How do scientists measure the distance of far off celestial objects? I know light years are the standard measurement for vast cosmic distances and I know what a light year is, but how do scientists figure it out? How do they figure out Alpha Centauri is exactly 4.3 light years from Earth for example?
Hello and thanks for asking! There are several ways that we determine distance to stars.
Parallax If you hold your finger out in front of you and close one eye, it appears in one spot. Now, close that eye and open the other. It looks like your finger has shifted position!! This is because each eye is looking at your finger from a slightly different angle, giving it a slightly different apparent location. We can do this with stars too - scientists take a picture of a star’s location when the earth is on one side of its orbit, and another when the earth is on the other side. Looking at how far the star appeared to shift over the course of six months, we can calculate its distance from us, using trigonometry and similar triangles. Since the distances involved are so large, we can approximate the distance using the formula d=1/p, where d is distance in parsec and p is the parallax angle, in arcseconds (a measure of distance across the sky) (image source)
Standard Candle Now, what about stars that are too far away to have a visible parallax angle (stars further than a few hundred light years away)? For distances this far, we use type 1a supernovae, which are called standard candles because they have essentially a standard luminosity. Using its observed brightness, we can calculate the distance it is (and the objects around it, like nearby galaxies).
Spectra, other stars We can also look at the spectrum of a star, classify its type, and from there estimate its luminosity. Based on our estimated luminosity, we can calculate the distance it would have to be to give us that observed brightness. This isn’t that accurate, by the way, and just yields an estimate. We can also look at different types of stars (Cepheid variables), which have specific brightnesses. Based on their observed brightnesses and expected luminosities,we can calculate its distance (and the distance of nearby objects).
Hubble Constant Now, some galaxies are so far away that their light is actually redshifted by the expansion of the universe! By looking at the spectrum of a galaxy, and looking at how far the spectral lines emitted by specific elements have shifted in the red direction, we can calculate its apparent recessional velocity (how fast it’s moving away from us). Then, we can solve for how far away it is given the Hubble constant: (image source)
So yeah, that’s how we determine distances to cosmic objects.Let me know if you have any other questions!! I’m happy to answer them.
13.05.17 // Updated my physics window for the first time in ages! Had some thoughts over the past few weeks surrounding a free scalar field universe model so I drew them up as well as some old game theory because I watched a Beautiful Mind and felt nostalgic. I hope you are all having wonderful days / evening / whatever plane of existentialism you currently observe 😉
my biology test was returned yesterday and i didn’t expect to actually get a good mark, but i did! yaay 🤓 here are my cosmology notes for today’s test 💫🌎🌟☄🌞🌛 one of the few tests i had to think through rather than rely on definitions, facts and other information! i hope u all have a productive weekend!!! 🤗💓
If you held out your thumb, every second about 65 billion neutrinos will pass through it. Besides photons, neutrinos are the most abundant particle in the universe, and by far the most unique.
The existence of the neutrino was first theorized by Wolfgang Pauli, after noticing how energy didn’t seem to be conserved in beta decay. He believed that the missing energy was being carried away by some “invisible” particle. He would later say “I have done a terrible thing, I have postulated a particle that cannot be detected.”
Although elusive, neutrinos can be detected, but it requires sensitive, and often massive detectors. After finding that neutrinos came in three types: electron, muon, and tau, a problem seemed to emerge. Electron neutrinos are created all the time in the Sun, as a by-product of nuclear fusion, but they would always find only a third of the total number of electron neutrinos they were expecting. So, where did the missing neutrinos go?
It turns out, neutrinos actually oscillate back and forth between the three different types. So, by the time the neutrinos from the Sun had reached Earth, two thirds of them have turned into muon and tau neutrinos. This discovery was especially surprising, since everyone thought neutrinos had no mass, like the photon. The fact that neutrinos could change in-flight implied that they could experience time, and due to special relativity, this means they must have mass.
While that mystery has been solved, we still have plenty to learn from these strange particles. Exactly how much do they weigh? Although we know they must have mass, they are so light, we can’t tell how much. Since they have no electric charge, is a neutrino its own anti-particle? Is there more than just three types of neutrinos? Answering these could help us uncover some of the biggest mysteries in physics today.
Images of the cosmos from the late 1950s and early 60s. Most are from the Mount Wilson and Palomar Observatories. Don’t get me wrong, I love all the high definition and detailed images coming out of Hubble and similar telescopes today, but there is something about these old photos. What they lacked in detail and resolution they made up for with wonder and mystery. Can you imagination how mind blowing these pictures would have been when they first came out of the developing tank in the 50′s?
Strange is our situation here on Earth. Each of us comes for a short visit, not knowing why, yet sometimes seeming to divine a purpose. From the standpoint of daily life, however, there is one thing we do know: that man is here for the sake of other men - above all for those upon whose smiles and well-being our own happiness depends.
The most beautiful thing we can experience is the mysterious. It is the source of all true art and science.
Happy 138th birthday to Albert Einstein, one of the brilliant fathers of modern physics and the founder of physical cosmology and relativity.
In Einstein’s General Theory of Relativity, space and time are unified in a single entity called spacetime. This is the “stage” in which the laws of physics operate.
In Einstein’s theory, the presence of mass and energy warps spacetime, and it is this curvature that affects objects in the way we perceive as gravity. The basic idea is that while we see objects accelerating towards a mass by the effect of a force, in reality is just the object attempting to follow a straight line in this four-dimensional warped space described by General Relativity.
In other words, things fall because they are following a straight line in spacetime.
In usual illustrations, the bending of space is represented as a flat rubber-sheet with masses pressing down on it. This has always bugged me, as it didn’t really represent the nature of 3D space being curved, and it never really addressed the fact that time is also distorted near masses.
This is my first attempt at a better depiction of the effects of General Relativity. Here, we see a 3x3x3 section of an imaginary spatial grid (that extends throughout all of space) being distorted by the presence of a mass. At the intersections of the grid lines there are clocks that show the rate of passage of time at each point in space, relative to a far away observer.
Notice how the clocks near the mass measure time at a slower pace than the clocks further away from the mass.
The distortion of spacetime is real, and can and has been measured experimentally several times. Modern telecommunication satellites and GPS systems all make use of the predictions of General Relativity in order to function.
While bizarre and complex, General Relativity has stood the test of time, and is one of the most well-tested and successful scientific theories ever conceived.
What’s happening to this spiral galaxy? Just a few hundred million years ago, NGC 2936, the upper of the two large galaxies shown, was likely a normal spiral galaxy – spinning, creating stars – and minding its own business. But then it got too close to the massive elliptical galaxy NGC 2937 below and took a dive.
Dubbed the Porpoise Galaxy for its iconic shape, NGC 2936 is not only being deflected but also being distorted by the close gravitational interaction. A burst of young blue stars forms the nose of the porpoise toward the right of the upper galaxy, while the center of the spiral appears as an eye. Alternatively, the galaxy pair, together known as Arp 142, look to some like a penguin protecting an egg. Either way, intricate dark dust lanes and bright blue star streams trail the troubled galaxy to the lower right.
In a billion years or so the two galaxies will likely merge into one larger galaxy.