What's New: September 2019

Jupiter Rules!

No amateur astronomer can be bored while Jupiter is in the sky, and it has provided superb views all summer. As September rolls around, the planet becomes visible almost due south shortly after sunset. On the 1st, it sets a little before midnight; by month's end, it will go down before 10 PM. We may want to take some last looks before the planet leaves the stage in the next few months.

When we look at Jupiter through a telescope, we do not see its surface. No one has ever seen its surface; it may not even have one! What we are seeing instead are the top layers of its atmosphere, which may be thousands of miles deep.

That atmosphere is far from bland. Even a small telescope will reveal one or two dark bands, or "belts," stretching across the planet's disk parallel to the equator. These are separated by light-colored "zones." Larger telescopes will reveal more alternating belts and zones, stretching toward the planet's polar regions. Though the individual features may change in brightness and color intensity from year to year, the overall structure is remarkable consistent, and a standard designation system has been developed.

Jupiter Belt Zones

Understanding the underlying mechanisms causing the banding of the planet has been much more difficult.

It is now thought that the white-colored zones are regions of upwelling, with material from deep in the planet's atmosphere rising to the top of the cloud deck. Once there, some chemical change – it's uncertain exactly what – in some component of the rising material is triggered by exposure to the Sun's ultraviolet light, resulting in changes of color and possibly composition. The now dark- colored material sinks back into the atmosphere in the belts. Strong winds blowing in opposing directions form at the boundaries separating the systems.