How do you calculate Cepheid distance?
Through observations of Cepheid variables, astronomers have determined the distances to other galaxies. They compare the Cepheid variable’s apparent brightness with its intrinsic brightness. The difference between observed and actual brightness yields the distance.
How do you find the luminosity of a Cepheid variable?
This discovery allows one to know the true luminosity of a Cepheid by simply observing its pulsation period. This in turn allows one to determine the distance to the star, by comparing its known luminosity to its observed brightness.
What is the relationship between period and luminosity of a Cepheid variable star?
Period-luminosity relation The longer the pulsation period, the more luminous the star. The period-luminosity relation for classical Cepheids was discovered in 1908 by Henrietta Swan Leavitt in an investigation of thousands of variable stars in the Magellanic Clouds.
What is the period-luminosity scale?
In astronomy, a period-luminosity relation is a relationship linking the luminosity of pulsating variable stars with their pulsation period. The best-known relation is the direct proportionality law holding for Classical Cepheid variables, sometimes called the Leavitt law.
How luminosity is measured?
Luminosity is an absolute measure of radiated electromagnetic power (light), the radiant power emitted by a light-emitting object over time. In SI units, luminosity is measured in joules per second, or watts. In astronomy, values for luminosity are often given in the terms of the luminosity of the Sun, L⊙.
What is the period-luminosity relationship quizlet?
The period-luminosity relationship discovered by Henrietta Leavitt for Cepheid variable stars, relating variability to over-all brightness says that. the shorter the period, the lower the luminosity of the star. The event that settled the debate between Curtis and Shapley about the ‘spiral nebulae’ was.
How are the luminosity distance and magnitude of a Cepheid variable related?
Using Cepheid Variables to Measure Distance Once the period of a distant Cepheid has been measured, its luminosity can be determined from the known behavior of Cepheid variables. Then its absolute magnitude and apparent magnitude can be related by the distance modulus equation, and its distance can be determined.
For what type of object is the period-luminosity relation used for determining distances?
For what type of object is the period-luminosity relation used for determining distances? Cepheids. The region on the H-R diagram where pulsating variables occur is called the: Instability strip.
Why are Cepheids used for measuring distance?
The important feature of a Cepheid Variable that allows it to be used for distance measurements is that its period is related directly to its luminosity . This relation allows us to work out how much brighter than the Sun the star is.
How does luminosity change with distance?
The intensity or brightness of light as a function of the distance from the light source follows an inverse square relationship. Notice that as the distance increases, the light must spread out over a larger surface and the surface brightness decreases in accordance with a “one over r squared” relationship.
What is the ratio of luminosity?
Thus if a star is twice is luminous as the Sun, L*/Lsol = 2. This approach is convenient as the luminosity of stars varies over a huge range from less than 10-4 to about 106 times that of the Sun so an order of magnitude ratio is often sufficient.
Why is the period-luminosity relationship important?
Because the luminosity of Cepheids can be easily found from the pulsation period, they are very useful in finding distances to the star clusters or galaxies in which they reside. Edwin Hubble measured the distance to the Andromeda Galaxy in 1923 using the period-luminosity relation for Type II Cepheids.
How is the luminosity of the Cepheid period measured?
The Classical Cepheid period-luminosity relation has been calibrated by many astronomers throughout the twentieth century, beginning with Hertzsprung.
What is the absolute magnitude of Cepheid variable stars?
The vertical axis shows absolute magnitude whilst period is displayed as a log value on the horizontal axes. The log of 4.76 days = 0.68. When this is plotted a value of about -3.6 results for absolute magnitude.
Why are Cepheids so valuable as distance indicators?
The Period-Luminosity relation. Why are Cepheids so valuable as distance indicators? It is well known that the apparent brightness of an object decreases as the square of its distance. If you know both the apparent and intrinsic brightness of a star, you can calculate how far away it must be.
What is the period of a Delta Cepheid star?
Phase lightcurve of variable star Delta Cephei. Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months.
