, there is a small drop in intensity
How do radio telescopes work?
Radio telescopes consist of a large concave dish that reflects and focuses radio waves into an antenna. Here, the antenna converts the radio waves into electrical signals that can be stored and processed
Why are radio telescopes built large?
Radio telescopes are large so they can achieve the best possible resolution by collecting as much radio waves as possible
What is Aperture Synthesis?
Aperture synthesis is when multiple telescopes are linked electronically to study the same source of radio waves. This converts many telescopes into one large one with an aperture equivalent to the largest distance between individual telescopes
Why are most radio telescopes located on high mountains?
The air is dry and steady. Also, there is a lack of clouds which obscure your view
Where is the optimum place to put a telescope?
Space
Why is space the best place to put a telescope?
The satellite is above atmosphere where there is:
- no air to blur or absorb light
- no day-night cycle where your viewing times are restricted
- no light pollution from skyglow
meaning it is in the optimum position to place a telescope in space
What are the disadvantages of having a satellite telescope?
Space telescopes have limited lifetimes, very difficult to construct, launch and maintain
What discoveries were first made using radio waves?
- Quasars
- The structure and rotation of our galaxy
- Pulsars
- Protoplanetary discs
- Jets from black holes
- SETI (Search for extraterrestrial intelligence)
What discoveries were first made using Infrared (IR)?
- Protostars
- Interstellar dust and molecular clouds
- ‘hotspots’ on the moon
What discoveries were first made using ultraviolet (UV)?
Corona and chromosphere structure of young stars
What discoveries were first made using X-ray?
- Active galaxies
- accretion disks surrounding black holes
- supernova remnants
What discoveries were first made using gamma(γ) rays?
Gamma ray bursts in distance galaxies
Where must other wavelengths observatories be put?
All wavelengths other than optical or radio, need to be put on fixed observing platforms orbiting the Earth. However, Infrared observatories can be sited on high mountains.
What is the distance modulus formula?
M = m + 5 - 5log(d)
M=absolute magnitude
m=apparent magnitude
d= distance
How can you use Spectroscopy and the H-R diagram to determine distances to stars?
First, you obtain a spectrum of the star and determine its spectral class. Then, using the H-R diagram you get its absolute magnitude (you use the main sequence band). You then observe the star to get its apparent magnitude. Finally, you use the distance modulus formula to calculate 𝗱
What are the first 5 letters in the greek alphabet?
α (alpha), β (beta), γ (gamma), δ (delta), ε (epsilon)
What is light intensity proportional to?
light intensity is proportional to 1
. . . . . . . . . . . . . . . . . . . . . . . .————–
. . . . . . . . . . . . . . . . . . . . . . . .distance²
How do calculate the ratio of light intensity of two stars?
intensity of light from α . (distance β)²
——————————— = ——————
intensity of light from β . (distance α)²
What is plotted against what in a typical Hertzsprung-Russell diagram?
Luminosity against Spectral type
How does temperature and absolute magnitude increase in a H-R diagram?
Temperature increases to the left and Absolute magnitude increases downwards
What spectral type is the Sun?
G2
How are absorption lines connected to the chemical composition of a star?
Light passing through the outer layers a star is made of all wavelengths / energy. Some of this light has the correct wavelength/energy to excite atoms in the star’s outer layers.
When the atoms de-excite they emit radiation/photons of the same wavelength/energy but in a random direction and not necessarily ‘outwards’. The wavelengths / energies at which these ‘reactions’ occur depends on the chemical element. Light received on Earth is dimmer and so darker at these wavelengths
What is the intensity of light proportional to?
d²
What type of variable star is used by astronomers to determine distances to stars?
Cepheid variable
What is a Cataclysmic variable star?
Cataclysmic variable stars are stars which irregularly increase in brightness by a large factor, then drop back down to a inactive state.
What is an example of Cataclysmic variable star?
Supernova
Why is there variability in brightness for eclipsing binary stars?
For most of the time, the primary and secondary stars are not aligned. This is their constant brightness.
The larger/primary ‘dip’ in a light curve occurs when the
dimmer/secondary star is directly in front of the brighter/primary star.
The smaller/secondary ‘dip’ occurs when the secondary star is behind the primary star.
This time, the corresponding drop in intensity is not as significant
What is SKA?
Square Kilometre Array
What is aperture synthesis?
The process of linking multiple telescopes together to increase aperture size
What is an impact of atmospheric refraction?
Stars near the horizon appear higher in the sky than they actually are
What discoveries were first made using radio waves?
- Quasars
- The structure and rotation of our galaxy
- Pulsars
- Protoplanetary discs
- Jets from black holes
- SETI (Search for extraterrestrial intelligence)
What discoveries were first made using Infrared (IR)?
- Protostars
- Interstellar dust and molecular clouds
- ‘hotspots’ on the moon
What discoveries were first made using ultraviolet (UV)?
Corona and chromosphere structure of young stars
What discoveries were first made using X-ray?
- Active galaxies
- accretion disks surrounding black holes
- supernova remnants
What discoveries were first made using gamma(γ) rays?
Gamma ray bursts in distance galaxies
Which part of a spectrometer splits up light from astronomical objects into a spectrum?
Diffraction grating
Which types of nebulae expand?
Supernova remnants and Planetary Nebulae
What is the Electromagnetic spectrum from shortest to longest wavelength?
Gamma X-Ray UV Visible IR Microwave Radio
