I've been debating a creationist youtuber for quite a while, and I pointed out that many celestial objects are so far away, if the universe is <10000 yearsold, their light would never have reached us, he countered by saying that we judge distance by brightness which is too arbitrary, when I brought up cepheids, he said that the nearest one(polaris) behaves erratically and thus cepheids do not make good standard candles. So, does anyone have any specific information on the correlation between a cepheid's variability period and luminosity, or information about polaris' behavior?
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Cepheid variables
- Thread starter GoodKat
- Start date
Ozymandyus
New Member
Yeah, Aught... it's called measuring by parallax - but its only good out to about 10k lightyears at the best because the movement is too small to measure(and that 10k was only reached in the last decade or two because of Hipparcos). Just tell him we used the standard candle method to predict the distance of stars we could not measure properly with parallax, and then when our technology caught up (hipparcos space astrometry mission)we were able to measure the parallax and the candle method had shown itself to be pretty good - its not perfect but it wasn't more than 15% off the distances for the new stars measured this way.
If he wants to make a stand about it, he can, but tell him that when the Space Interferometry Mission (SIM) gets going soon (was supposed to be 2009 but budget cuts pushed it to 2015...ish) we will be able to up the ability to determine distance by parallax to something near 100000 lightyears or better, and then he can suck it. And Gaia is scheduled to launch in 2010, which will also expand our ability to measure by parallax.
If he wants to make a stand about it, he can, but tell him that when the Space Interferometry Mission (SIM) gets going soon (was supposed to be 2009 but budget cuts pushed it to 2015...ish) we will be able to up the ability to determine distance by parallax to something near 100000 lightyears or better, and then he can suck it. And Gaia is scheduled to launch in 2010, which will also expand our ability to measure by parallax.
AndromedasWake
New Member
Cepheid variable stars are very accurate candles. Polaris is not erratic, but its variability is declining. But Polaris is one of only thousands of CVs used today.
Coma White
New Member
Why not just counter with radiation dating techniques? Half-life, and so forth. Forget celestial bodies and the speed of light. The Earth cannot exist without the universe, and we can prove beyond all rational doubt that the Earth is far, far older than 10,000 years.
CW
CW
He hasn't really expressed his opinion on radiation dating yet, probably because he knows it's unscientific. He likely thinks what I thought when I was a fundie, that God created the earth with "apparent age", far away stars present one of the best problems for this because if God did indeed create the universe only <10,000 years ago, and the stars we see never existed, then He intentionally set up a vast, completely unnecessary illusion to fool us.Coma White said:
monitoradiation
New Member
Well you should just ask him how close he thinks the closest star is first, and if it's more than 6000 lightyears away. If he says something stupid like "Oh, the closest star is like millions of lightyears away BUT god put the light enroute to earth only 6000 light years away so we can see it" bullcrap, then I don't think there's any more reason to keep talking to him, there's just no winning with some people.
Polaris is not a typical Cepheid (it's a so-called first-overtone pulsator). The prototype of the Cepheid variable stars is Delta Cephei (from which the name Cepheid is derived). The construction of the Cepheid Distance Scale has a long and complicated history (for an overview, see here), but after the correlation of several hundred Cepheids with their Hipparcos parallaxes (Feast & Catchpole, 1997), and corrections like metallicity effects (Macri et al. 2006) the accuracy of Cepheid distances is now very reliable. And when the Gaia mission with expand the parallax data to a staggering 1 billion stars upto 30 000 light-years away, the subsequent Cepheid Distance Scale will also improve considerably.
And we know it works. Not only do Cepheid distance measurements agree with each other (we can see dozens of Cepheids in nearby galaxies), they also agree with other techniques. And this is something fundies don't seem to get. Just like they seem to think that only carbon dating exists, they're only aware of parallax and Cepheids (or not even that). Yet there's a vast number of distance measurements. A classic example is the Large Magellanic Cloud, where many distance measurements yield consistent results (for instance, the famous distance measurement of supernova SN1987A based on the time it took for the light to reach the outer ring). If you want an overview of the most-used distance measurement methods, see this list, which has more than 30. Or wiki. And new methods keep being discovered, like ultra long period cepheids.
And we know it works. Not only do Cepheid distance measurements agree with each other (we can see dozens of Cepheids in nearby galaxies), they also agree with other techniques. And this is something fundies don't seem to get. Just like they seem to think that only carbon dating exists, they're only aware of parallax and Cepheids (or not even that). Yet there's a vast number of distance measurements. A classic example is the Large Magellanic Cloud, where many distance measurements yield consistent results (for instance, the famous distance measurement of supernova SN1987A based on the time it took for the light to reach the outer ring). If you want an overview of the most-used distance measurement methods, see this list, which has more than 30. Or wiki. And new methods keep being discovered, like ultra long period cepheids.
Einstein's_Advocate
New Member
GoodKat said:
I don't know anything about cepheids, but I do see a very large flaw in his reasoning. One method of determining distance in astronometry is by brightness. The problem is, brightness of a star is a complete red herring. In order for you to be able to use brightness, you have to have the light reach you in the first place. And light travels at a finite rate, which means that it would take a hell of a lot of time in order for that light to reach you (millions or billions of years), regardless of anything else. We also measure distance by things like gravitational lensing and red shift.
So, he's fantabulously wrong in his first premise.
Einstein's_Advocate
New Member
GoodKat said:
Then he's an idiot. We measure distances, from my understanding, on blue shift and red shift. So I'm assuming then he's contesting general relativity then?
aeroeng314
New Member
Not really. That tells you about relative velocity, not distance (at least not until you correlate the frequency shift with Hubble's law and work out a rough distance from that, but that's not really used for anything but the largest distances where motion of the observed object has a smaller effect).
Netheralian
New Member
GoodKat said:
So he is claiming the the entire mass of the universe is within a 10,000 LY radius? Since we know that it takes a certain mass of object for a fusion reaction, there would have to be the total number of light emitting objects in the universe within 10,000 years of us. Without trying any numbers I would expect your would have a pretty fast gravitational collapse of the entire universe if that was the case (even if all the stars were the minimum possible mass).
A second argument would be that the galaxies that we see in the distance, if they were 10,000 LY away, would have to be so tightly packed with stars they just wouldn't be gravitationally stable (or even fit!). Take NGC4414 for example (only because it was the first galaxy that came up in Wiki). It is 62.3 MLY away and is some 55,000 LY in diameter (apparent size ~3'6 x 2'0). If it was 10,000 LY away (and obviously I could have picked a much further galaxy which would make the calculation even worse) there would be some 10 billion stars in a diameter of some 8.8 LY. I.e. an entire galaxy where Alpha centauri to the sun makes the galactic radius...