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In the southeastern sky, after dusk, on the evening of Wednesday, June 27, the full moon will sit one degree above Saturn, yellowish and shining. The two objects will cross the sky together during the night and will easily fit into the field of a small telescope at low magnification (orange circle). Meanwhile, the moon's separation from the bright planet will increase noticeably as the moon slides east into its orbit. The group of stars open Messier 25 will sit at 3 degrees in the upper left of the moon and Saturn.
Credit: Starry Night Software
Late Wednesday night (June 27), the moon and Saturn will be extremely close in the sky, and both will be at the opposite of the sun – a range that will attract the attention of even casual sky watchers.
Sometimes sky almanacs referring to the position of the planets will use the term "opposition". But what exactly does that mean? Seen from our point of view here on Earth, the opposition refers to whenever a planet is located in the sky in a position that is directly opposite to the sun.
This is also the moment when the planet in question appears at its best position for observation. For all intents and purposes, it is in the sky all night long: rising to the east when the sun sets to the west, reaching its highest point in the sky at midnight (or 1 o'clock in the morning if summer time is in effect), and lie down in the west as the sun is about to rise to the east. [When, Where and How to See the Planets in the 2018 Night Sky]
This situation only occurs for so-called higher planets – that is, planets farther away from the sun than they are from the Earth. Among the planets shining to the naked eye, only Mars, Jupiter and Saturn can appear in opposition, or diametrically opposed to the sun of our sky.
The two "lower" planets, Mercury and Venus, can never appear in front of the sun because they are closer to the sun than they are to the Earth. On the contrary, the best time to try to see these two inner worlds is when they are at the greatest elongation, which is their greatest angular distance from the sun. The mercury can get away from the sun enough to be visible until 90 minutes before sunrise or after sunset. Venus can be visible until 4 hours before sunrise or after sunset. But neither can stay in sight for a whole night.
Intervals of opposition
In the case of a higher planet, three celestial bodies must be properly aligned in this order: the Sun, the Earth and the planet. The Earth, of course, is in the middle, flanked on one side by the sun and on the other by the planet in question.
In other words, when the Earth, which takes a year to move around the sun, passes (or "rides") a slower outer planet, it is the moment of opposition. Because Mars takes 684 days to do a sun tour, Earth catches up with Mars every 2.2 years. March will come to the opposition on July 27 this year. His next opposition will come in October 2020, followed by another in December 2022.
Jupiter moves much more slowly on the sun than Mars, taking almost 12 years to complete a complete orbital circuit. For this greatest of all planets, oppositions come about a month later each year. Jupiter was in opposition this year on May 10. Next year, the opposition will come on June 12 and in 2020, it will take place on July 15.
For ancient astronomers, before they knew more distant worlds like Uranus and Neptune, Saturn was known as the most distant planetary vagabond. Saturn was the Roman equivalent of the Greek god Cronos, the god of time. And for the ancients, Saturn seemed to take a long time to switch from one zodiac sign to another – in some cases, up to two and a half years. In fact, Saturn takes 29 years and a half to orbit the sun. For this reason, Saturn's oppositions only come about two weeks later in the calendar each year.
Saturn and the moon will align
Saturn will come into opposition to the sun this week. It happens on Wednesday. the moment it will be directly opposed to the sun will occur at 13:00 GMT. It is 9 o'clock EDT and 6 o'clock PDT. Of course, Saturn will not be visible at the moment in North America because it will be the day.
Skywatchers in this region will have to wait later in the evening, after sunset, to see Saturn in the east-southeast sky. But he will not rise alone; he will stay with the moon, which will be almost full. In fact, another way of defining a "full" moon would be to say that the moon is in opposition. Full phase occurs when the moon is opposite the sun in the sky and its entire disk is fully illuminated by sunlight. This happens at intervals of about 29.5 days. The timing of the complete phase will be at 0453 GMT on Thursday morning, or 12:53 pm EDT and 9:53 pm. PDT Wednesday night. [Full Moon Calendar 2018: When to See the Next Full Moon]
Or, put yet another way, the moon will reach a point in the sky opposite the sun 15 hours and 53 minutes after Saturn. And en route to reach the complete phase, the moon will pass rather near Saturn. In the sky, the moon will appear at the top left of Saturn while both rise above the east-southeast horizon on Wednesday night.
Depending on your location, however, the view will be somewhat different. For those in the Eastern time zone, the moon and Saturn will be closest together – at about 1 degree intervals – around 11:30 pm. In the central time zone, the pair will be closest to 22 hours. From the time zone of the mountains, the moon and Saturn will be the closest around 9 pm, in a bright twilight. For Pacific states, the time of the closest approach will coincide with the local sunset (around 8:30 pm), and the gap between the two will have widened to about 1.3 degrees.
The Seeliger effect
The Seeliger effect of opposition, when a planet is in front of the sun in the sky of the Earth, will be strong for Saturn this year. Skywatcher Frank J. Melillo of Holtsville, New York, writes: "The icy particles of the rings will ride their shadow behind them, which means that the rings will have an" extra "brightness on the night of opposition. late next month, say the end of July, you will certainly see the difference and the rings will be much paler or duller … For example, I post for Space.com readers a two-image animation of the # 39; last year. Pulsation of the brightness of the rings at the night of opposition then 25 days later. " Credit: Frank J. Melillo
When a higher planet is in opposition, it will also be close to the point in its orbit where it is closest to the Earth, which means that it will also shine with its greater radiance. In the case of Saturn, it will seem to shine serenely with a yellow-white tint of magnitude 0.0. To compare this with the brightest stars of the summer, Vega blue-white and Arcturus orange, the brightness of Saturn will match Vega and will appear only a little weaker than that of Arcturus. At this brightness, there will be no problem visually seeing Saturn, despite its proximity to the dazzling full moon.
And if you train a telescope on Saturn, its famous ring system will also appear a little brighter than normal, but for a different reason. The rings are composed of a multitude of highly reflective ice particles ranging in size from dust to rocks, grouped into intricate subsystems of rings inside the rings. And for a day or two before and after the opposition, the shadows of these ice particles will be hidden, just as sunlight hits the rings straight. As a result of this geometry, the rings seem to increase in brightness compared to the gaseous globe of the planet. This brightness enhancement – known today as the Seeliger effect – owes its name to the German astronomer Hugo von Seeliger (1849-1924), who used it as circumstantial evidence that the mysterious rings were composed of individual particles rather than solid discs.
While there is no doubt that this summer will definitely belong to Mars because of its unusually close approach to the Earth in late July, at least Wednesday night, attention will be focused on "The Lord "The Rings", which will appear at The Best in 2018. And accompany it through the sky from dusk until dawn that same evening will be our closest neighbor in the space.
Joe Rao is a partner at Hayden Planetarium in New York. He writes on astronomy for Natural History magazine, Farmer's Almanac and other publications, and he is also a meteorologist on camera for Verizon FiOS1 News in New Lower Hudson Valley. York. follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.
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