Exploring Starlight Flashcards
(32 cards)
What is magnitude?
Magnitude is a measure of a star’s brightness. Magnitudes from 1(brightest) to 6 were used in ancient times, but now modern instruments mean the scale extends up to 60. A magnitude difference of 1 corresponds to a 2.5 x greater brightness. This increases proportional to the square, so a difference of 2 is a ratio of 2,5 squared.
What is the difference between apparent and absolute magnitude?
Absolute magnitude refers to a stars true brightness - the stars apparent magnitude is it were 10 parsec away.
Apparent magnitude is how bright a star appears in the night sky. This depends on many factors, including the distance to the star, the stars absolute magnitude, and the amount of light scattered by the atmosphere. Absolute magnitude refers to a stars true brightness - the stars apparent magnitude is it were 10 parsec away.
Distance modulus formula and how to use it
M = m + 5 - 5log(10)d where d is distance in parsec
To find distance
d = 10 the power (m-M+5/5)
What is and what can be obtained from a stellar spectrum
A stellar spectrum is a set of dark lines on a continuous ply coloured background. These spectral lines correspond to the wavelength in which atoms in the star absorb light. This tells us which chemical elements are present in the star, as well as the star’s temperature, and its radial velocity.
How can stars be classified according to spectral type?
The ratios of elements can be used to classify stars on a spectrum with the following acronym. OBAFGKM. Finer divisions are made with numbers, e.g. O1, K7
How do a stars colour and spectral type link to surface temperature?
In stars, red is the cooler, moving up to yellow and blue / white is the hottest. As the spectral type moves from O to M, the star’s temperature cools from ~40000k to ~25000K.
How to sketch and place star on a simple Hertzprung -Russel diagram.
A scatter graph of temperature/spectral type against magnitude/luminosity. The main-sequence lies in a diagonal line across the centre. The sun is about 1/3 of the way up the main sequence. Red and Boue giants and giants lie above the main sequence, white dwarfs below, and supergiants in the top right.
How does a stars life cycle relate to its position on the H-R diagram?
Main sequence stars are at a normal stage of life. Giants and supergiants have moved off the main sequence as their hydrogen fuels runs out towards the end of their lives. White dwarfs are in their final stage of life as their nuclear fuel runs out.
What is the relationship between distance and brightness / light intensity
An universe square law, light intensity = 1/distance squared
How to divide up angles of 1 degree?
1 degree compromises of 60minutes of an arc (arcmin), each of which is made up of 60 seconds of an arc (arsec)
How to determine distances using the heliocentric parallax?
The parallax effect in when nearby objects appear to move more than far away ones. This is also true of stars, when seen from the two sides of Earth’s orbit, the nearby stars make a small shift in position know as the parallax angle. Distance (in parsec) = 1/parallax angle in arsec( half of angle moved)
How to use the H-R diagram to determine to distance to stars
Once a main sequence stars spectral type in known, it’s absolute magnitude can be read off and substituted into the distance modulus equation with apparent magnitude to find d in parsec
What are the light curves of variable stars?
Short period variable stars rise and fall evenly approx. once a day, while long period variable stars take months to complete 1 rise and fall. Cepheid variable stars fall slowly and rise quickly over periods of a few days. Supernovae jump to extremely high magnitudes before steadily falling. Eclipsing binary stars experience 1 large drop and 1 small drop each cycle.
What causes the light curve if an eclipsing binary stars
They experience a large drop in brightness when the brighter primary is obscured by the secondary stars, and a smaller drop when the secondary is obscured by the primary.
How to use the period of cepheid variable stars to determine distances?
The period of a cepheid variable is the amount of time between greatest and smallest magnitude as they expand and contract. Using Leavitt’s period luminosity law, we can deduce the absolute magnitude of a cepheid variable from its period, and then substitute that into the distance modulus equation to find distance.
Describe the structure of multi star systems
Binary star systems consist of two stars orbiting a common centre of mass.
Open star clusters are gravitationally bound collections of stars formed from the same molecular cloud, consisting of tens of thousands of stars
Globular clusters are spherical collections of stars which orbit a galactic core. They are more tightly bound then open star clusters
How can the period of an eclipsing binary star be deduced from its light curve
First look for a repeating pattern to determine the primary and secondary drops. Then measure the time between two primary or two secondary drops. Primary are easier to observe
What do star trail periods show us?
They show curved motion, which shows that Earth rotates, and this cycle takes 23hr 56min, showing us the time taken to rotate 360 degrees or the length of a sidereal day.
How are most modern astronomical observations recorded?
Using digital sensors which convert light into electrical signals which can be processed and stored as data files.
How do astronomers obtain spectral lines?
By collecting light using large telescopes and splitting up the light with a diffraction grating to obtain a spectrum.
What telescopes should be used on Earth’s surface and why?
Only optical and radio telescopes should be used, as Earth’s atmosphere blocks almost all the wavelengths of electromagnetic radiation bar visible light and radio waves.
How do radio telescopes work?
A large dish captures radio waves and projects them into an aerial, which can convert them to electrical signals and store them.
What do radio telescopes need large apertures?
Because resolution of a telescope depends inversely on wavelength, and radio waves have a longer wavelength than visible light.
