The Planet Jupiter offers amateur astronomers the best opportunity to see atmospheric features of all the planets in the Solar System. With Jupiter, amateurs are offered striking views of features like the Red Spot, distinctive bands of color, moons that orbit faithfully, sometimes coming between the Sun and Jupiter and causing observers on Earth to see fantastic dark shadows marching across the disk.

For planetary observing with an amateur instrument, use the highest power the conditions of the sky will allow on any given night. Don't underestimate the power of a barlow. I find sometimes a lower power eyepiece used with a barlow is better than a higher power. Using a blue or yellow filter can often bring out details you may otherwise have missed. I use a pale yellow filter on the planet under "normal" circumstances. I also like neutral density filters. Magnification is the key to observing. Always push your scope to give the highest power on planets.

When looking at Jupiter, imagine a line down the center of the disk. [The satellites help to determine North and South on the disk because they orbit Jupiter at its equator (roughly).] This is the central meridian of Jupiter. Watch for the Red Spot as it cross the center of the disk. In planetary observing, the leading edge of a feature is called the preceding edge and the later edge is called the following edge. Local time of impact transits over the central meridian should be available from astronomical sources. This is the key to knowing when to look for the Red Spot.

One technique for seeing planetary detail on Jupiter is to focus the eye on some spot on the SEB (Southern Equatorial Belt). But concentrate on seeing the details in the south polar area. This is averted vision for planetary observers. Storm features on Jupiter will move quickly as the planet rotates, so try some quick sketches. You will soon discover the best arrangement of your optics.

One more thing, sometimes good results can be obtained by making an aperture stop for your telescope. With a 12.5-inch mirror on a telescope with a conventional spider, an aperture of nearly 4-inch can be obtained. A direct benefit from this arrangement, is that much of the light from the planet is eliminated. Secondly, this will be a clear aperture, with none of the support structure in the way. Some mirrors that suffer from bad edges can get improved results. Making a 12-inch aperture stop for a 12.5-inch can make a difference.

What is considered optimum magnification for planetary observing is 30 power per inch of aperture. Because cutting down the aperture of the mirror doesn't change the focal length of the instrument, the same magnification results. On a 10-inch instrument 100X is 10X per inch of aperture. If the aperture is cut down to 2-inch, 100X is 50X per inch of aperture. I find the more power per inch the better. As always, atmosphere and local conditions are limiting factors.

Read About Jupiter's New Red Spot - an article by Astra

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