Today – April 8, 2017 – the planet Jupiter is closest to Earth for this year.
Yet yesterday was Jupiter’s opposition, when Earth flew between Jupiter and the sun, placing Jupiter opposite the sun in our sky. You’d think Jupiter was closest to Earth for 2017 yesterday as well … and yet it wasn’t. It’s closest to Earth for 2017 today, April 8, coming to within 414 million miles (666 million km).
Jupiter’s closest approach to Earth for the year always falls on or near its opposition date. Why near? Why not always on the date of opposition?
The reason is that the orbits of Earth and Jupiter aren’t perfect circles. They’re both very nearly circles, but not quite. Jupiter’s distance from the sun varies by only about 10.1% between perihelion (closest point to sun) and aphelion (most distant point from sun). If our planets’ orbits were perfect circles, then yes, we’d be closest together on the date Earth passes between Jupiter and the sun. But Earth’s orbit, and Jupiter’s orbit, are elliptical, like circles someone sat down on.
View larger. | Jupiter at its April 7, 2017 opposition with the Great Red Spot and moons Io, Europa, and Ganymede (L to R). Photo by Rob Pettengill in Austin, Texas.
Jupiter’s elliptical orbit means its distance from the sun varies (as does Earth’s distance from the sun). Jupiter just passed an aphelion on February 16, 2017, an event that occurs once in each of the giant planet’s 11.9-year orbits around the sun. At aphelion, it lay about 507 million miles (816 million km) from the sun.
Since February 16, Jupiter has been heading toward another perihelion. It will reach its perihelion on January 20, 2023, when it’ll lie 460 million miles (741 million km) from the sun.
Earth’s perihelion comes every year in early January. So we’re getting a bit farther from the sun each day now. But Jupiter is now getting closer to the sun – bit by bit, closer and closer – every earthly day. And that’s how Jupiter can be closest to Earth for 2017 one day after our planet’s April 7, 2017 pass between Jupiter and the sun.
It can be closest to us today (April 8) because it’s closer to the sun today than it was yesterday.
Jupiter is now ascending in the east after sunset. The moon will pass Jupiter (and Spica) on April 9, 10 and 11. Read more.
Bottom line: You’d think Jupiter would be closest to Earth on the day we pass between it and the sun. We did that on April 7, 2017, though, and our 2 worlds are closest on April 8. Why?
from EarthSky http://ift.tt/2oMI2Gd
Today – April 8, 2017 – the planet Jupiter is closest to Earth for this year.
Yet yesterday was Jupiter’s opposition, when Earth flew between Jupiter and the sun, placing Jupiter opposite the sun in our sky. You’d think Jupiter was closest to Earth for 2017 yesterday as well … and yet it wasn’t. It’s closest to Earth for 2017 today, April 8, coming to within 414 million miles (666 million km).
Jupiter’s closest approach to Earth for the year always falls on or near its opposition date. Why near? Why not always on the date of opposition?
The reason is that the orbits of Earth and Jupiter aren’t perfect circles. They’re both very nearly circles, but not quite. Jupiter’s distance from the sun varies by only about 10.1% between perihelion (closest point to sun) and aphelion (most distant point from sun). If our planets’ orbits were perfect circles, then yes, we’d be closest together on the date Earth passes between Jupiter and the sun. But Earth’s orbit, and Jupiter’s orbit, are elliptical, like circles someone sat down on.
View larger. | Jupiter at its April 7, 2017 opposition with the Great Red Spot and moons Io, Europa, and Ganymede (L to R). Photo by Rob Pettengill in Austin, Texas.
Jupiter’s elliptical orbit means its distance from the sun varies (as does Earth’s distance from the sun). Jupiter just passed an aphelion on February 16, 2017, an event that occurs once in each of the giant planet’s 11.9-year orbits around the sun. At aphelion, it lay about 507 million miles (816 million km) from the sun.
Since February 16, Jupiter has been heading toward another perihelion. It will reach its perihelion on January 20, 2023, when it’ll lie 460 million miles (741 million km) from the sun.
Earth’s perihelion comes every year in early January. So we’re getting a bit farther from the sun each day now. But Jupiter is now getting closer to the sun – bit by bit, closer and closer – every earthly day. And that’s how Jupiter can be closest to Earth for 2017 one day after our planet’s April 7, 2017 pass between Jupiter and the sun.
It can be closest to us today (April 8) because it’s closer to the sun today than it was yesterday.
Jupiter is now ascending in the east after sunset. The moon will pass Jupiter (and Spica) on April 9, 10 and 11. Read more.
Bottom line: You’d think Jupiter would be closest to Earth on the day we pass between it and the sun. We did that on April 7, 2017, though, and our 2 worlds are closest on April 8. Why?
from EarthSky http://ift.tt/2oMI2Gd
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