APOD: Driving to the Sun (2020 Oct 03)

[APOD Robot]

Driving to the Sun

Explanation: How long would it take to drive to the Sun? Brittany age 7, and D.J. age 12, ponder this question over dinner one evening. James also age 7, suggests taking a really fast racing car while Christopher age 4, eagerly agrees. Jerry, a really old guy who is used to estimating driving time on family trips based on distance divided by speed, offers to do the numbers. "Let's see ... the Sun is 93 million miles away. If we drove 93 miles per hour the trip would only take us 1 million hours." How long is 1 million hours? One year is 365 days times 24 hours per day, or 8,760 hours. One hundred years would be 876,000 hours, but that's still a little short of the 1 million hour drive time. So the Sun is really quite far away. Christopher is not impressed, but as he grows older he will be. You've got to be impressed by something that's 93 million miles away and still hurts your eyes when you look at it!

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[daddyo]

Wow, great way to put scale into tangible perspective, about 100 years to get there driving 100 mi/hr.

[heehaw]

And yet at the time of Galileo, almost everyone on Earth thought that that Sun, that object: went around the Earth every day! They knew how far away it was. Did they work out how fast it must be moving to do that?

[sillyworm 2]

On one hand the sun helps you produce vitamin D..on the other..you can get one helluva sunburn.Good cop Bad cop.

[neufer]

And yet at the time of Galileo, almost everyone on Earth thought that that Sun, that object: went around the Earth every day! They knew how far away it was. Did they work out how fast it must be moving to do that?

• Few folks who thought the Sun went around the Earth had any idea how far away it was.
  
  (Almost everyone agreed that the star field was the furthest away, however.)

<<Aristarchus of Samos (Ἀρίσταρχος ὁ Σάμιος, Aristarkhos ho Samios; c. 310 – c. 230 BC) was an ancient Greek astronomer and mathematician who presented the first known heliocentric model that placed the Sun at the center of the known universe with the Earth revolving around it. He was influenced by Philolaus of Croton, but Aristarchus identified the "central fire" with the Sun, and he put the other planets in their correct order of distance around the Sun. Like Anaxagoras before him, he suspected that the stars were just other bodies like the Sun, albeit farther away from Earth. His astronomical ideas were often rejected in favor of the geocentric theories of Aristotle and Ptolemy. Nicolaus Copernicus attributed the heliocentric theory to Aristarchus.

[However,] the only known surviving work usually attributed to Aristarchus, On the Sizes and Distances of the Sun and Moon, is based on a geocentric world view. Aristarchus claimed that at half moon (first or last quarter moon), the angle between the Sun and Moon was 87°. He might have proposed 87° as a lower bound, since gauging the lunar terminator's deviation from linearity to one degree of accuracy is beyond the unaided human ocular limit.

---

Aristarchus began with the premise that, during a half moon, the moon forms a right triangle with the Sun and Earth. By observing the angle between the Sun and Moon, φ, the ratio of the distances to the Sun and Moon could be deduced using a form of trigonometry.

The diagram is greatly exaggerated, because in reality, S = 390 L, and φ is extremely close to 90°. Aristarchus determined φ to be a thirtieth of a quadrant (in modern terms, 3°) less than a right angle: in current terminology, 87°. Trigonometric functions had not yet been invented, but using geometrical analysis in the style of Euclid, Aristarchus determined that the distance to the Sun was somewhere between 18 and 20 times greater than the distance to the Moon. This value (or values close to it) was accepted by astronomers for the next two thousand years, until the invention of the telescope permitted a more precise estimate of solar parallax. Aristarchus also reasoned that as the angular size of the Sun and the Moon were the same, but the distance to the Sun was between 18 and 20 times further than the Moon, the Sun must therefore be 18–20 times larger.>>

[mike smith]

How long to fly a 747 around the sun at 30,000 ft?
How long b4 we would melt.

[orin stepanek]

A train at night; coming down the track at night parallel to the
highway is no fun; especially with those three bright light lights
almost blinding you! I don't want to even think
of looking at the sun!

[Chris Peterson]

And yet at the time of Galileo, almost everyone on Earth thought that that Sun, that object: went around the Earth every day! They knew how far away it was. Did they work out how fast it must be moving to do that?

Hmmm... the same speed as the Earth must be moving around the Sun assuming a heliocentric model?

[neufer]

How long to fly a 747 around the sun at 30,000 ft?

Around 200 days (assuming a cruise velocity of just 900 km/s is still sufficient under a 28g gravity).

Since the Sun itself rotates once every 25 days (at the equator)
one will observe the Earth to rise & set about 9 times in those 200 days.

[neufer]

And yet at the time of Galileo, almost everyone on Earth thought that that Sun, that object: went around the Earth every day! They knew how far away it was. Did they work out how fast it must be moving to do that?

