Stars have always been considered from a romantic and poetic perspective. But how far are stars? Do they really are so distant from us? And how can we measure such tremendous distances? Are there any valid techniques? A lot of surprising things can be said about these questions.
-------------------------------------------------------------------------------------------
Is it possible to calculate star distances? Definitely yes, but some further explanations must be clarified. Obviously, we can’t measure such a huge gap with the normal methods we are used to on earth. We must calculate distance in an indirect way. What does it mean? We need to measure two different quantities that are related to each other through distance; then, with a simple equation, we can easily derive how far the star is from us.
Let’s make an example: if we want to measure how many kilometers are there between two cities, we can drive at a constant velocity and measure directly how much time does the journey take. After that we can just get information about the distance.
Similarly, physicists utilize the different types of brightness of a star that depend on distance to know how far the star actually is.
Before going on more rigorously on this subject we must list the major units of measure used to identify the distance of a star.
The first one is astronomical unit, which is exactly the gap that separates Earth from the sun, corresponding to 1011 meters or 8 minute at the speed of light.
The other one is parsec, nearly around 1016 meters or 3,26 light years, which represents the distance that causes a change of one degree in the sky over an entire year. This phenomenon is also known as parallax, but we’ll discuss it later.
In order to understand the major techniques used in astronomical researches, we need to take a little step back and define some important physical quantities.
The first one is absolute luminosity, which is the radiation power of a light emitting object. Consider it as the measurement of its brightness: a small lamp has a lower luminosity than a lighthouse. Moreover, we can define another quantity that derives by the previous one and it is named apparent luminosity. It is proportional to the inverse of square distance. Shortly, apparent luminosity is higher when the star is closer and viceversa. A lighthouse is certainly brighter than a lamp, but if it’s 10 or 20 times more distant the lamp will “seem” having a greater power. Apparent luminosity is a sort of superficial density of power.
In parallel, physicists defined apparent magnitude which is greater when luminosity is lower and smaller when luminosity is higher. As a matter of fact, the brightest star visible from Earth, which is known as Vega, has a conventional value of zero. Obviously, it is dependent on distance and can be considered as an equivalent of apparent luminosity. In addiction, another quantity called absolute magnitude has been introduced by scientists: it measures the magnitude that all stars would have at a distance of 10 parsec.
Similarly to what we did before with velocity and time, astronomers usually utilize absolute and apparent magnitude to derive distance.
Since apparent magnitude can be measured through telescope observations, it is necessary to find objects that have a well-known absolute magnitude. These stars or galaxies are also called “standard candles” are they’re crucial for measuring distances of stars.
The first object that is very useful for this method is a cepheid. Its major characteristic is the emission of electromagnetic waves: its intensity varies with time according to specific laws.
How far can we find star distances thanks to this method? Around 1 kpc, just the closest ones can be detected using Cepheids as standard candles.
As opposed to this technique, there’s even another way of revealing star distances at this scale just by using geometric properties. Did you know that?
Its name is Parallax.
-------------------------------------------------------------------------------------------
"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 Lorenzovareseaziendale@gmail.com and we will correct it immediately"

"Some of our visual content is under an Attribution-ShareAlike license. ([ Ссылка ]) 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: Mark A. Garlick / markgarlick.com
Credits: Ron Miller
Credits: Nasa/Shutterstock/Storyblocks/Elon Musk/SpaceX/ESA
Credits: Flickr
Credits: ESO

Video Chapters:
00:00 Introduction
01:36 Calculating Star Distances
06:18 Parallax

#insanecuriosity #stars #astronomy

свернуть