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Episode 124 - The Astronomical Distance Ladder

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Recap: Measuring distance in every-day life requires some basic tools like a ruler. But who holds the other end when we want to measure the distance to the next galaxy? In response to young-Earth creationist claims, this episode delves into some of the science of how we measure distances across the cosmos and how all those different measurements fit together in what we call the Astronomical Distance Ladder.

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Episode Summary

Claim: I’ve been wanting to do this episode for over two years, but I haven’t been able to find a good angle. Then I found an old Coast to Coast episode from almost exactly 16 years ago when Art interviewed the now-convicted felon, Kent Hovind, a young-Earth creationist. In it, Mr. Hovind tried to claim in typical creationist spin that we have no idea how far away objects are, therefore you can’t claim that objects are billions of light-years away, therefore the claim that light had to travel that long to get here is moot and you don’t even have to invent new physics about light speed changing to make the universe only 6000 years old, which was the topic of Episode 81. So, that’s my vault to launch into an episode of how we know how far away things are in the universe.

Kent Hovind: Overview

Before we really get started, I’m going to give a gratuitous and very brief overview of Kent Hovind. He is a young-Earth creationist of the extreme kind. If you listen to him speak for any period of time, you will hear him deny basic science - which is significant considering he was a grade school science teacher for many years - you will hear him double-talk and avoid direct questions to answer the question he wants to, you will hear him say that dinosaurs are still alive and are what cryptids are like the Lake Ogopogo monster and Nessie, and then stuff that he doesn’t want to address he will simply say is “baloney,” such as how the dinosaurs died, or that there are areas of reversed magnetic field in Earth’s crust. I’ve used a few of his clips before in past creationism-themed episodes.

Mr. Hovind is not a Ph.D. despite calling himself a “Doctor.” His degree comes from a diploma mill in Colorado, Patriot University, in 1991. The introduction to his thesis starts with, “Hello, my name is Kent Hovind. I am a creation/science evangelist. I live in Pensacola, Florida. I have been a high school science teacher since 1976.” And it goes downhill from there with sentence structure you would expect of an elementary school student, including multiple exclamation points at the end of sentences, lengthy quotes so he doesn’t have to write, the insertion of random poems he wrote, not knowing that A.D. goes before the year, and various other things that would be rejected by any real thesis committee. That is why I will not refer to him as “Dr. Hovind."

Who is also in jail. Serving time in federal prison, as is his wife, for tax fraud. Effectively claiming he was in the kingdom of god and therefore not subject to US taxes. Yes, there are lots of other bits to the case and those aren’t his exact words, but that’s the basic idea if you look into it.

With that said, as with many of the Coast to Coast guests that I have used clips from in various episodes, he is incredibly frustrating to listen to. And now that I got that out of my system, you get to listen to him for a few minute — and I promise, this is the only clip in this episode, the rest is me droning on about science, but you need to get an idea of how he makes his argument.


Clip from Coast to Coast AM, January 06, 1998, starting at 48:15 into the program:

Art Bell: “Now, that does lead us to a rather intriguing question, and that is, we are receiving light, Doctor, from stars that are as many as 15 or more billion years out, in light-years, how could that that be if Earth is 6000 or even 100,000 years old?”

Kent Hovind: “Well, which of those do you wanna tackle first?"

AB: “I don’t care, you pick it.”

KH: “This is a typical, uh, uh, ploy of an evolutionist who’s getting desperate. They will say something like uh, ‘You have to discard all of biology, you know, uh, etc.,’ as if all of those — just by calling those names of those sciences, that’s somehow is evidence for evolution—”

AB: “And … ?”

KH: “—which it certainly is not. Uh I like all of those sciences, I collect information on all of that. And, and taught it, and loved it. And still study on it. And there’s definitely nothing in all of those sciences to-to go against the creation, uh, uh, philosophy. There’s no uh, hard science in those branches.”