Hmmm... the same speed as the Earth must be moving around the Sun assuming a heliocentric model?

Hmmm... 365 times the speed the Earth must be moving around the Sun assuming a heliocentric model?

[Chris Peterson]

And yet at the time of Galileo, almost everyone on Earth thought that that Sun, that object: went around the Earth every day! They knew how far away it was. Did they work out how fast it must be moving to do that?

Hmmm... the same speed as the Earth must be moving around the Sun assuming a heliocentric model?

Hmmm... 365 times the speed the Earth must be moving around the Sun assuming a heliocentric model?

Oh. Yeah.

[stevie]

I'm with Christopher. Why don't we try a super fast space ship instead?

They should bring back Candid Camera. Kids say the darndest things...

[vstill]

"You've got to be impressed by something that's 93 million miles away and still hurts your eyes when you look at it!"

[img/Users/vstilliMac/Desktop/3210.jpg][/img]

[E Fish]

Just for some historical perspective. The first record we have of a person stating that the objects in the heavens were actual things that could be understood was Anaxagoras (a philosopher from Miletus in the 5th cent. B.C.). He described the Sun as a burning stone the size of the Peloponnese (that's the southern part of Greece). This is especially significant because, after Aristotle (about a century later), most scholars believed that the heavens were made out of the celestial ether and the four elements of the earth were confined to the earthly realm. That idea took more than a thousand years to change. But even with a geocentric understanding of the universe, they still knew how eclipses worked and that the Moon shone with reflected light from the Sun.

[neufer]

Just for some historical perspective. The first record we have of a person stating that the objects in the heavens were actual things that could be understood was Anaxagoras (a philosopher from Miletus in the 5th cent. B.C.). He described the Sun as a burning stone the size of the Peloponnese (that's the southern part of Greece). This is especially significant because, after Aristotle (about a century later), most scholars believed that the heavens were made out of the celestial ether and the four elements of the earth were confined to the earthly realm. That idea took more than a thousand years to change. But even with a geocentric understanding of the universe, they still knew how eclipses worked and that the Moon shone with reflected light from the Sun.

• (Flat Earther) Anaxagoras described the Sun as a mass of blazing metal, larger than the Peloponnese (i.e., larger than 103 miles across)

<<Anaxagoras (Ἀναξαγόρας, Anaxagoras, "lord of the assembly"; c. 500 – c. 428 BC) was a Greek citizen of the Persian Empire and had served in the Persian army; he may have been a member of the Persian regiments that entered mainland Greece during the Greco-Persian Wars. Though this remains uncertain, "it would certainly explain why he came to Athens in the year of Salamis, 480/79 B.C."

Anaxagoras brought philosophy and the spirit of scientific inquiry from Ionia to Athens. His observations of the celestial bodies and the fall of meteorites led him to form new theories of the universal order, and to prediction of the impact of meteorites. Plutarch says "Anaxagoras is said to have predicted that if the heavenly bodies should be loosened by some slip or shake, one of them might be torn away, and might plunge and fall down to earth". According to Pliny he was credited with predicting the fall of the meteorite in 467. He attempted to give a scientific account of eclipses, meteors, rainbows, and the Sun, which he described as a mass of blazing metal, larger than the Peloponnese (i.e., larger than 103 miles across); his theories about eclipses, the Sun and Moon may well have been based on observations of the eclipse of 463 BCE [whose width of totality over Greece ~ 100 miles], which was visible in Greece. He also said that the Moon had mountains and believed that it was inhabited. The heavenly bodies, he asserted, were masses of stone torn from the Earth and ignited by rapid rotation. He was the first to give a correct explanation of eclipses, and was both famous and notorious for his scientific theories, including the claims that the Sun is a mass of red-hot metal, that the Moon is earthy, and that the stars are fiery stones. He thought the Earth was flat and floated supported by 'strong' air under it and disturbances in this air sometimes caused earthquakes. These speculations made him vulnerable in Athens to a charge of asebeia (impiety). Diogenes Laërtius reports the story that he was prosecuted by Cleon for impiety, but Plutarch says that Pericles sent his former tutor, Anaxagoras, to Lampsacus for his own safety after the Athenians began to blame him for the Peloponnesian war.

Asebeia (ἀσέβεια) was a criminal charge in ancient Greece for the "desecration and mockery of divine objects", for "irreverence towards the state gods" and disrespect towards parents, dead ancestors and Starship Asterisk* moderators. It translates into English as impiety or godlessness. Most evidence for it comes from Athens. The antonym of asebeia is eusebeia (εὐσέβεια), which can be translated as "piety". As piety was the generally desired and expected form of behaviour and mindset, being called and regarded impious (ἀσεβής) was already a form of punishment. The charges against Anaxagoras may have stemmed from his denial of the existence of a solar or lunar deity. According to Laërtius, Pericles spoke in defense of Anaxagoras at his trial, c. 450. Even so, Anaxagoras was forced to retire from Athens to Lampsacus in Troad (c. 434 – 433). He died there in around the year 428. Citizens of Lampsacus erected an altar to Mind and Truth in his memory, and observed the anniversary of his death for many years. They placed over his grave the following inscription: Here Anaxagoras, who in his quest of truth scaled heaven itself, is laid to rest.>>

[praxnex@gmail.com]

Would gravity decrease time by accelerating car toward sun?

