Earthsky Tonight - Nov 10 2009

Jupiter at eastern quadrature on November 10

Tonight is NOV 10, 2009

Today, the planet Jupiter is at eastern quadrature – or 90 degrees east of the sun. If you could look down upon the solar system plane from outer space, you’d see that the sun, Earth and Jupiter form a 90-degree angle today. By the way, when the moon is at first quarter phase, it is also at eastern quadrature – or 90 degrees east of the sun.

Some 3 months ago – on August 14, 2009 – Jupiter was at oppostion. At opposition, Jupiter resides opposite the sun in Earth’s sky, or 180 degrees from the sun. If you had looked down upon the solar system on August 14, you would have seen the sun, Earth and Jupiter making a straight line in space.

So why are opposition and quadrature so significant? First of all, opposition and quadrature can only happen to solar system planets that orbit the sun outside of Earth’s orbit. Planets that orbit the sun inside of Earth’s orbit can never reach opposition or quadrature – or get as far as 90 degrees from the sun.

For another thing, Jupiter’s oppositions and quadratures enabled the innovative astronomer Copernicus (1473-1543) to compute Jupiter’s distance from the sun. He did this by charting Jupiter’s (and the Earth’s) change of position from opposition to quadrature. All the while, Copernicus presumed that Jupiter and Earth both orbit a central sun.

By using the Earth-sun distance as his baseline, Copernicus relied upon the magic of geometry to figure out that Jupiter is over 5 times the Earth’s distance from the sun!

Written by Bruce McClure

Comments (9)

at 02.47 am on 11-09-2009 leigh

wow how fasanating how don u work this stuff out

Reply

at 12.09 pm on 11-09-2009 leigh

Sorry, I was drunk when I wrote that...

I meant:
Wow! How fascinating! How does one figure this stuff out?

at 10.32 am on 11-10-2009 matt

stars are always more fun when drunk

at 1.50 pm on 11-09-2009 Bruce McClure

Leigh,

From opposition to quadrature, Copernicus knew how many degrees the Earth and Jupiter revolved around the sun. By subtracting the number of degrees traveled by Jupiter from the number of degrees traveled by Earth, Copernicus was able to compute the Jupiter-sun-Earth angle at quadrature. Furthermore, since Jupiter was at quadrature, Copernicus knew the Jupiter-Earth-sun angle was equal to 90 degrees. This gave Copernicus a right triangle and three known angles to work with, so he could measure out the lengths of the Earth-Jupiter line and the sun-Jupiter line relative to the sun-Earth line. The hypotenuse (sun-Jupiter line) of this triangle told Copernicus that Jupiter was a bit more than 5 times the Earth's distance from the sun.

Bruce

Reply

at 10.26 am on 11-10-2009 Mike Davidsin

i believe in evolution!!!!

Reply

at 8.13 pm on 11-10-2009 Sudha

Are we seeing Jupiter a lot in the sky this year or is this usual?

Reply

at 08.34 am on 11-11-2009 Bruce McClure

Hi Sudha,

No, we're not really seeing more of Jupiter in the evening sky this year than we usually do. Jupiter lights up the evening sky for several months every year. At opposition, Jupiter rises around sunset and sets around sunrise, so it is out all night long. At quadrature, Jupiter is in your southern sky at sunset and sets roughly 6 hours after the sun. Jupiter's opposition and quadrature come about one month later yearly, so Jupiter's evening showing comes about a month later every year, though it's still in the evening sky for several months. This year, we see Jupiter in the autumn evening sky. Three years from now, we'll see Jupiter in the winter evening sky. Six years from now, we'll see Jupiter on spring evenings. Nine years from now, it'll be in summer.

Bruce

at 07.45 am on 11-18-2009 Bonnie

Dear Bruce,

Thanks for writting this in terms that a layman like myself can understand. I am deeply appreciative of your true talent with words that help others just like me to learn something complex in such a concise - understandable way. I am so glad to have learned something new!!!

Thanks again!
Bonnie

Reply

at 10.08 am on 11-18-2009 Bruce McClure

Bonnie,

You have bestowed upon me the highest honor that I could ever hope for. I try my best to make things clear and understandable. But should I write something that falls short of this objective, I certainly welcome the reader to contact me and to ask for clarification.

Thank you for writing!
Bruce

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