AB: “Well, let us— let us pick astronomy, since we gave that— [unintelligible]”

KH: “Okay, if someone tells you a star is 15 billion light-years away, I would like to know how they figured that number, uh, you know, who held the other end of that ruler, how did you measure that? I taught trigonometry, um— From trigonometry, you-you can only measure, uh– You can measure a triangle if you know two sides and one angle, or two angles and one side. You can get a little further by using what’s called a “parallax method,” where you— One-once you know one point, you compare it to another point as we move around the sun. But Earth’s orbit around the sun is uh, 16 light-minutes across. If we convert this all to uh, um, inches, to make it easier, let’s say Earth’s orbit is 16 inches across, Art, and we can look at a star in January and look at the star in June. We have two observation points. We can now make a triangle, out to the star. The problem is there’s over half a million - 526,000 minutes - in one year. If I told you to draw a triangle that is, uh, Point A and B are 16 inches apart, Point C is 526,000 inches away. You now have a very skinny triangle.”

AB: “You sure do."

KH: “That would be like having Points A and B uh one foot apart, and Point C 6.2 miles away. You get two surveyors to set up their transits 1 foot apart, focus in on a dot six miles away, and tell me the angle. Of the distance."

AB: “So what you’re saying is, it is impossible for them to measure."

KH: “That’s absolutely correct. Nearly all astronomy books, uh, will say, ‘Using parallax trigonometry,’ - the only real hard science to measure these distances - ‘we’ll give you a maximum of 100 light-years.’ I think even 100 light-years is stretching it as far as being able to prove anything, you know, accurately, because you’re dealing with such minute measurements. You’re dealing this out to, I don’t know, 15 decimal places as far as measuring your angle. It just– it can’t be done. Okay, that does— I’m not saying the stars aren’t that far away. They might be. But I think modern scientists have this tendency to want to make everybody think, ‘Hey, we’re smart and we know everything,’ and that’s simply not true. There’s an awfully big universe—"

AB: “So you’re not completely discounting?"

KH: “Oh no, they could be that far away.”

AB: “But if they are, God put them that far away so we could look up into the night sky and observe all this, um, endless depth of beauty.”

KH: “Sure, and oh wow, is the effect. There’s three things I would point out as far as the question of star light. Number one, we simply cannot measure those distances, no matter what anybody says. So they’re making up those numbers. They’re basing it— they-they’re-they’re making up the numbers based on the luminosity — You know, ‘Well, it looks pretty bright, therefore it must be close, or it doesn’t look too bright, therefore it must be pretty far away.’ Pretty shaky ground, you know, take that to any court of law and see how far you get. [Art chuckles] Um, so they could be that far away, my point is they can’t measure it. Secondly, there’s absolutely no way to prove the speed of light has always been consistent all through space and all through time. The whole idea behind a black hole is that light can be affected by gravity, and therefore cannot escape because the escape velocity of this dense material is beyond 186,000 miles a second."

AB: “Right you are!"

KH: “So if light’s affected by gravity, is the speed of light a constant? Could light be accelerated toward galaxies and decelerated away from galaxies? Um, there’s no way to prove the speed of light has been the same, you know, all through history. All we’ve ever measured is here on Earth in our atmosphere. So, we don’t know the speed of light is a constant, necessarily."

AB: “Well I believe science does try and determine the distance, uh, by the amount of redshift.”

KH: “Okay. Nobody knows for sure what’s causing the redshift. They think it might be the Doppler effect, um, if the planet or the star is moving away, uh you get the same effect as if you’re sitting at a train track and you hear a train coming in, the-the-the pitch in the train whistle changes as it passes you."

AB: “That’s for sure.”

KH: “That’s called the Doppler effect of sound. Uh, the theory is, that maybe the same effect effects light, that light is shifted by a Doppler effect. And could be. I’m not arguing. But, if the star is moving toward us, it would get a blueshift. And certainly, some of the stars do exhibit a blue shift. […] And some of the stars give a red shift some of the time and a blue shift some of the time.”