[Chris Peterson]

Would gravity decrease time by accelerating car toward sun?

The calculation is based on traveling at a constant speed. If you want to allow for the effects of gravity, you have to design some kind of ballistic path, in which case the calculation of travel time becomes more complex.

[Cousin Ricky]

Would gravity decrease time by accelerating car toward sun?

The calculation is based on traveling at a constant speed. If you want to allow for the effects of gravity, you have to design some kind of ballistic path, in which case the calculation of travel time becomes more complex.

Even more complex would be trying to explain all this to a 4 year old.

[Chris Peterson]

Would gravity decrease time by accelerating car toward sun?

The calculation is based on traveling at a constant speed. If you want to allow for the effects of gravity, you have to design some kind of ballistic path, in which case the calculation of travel time becomes more complex.

Even more complex would be trying to explain all this to a 4 year old.

While we're at it, we might as well throw in relativistic effects, which are certainly measurable at the speeds and timescales we're talking about here.

[neufer]

Would gravity decrease time by accelerating car toward sun?

The calculation is based on traveling at a constant speed. If you want to allow for the effects of gravity, you have to design some kind of ballistic path, in which case the calculation of travel time becomes more complex.

• Elon Musk's Tesla Roadster takes just ~5 months "to get to Mars":

SpaceX Roadster's trajectory.

---

<<Elon Musk's Tesla Roadster is an electric sports car that served as the dummy payload for the February 2018 Falcon Heavy test flight and became an artificial satellite of the Sun. "Starman", a mannequin dressed in a spacesuit, occupies the driver's seat.

The Roadster is in a heliocentric orbit that crosses the orbit of Mars and reaches a distance of 1.66 au from the Sun. With an inclination of roughly 1 degree to the ecliptic plane, compared to Mars' 1.85° inclination, this trajectory by design cannot intercept Mars, so the car will neither fly by Mars nor enter an orbit around Mars. Nine months after launch, the Tesla had travelled beyond the orbit of Mars, reaching aphelion at 12:48 UTC on November 9, 2018, at a distance of 1.664 au from the Sun. The maximum speed of the car relative to the Sun will be 121,005 km/h (75,189 mph) at perihelion.>>

• It took the Parker Solar Probe 25.5 months to go 91% to the Sun:

Parker Solar Probe's trajectory from August 7, 2018 to August 29, 2025

---

<<Flight controllers at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, received a “Status A” signal from the spacecraft through NASA’s Deep Space Network at 4:45 a.m. EDT; Status A is the best of four possible status signals, and indicates that the spacecraft is operating nominally.

The beacon comes after a six-day stretch when communications with the spacecraft were not possible as it wheeled around the Sun. This is the first sign of a successful solar encounter; this sixth solar encounter began Sept. 21 and continues through Oct. 2.

At closest approach (called perihelion) on Sept. 27, Parker Solar Probe came within about 8.4 million miles (13.5 million kilometers) of the Sun’s surface — less than one-tenth of the distance between Earth and the Sun — while reaching a top speed of 289,927 miles per hour (466,592 kilometers per hour), breaking its own records for speed and solar distance.>>

[neufer]

Even more complex would be trying to explain all this to a 4 year old.

While we're at it, we might as well throw in relativistic effects, which are certainly measurable at the speeds and timescales we're talking about here.

I'd wait until the kid was 5 before throwing in relativistic effects.

[E Fish]

• (Flat Earther) Anaxagoras described the Sun as a mass of blazing metal, larger than the Peloponnese (i.e., larger than 103 miles across)

Ah, I stand corrected. But I will admit that it's the first time I've ever seen anything attribute a flat earth concept to Anaxagoras. The flat earth hypothesis was rare in the ancient world. And I have no real excuse because I have a book of early Greek philosophy and the description is in there. Even though we have nothing Anaxagoras wrote himself, it does seem to fit with the rest of his wild ideas.

[neufer]

Would gravity decrease time by accelerating car toward sun?

If the Sun was a point gravitational source an object at 1 AU with zero angular velocity would take (1/2)^(5/2) years ~ 64 days to drop to the Sun based upon a Keplerian ellipse with semi major axis of (1/2) AU. So think about 2 months.

[wallyware]

Jerry is an exceptionally old guy.

[TheZuke!]

Would gravity decrease time by accelerating car toward sun?

It worked for Kirk when he brought back (forward) the whales!