is tomorrow, Thursday June 15
at 10 Universal Time, which is 4 AM in America’s Central time zone. So if you watch Saturn rising in the southeast this evening of the 14th, it is only a couple of hours before opposition.
You can see in our diagram that Saturn is very close to what I call the anti-Sun, which can also be thought of as Earth’s shadow (it would cause a lunar eclipse if the Moon were there). Saturn in this part of its slightly inclined orbit passes 1.22° north of the anti-Sun point.
Saturn has not quite reached the southernmost part of its orbit. That will come next year, and at the next opposition, 2018 June 27, it will be about half a degree farther south. Being near to the southernmost part of the ecliptic implies that the opposition date will be nearer to our summer solstice, with the shortest night.
Already night-time seems shortest if you are a riser-before-dawn, because rhe earliest sunrise comes today, June 14, for parts of the Earth around latitude 40° north. We’ve previously had to discuss why earliest and latest sunrise and sunset do not coincide exactly with the solstices.
And Saturn is in the part of its orbit where the northern surface of its rings is tilted widely open toward us. Actually the maximum of this openness will come on October 17, though the difference between now and then is slight.
Hello Guy,
I take it that the “Anti-Sun” as depicted in the diagram represents the actual size of the Earth’s umbra at lunar distance (about a quarter million miles) from the Earth. I assume the antumbra begins (and the umbra ends) at a point about four times that distance and extends infinitely out from there.
My question: Does Saturn ever manage to pass through the Earth’s antumbra at opposition so that the Saturnians see a transit of the Earth across the face of the Sun?
Yes, the width of both parts of Earth’s shadow (umbra and penumbra) vary with distance, so I make the program draw a sort of average shadow at the average distance of the Moon. If the Moon is near and goes into an eclipse, I make the shadow scaled up by the same factor as I’ve chosen for the Moon.
Yes, since the Earth’s penumbra widens infinitely, many bodies could pass within it and thus theoretically see transits of Earth over the Sun. Jupiter certainly can: Jean Meeus has six and a half elaborate pages on “Transits of Earth as seen from Jupiter”, in book IV of his Morsels series. He doesn’t seem to mention transits of Earth as seen from planets beyond Jupiter, but does mention that “on 2061 May 29 a much rarer transit of Saturn will be visible from Neptune”!
If I had the patience I suppose I should calculate all the oppositions of Saturn over a long span and examine those at which Saturn’s latitude is close to zero.
Yup! I’ve got my Canon all set up and LiveView ready for a night of remote imaging tonight and tomorrow night, pending rain clouds in our area.
By my very rough calculation, here at 37 degrees north latitude the earliest sunrise was yesterday, June 13. But I could easily be off by a day or two. According to my tide table, the Sun rises at 0547 for seven days in a row, and June 13 was the fourth of these seven days.
Saturn has been much too low in the evening sky to be worth trying to observe through a telescope, and I haven’t been able to stay up until midnight recently. But last night, June 13, Saturn was noticeably brighter than usual to the naked eye and through binoculars. I think this is due to the wide-open rings and the Seeliger effect — Saturn’s icy rings reflect light back toward the Sun, and when the Earth passes between Saturn and the Sun that reflected light is shining at us, too.