September 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.
The Red Planet Arrives
The next couple of months will offer the best views of Mars – The Red Planet – for many years to come. Mars reaches opposition – lying in the sky opposite of the Sun – on October 13. Opposition of Mars occur every 2 years and 2 months (780 days). Mars is showing a steady increase in brightness, surpassing Jupiter’s brilliance on September 24 to become the second brightest planet after Venus. Mars will remain bright well into November. To the naked eye the salmon pink color of Mars is an unmistakable sign that you are looking at the Red Planet.
Now is a good time to observe Mars because it will appear much larger than usual in a telescope. As the distance between the Earth and Mars shrinks, Mars brightens considerably, while expanding in size through the eyepiece of a telescope to be large enough for surface detail to be seen. The last time Mars was at opposition was in 2018. We had a view of it with a large apparent size – larger in fact than this year. However, because of the location of Mars on the Ecliptic, the planet was lower and close to the horizon as seen from the northern hemisphere and this generally spoiled the view for most observers in the northern USA. This year the Red Planet will get to a much higher altitude in the night sky, lying above the celestial equator in the constellation of Pisces. This makes 2020 the year to see this fascinating world through a telescope – Mars will have a maximum apparent size only slightly smaller than that seen in 2018.
The next couple of months will offer the best views of Mars – The Red Planet – for many years to come. Mars reaches opposition – lying in the sky opposite of the Sun – on October 13. Opposition of Mars occur every 2 years and 2 months (780 days). Mars is showing a steady increase in brightness, surpassing Jupiter’s brilliance on September 24 to become the second brightest planet after Venus. Mars will remain bright well into November. To the naked eye the salmon pink color of Mars is an unmistakable sign that you are looking at the Red Planet.
Now is a good time to observe Mars because it will appear much larger than usual in a telescope. As the distance between the Earth and Mars shrinks, Mars brightens considerably, while expanding in size through the eyepiece of a telescope to be large enough for surface detail to be seen. The last time Mars was at opposition was in 2018. We had a view of it with a large apparent size – larger in fact than this year. However, because of the location of Mars on the Ecliptic, the planet was lower and close to the horizon as seen from the northern hemisphere and this generally spoiled the view for most observers in the northern USA. This year the Red Planet will get to a much higher altitude in the night sky, lying above the celestial equator in the constellation of Pisces. This makes 2020 the year to see this fascinating world through a telescope – Mars will have a maximum apparent size only slightly smaller than that seen in 2018.
Some Mars oppositions are distinctly better than others. The maximum apparent size of Mars varies in a cyclical manner through subsequent oppositions because the orbits of Earth and Mars are not exactly circular: they’re elliptical. When Mars is far from opposition, its disc can shrink as small as 3.5 arcseconds – similar to the apparent size of larger but far more distant Uranus. By the beginning of September, Mars appears 19 arcseconds across, and on September 25 the planet will appear 22 arcseconds across. It maintains this size through to the middle of October, dropping to 20 arcseconds by November 1. The planet’s largest telescopic size occurs when it is closest to Earth and this typically occurs a few days from the opposition date. For 2020, Mars is closest to Earth on October 6 and appears 22.6 arcseconds across, a week before the actual opposition on October 13.
Mars apparent diameter will decrease for a number of future oppositions. At the 2022 opposition, the Red Planet’s disc gets up to 17.0 arcseconds, while the 2025 opposition presents a 14.5 arcsecond disc. It shrinks further still for the 2027 opposition, when it will appear 13.8 arcseconds across. With these facts in mind, we can see that the 2020 opposition of Mars will be the most favorable for northern hemisphere viewing for some time – it won’t be this large again until 2035.
Mars apparent diameter will decrease for a number of future oppositions. At the 2022 opposition, the Red Planet’s disc gets up to 17.0 arcseconds, while the 2025 opposition presents a 14.5 arcsecond disc. It shrinks further still for the 2027 opposition, when it will appear 13.8 arcseconds across. With these facts in mind, we can see that the 2020 opposition of Mars will be the most favorable for northern hemisphere viewing for some time – it won’t be this large again until 2035.
What Does Mars Look Like Through a Telescope?
Mars has a rich history of observation. However, unlike the Moon, details on Mars can be a little difficult to see due to their relatively low-contrast. Features are there but subtle, especially if you’re new to observing the Red Planet. It’s common to see a pink slightly blurry disc at first, but with time you’ll gradually see more, especially in the moments of reduced atmospheric turbulence (good "seeing" conditions). Start using a low magnification, say 25x the size of your telescope’s aperture in inches. For a 4-inch (100mm) this means starting off around 100x. Increase the magnification if the view is steady. If you go too high under unsteady conditions it will simply reduce the quality of the view, so back off on the magnification until seeing conditions are better.
Mars has a rich history of observation. However, unlike the Moon, details on Mars can be a little difficult to see due to their relatively low-contrast. Features are there but subtle, especially if you’re new to observing the Red Planet. It’s common to see a pink slightly blurry disc at first, but with time you’ll gradually see more, especially in the moments of reduced atmospheric turbulence (good "seeing" conditions). Start using a low magnification, say 25x the size of your telescope’s aperture in inches. For a 4-inch (100mm) this means starting off around 100x. Increase the magnification if the view is steady. If you go too high under unsteady conditions it will simply reduce the quality of the view, so back off on the magnification until seeing conditions are better.
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During the 2020 opposition, it’s Mars’s southern hemisphere and polar cap that are tilted towards us. Through the eyepiece, Mars appears impressive during September as its apparent size increases from 18.9 to 22.4 arcseconds. Its darker features and bright southern polar cap (SPC) should be observable with magnification. Bathed in sunlight over past months, the SPC will have shrunk in size and during September appears small. As Mars appears to get larger, its surface detail should be easier to see. In addition to the bright southern polar cap, the planet presents lighter and darker areas, representing deserts and exposed rock. These are known as albedo features: areas that appear bright or dark due to the amount of light they reflect. The larger and darker an albedo feature, the easier it is to see through a small telescope.
Although Mars has a very thin atmosphere, there’s enough to support weather and the formation of hazy clouds. Bright orographic clouds form when the Martian atmosphere is forced to a higher altitude and can be particularly noticeable over the peaks of the huge volcanoes that sit on Mars's vast desert plains.
If you’re observing Mars from one night to the next, be aware that the planet’s rotation period is almost 40 minutes longer than Earth’s, at 24 hours, 39 minutes and 35 seconds. This means that features are centrally located on Mars’s disc 40 minutes later on each consecutive night. Observed at the same time each night, the surface features of Mars reset their position on each consecutive night, giving you a view of extra new surface along the western limb before it returns to what you saw on previous nights. Eventually you will get to see the entire globe.
If you’re observing Mars from one night to the next, be aware that the planet’s rotation period is almost 40 minutes longer than Earth’s, at 24 hours, 39 minutes and 35 seconds. This means that features are centrally located on Mars’s disc 40 minutes later on each consecutive night. Observed at the same time each night, the surface features of Mars reset their position on each consecutive night, giving you a view of extra new surface along the western limb before it returns to what you saw on previous nights. Eventually you will get to see the entire globe.
Mars rotation by renowned planetary imager Damian Peach.
Sometimes dust storms on Mars may be seen as lighter patches, often yellowish in color, and they occur seasonally. In 2018 a massive planet-wide dust storm killed the Opportunity rover on the Mars surface. Large planet-engulfing dust storms are fortunately rare; we’ll just have to wait and see whether one develops this season.
Gas Giants Continue To 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. 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.
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. 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.
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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.
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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. |
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Ring Systems
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 arcseconds 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.
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.
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