​July Night Sky

Sky events for this month & objects for observation can be found here.

Courtesy of Orion Telescopes & Binoculars

Click to enlarge. A larger printable version of this chart can also be found here.
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​Gas Giants Dominate Evening Sky

As seen in the evening all-sky chart, the brightest two gas giant planets of our Solar System - Jupiter and Saturn - dominate the evening sky this summer. ​Gas giants are large planets that contain more than 10 times the mass of Earth, they are also known as the Jovian or Outer Planets. Their compositions are mostly gases, such as hydrogen, and small amounts of rocky material (mostly at their cores). The four gas giants in our solar system are Jupiter, Saturn, Uranus, and Neptune.

Composition of the gas giants Jupiter and Saturn.

The sizes of the four gas giants of the outer Solar System compared to the four terrestrial planets of the inner solar system.

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• The gas giant planets take longer to orbit the Sun because of their great distances. The farther away they are, the more time it takes to make one trip around the Sun.
• The densities of the gas giants are much less than the densities of the rocky, terrestrial worlds of the solar system.
• Gas giants are not all gas. Beneath the heavy atmospheres of these Jupiter and Saturn are layers of molecular hydrogen and liquid metallic hydrogen.
• Uranus has an icy layer over its solid rock core, and covered with a gaseous atmosphere. Neptune has a water-ammonia ocean for a mantle overlying its rocky core.
• The metallic hydrogen layers in Jupiter and Saturn conduct electricity.
• The cores of the gas giants are crushed under tremendously high pressures and they are very hot (up to 20,000 K), while the cores of the ice giants Uranus and Neptune are at 5000K and 5,400K respectively.
• Gas giants have been found around more than a thousand stars by the Kepler mission. These large exoplanets are often referred to by such names as Hot Jupiters, Super-Jupiters, and Giant Neptunes.

Opposition is a milestone each year for observing any superior planet (planet orbiting the sun outside Earth’s orbit). When the Earth lies between a superior planet and the Sun, the planet is generally closest to Earth and brightest for that year.

On the night of July 14, 2020, our planet Earth lies between the Sun and the outer planet Jupiter. Our faster motion places Jupiter – largest world in our solar system, and an exceedingly bright planet in our sky – opposite the sun about once each year. Astronomers call this event an opposition of Jupiter. Jupiter reaches opposition on July 14, at 8:00 UTC - 1 a.m. Pacific Daylight Time. A little over a week later, Earth lies between Saturn and the Sun, bringing Saturn’s opposition on July 20, 2020, at 22 hours UTC, 3 p.m. PDT.

Ring Systems
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The largest ring system in the solar system is the one around Saturn. Jupiter, Uranus and Neptune also have rings, and at least one asteroid is known to have a small ring as well. Although Saturn's is the most spectacular ring system in our solar system, discovered with the first telescopes 400 years ago, more recently it has been discovered with better telescopes and space probes that all of the gas giants have rings. A ring system around a planet or asteroid is a disk made up of dust, chunks of material (ice, in the outer solar system), and small moons. This orbiting material forms a ring (or rings) around its parent body. 

Jupiter with its four bright Galilean moons and Saturn with its spectacular rings are two of the most lovely sights to be seen in a telescope. Jupiter is a very good and easy target for a telescope. It is large, bright and shows some color even when using a small telescope. At 35 arc seconds in diameter it is bright because a lot of sunlight is reflected off the light colored clouds that cover its surface.

Fit a low power eyepiece into the focuser. Use the telescope finder to locate Jupiter. Center Jupiter in the finder. Look through the low power eyepiece and use the focusing knob to adjust the focus until the edge of Jupiter looks sharp. The four large moons should be in a line to the sides of Jupiter and should appear as sharp points of light (looking like stars). They may sometimes all be to one side or one might be missing as it passes in front or behind the planet. Adjust the focus if necessary until the moons appear as points of light.

Center Jupiter in the field of view and gently replace the low power eyepiece with the higher power eyepiece and re-focus. Jupiter will now appear larger and two darker (brown) parallel bands should be visible on the planet. The positions of Jupiter's Galilean moons for a given date and time can be calculated here.

Saturn is spectacular due to its beautiful ring system. The planet appears about half the diameter of Jupiter but only a quarter of the surface area. Farther away than Jupiter, it receives less than half the sunlight of Jupiter and therefore is less bright because it reflects much less light back to us. However the rings stretch over half the diameter to each side making it a larger target. The rings vary in tilt as the planet orbits the Sun and are tilted about 80% of their maximum inclination towards us this year, but they will be narrowing in the coming years. Use the same technique to find Saturn as was described above for Jupiter, starting with the low power eyepiece. The positions of Saturn's brighter moons for a given date and time can be calculated here.

Jupiter and Saturn as seen through an 8 inch telescope under excellent atmospheric conditions.