Dale Hachtel People’s Astronomy Club
During our monthly public observing sessions at Niabi Zoo and during other observing programs, one of the most asked questions is: “What planets can we see in the sky tonight?” During this spring, the answer to this question was “None”. This is because there is a somewhat unusual event this year, in which no planet is visible in the sky before midnight.
The planets are, of course, always there in the solar system orbiting the Sun. In early July, most are on the same side of the Sun.
Now they happen to be on the side of the Sun that we see from Earth in the morning before sunrise. As the Earth also travels its orbit around the Sun, by October most planets will be visible in the evening sky.
At the beginning of July, four planets follow one another in the morning sky: Venus, Mars, Jupiter and Saturn. In the morning before sunrise, you can see Jupiter as the brightest object in the southeastern sky, with Mars to the left (east) and Saturn about twice as far to the right (south-southwest). Venus can only be visible if you have a clear view of the east-northeast horizon and can watch the planet rise in morning glow just before sunrise.
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A few weeks ago, Mercury, the planet closest to the Sun, was visible in this row, but it is now too close to the Sun to be seen from Earth. The photo accompanying this article, taken shortly before sunrise on June 23, shows where all the planets were that morning, with the visible planets (Venus, Mars, Jupiter and Saturn) in their actual order of distance from each other. under the sun.
The Earth, which is of course the large planet represented in part at the bottom of the image, is located between Venus and Mars at a distance from the sun. On June 23, the moon was also in this line with the planets.
The locations of other astronomical objects in the solar system, although not visible without a telescope, are also shown in the image. The planets Uranus and Neptune, and Vesta, one of the largest asteroids, also lay along this line of planets.
The Earth orbits the Sun on a plane called the ecliptic. All the other planets orbit the Sun on a plane slightly inclined with respect to the ecliptic. The Moon also orbits the Earth on a plane slightly inclined with respect to the ecliptic.
Because their orbits are on nearly parallel planes, it is possible for the planets to arrange themselves along a line seen from Earth. As the planes are slightly inclined with respect to the ecliptic, the line is not perfectly straight.
The planets all travel around the sun at different speeds, which makes the view from Earth look like the planets are all moving along this line. We have just observed a rare moment when the planets, other than Earth, are all on the same side of the sun. As we progress through the months and years to come, we will see the planets move in their apparent spacing from each other as seen from Earth, but they will always appear close to this line which represents the plane of the ecliptic.
It was this observation of the motion of the planets – named after the Greek phrase “wanderer” – that led early astronomers to determine that the planets revolve around the Sun in the solar system. If you continue to watch and observe the movements of the planets, you realize that although the distant stars in the background of the sky never seem to change, the planets and other objects in the solar system are in constant motion.
We will never see this exact alignment of the planets again in our lifetime. It’s just another reason to keep looking.
The Popular Astronomy Club hosts a public viewing program on the third Saturday of each month from March through November in the Niabi Zoo parking lot at sunset. The next one is scheduled for July 16.
Check our website or Facebook page if cloudy weather threatens to cancel the event. Visit popularastronomyclub.org for more information on public observing programs, monthly meetings, and other events.