After a minute-long digression into the big bang, Hovind gave the third reason as being that God simply could have made everything look old even though it’s recently made.

Distance Ladder: Idea

Now that you have an idea of what some young-Earth creationist types claim, I can spend the rest of the episode completely ignoring them and talking about this important concept. Like much of astronomy today, this is something that required the technological advances of the 20th century to be developed.

The entire concept is that there are different types of methods for figuring out how far away an object or group of objects is in space, and each method has a limited distance over which it works. But, because there are so many, they overlap, and therefore each overlap is used to calibrate, or bridge, between different techniques.

In this sense, you would use the lowest rung on the ladder to measure close objects, another rung to measure farther away objects, and another for more distant ones, and each one is calibrated by neighboring rungs.

Distance Ladder: Solar System

One of the most basic and fundamental units of measure in the distance ladder is the astronomical unit or “AU”: The average distance between Earth and the Sun. This is important because knowing how big it is is required for our second rung on the ladder, which I’ll talk about in a minute or so.

Kepler’s Three Laws of Planetary Motion are what set us up for measuring distances across the solar system. His third law, that the cube of a planet’s distance from the sun is equal to the square of its year, provides us with a direct way to measure how far away objects are. His form was a proportion, where the planet’s distance was measured in AUs and the year was measured in Earth years.

Newton’s form of Kepler’s Third Law allowed us to put real numbers in once the gravitational constant was determined two hundred years later, but we still didn’t have a good measure of the AU, this fundamental unit of measure in the solar system.

To get that, we measured Venus going across the surface of the sun. Some of you who pay attention to astronomy and are more than 15 years old (and just saying that makes me feel old) may remember in 2004 and 2012 when there was a lot of hubbub about the transit of Venus in front of the sun. This is the rare case where, because Venus’ orbit is tilted relative to Earth’s, you only get pairs of transits 8 years apart and then 121.5 or 105.5 years apart.

This event was touted in the media because the last pair, back in 1874 and 1882, represented the last time we could measure the AU by the only method that, at the time, was thought to be able to give that measurement. What I mean is that since 1882, we developed other methods, but back in 1882, it was thought this was the only way to measure the AU. The previous pair, in 1761 and 1769, was the first major effort by the world’s population of scientists that the AU was attempted to be measured.

The idea is that we know from Kepler’s laws that Venus is at about 0.7 AU from the sun. And, we know that Earth has a certain size. If you are at one part of Earth, and a friend is at another part of Earth, and you know the distance between, then you can both observe when Venus first starts to transit the sun. It will be slightly different. If you and your friend are the same distance apart and the AU was really big, then Venus would appear to enter the sun’s disk at nearly the same time. If you and your friend are the same distance apart and the AU was really small, then Venus would appear to enter the sun’s disk at very different times. And by “very different,” I mean many minutes.

So, it all gets down to geometry. Two observers at different spots will observe the event happen at slightly different times because of the angles being different.

When this was first attempted by Jeremiah Horrocks in 1639, he got a distance of about 59.4 million miles or 95.6 million meters, off by a factor of a third. In 1761 and 1769, many world governments sent out observers carrying the latest clocks and observing equipment. When the numbers were crunched, different people got values off by only 1%. In 1874 and 1882, more observers were sent out, and based on the observations, we knew the AU to better than 0.2%, or about 310,000 miles.

The techniques of measuring the AU today are different, and they are much more precise: They involve radar sounding of Venus, basically hitting it with high-intensity radar and seeing how long it takes the radar signal to return. We use not only Venus, but spacecraft and asteroids, too. Since we have incredibly precise measures of the speed of light today, the AU can be calculated to a precision of about ±30 meters, or 0.000,000,02%.

