Jupiters Moons ?

[gaa_ian (Ian)]

I have had this question posed to me, I dont know the answer ?
But I suspect that one of you learned folks here will:

"In 1676, the Danish astronomer Ole Romer (1644-1710) was studying the orbits of Jupiter's Galilean satellites. Over a period of many months, Romer noticed that the orbits of the moons of Jupiter lose time for about six months, and then gain time over the next six months, losing and gaining about eight minutes each cycle between successive oppositions. What physical phenomenon provided the explanation for this anomaly?"

[iceman (Mike)]

What do you mean by "lose time"? That their orbit slows down?

[Dennis]

I believe this is how Romer first measured the speed of light. The Galilean moons are so far away that light takes a significant time to reach the Earth causing those apparent discrepancies.

Cheers

Dennis

[h0ughy (David)]

Originally Posted by Dennis

I believe this is how Romer first measured the speed of light. The Galilean moons are so far away that light takes a significant time to reach the Earth causing those apparent discrepancies.

Cheers

Dennis

are we talking retrograde here

[Dennis]

From http://www.ccmr.cornell.edu/education/ask/?quid=137

"The first person who observed and measured such a delay was the Danish astronomer Olaf Romer in 1676. He made careful observations of the "moons" of Jupiter. The innermost moon goes around Jupiter in less than two days and is eclipsed by Jupiter once in each orbit. Romer found that this moon did not reappear at exactly the time he expected. Instead, the time of the eclipses varied periodically during the year. When the Earth was farthest from Jupiter, the eclipses were about 11 minute late; when the Earth was nearest Jupiter (about 6 months later), they were about 11 minuets early. Romer deduced that this variation must be due to the annual variation in the distance the light had to travel to get to the Earth from near Jupiter. The 11-minute delay must be about he time that it takes light to travel a distance equal to the radius of the Earth's orbit. More refined measurements of the eclipses gave a value of about 186,000 miles per second for the velocity of light. That is a million times faster than sound!"
Cheers

Dennis

[robagar]

It amazes me that in the 17th century he was able to measure galilean moon events accurately enough to even notice the anomaly! What kind of clock would he have been using?

[h0ughy (David)]

Originally Posted by Dennis

From http://www.ccmr.cornell.edu/education/ask/?quid=137

"The first person who observed and measured such a delay was the Danish astronomer Olaf Romer in 1676. He made careful observations of the "moons" of Jupiter. The innermost moon goes around Jupiter in less than two days and is eclipsed by Jupiter once in each orbit. Romer found that this moon did not reappear at exactly the time he expected. Instead, the time of the eclipses varied periodically during the year. When the Earth was farthest from Jupiter, the eclipses were about 11 minute late; when the Earth was nearest Jupiter (about 6 months later), they were about 11 minuets early. Romer deduced that this variation must be due to the annual variation in the distance the light had to travel to get to the Earth from near Jupiter. The 11-minute delay must be about he time that it takes light to travel a distance equal to the radius of the Earth's orbit. More refined measurements of the eclipses gave a value of about 186,000 miles per second for the velocity of light. That is a million times faster than sound!"
Cheers

Dennis

[Lester]

Interesting and thanks for the explanation Dennis.

[Pascha]

Originally Posted by gaa_ian

I have had this question posed to me, I dont know the answer ?
But I suspect that one of you learned folks here will:

"In 1676, the Danish astronomer Ole Romer (1644-1710) was studying the orbits of Jupiter's Galilean satellites. Over a period of many months, Romer noticed that the orbits of the moons of Jupiter lose time for about six months, and then gain time over the next six months, losing and gaining about eight minutes each cycle between successive oppositions. What physical phenomenon provided the explanation for this anomaly?"

Olof Roemer calculated light's speed in 1676 - result 214 300 km/s

Pascha

[sheeny (Al)]

Interesting thread!

Thanks guys!

Al.