Cosmology Standard Candle not so Standard After All
01.12.11
PASADENA, Calif. -- Astronomers have turned up the first direct proof that "standard candles" used to illuminate the size of the universe, termed Cepheids, shrink in mass, making them not quite as standard as once thought. The findings, made with NASA's Spitzer Space Telescope, will help astronomers make even more precise measurements of the size, age and expansion rate of our universe.
Standard candles are astronomical objects that make up the rungs of the so-called cosmic distance ladder, a tool for measuring the distances to farther and farther galaxies. The ladder's first rung consists of pulsating stars called Cepheid variables, or Cepheids for short. Measurements of the distances to these stars from Earth are critical in making precise measurements of even more distant objects. Each rung on the ladder depends on the previous one, so without accurate Cepheid measurements, the whole cosmic distance ladder would come unhinged.
Now, new observations from Spitzer show that keeping this ladder secure requires even more careful attention to Cepheids. The telescope's infrared observations of one particular Cepheid provide the first direct evidence that these stars can lose mass—or essentially shrink. This could affect measurements of their distances.
"We have shown that these particular standard candles are slowly consumed by their wind," said Massimo Marengo of Iowa State University, Ames, Iowa, lead author of a recent study on the discovery appearing in the Astronomical Journal. "When using Cepheids as standard candles, we must be extra careful because, much like actual candles, they are consumed as they burn."
The star in the study is Delta Cephei, which is the namesake for the entire class of Cepheids. It was discovered in 1784 in the constellation Cepheus, or the King. Intermediate-mass stars can become Cepheids when they are middle-aged, pulsing with a regular beat that is related to how bright they are. This unique trait allows astronomers to take the pulse of a Cepheid and figure out how bright it is intrinsically—or how bright it would be if you were right next to it. By measuring how bright the star appears in the sky, and comparing this to its intrinsic brightness, it can then be determined how far away it must be.
This calculation was famously performed by astronomer Edwin Hubble in 1924, leading to the revelation that our galaxy is just one of many in a vast cosmic sea. Cepheids also helped in the discovery that our universe is expanding and galaxies are drifting apart.
Cepheids have since become reliable rungs on the cosmic distance ladder, but mysteries about these standard candles remain. One question has been whether or not they lose mass. Winds from a Cepheid star could blow off significant amounts of gas and dust, forming a dusty cocoon around the star that would affect how bright it appears. This, in turn, would affect calculations of its distance. Previous research had hinted at such mass loss, but more direct evidence was needed.
Marengo and his colleague used Spitzer's infrared vision to study the dust around Delta Cephei. This particular star is racing along through space at high speeds, pushing interstellar gas and dust into a bow shock up ahead. Luckily for the scientists, a nearby companion star happens to be lighting the area, making the bow shock easier to see. By studying the size and structure of the shock, the team was able to show that a strong, massive wind from the star is pushing against the interstellar gas and dust. In addition, the team calculated that this wind is up to one million times stronger than the wind blown by our sun. This proves that Delta Cephei is shrinking slightly.
Follow-up observations of other Cepheids conducted by the same team using Spitzer have shown that other Cepheids, up to 25 percent observed, are also losing mass.
"Everything crumbles in cosmology studies if you don't start up with the most precise measurements of Cepheids possible," said Pauline Barmby of the University of Western Ontario, Canada, lead author of the follow-up Cepheid study published online Jan. 6 in the Astronomical Journal. "This discovery will allow us to better understand these stars, and use them as ever more precise distance indicators."
Other authors of this study include N. R. Evans and G.G. Fazio of the Harvard-Smithsonian Center for Astrophysics, Cambridge, Mass.; L.D. Matthews of Harvard-Smithsonian and the Massachusetts Institute of Technology Haystack Observatory, Westford; G. Bono of the Università di Roma Tor Vergata and the INAF-Osservatorio Astronomico di Roma in Rome, Italy; D.L. Welch of the McMaster University, Ontario, Canada; M. Romaniello of the European Southern Observatory, Garching, Germany; D. Huelsman of Harvard-Smithsonian and University of Cincinnati, Ohio; and K. Y. L. Su of the University of Arizona, Tucson.