The techniques of measuring the AU today are different, and they are much more precise: They involve radar sounding of Venus, basically hitting it with high-intensity radar and seeing how long it takes the radar signal to return. We use not only Venus, but spacecraft and asteroids, too. Since we have incredibly precise measures of the speed of light today, the AU can be calculated to a precision of about ±30 meters, or 0.000,000,02%.

The AU forms the foundation of our distance ladder and is a fundamental measurement based on the size of Earth, the speed of light, and the physics of Kepler’s Laws which are a manifestation of the Law of Gravity.

Distance Ladder: Stellar Neighborhood

The next rung on the distance ladder is the only other direct method of measuring distance, based on simple, every day geometry, and it requires knowing the AU. It’s called parallax.

The idea behind parallax is that you have two observation points, and because each observation point is looking at an object at a slightly different angle, it will appear to be in a slightly different place relative to a more distant object. The classic, simple example of this that you can do even if you’re listening to this on your morning commute, unless you’re in heavy traffic, is to hold up one finger a little in front of your face, and close one eye. Line your finger up with a somewhat nearby object, like a light post. Now open the other eye and close the first one. Your finger will no longer block the light post. That’s the effect of parallax.

Now, use that same idea but with not your two eyes as the two observation points, but Earth, in its orbit around the sun, six months apart. Exactly six months apart, and Earth gives you a baseline of 2 AU. Take a very careful picture of the sky at each point, and look for stars that have moved from one picture to the next. A star that’s close will appear to have moved relative to stars that are farther away.

You might be thinking that this takes ridiculously careful and precise observations and measurements. And it does. The first stellar parallax wasn’t discovered until 1838 for star 61 Cygni, which is about 3.498±0.007 parsecs away.

And now, I’ve introduced a new unit of measure: The parsec. Parsecs are based on the fundamental unit of measure in the solar system - the AU - and 1 arc second. Remember that there are 360 degrees in a circle, each degree is made of 60 arc minutes, and each arc minute is made of 60 arc seconds. To give you an idea of how small these angles are, the moon is about half a degree across, or about 30 arc minutes, or about 1800 arc seconds. A human hair, held 10 meters (30 ft) away, is 1 arc second across. Very small.

Why do we care? Because a parsec is defined as the distance an object must be from Earth to show a parallax movement against the sky of 2 arc seconds in 6 months. Why 2? Because the parallax is actually defined as half of the motion so you can use right triangles to make the math easier. It’s one of those things that really doesn’t matter for this discussion: The take-home message is that if you measure a star move against the background of stars by the width of two human hairs held 10 meters away over the course of 6 months, then it is 1 parsec away. Which is about 3.26156 light-years.

This is a VERY small motion, but it is visible. It is also why you’ll hear a lot of astronomers who do astrometry - the study of precisely measuring positions - will talk about distances in parsecs rather than lightyears. You’ll also hear a lot of galactic astronomers talk in units of parsecs or kiloparsecs (kpc) or megaparsecs (Mpc) because the distances to their objects are based on the distance ladder which has, as its second rung, parallax, which uses parsecs as its primary distance of measure.

This is also why I said you have to know the AU to know a parsec: The AU is your baseline. So you can measure all these angles and report distances in parsecs, but unless you know the value of the AU, you can’t convert that parsec into a real, physical measurement. In fact, based on the dates I’ve given you in the last few minutes, we were measuring stellar parallax decades before we had a good estimate for the AU. This is also why you’ll still often see distances given in parallax units - the angle of milliarcseconds (“mas") - rather than real physical units: The angular measurement is the more fundamental, observational number, while the conversion to light-years or something else is based on other rungs of the distance ladder.

With all that said, how far does parallax get us? Again, for an object to be 1 parsec, it has to move a tiny amount. But, astronomers are really good at making very VERY precise measurements. So good that precision is typically on the order of milliarcseconds. And, we’ve sent satellites up with the singular goal of doing this for a whole lotta stars.

