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"To The Infinite And Beyond!" - The Cosmic Distance Ladder

To the infinite and Beyond! The Cosmic Distance Ladder The cosmic distance ladder (also known as the extragalactic distance scale) is the succession of methods by which astronomers determine the distances to celestial objects. Let's suppose we are observing two stars in the night sky, and we are wondering which one is the most distant from us. This is not a simple question to answer. For example, if the two stars were lying at the same distance from us and had the same intrinsic luminosity, we would see them showing the same brightness. But...what if one of them was more distant from us than the other? We would expect to detect a difference in brightness: the more distant a star is, the less bright it will appear in the sky. And that's exactly what we observe: apparent brightness. Since intrinsic luminosity provides us with a huge quantity of information about stars, their atmosphere, their surface temperature, and their radius, it has been worth it to spent a lot of effort in the computing of distances. Finally, when we observe the sky, we are seeing a 2-dimension space, without no information about the 3rd one: the stars that form constellations, they are in general separated in the depth dimension. Follow me on this journey to learn more about this topic, and to understand how astronomers are measuring the distances in the universe, starting from the measure of Astronomic Unit until we get to the famous Hubble's Law! So now we know that if we want to understand the physics behind an astronomical phenomenon, we need to quantify the basic properties of the system under observation. Many of these properties cannot be determined unless we know the distance to the object in question. Although we are not able to determine many of the absolute properties of astronomical phenomena without distance information, we can compare their relative properties. For example, the stars in any galaxy outside our own are all at essentially the same distance from us. Thus, if observations of a nearby galaxy reveal that all the stars of a particular type have the same apparent brightness, then we know that this class of objects all have the same intrinsic luminosity. We can use this property to measure the relative distances to other galaxies: if we can identify the same type of star in these galaxies and measure their apparent brightness, then the ratio distances follows directly from the ratio of apparent luminosity fluxes. Sources with identical intrinsic luminosities which can be used in this way are known as “standard candles”. Think about the procedure once again: the distance to a nearby galaxy might be determined by comparing the apparent brightness of its individual stars to those of similar stars in the Milky Way, the distance to a more remote galaxy whose individual stars cannot be resolved can then be measured by comparing the properties of the galaxy as a whole to the properties of the nearby galaxies, and so on... This bootstrapping approach has been dubbed the “cosmic distance ladder”, where each rung up the ladder takes us to a greater distance. But how do we calibrate the cosmic distance ladder? We first need absolute methods that give us absolute distance measurements. So, first: Absolute distance estimators. We use some simple geometric techniques as absolute distance estimators. The available method includes, for example, the trigonometric parallax. Let's see how the Trigonometric Parallax Method works. "If You happen to see any content that is yours, and we didn't give credit in the right manner please let us know at [email protected] and we will correct it immediately" "Some of our visual content is under an Attribution-ShareAlike license. (https://creativecommons.org/licenses/) in its different versions such as 1.0, 2.0, 3,0, and 4.0 – permitting commercial sharing with attribution given in each picture accordingly in the video." Credits: Ron Miller, Mark A. Garlick / MarkGarlick.com Credits: Nasa/Shutterstock/Storyblocks/Elon Musk/SpaceX/ESA/ESO/ Flickr Video Chapters: 00:00 Introduction 00:07 THE COSMIC DISTANCE LADDER 02:30 HAVE THE SAME INTRINSIC LUMINOSITY L 02:46 The ratio distances follow directly from the ratio of apparent luminosity fluxes 03:50 ABSOLUTE DISTANCE 04:00 TRIGONOMETRIC PARALLAX 06:07 PRIMARY DISTANCE ESTIMATORS 06:38 The brighter the star the longer the period 09:24 Tully Fisher relation Faber Jackson Relation 09:43 There is a connection between the shift in spectral lines of an object and its distance from us 10:42 Hubble-Lemaître law #insanecuriosity #cosmicdistanceladder #intergalacticdistance