Table of Contents
- 1 How far away can Cepheid variables be used?
- 2 What property of a Cepheid variable can you determine if you know the period?
- 3 How do astronomers measure the distance to a periodic variable star?
- 4 How Cepheid variables can be used to measure the distances to galaxies?
- 5 How far away can we see Cepheid variables?
- 6 How do we measure the luminosity of a Cepheid star?
How far away can Cepheid variables be used?
about 20 million light years
Use in Astronomy: Cepheid variables can be seen and measured to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for Earth-based parallax measurements and just over 326 light years for the ESA’s Hipparcos mission.
How far away is the most distant Cepheid astronomers can observe?
about 60 million light-years
The most distant known variable stars are all cepheids, with some about 60 million light-years away.
Why are Cepheid variable stars useful for finding the distances to galaxies are there any limitations on their use for this purpose?
Cepheid variable stars are useful for finding distances because they are are very luminous, they re recognizable due to their variation, and a definite relation exists between their periods and their luminosities. Their use is limited to the range where they can be seen as individual stars.
What property of a Cepheid variable can you determine if you know the period?
All Cepheids with a certain period are assumed to have the same absolute magnitude. Measuring the apparent magnitude of a Cepheid then allows us to determine its distance using the period-luminosity relationship. If two Cepheids have the same period but is fainter than the other it must be further away.
How far out can we measure distances using main sequence fitting?
Main sequence fitting can be used out to distances of about 7kpc, still not reaching out of our galaxy. We now see why we use the phrase ‘cosmic distance ladder’. The parallax method reaches out to about 1000pc.
What objects are used to measure the furthest distances in space?
Answer:
- Radar – measuring distances in our solar system.
- Parallax – measuring distances to nearby stars.
- Cepheids – measuring distances in our Galaxy and to nearby galaxies.
- Supernovae – measuring distances to other galaxies.
- Redshift and Hubble’s Law – measuring distances to objects far, far away.
How do astronomers measure the distance to a periodic variable star?
By observing the apparent luminosity, dimmed by the inverse square law of light traveling across the vast reaches of space, and comparing this with the predicted luminosity, astronomers can calculate the distance to that star.
What factors limit the distance we can see into the universe?
The amount of time that’s passed since the Big Bang, the speed of light, and the ingredients in our Universe determine the limit of what’s observable. Any farther than that, and even something moving at the speed of light since the moment of the hot Big Bang will not have had sufficient time to reach us.
What are the limitations of using Cepheid variables in this fashion?
Problems with Cepheids and Measurements One of the problems that occurs with using Cepheid variables as yardmarkers is that some of the light from the star can be absorbed en route to Earth. If the star loses some light due to intervening dust, it will appear fainter and therefore further away than it really is.
How Cepheid variables can be used to measure the distances to galaxies?
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.
What is the limit to the Fisher Tully relation for measuring galactic distance?
The Tully-Fisher relation is a correlation between the luminosity and the HI 21cm line width in spiral galaxies (LLW relation). It is used to derive galaxy distances in the interval 7 to 100 Mpc.
Why does the main sequence have a limit at the lower end?
The main sequence has a limit at the lower end because a. low mass stars form from the interstellar medium very rarely. the lower limit represents when the radius of the star would be zero.
How far away can we see Cepheid variables?
Cepheid variables can be seen and measured to a distance of about 20 million light years, compared to a maximum distance of about 65 light years for Earth-based parallax measurements and just over 326 light years for the ESA’s Hipparcos mission.
How far away are the Cepheids in the SMC?
He used his data on nearby Cepheids to calculate the distance to the Cepheids in the SMC as 37,000 light years away. Harlow Shapley, an American astronomer using a larger number of Cepheids, recalibrated the absolute magnitude scale for Cepheids and revised the value of the distance to the SMC to 95,000 light years.
What is the difference between stellar parallax and Cepheid variable?
While stellar parallax can only be used to measure distances to stars within hundreds of parsecs, Cepheid variable stars and supernovae can be used to measure larger distances such as the distances between galaxies. This video, Measuring the Universe, gives a great introduction to this topic.
How do we measure the luminosity of a Cepheid star?
In addition, a Cepheid star’s period (how often it pulsates) is directly related to its luminosity or brightness. Cepheid variables are extremely luminous and very distant ones can be observed and measured. Once the period of a distant Cepheid has been measured, its luminosity can be determined from the known behavior of Cepheid variables.