The Hipparcos satellite in the 1990s measured parallaxes for over 100,000 stars out to a few hundred parsecs. Its successor, Gaia, is currently taking data and has the goal of measuring distances to 1 BILLION objects by being able to measure accurately to about 20 MICROarcseconds (µas). Meanwhile, Hubble, with its current WFC3, can also measure to about 20-40 µas. This kind of precision allows us to measure objects about 5000 pc away, or about 5 kpc. That is still within our galaxy, but it lets us get to the next rung of the distance ladder, which takes us out of the realm of direct measurements and into the realm of standard candles.

And I lied a few minutes ago because I’m going to go back to the creationism claim: Already, with just these direct measurements, we are well beyond 6000 light-years, and that’s still within our own galaxy.

And another quick note before we get to standard candles is that there are other kinds of parallax known as “statistical parallax,” “moving cluster parallax,” and “expansion parallax.” I’ll just mention that the statistical parallax lets you get farther because it relies on measuring red shift and blue shifted spectra of a tight group of stars and this is an easier measurement to make than astrometrical positions. But, that’s all I’m going to say about it.

Distance Ladder: Aside for Standard Candles

The idea behind a standard candle is in its name: It is a standard candle. A candle, made to a certain standard, such that they are all the same. So, if I open a box of candles and I assume they are all the same, and I have a friend light several of them and place them at different distances from me in a darkened room, then I can assume that the ones that are dimmer are farther away.

In fact, if I precisely measured the amount of light coming from each one, I could use the inverse-square law for light (that the intensity drops off by the square of the distance to the object) to determine how far away it is relative to all the other ones I measure. So, if I measure the brightest candle, and then measure another and is only 25% as bright, I know it is twice as far away from me as the first one.

Now, all I have to do, or all I need, is to know the real distance to the first one, and then I can use the principle of these being standard candles to know the distance to all the others. Fortunately, I know how far apart my eyes are and that first one is close enough that it shows a parallax.

Distance Ladder: Galaxy

And THAT is the idea of the distance ladder: We use lower rungs to calibrate the closest objects on the higher rungs. The most popular standard candle that is closeby is known as a Cepheid variable star. Cepheids are easy to identify, are very bright, and they are a standard candle.

They are a variable star and first proposed to be used as a standard candle by the Harvard astronomer Henrietta Swan Leavitt in 1908, which I like to point out because not only are Cepheids incredibly important, but this was an early contribution to astronomy by a female scientist in days when the field was still almost exclusively done by men.

Cepheid variable stars, named for the type star that was first studied in detail, delta Cephei, pulsate in brightness on cycles ranging from days to months. And, based on those that can be directly measured distance-wise with parallax, there is a direct relationship between how long the pulsation lasts and how bright it really is.

Remember: We have an inverse-square law for light, so we can measure how bright something appears to be, but we don’t know how bright it REALLY is unless we can measure its distance. So, when we can get the distance by parallax, we can know how bright it really is. And the pulsation period just takes simple observation that most amateur astronomers can do these days, and there are whole societies built around, like AAVSO (American Association of Variable Star Observers).

So, we calibrate the Cepheid period-luminosity relationship with parallax. Then, because Cepheids are very bright, we can observe them throughout our own galaxy, but also we can observe them in neighboring galaxies like Andromeda.

Understanding the Cepheid period-luminosity relationship is a critical part of the distance ladder, and it was one of the original primary goals of the Hubble Space Telescope: Get the parallax to more distant Cepheids so we can better calibrate this rung of the distance ladder.

With that in mind, some Cepheids are anomalous and there are some unresolved issues. However, they do not contribute significantly to the uncertainty in the method, and Cepheids are very good for measuring distances out to about 1 Mpc, the Andromeda Galaxy. In fact, it was Edwin Hubble who used Cepheids in 1924 to show that the Andromeda Galaxy was much farther away than anything in our galaxy, which solved what, at the time, was known as the Great Debate in astronomy.

