Over a several-hour period during these ongoing short summer nights, it is possible to view the four brightest planets of our solar system.
Although each is easily visible to the naked eye, Bear Branch Nature Center (BBNC) has been opening its observatory to the public for free views of the planets, weather permitting. The four planets involved are Venus, Mars, Jupiter and Saturn.
We’ll discuss each of the four planets in the order that they appear in the sky, from west to east, after sunset, and look at basic information and interesting facts you need to know about each one, including where and when to look. At the end we’ll address the upcoming observing opportunity at BBNC.
Venus is bright and visible in the western sky soon after sunset. Only slightly smaller than the Earth, Venus is the closer of the two to the sun. Thus, Venus’ orbital path around the sun is fully within the Earth’s own path. Therefore, the position of Venus in our sky is never very far from the sun. It’s usually observed in morning or evening twilight, or even during daytime. In other words, you’ll never see Venus hanging around in the sky at midnight, unlike the outer planets such as Mars.
As Venus revolves around the sun in its orbit there comes a point when its angular separation from the sun is at is maximum. This point, called “greatest elongation” occurs on Aug. 17. In its orbit around the sun, Venus is currently “catching up” to the Earth and thus drawing nearer to us. An observer on Earth with a telescope should notice two interesting changes from day to day.
First, Venus’ apparent size is changing as Its angular diameter grows larger because Venus is approaching Earth. Later, after it passes by us and begins to recede it will begin shrinking again. Second, Venus shows phases just like our moon. Currently, Venus is about half full when viewed through a telescope.
Venus is the brightest of the evening’s four planets, at mag. -4 (minus 4). In darkening twilight, Venus is easily viewed in the western sky at 8:30 p.m. Venus sets a little after 10 p.m.
The next planet is the gas giant Jupiter. Jupiter is the largest planet in the solar system. Even a small telescope will show up to four moons or satellites plus revealing some of the dark cloud bands on the planet. The four brightest moons of Jupiter are called the “Galilean Satellites” after their discoverer.
Jupiter is well placed for twilight viewing by 9 p.m. above the southwest horizon about one-third of the way to the zenith (the imaginary point straight overhead). At mag. -1.5 Jupiter is fainter than Venus, but is still considerably bright and noticeable.
Already sinking toward the west, Jupiter sets shortly after midnight.
Saturn’s up early, but it’s worth waiting until it’s at it highest point in the sky. Saturn transits the meridian due south at 10:30 p.m. A half-hour on either side is a great time for viewing Saturn.
Currently Saturn is at a point in its 29-year orbit around the sun such that its rings are wide open. If not for the shadow of the planet’s ball falling on the rings behind it, the rings could be viewed unbroken all the way around the planet.
At mag. +0.5 Saturn is fainter than both Jupiter and Venus. Saturn sinks slowly toward the west and sets after 3 a.m.
Mars is looming bright and reddish-orange in the southeast as it rises and keeps climbing in the hours up until midnight. By 11 p.m., mag. -2.5 Mars is well placed for viewing in the south-southwest. Mars reaches its maximum altitude over the southern horizon just after 12:30 a.m.
Mars was at “opposition” when it is closest to the Earth in late July. That means that Mars currently appears at its largest. This is a particularly favorable opposition as Mars is closer to the Earth than it has been for 15 years.
In a telescope at high magnification Mars reveals some of its surface features. These are specifically named darker and lighter areas as well as its white southern polar cap. Unfortunately, Mars has been currently undergoing a widespread dust storm, disappointing earth-based telescope users.
In late July a guest at a solar viewing happy hour at the Milkhouse Brewery mentioned that with his telescope at home he was able to see the polar cap on Mars although the bulk of the planet was obscured by dust. Will the dust storm clear in time for us to get a satisfying glimpse of Mars and its surface features before it begins to shrink while moving farther away? Keep your fingers crossed.
BBNC designated the nights of the last two Fridays in July and the first Friday in August as the “parade of planets and the approach of Mars.” On these evenings guests are invited to view the planets through telescopes belonging to members of the Westminster Astronomical Society as well as the telescope inside BBNC’s domed Blaine F. Roelke Memorial Observatory.
The schedule of objects slated for viewing with the observatory’s 14” Schmidt-Cassegrain telescope are: 8:30 p.m. Venus; 9 p.m. Jupiter; 10 p.m. Saturn; and 11 p.m. Mars.
This is only a suggested schedule. The actual viewing times may be impacted by circumstances such as clouds and crowd size.
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The final parade night is Friday Aug. 3, weather permitting. There is no cost and the event is open to the public. BBNC is located at 300 John Owings Road, north of Westminster.