It is only possible for us to precisely and directly measure objects 1000 light years away using telescopes. Therefore, astronomers use the cosmic distance ladder, which is a series of methods, to find the distance of far away celestial bodies. There are five different way used to find the distances of planets, stars, galaxies and more. The first way is using radar ranging to measure how far away objects in our solar system are. The distance between us and nearby stars, 100 light years away are measured using spectroscopic parallax. Main-sequence fitting is used to find the distance between the Earth and objects on the other side of the Milky Way galaxy, approximately 100,000 light years away. A method called Cepheids measures objects 10,000,000 light years away in nearby galaxies. Finally, the distance to galaxy clusters and objects further away than that are measured using Hubble’s Law equation of d=v/Ho. Radar Ranging is when a signal, such as a radio pulse, is fired at a nearby celestial object. This signal is then reflected back to Earth and by dividing the time it took for the pulse to be sent and received by two, we can work out the distance of the object. This method is one of the most accurate ones of the cosmic distance ladder. The spectroscopic parallax method uses the Hertzsprung-Russell (HR) diagram to measure the distance between Earth and a nearby star. Firstly, by using the different types of spectral lines in the star’s spectrum, astronomers can find where the star belongs on the x-axis of the HR diagram by determining the star’s spectral type. Next, astronomers work out where the star belongs on the y-axis depending on its luminosity (between I and V). A V classed star would have thick absorption lines on its spectrum. This is because the density of atoms in the outer layers of the star is high. However, a star classed as I would have very thin spectral lines due to the low density of the absorbing atoms. So by using where the lines of the plotted x-axis and y-axis meet, astronomers can work out the absolute magnitude of the star. By using this, and the apparent magnitude, the distance to the star can be worked out through the equation m - M = 5 * log (D/10). Main-sequence fitting also uses the HR diagram, but only is used for a cluster of stars. 90% of the stars in the cluster are on the main sequence because they are all gravitationally bound, located at the same distance from Earth and formed at approximately the same time from the same cloud of dust and gas. The method of main sequence fitting compares the apparent magnitude and the absolute magnitude of the main sequence for the cluster of stars. The vertical position of the main sequence of the cluster is adjusted so that it lines up with the main sequence of nearby stars. The distance is worked out by how much the main sequence of the cluster was adjusted. Cepheids are variable stars meaning they change brightness on a regular pattern. They were discovered by Henrietta Leavitt, an American astronomer, in the early 1900’s. Astronomers measure the pulsation period of Cepheids to work their absolute magnitude and therefore their apparent magnitude. By using the equation m - M = 5 * log (D/10) astronomers can work out the distance between Earth and nearby galaxies. Hubble’s Law states that the redshifts in the spectra of distant galaxies are proportional to their distance. In 1929 Edwin Hubble realised that the universe was expanding and estimated that it was doing so at a rate of around 65 km/sec/Mpc (known as Hubble’s constant). However, the exact expansion rate is still unknown. So by finding the velocity of a celestial body (by using the Doppler shift), we can use the equation d=v/Ho to work out the distance between us and the object.
In conclusion, the cosmic distance ladder offers a range of methods for astronomers to measure the distance of objects in the universe, whether in our solar system or outside our galaxy. Selina, Year 11 (Before we start, these are all only theories and would occur in billions of years time so no need to freak out!) There are 3 main theories as to how the universe will end, depending on which of these becomes dominant - gravity, entropy or expansion. 1 - The Big Rip - Expansion Wins The universe is expanding at an accelerating rate, therefore we can assume that at some point the universe will expand so fast that gravity cannot compensate for the expansion. This would result in everything, including atoms, being torn apart. Eventually, the universe would expand faster than light. As the speed of light cannot be exceeded by any particle, no particle would ever be able to interact with any other particle again, turning the universe into a strange timeless void. 2 - Heat death - Entropy wins In this (intense sounding) theory the universe continues to expand forever, and while this happens all matter slowly decays and spreads out, until it is all converted into radiation. The universe gets colder. The is eventually no activity in the universe as it has reached maximum entropy, which means that all energy as evenly spread out and the universe has reached equilibrium, and no work (energy transfers) can ever be done again. However, it may be possible to have a spontaneous entropy decrease after very long time, leading to a new big bang. 3 - Big crunch and big bounce - gravity wins If the universe's expansion stops, gravity becomes the dominating force - so the universe contracts instead of expands. As the universe gets smaller, it also gets hotter. 100,000 years before crunch, background radiation everywhere would be hotter than the surface of the sun. Eventually all black holes would merge into one black hole containing the entire universe’s mass, which then consumes the whole universe including itself!? The Big Bounce theory states the universe is in an infinite cycle of expansion and contraction. The fate of the universe essentially depends on the shape of the universe and the role of dark energy. Currently many cosmologists believe that the universe is flat and will continue to expand forever, so at the moment the most likely theory is thought to be the Big Rip.