Distance Ladder: Local Group

Since Cepheids get us to neighboring galaxies, they get us to supernovae. Specifically our next standard candle, Supernovae of Type 1a, or abbr. as Sn1a.

Often, the only kind of supernova that people think of is an exploding giant star at the end of its life. That would by Type 2.

Type 1a is a very specific kind of stellar explosion and because it is so specific, it is a standard candle. It happens when you have a binary star system, so two stars orbiting each other, and one of the stars is a white dwarf. This white dwarf - the burnt-out core of a previous star - is so close to its companion that it pulls material onto its surface. When it reaches 1.44 solar masses of material - called the Chandrasekhar Limit after its theoretical discoverer - the force of gravity on the core of the star is too much, and it collapses into a neutron star.

I should note that this is what I was taught and still seems to be the broad consensus view, but there is a different mechanism in the literature as to why these happen. Regardless, however, because of the fundamental physics limit of stars being able to support themselves, the energy released is the same from event to event, and so we have a standard candle. And, this standard candle, because its rarer than Cepheids, and hazardous to life on Earth, hasn’t happened nearby such that we’ve been able to observe it.

So, the distances to Type 1a supernovae are calibrated with Cepheids. And, because they are about 5 billion times brighter than the sun, they are visible across a lot of the universe, getting us out to GIGAparsecs (Gpc). The observation of Sn1a are so important as standard candles that there are telescope facilities that have a standing policy that if any Sn1a are discovered, they immediately stop observing what the astronomers who had it that night wanted to observe, and they instead observe the supernova.

By measuring its light curve, which is the brightness over time, we can get how bright it appears at its brightest from Earth. Then, again, by using the inverse-square law for light, since we know how bright it should have been if it were a known distance away because of Cepheid variable calibration, we know how far it really was based on how bright it appears.

By using this, we can get distances of all types of galaxies more than half-way across the visible universe — billions of light-years away.

Distance Ladder: Distant Galaxies

The final rung of the distance ladder that I’m going to discuss in detail is Hubble’s Law, which relies on redshift. Hubble’s law is based on the fundamental picture of the universe that it is expanding. Which even creationists tend to recognize because it states in the Bible something about God stretching out the heavens.

Hubble’s law can be succinctly thought of like a moving walkway on a moving walkway on a moving walkway ad infinitum. But let’s just picture a person on a sidewalk. That’s us, and the sidewalk is the universe. As we stand on a busy sidewalk, we see people moving around us in different directions at different speeds. That would be a static universe.

Now, picture a moving sidewalk that is set up in such a way that it moves away from you in all directions. And, the farther it is from you, the faster it is moving — hence the idea of a moving sidewalk on top of a moving sidewalk on top of a moving sidewalk, or something like that.

So, nearby, people can still move around you in all directions at all speeds. Their own motion is very large in comparison with the motion of the sidewalk that is trying to carry them away. But, as someone get farther and farther away, their own motion is minuscule compared with the motion of the sidewalk, and so they are ALL moving away from you once you get to a certain distance. And, if you measure a big group of them that are all the same distance away — perhaps because they’re all holding a standard candle — then you can average out their individual motions and get a pretty good estimate for how fast the walkway is trying to carry them away from you.

That’s the idea behind Hubble’s Law: Once you get out to about 10 Mpc, the expansion of the universe dominates over individual motions, and the distance is simply the velocity the object is moving away divided by Hubble’s Constant.

I said “simply,” didn’t I? This was actually the subject of a lot of debate as I was entering undergrad, but it’s been pretty much consensus-ized since then.

The velocity measurements are easy: Redshift. This is another DIRECT measurement that can be made the requires no assumptions. You measure the spectrum of a distant object, and you compare it with a similar object from Earth — like looking for specific hydrogen lines in stars. Those hydrogen lines must be at certain wavelengths of light because of quantum mechanics. But, in these distant objects’ spectra, they will be at different wavelengths once they get to Earth, stretched out due to the expanding universe. All you have to do is measure where they are now relative to where they should be, and that’s the redshift, or “z” value.

