Let's travel around the universe "" American astronomer Harlow Shapley gave this invitation to an audience in Washington DC in 1920. Fellow was participating in the so-called Great Debate with Curtis to be a co-scientist with the scale of the universe.
Shelley believed that our Milky Way galaxy spanned 300,000 light-years. According to the latest thinking, it is actually three times as much, but its measurements were quite good over time. In particular, he calculated the exact proportional distance through the Milky Way galaxy - for example, the position of our Sun relative to the center of the galaxy.
By the beginning of the twentieth century, however, 300,000 light-years seemed almost unreasonably large to most of Shapley's contemporaries. And like other Milky Way spiral galaxies - which can be seen through binoculars - the idea was equally external.
In fact, Shelley herself believed that the Milky Way must be exceptional. "Even if the spirals are stellar, they are not comparable in size to our star system," he told his audience.
Curtis disagreed. He thought, rightly so, that there are many more galaxies that have their own spread across the universe. Interestingly, however, his starting point was a belief that the Milky Way was much smaller than the Shapley count. According to the calculations used by Curtis, the Milky Way was only 30,000 light-years in diameter - or, about three times smaller than modern measurements.
Three times too large; Three times too small - when we talk about such a huge distance, it is understandable that forgery scientists may have found their images somewhat wrong about a century ago.
Today we are fairly confident that the Milky Way probably contains between 10,000,000 and 150,000 light years. The observable universe is certainly much larger. According to current thinking, it is about 93 billion light-years in diameter. How can we be sure? And how did we come up with such a measure on earth right from here?
Ever since Copernicus argued that the earth was not the center of the solar system, it seems that we have always found it difficult to rewrite our idea of what the universe is - and especially how big it can be. As we can see today, we are gathering new evidence to give advice to the whole world that may be much larger than some people recently thought.
Caitlin Casey, an astronomer at the University of Texas at Austin who knows the universe as we know it, noted that astronomers have used a system to calculate the spans and calculations of the distance between galaxies and the clearly observable universe.
According to the calculations used by Curtis, the Milky Way diameter was only 30,000 light-years
The measure of all these things is known as the "ladder of cosmic distance". The first couple of ladders made it easy enough for us and these days it depends on modern technology.
"We can only bounce radio waves from neighboring planets like Venus and Mars in the solar system and measure the time it takes for those waves to return to Earth," Casey said. "It gives us a very accurate measure"
Large radio telescopes like the Puerto Rico Archibo can do just that - but they can do more than that. Arecibo, for example, can detect flying asteroids around the solar system and even create images of them based on how radio waves reflect the surface of the asteroid.
However, it is not practical to use radio waves to measure distances outside our solar system. The next step in the cosmic distance ladder is known as the parallax measurement.
We do it all the time without realizing it. Humans, like many animals, intuitively recognize the distance between themselves and objects, thanks to the fact that we have two eyes.
If you hold an object in front of you - say your hand - and keep it with one eye open, just switch to using the other eye, you will see your hand move slightly to the side. This is called parallax. The difference between these two observations can be used to determine the distance of the object in question.
At this distance, we are still not near the edge of our own galaxy
Our brains do this naturally with information from both our eyes, and astronomers do exactly the same thing with nearby stars without using different sensors: binoculars.
Imagine two eyes floating in space on either side of our sun. Thanks to Earth's orbit, we have exactly what we have, and in this way we can see the movement of stars compared to objects in the background.
“We make a measurement of where they are in the sky in January and we wait six months and in July we measure those same stars when they are opposite the sun,” Casey said.
However, there is a point where objects are so far away - about 100 light-years - the observed transition is too small to provide useful calculations. At this distance, we are still not near the edge of our own galaxy.
The main sequence stars, when used for this analysis, are considered a kind of "standard candle"
The next step is a technique called “key sequence fitting”. It depends on our knowledge of how a certain size star over time - known as the original sequence star - is formed over time.
For one thing, they change color and gradually turn red with age. By accurately measuring their color and brightness and then comparing it with what is known about the distances of close major sequence stars measured by Laralax we can determine the position of more distant stars.
The principle that supports these calculations is that stars of the same mass and age will appear equally bright at the same distance from us. Since they are not often, we can use this measurement difference to see how far they actually work.
The stars of the main sequence, when used for this analysis, are considered a kind of "standard candle" - meaning a body whose length (or luminosity) we can calculate mathematically. These candles are dotted around the space, illuminating the universe in a predictable way. But the main sequence is not the only example of stars.
To understand how brightness is related to distance, it is quite basic to work on the distances of even the most distant objects - just like the stars in other galaxies. The original sequence fitting won't work there, although the light from those stars - which are millions of light-years away - is difficult to analyze accurately.
They can calculate its distance by actually observing how bright it looks to us
However, in 1906, Henrietta Swan Levitt, a scientist at Harvard, came up with a remarkable discovery that helped us measure such vast distances. Swann Levitt realized that there was a special class of stars called the Kefid variable.
"He made the observation that a certain type of star changes its brightness over time, and that the vibrations of these stars are directly related to how bright they are internally."