Izzy, Year 11 The first thing to clear up is that you can’t actually hear anything in space as we can on Earth. The only way you would be able to hear anything occurring in space is if a supernova exploded really close to the Earth. Even then, it’s not the sound of the explosion that you would hear, it would be the sound of our own atmosphere being ripped to shreds as the debris and light pressure produced hit it. Then we’d all be dead. The reason why we can’t hear anything in outer space is because sound waves are transmitted as particles collide with each other. In space, there are none of these particles, because space is a vacuum. Actually, to be more specific, not all of space is a total vacuum (think of the stars and the planets, etc.), but interstellar space, the space between these massive objects, has so few particles that they will never collide into each other. This means that, for example, any sound produced from you hitting the side of a satellite without a spacesuit on (imagining that you aren’t already dead), wouldn’t reach your ears. However, if you did have a space suit on, and you hit your head against the side of the said satellite, you would hear the noise, as the waves could travel through the particles in your helmet. Similarly, it is possible to hear radio transmissions from other astronauts, as radio waves use electromagnetic waves, which, like light waves, do not require matter to travel. Once these waves reach your radio, the radio can convert the signal back into sound for you to hear through your helmet. However, after everything I’ve just told you, these electromagnetic waves are what actually enable us to ‘hear’ in space, to some degree. Various space probes have recorded electromagnetic vibrations which naturally occur in the vacuum of interstellar space. They do this by recording interactions between solar winds and our planet, as well as the rings of Saturn and Jupiter, and the moons Io and Miranda. When these recordings are sent back down to Earth, scientists can convert them into sounds, like the radios do inside the astronaut’s helmet. It can create eerie sounds like these, which were recorded at saturn’s rings: The deepest ever note detected in our universe was a B♭, which was detected from a supermassive black hole located in one of the cluster of galaxies in the constellation Perseus, 250 million light years from Earth. It’s actually impossible to hear the note as a human, as 9.6 million years is the estimated time period of its oscillations! As well as this, it is 57 octaves below the note ‘middle C’, which the note in the middle of the piano, which is far beyond human hearing range.
Eleanor, Year 11 All the matter that is known to us only accounts for less than 5% of the matter in the entire universe. About 27% is dark matter and 68% is dark energy. Scientists do not know what dark matter or dark energy is or how they work. They have just come up with many theories that still have to be proven. At the moment, scientists are unable to detect or measure dark energy and matter because they do not act like the matter that we know. Scientists only know 3 factors that prove that dark matter and energy must exist:
The gravity of normal matter is not strong enough to form complex structures such as galaxies. Stars would just be randomly placed with no order throughout the universe. Something else must be around normal matter with enough gravity to hold stars and normal matter together. Dark matter does not emit or reflect light as we are unable to see it or sense it. Places with a high concentration of dark matter bend light passing by. The only possible solution to this is something else that we are unable to detect. At the moment, scientists know what dark matter is not more than what it is. Dark matter is not cloud of normal matter without stars because it would emit particles that we would be able to detect. Dark matter is also not antimatter as antimatter creates gamma rays when it reacts with normal matter. As well as that, dark matter is not made up of black holes as it is scattered everywhere. We cannot measure or detect dark energy but we do see its effects. It is what causes the constant acceleration of the expansion of the universe and it is stronger than anything we know. Also, dark energy has to be becoming stronger and stronger. Empty space has more energy than everything else in the universe combined. Scientists have 4 possible theories on what dark energy could be:
So overall, no one actually has any idea what dark matter or dark energy is. We just knows that it has to exist otherwise many things in the universe would not be as they are. Considering scientists do not know how to measure or detect dark energy and dark matter, it could be a while till we find real evidence that they do exist and a theory is proven. Selina, Year 10 |
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