As a side note: Just like star distances are often quoted in parsecs which rely on just the angle of motion, if you look at measurements of distances to far-away galaxies, they will often be quoted in terms of “z” measurements. Since THOSE are the actual data being measured.

Converting the z value to a real unit of distance requires knowing the Hubble Constant, and that was the value that was argued over for decades. The units are (km/s)/Mpc, which tells you the additional speed an object moves away from you for every megaparsec it is distant.

The first good measurement of this was in 1958 by Allan Sandage, who estimated 75, but for 50 years, it was fought over. There was the big camp that kept measuring it to be 100, and the little camp that was measuring it at 50. But, over the last 15 years, this has been measured very carefully with space-based missions.

Again, it was a fundamental question driving the Hubble Space Telescope, which based on data from 2001 to 2005, using another distance technique that I haven’t talked about (the Sunyaev-Zel’dovich effect), measured it to be 72±8. WMAP in 2007 measured it at 70.4±1.5 in 2007 and then narrowed that by 2012 to 69.32±0.80, and the Planck mission just under two years ago released a value of 67.80±0.77. So, it’s converging on a value of about 67-70.

Not incredibly precise when you compare that with how well we know the AU, but this is really the top rung of the distance ladder and so all of the compounding uncertainties from the rungs below it play a role in this uncertainty, or at least all the ones that go into it.

But again, the point is that this is another rung on the ladder, and while this one is only useful once the galaxy is beyond our own local group, it gets us to the very edge of the observable universe, and hence it forms the top-most rung of the Astronomical Distance Ladder.

Wrap Up

I have left A LOT out of this discussion. There are a lot of other rungs on the ladder, all used to calibrate each other. For example, the planetary nebula luminosity function, which is something I briefly worked on calibrations for when I was a graduate student, gets you to galaxies that are also a few billion light-years away, helping to calibrate Cepheids to Type 1a Supernovae.

There’s also the Tully-Fisher relationship between spiral galaxies’ spin rate - which can be measured with spectra - and their brightness. This is calibrated by Sn1a and used throughout the observable universe. then there’s the Faber-Jackson relation which is the same as the Tully-Fisher, but for elliptical galaxies. These both calibrate between Supernovae and Hubble’s Law.

Closer to home, there is main sequence fitting, which is where you have a group of stars like an open cluster that all formed at the same time, you map out their brightness relative to their color, and most will plot along a set line on a graph. By knowing how bright that line should be from stars from parallax, we know how far away that cluster is. That is another way we can get from our galaxy to nearby ones.

Similarly, there are RR Lyrae variable stars which are red giant stars which get us distances within our galaxy and to nearby galaxies.

All of these have very important roles in astronomy, and all are inter- and intra-calibrated and extended in distance range at every opportunity. The Distance Ladder is still an active area of research in astronomy, but that shouldn’t be taken to mean that its poorly known.

It starts from basic geometry with the direct methods of measuring the AU and parsecs, and then we use these to identify distances to standard candles, each candle overlapping in range with other candles to form a network to understand our place in the universe. And, even with just the direct measurements, we can show the universe is much larger than 6000 light-years, and hence older than 6000 light-years, unless you want to assume that an all-powerful deity is trying to trick us.

Choosing to ignore this science is something that Mr. Hovind and other creationists like him clearly do. They ignore the countless hours of very meticulous work and observations that go into making these measurements. They ignore the basic science that goes into understanding how these are set up and how they work and why they are reliable. I suppose it shouldn’t surprise most people listening to this when I say that it’s obvious from this that it’s another case of creationists ignoring basic science, but sometimes - and I’m not sure why - I’m just amazed by how much they simply choose to go through life with their fingers in their ears and their heads up their collective ———

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