In other words, a bright chiffon will “pulsate” more slowly (for most days, in reality) than a faded chiffon. Since astronomers can measure the branch of a seafood relatively easily, they can estimate how bright they are. Then, they can calculate its distance by observing how bright it actually looks to us.
It is similar in principle to the original sequence fitting method, that brightness is again the main issue. The point is, distances can be measured in a variety of ways. And the more ways we have to measure distances, the more we can understand the true scale of our cosmic backyard.
It was the identification of stars within our own galaxy that convinced Harlow Schaepley about his great size.
In the early 1920s, Edwin Hubble detected cephalic variables in the nearby Andromeda galaxy and realized that it was just under a million light-years.
There is another feature of the universe that can help us measure true ultimate distances.
Today, our best estimate is that the galaxy is actually 2.5 million light-years away. But it does not shame Hubble's measure. In fact, we're still trying to come up with a better estimate for the Andromeda distance. The 2.54 million light-year figure is the average of several recent calculations
This is the point where the perfect scale of the universe still haunts our minds. We can guess very well, but it is really very difficult to measure the distance between galaxies with subtle precision. The universe is really that big. And it doesn’t stop there.
Hubble also measured the brightness of the exploding white dwarf star - type 1A supernova. They are found in distant galaxies billions of light-years away.
Since the luminosity of this explosion is calculatable, we can determine exactly the same with cepheid variables as they are type 1 supernovae and cepheid variables, both of which astronomers call the standard candle an additional example of this.
But there is another feature of the universe that can help us measure ultimate distances. This is called redshift.
If an ambulance or a siren-blanked police car ever throws you on the road, you will be familiar with the Doppler effect. As soon as the ambulance approaches you the siren seems to pitch higher and then, as it passes by you it falls again.
As the universe expands, each galaxy moves away from the other
The same thing happens with light waves, on much finer scales. We can detect the change by analyzing the spectrum of light from a distant body. This spectrum will have dark lines because certain colors are absorbed by the light source and the elements around it - for example the surface of stars.
The farther away the objects are from us, the more those lines will move towards the red edge of the spectrum. This is not only because objects are so far away, but because they have actually moved farther away from us over time, thanks to the expansion of the universe. And seeing the redshift of light from distant galaxies is a way to prove that the world is actually expanding.
It's like putting a dot on the page of a balloon - each representing a galaxy - and then inflating the balloon, says NASA program scientist Kartik Seth. As the distance between the points on the surface of the balloon increases. "As the universe expands, each galaxy moves away from the other."
"Originally, a wave could be the same amount of frequency that was usually emitted, but now you're expanding space-time itself so the wave looks longer."
Light has reached us from 13.8 billion year old galaxies
The faster the galaxy moves away from us, the farther away it will be - its light will be more redshided when we re-analyze it on Earth. It was Edwin Hubble who discovered that there was a proportional relationship between distant galaxies and how the light of g galaxies was re-nurtured.
Now comes the big key to our puzzle. The redshifted light we can detect in the observable universe indicates that the light has reached our galaxies, which are 13.6 billion years old.
Because it is the oldest light we have found, it gives us a measure of the age of the universe.
But over the last 13.6 billion years, the universe has been expanding - and at first it happened so fast. With this in mind, astronomers have worked out that the galaxies at the edge of the observable universe, whose light took 13.7 billion years to reach us, must now be 446.5 billion light-years away.
One possibility is that, somewhere, some of our calculations are not quite accurate
This is our best measure for the radius of the observable universe. It must have doubled its diameter: 93 billion light years.
This figure relies on many other measurements and bits of science and is the culmination of centuries of work. However, as Casey notes, it’s still a bit rough.
For one thing, given the complexity of some of the oldest galaxies we can identify, it is not clear how they were able to form so quickly after the Big Bang. One possibility is that, somewhere, some of our calculations are not quite accurate
“If one of the cosmic distance ladders is closed by 10%, everything closes by 10%, because they depend on each other,” Casey says.
The entire universe is about 250 times larger than the observable universe
And when things get really complicated we try to think of the universe beyond what is observable. The "whole" universe, as it were. The whole universe can actually be finite or infinite, depending on the shape of the universe you choose.
Recently, Mihran Vardhanian and colleagues at Oxford University in the UK analyzed known information about the objects in the observable universe to see if they could do anything about the size of the entire universe.
The result, after using computer algorithms for meaningful patterns in data, was a new guess. The entire universe is at least 250 times larger than the observable universe.
We never see these more remote areas. Yet, the observable universe alone should be large enough for most people. In fact, it has remained a constant source of fascination for scientists like Casey and Seth.
We are not even at the center of our solar system or at the center of our galaxy
"Everything we've learned about the universe - how big it is, all the amazing things in it - we just collect photos of this light that has traveled millions of years just to come and die on our detectors, our cameras or radio telescopes," Seth said. Says.
"It's rather numb," Casey said. "Astronomy has taught us that we are not the center of the universe, we are not the center of our solar system or the center of our galaxy."