You look at the Sun. You look at the Moon. How do you tell which one is closer?
How would you, say, measure the distance to the Sun? Once you had that, you could next measure the distance to the Moon. That way you would know whether it is the Sun or the Moon which is closer.
You can’t tell which is closer by perspective. I can look out my window and see two buildings. One building looks much larger than the other. From this I can tell that the smaller building is further away. But the perspective method wouldn’t work for trying to figure out if the Moon or the Sun was closer. Maybe, for example, the Moon is really big and that makes it seem closer than it really is.
You can’t just take a tape measure and unwind it as you travel out to the Moon. And if you tried that with the Sun, you and the tape measure would burn up!
In 2012, the International Business Times reported how 17th-century astronomers Giovanni Cassini and Jean Richer pegged the distance from the Earth to the Sun as 140 million kilometers. This Earth-to-Sun distance has come to be called “the astronomical unit.” Cassini and Richer “calculated the astronomical unit by using observations of Mars from two different spots on Earth, then used the difference between those two observations to calculate our distance from Mars, which they then used to determine our distance from the sun.” 
So you can see that measuring the distance to the Sun and the Moon is not exactly a trivial problem. But what if you wanted to measure the distance to, for example, the M80 globular cluster of stars embedded in the Milky Way? Or what if you wanted to measure the distance to someplace outside our galaxy? There is a supposed way this is accomplished: “Redshift.”
Redshift is explained by author Hilton Ratcliffe as akin to the idea of a screaming ambulance passing in the background. Without even looking we know when the ambulance is moving away from us because the pitch of the siren drops. “The departing ambulance stretches the sound waves and audibly lowers the sound frequency. In light waves, it’s called Doppler redshift.” 
But this “Doppler Effect” – “increasing wavelength caused by recessional velocity” – which is used to calculate far distances in space is only one of many possible causes for a shift towards red in the spectrum of light. For example Edwin Hubble is quoted by Ratcliffe (op. cit.) as having stated, “…it seems likely that red-shifts may not be due to an expanding Universe, and much of the speculation on the structure of the universe may require re-examination.”
Hubble is questioning here “the Standard Model” of an “expanding Universe.” About 13.7 billion years ago (that number keeps shifting) there was supposed to have been a “Big Bang” and the Universe after that expanded, like debris blowing outward from the explosion. (But expanding into what? What was the Universe expanding into? Did “Big Bang” blow out a “shell” of some sort, and “expand” beyond the shell?)
Increasing doubts about “Big Bang” led to the birth, in 2004, of the Alternative Cosmology Group (ACG). An “Open Letter on Cosmology” was written to the scientific community by ACG and published in New Scientist on May 22, 2004. The big bang theory can’t survive without “fudge factors,” complained ACG. These “fudge factors” were hypothetical band-aids being hastily attached to the feeble body of “Big Bang.” Dark Matter and Dark Energy were prominent among the emergency band-aids. Direct observations were being interpreted through a biased filter, judged right or wrong depending on whether or not they support the big bang. Discordant data on red shifts, lithium and helium abundances, and galaxy distribution, among other topics, were ignored or ridiculed. 
What sort of “science” was this!? A “science” with an embedded theory which caused it to close its eyes to a barrage of conflicting data! It gets worse, as (hopefully) will be shown in future installments of the planned series, “Crisis in Cosmology.”
——- Sources ——-
 “Astronomers Reach Verdict On Distance From Earth To Sun, Finally”, by Roxanne Palmer. International Business Times, September 18, 2012. http://www.ibtimes.com/astronomers-reach-verdict-distance-earth-sun-finally-790128
 The Static Universe, by Hilton Ratcliffe. Montreal: Apeiron, 2010. http://redshift.vif.com/
 “Alternative Cosmology Group”, http://www.cosmology.info/