The king of planets, Jupiter, dominates the southeastern sky as dusk falls in early July.


 


The king of planets, Jupiter, dominates the southeastern sky as dusk falls in early July.

Jupiter is given kingly status because it is the largest planet in our solar system and because it was named by the ancient Romans, whose head deity went by that name. The Romans had no idea that coincidentally, Jupiter was the largest!

July 9 is when Jupiter reaches “opposition,” situated on the opposite side of the sky from the sun. That’s when the planet rises in the southeast just when the sun sets in the northwest and is up in the sky the entire night.

The moon, stars and other planets reach opposition as well at their appointed time. In fact, every night, whatever lies in the eastern sky at sunset is at opposition. Of course at that very moment you will not see those stars as they rise over the horizon, because the sun is only just setting and the sky is bright. You may have seen the full moon sitting on a low eastern horizon at sunset -- a beautiful sight.

The full moon is at opposition exactly opposite from the sun every month, and is up all night long.

While on the subject of looking east at sunset, the next clear evening notice the deep blue or violet band of color in the east, a few minutes after the sun sets. The band’s upper edge blurs into the lighter blue twilight sky. What you are witnessing is the shadow of Earth, extending through our atmosphere and into outer space. Other times you may tell the presence of Earth’s shadow are during rare lunar eclipses, and any night if you watch the many satellite spacecraft orbiting Earth. You will notice how the satellites, which look like quickly moving stars, suddenly fade out as they dip into the shadow.

When does Earth’s shadow reach opposition? Answer: All the time! By nature, Earth’s shadow is always directly opposite the sun, so it rises at sunset and is present all night, dipping down in the west in the morning as the sun rises again in the east.

When Jupiter or another planet reaches opposition, it is also at its closest point to Earth. Thus, Jupiter is a bit brighter at this time. That isn’t necessarily true for the full moon, since the moon is in orbit around Earth and may reach its closest point at various times in its orbital cycle.

Opposition also brings a planet, a star or the moon due south at midnight.

Jupiter appears as a brilliant star, but even in a small telescope, you will see interesting detail. It is better to wait till the planet appears higher to get a better view in the telescope. That’s because if you train your telescope at anything very low to the ground, you are looking through a lot more atmosphere. The blanket of air around our world is full of dust and vapor, and it is often turbulent. All of these conditions affect the “seeing” at the eyepiece, or how much detail you will discern. When the air is especially wavy, even a look at the moon will be spoiled except at very low magnification.

Planets appear much smaller than the moon in the telescope and require a lot more magnification to see detail. Calm nights are best, as well as allowing the planet to rise farther in the sky. A little patience can be very rewarding, as moments of excellent seeing will usually come and sharp detail you never thought you’d ever see stands out briefly.

A small telescope will reveal Jupiter’s flattened disc and its four bright moons. The planet rotates once around in about 10 hours. This is so fast that centrifugal forces somewhat flatten the clouded, gaseous atmosphere of Jupiter at both its north and south poles. You may also detect dark clouds bands and possibly dark spots. These markings change through the weeks and are amazing to follow if you have proper equipment and good seeing. The moons, however, are there to enjoy with even the smallest backyard telescope. Named Io, Europa, Ganymede and Callisto, you can watch them shift positions night to night. On certain occasions, one of the moons will cross the face of the planet; while you probably will not see the moon, its ink-black shadow on Jupiter’s cloud tops appears as a tiny spot.

The planet’s brightness is currently rated as magnitude - 2.7, more than eight times as bright as the brightest star currently in the evening sky, orange Arcturus. You can also find Venus this month, low in the western sky after sunset, gleaming even brighter than Jupiter.

On July 17, the nearly full moon passes only 3 degrees from Jupiter.

July 5 and 6, look west after sunset for Saturn, Mars and the bright star Regulus in a tight line (left to right), with the crescent moon just below.

First-quarter moon is on July 10, appearing due south at sunset. That evening, look for Saturn very close and to the upper left of Mars, low in the west after dusk.

Anyone wishing to share what you have observed in the sky, or if you have an astronomy-related question, is welcome to contact the writer.

Keep looking up!

Part of this information was gleaned from Astronomy Magazine and Sky & Telescope Magazine.

Peter W. Becker is managing editor at The Wayne Independent in Honesdale, Pa. He has been an amateur astronomer since the age of 12, in 1969. He may be reached at pbecker@wayneindependent.com.