how do scientist calculate the distance between earth and stars,planets galaxies
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NEAR - PARALLAX
Parallax is used to determine distance to stars closer than ~650 light years. The process is limited by the resolution of the equipment and the angle producible from the diameter of the Earth's orbit. Currently the limit is ~0.005 arc seconds. If we put an observatory on Mars we could use it for more distant stars.
MEDIUM - BRIGHTNESS
The color of a star is strongly correlated with its intrinsic brightness. If a star of a certain color appears brighter or dimmer than expected, that is an indication that it is closer or farther away. Calculating how much dimmer a star would appear at a different distance is pretty straightforward.
FAR - REDSHIFT
The Doppler effect tells us that if an object is moving towards us, the waves it emits are compressed and if it is moving away from us, the waves are elongated. You may notice this when a police car or ambulance passes you, that the siren sounds different as the vehicle is approaching you than when it is moving away. The same thing happens with color.
So, if an object is approaching, the light it is emitting will be shifted slightly in the direction of blue. If the object is moving away, it will be shifted slightly in the direction of red.
If we start with the premise that the big bang happened - that the universe, at the beginning, was infinitesimally small and has been expanding ever since, we can imagine that the galaxies are all moving away from each other. The word choice here can get a little finicky. It isn't necessarily so much that the galaxies are being propelled away, but space is expanding, between those galaxies, so they are becoming farther apart.
That means if we look at a very far away galaxy, it should appear more red than we would expect it to be. We can analyze the components of a galaxy and based on its size, mass, temperature and activity determine what color it should naturally be. The difference between the color it should be, and the color it appears to us is called the redshift. If we correctly understand how fast space expands, we can derive the distance between the two objects. That rate of expansion is called the Hubble Constant (H0). H0 = v/d where v is the radial velocity of the galaxy we're observing and d is the distance from Earth.
Parallax is used to determine distance to stars closer than ~650 light years. The process is limited by the resolution of the equipment and the angle producible from the diameter of the Earth's orbit. Currently the limit is ~0.005 arc seconds. If we put an observatory on Mars we could use it for more distant stars.
MEDIUM - BRIGHTNESS
The color of a star is strongly correlated with its intrinsic brightness. If a star of a certain color appears brighter or dimmer than expected, that is an indication that it is closer or farther away. Calculating how much dimmer a star would appear at a different distance is pretty straightforward.
FAR - REDSHIFT
The Doppler effect tells us that if an object is moving towards us, the waves it emits are compressed and if it is moving away from us, the waves are elongated. You may notice this when a police car or ambulance passes you, that the siren sounds different as the vehicle is approaching you than when it is moving away. The same thing happens with color.
So, if an object is approaching, the light it is emitting will be shifted slightly in the direction of blue. If the object is moving away, it will be shifted slightly in the direction of red.
If we start with the premise that the big bang happened - that the universe, at the beginning, was infinitesimally small and has been expanding ever since, we can imagine that the galaxies are all moving away from each other. The word choice here can get a little finicky. It isn't necessarily so much that the galaxies are being propelled away, but space is expanding, between those galaxies, so they are becoming farther apart.
That means if we look at a very far away galaxy, it should appear more red than we would expect it to be. We can analyze the components of a galaxy and based on its size, mass, temperature and activity determine what color it should naturally be. The difference between the color it should be, and the color it appears to us is called the redshift. If we correctly understand how fast space expands, we can derive the distance between the two objects. That rate of expansion is called the Hubble Constant (H0). H0 = v/d where v is the radial velocity of the galaxy we're observing and d is the distance from Earth.
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