The Spitzer observations were made before it ran out of its liquid coolant in May 2009 and began its warm mission.
NASA's Jet Propulsion Laboratory, Pasadena, Calif., manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at the California Institute of Technology, also in Pasadena. Caltech manages JPL for NASA. For more information about Spitzer, visit //spitzer.caltech.edu/ and //www.nasa.gov/spitzer .
To measure the expansion of the Universe, cosmologists utilize standardized references. One such standard reference is standard candles. These are objects where the intrinsic luminosity of the object is known – that is, how much light/radiation is emitted by the object at source. By comparing this amount with how much light from the objects reaches us, the apparent luminosity, we get a measure of how far away the object is from us. Combined with an estimate of the relative size of the Universe at the time the object emitted the light, we can then map the expansion history of the Universe.
Two key aspects of establishing a standard candle is the class definition (how to define and select the objects) and calibration (how to bring the objects to a common reference point). The class definition must be restricted enough to provide something standardizable, and calibration must be accurate enough to provide good distance measurements.
The most important standard candles today are Type Ia supernovae, whose pioneering use led to the discovery of dark energy, based on the Phillips relationship discovered by Mark M. Phillips in 1993. The first discovered standard candles are cepheid variables, stars whose period of variation in luminosity can be translated into a distance. These were first identified by Henrietta Swan Leavitt in 1908, and more conclusively established in 1912. Thanks to the cepheid standard candles, Edwin Hubble could later measure the distance to nebulae and show that they were located outside the Milky Way. Thereby, “the Great Debate” on whether the Milky Way constitutes all of the Universe or whether there are other distant galaxies was settled.
Links
Wikipedia: Standard candles >
The Universe Review: Standard candles in astronomy >
Author: Martin Sahlen >Cosmos > | Discoveries > |
A standard candle is an astronomical object that has a known absolute magnitude (intrinsic brightness). They are extremely important to astronomers since by measuring the apparent magnitude of the object the distance to the source can be determined by using the inverse square law. Examples of such objects are Cepheid variable stars, whose absolute magnitude is proportional to their period of variability and also the Type-1a supernovae, since it is believed that they all have essentially the same peak absolute magnitude.
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 2
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 3
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 4
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 5
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 6
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 7
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 8
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 9
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 10
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 11
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 12
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 13
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 14
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 15
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 16
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 17
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 18
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 19
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 20
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 21
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 22
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 23
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 24
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 25
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.
Page 26
If you see a faint light in the distance, it might be truly dim, or it might be quite bright but very far away. If you had some way of knowing how bright it really is and could measure how bright it appears to be, you could use those two pieces of information to calculate the actual distance to it.
As you might imagine, this problem comes up all the time in astronomy. All we can directly observe from here on Earth is how bright things appear to us.
Fortunately, several classes of celestial objects serve as “standard candles:” we know how bright they actually are, and therefore we can calculate the distance to them by measuring how bright they appear to us as seen from here on Earth.
The nearest celestial standard candles are ordinary stars relatively close by in our own galaxy. Their actual brightness is related to their temperature, which can be determined by looking at the stars’ colors.
Farther out, both in our galaxy and nearby galaxies, there are bigger stars that emit light in periodic pulses; the time between two pulses, which can be directly observed, is related to their actual brightness.
The most distant, currently known standard candles are a class of star explosions called Type-IA supernovae, where the time it takes light to diminish after the explosion is related to the actual brightness of the explosion itself. The 2011 Nobel Prize in Physics recognized the use of Type-IA supernovae as standard candles to measure vast cosmic distances and establish the acceleration of the expansion of the universe, which scientists attribute to a mysterious force known as dark energy.
Increasingly precise measurements of the distances to very far objects is a major component of projects that will tell us more about the properties of dark energy such as the Dark Energy Survey, the Large Synoptic Survey Telescope, and the planned space-based Wide-Field Infrared Survey Telescope.