I was looking in the exoplanet catalog yesterday at one of 373 listed exoplanets. What surprised me most was that the distance to its star was listed as 200 pc +/- 100 pc. Wow, that’s a very uncertain number. I guess the primary distance measuring method for stars is parallax. Our baseline for measuring is ~2 AU or 186 million miles. That seems harder than just measuring a simple change in angle. We’re measuring from a spinning Earth, so you have to take the measurement at the exact second. Making it even trickier is that a star that appears at night will be in daylight 6 months later when earth is on the other side of its orbit. Tricky calculations indeed!
Turning to galaxies, I thought about what I’ve heard as the distance to Andromeda. Estimations range from 2,000,000 LY to 3,000,000 LY, but mostly around 2.5 million LY. Still, not too specific. I suppose distances to galaxies are estimated using two methods. First, there’s the red shift, but galaxies tend to jostle around a bit and so nearby galaxies like those in the local group … red shift doesn’t have much value. At greater distances, like more than 1 billion LY, expansion would cancel out local jostling. Andromeda in fact is getting closer, so its blue shift doesn’t lend itself to that method. Another method is “standard candles” (Type II-plateau supernovae) but since a galaxy might only have one supernova in 100 years (and not necessarily a Type II-plateau supernova, it too doesn’t seem very useful in measuring distance to a particular galaxy.
My questions: are these methods (parallax, red shift, and standard candle) the only methods at our disposal; and are the examples above really the best we can do in pinning down large astronomical distances? Exactly how consistent is the brightness of Type II-plateau supernovae?
Turning to galaxies, I thought about what I’ve heard as the distance to Andromeda. Estimations range from 2,000,000 LY to 3,000,000 LY, but mostly around 2.5 million LY. Still, not too specific. I suppose distances to galaxies are estimated using two methods. First, there’s the red shift, but galaxies tend to jostle around a bit and so nearby galaxies like those in the local group … red shift doesn’t have much value. At greater distances, like more than 1 billion LY, expansion would cancel out local jostling. Andromeda in fact is getting closer, so its blue shift doesn’t lend itself to that method. Another method is “standard candles” (Type II-plateau supernovae) but since a galaxy might only have one supernova in 100 years (and not necessarily a Type II-plateau supernova, it too doesn’t seem very useful in measuring distance to a particular galaxy.
My questions: are these methods (parallax, red shift, and standard candle) the only methods at our disposal; and are the examples above really the best we can do in pinning down large astronomical distances? Exactly how consistent is the brightness of Type II-plateau supernovae?
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