Hubble's Law

OK, so there ARE lots of other galaxies, beyond the Milky Way: Are they moving?

Spectroscopy, which can identify objects via unique combinations of so-called “spectral lines,” can also be used to measure velocity, thanks to the Doppler effect.   Leavitt used the “identification” properties of spectroscopy to find her law, but to find his, Hubble needed to focus on velocity measurements as well.  He made extensive use of the measurements of Vesto Slipher, who was the first astronomer to measure Doppler shifts to higher velocity (...

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How Big is the Milky Way--is it the whole Universe?

By the early 20th century, it was possible to see and measure a very different Universe than was accessible to the Ancients, or even to Galileo and Newton.   It had many more stars, and it had beautiful collections of stars (then called “nebulae”) with crazy patterns—like spirals.  (See the modern image of M31 shown here in color, for a good example of a “Spiral” galaxy.) 

Spectroscopy hinted that faraway objects were composed of elements not unlike those in the Sun, and that they were...

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Supernatural Solutions

Of course, these two tricky questions can be avoided if a supernatural power pressed a "start" button on time, and controls whatever is "beyond" our Universe.  In Ancient times thinkers across cultures believed the Universe was controlled at least in part by supernatural forces. 

Even by the 17th century, when Galleo’s telescopic observations of Jupiter had effectively disproven the Ancients’ Earth-centered Solar System, and Isaac Newton had shown how gravity controlled the...

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Why does Hubble’s Law often confound those born and raised on Earth?

A wide variety of modern astronomical observations clearly show that our Universe had a beginning in time, known as the “big bang.”  But, those same observations also show that the Universe expands in all directions simultaneously, meaning that it has no single birthplace in space. 

Unless time is treated as a fourth dimension, akin to the three dimensions of space, these ideas--a starting time, but not a starting place, are...

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