Jupiter and Spica

Jupiter is now low in the evening sky,

only 35 degrees from the Sun, so that it will be hard to see Spica below it.  The magnitudes of Jupiter and Spica are -1.7 and +1.0 – meaning that the star is 12 times dimmer.

They are closest (3.1°) at 1 Universal Time on Sep. 12, which for clocks in America is back in Sep. 11.  In fact for the U.S. Central time zone it is 8 PM EDT, the time of our picture.

This is the second meeting of these two in the year.  Back in February, Jupiter came to its stationary moment, about half a degree farther north of the star than it is now.

Detail from the chart of Jupiter for 2017.

Notice that, at that time, the place where Jupiter came to a standstill was north of Spica in right ascension – that is, parallel to the sloping lines marked “13h” and “30m” – but it never arrived north of Spica in ecliptic longitude, the framework of this chart.  So there was a conjunction in right ascension on Jan, 20; then an appulse, or nearest approach, on Feb. 1, essentially the same as the moments on Feb. 6 when Jupiter was stationary; then a second conjunction in right ascension on Feb. 23.

After that, Jupiter was retrograding – appearing to move back westward as we overtook it – and was nearest (at opposition) in April, and, becoming more distant, began in June to resume apparent forward motion, while gradually being overtaken by the Sun.

View from 15° north of the ecliptic plane, showing the planets’ paths in September, and sightlines from Earth to Sun and Jupiter (and the other planets) at Sep. 12.

Jupiter is 6.24 astronomical units (Sun-Earth distances) from us, Spica about 260 light-years – about 3,150,000 times as far.

 

9 thoughts on “Jupiter and Spica”

  1. My daughter and I observed the eclipse in Niota, Tennessee, about half-way between Chattanooga and Knoxville. We had a great view from our location almost right on the centerline. I was very interested in Rick’s comments and your response about the edge phenomena because of my own experience.

    The only total eclipses that I’ve seen are the 1991 eclipse from Mexico and this one in 2017. My parents and I were on the “Eclipse Edge Expedition” led by the astronomer Tom Van Flandern, along with Guy. My personal advice for a novice eclipse watcher is to go to the centerline. My experience tells me that, unless you are extremely disciplined, you won’t be able to remain organized enough during the frantic moments of totality to see all of the edge phenomena. In Mexico in 1991 I think we had about 1 minute 45 seconds of totality as opposed to over 6 min 30 sec for those on the centerline.

    In hindsight, I wish I would have gone to the centerline then to experience the overall scene of the corona and the black hole in space for as long as possible. In Tennessee this time, even though I wanted to look for planets and stars, I was only able to see Venus with unaided eye and couldn’t even find Jupiter. I did notice Regulus in binoculars, very close to the Sun. This was the fastest 2 min 30 sec I’ve ever experienced. Time really does fly when you’re under-standing an eclipse!

    1. I’ve done a calculation that I hope is right. If the umbra is 70 miles wide, and if you are only 3, 4, or 5 miles inside the path edge, then the length of totality is respectively .405, .464, and .515 of the length of totality on the centerline. This rather surprising result is because it’s a sine function – the chord across the circle of the umbra diminishes only slowly as you go away from the center, quickly only toward the edge.

      1. I’m happy you had a surprising result! I’m not adept at math but I have heard of sine. Looking up its definition I came across the term chord. So at least I learned that chord is a trigonometry term.

        I followed your advice and read “Further Aspects of the 1991 Eclipse” in UE. It would be cool to see the chromosphere during all of totality.
        Were the southern lunar mountains visible against the backdrop of the chromosphere?

        I’m still curious about which stars and planets you observed during totality in Greenville.

        1. From 1991, whether I or we noticed lunar mountains silhoutted against the chromosphere or breaking it into red beads is a detail I don’t remember. Though the chromosphere was visible quite a long time, there were other things to do during that time.

          From Greenville, I noticed no star other than Venus, because I had too many distractions.

          For some past eclipses and other events, Raymond Brooks developed and circulated very detailed timetables or checklists of things to watch for; I don’t know whether he did that for last August or will be doing it for 2024.

      2. Guy, I couldn’t resist using Excel to try to duplicate your calculations, and am happy to report that I got exactly the same thing that you did. I was calculating the length of the chord across a circle centered on the centerline. I must confess, however, that I can’t really make the mental leap from “length of chord of circle centered on the centerline” to “duration of totality”. It seems reasonable that they are the same, but are they really? Certainly, based on limit theory, the eclipse at centerline is maximum, and the eclipse at edge is 0, and the chord length does decrease with the sine or cosine of whatever angle you choose, so it seems right. From the table of numbers I generated in Excel, if you were half-way from the centerline to the edge, you would experience about 86% of the maximum duration.

        But even though the duration may still be a substantial fraction of the maximum possible if you are far from the centerline, I’m sure that the depth of the darkness you experience will be much less.

        1. The relation is close rather than exact, because the footprint of the umbra is not a perfect circle.

          I think the darkness should be the same whenever the sun’s photosphere is totally hidden, whether it is centered for you behind the moon or not. However, time into totality will let your eyes adapt more to the darkness.

    2. You still have 2024 to be on the centerline.

      I’m torn between going to the centerline or the edge in ’24. I think 6 minutes at the centerline would be enough time for a checklist . Perhaps 1 minute looking at shadow bands, 1 minute at the sunset colors, 1 minute observing animal behavior, etc. But then I might miss the chromosphere. Maybe someone will invent a supersonic jet with a glass roof by 2024 that can follow the shadow and veer from edge to edge.

  2. I saw Spica during the total eclipse since Jupiter caught my eye and Spica was so close to it. I also noticed Venus.
    I studied Understanding Eclipses for a couple months before the eclipse but I didn’t get as far as page 58 or I would have looked for Sirius, Castor, Pollux, Regulus, and Capella.

    I forgot to look for the shadow bands. Maybe next time I’ll make a list of things to look for.

    I tried to see Bailey’s beads before totality but the crescent seemed to morph straight into the diamond ring (at least through my solar glasses). Nor could I see the beads after totality. When the diamond reappeared I immediately put on my glasses but by the time my eyes adjusted, the Bailey’s beads were already gone and all I could see was a crescent.

    Also, I did not see the red streak before totality. I took off the glasses right when the diamond ring blinked out but I didn’t think about the red streak. As you stated, events do speed up closer to totality, and I simply forgot to look for it.

    In 2024 I’ll try looking at Sol with the naked eye when the diamond appears before totality (with fleeting glimpses so as not to damage the retina) so that I can try to see the red streak as soon as the diamond blinks out. I’ll look for it after totality too. My thinking is that It’s probably safer to see the chromosphere after totality because then the eyes can be averted when the diamond reappears.

    As I stated before, I was most impressed with the black disc where the sun should be. The corona and the diamond ring were also unforgettable. I was surprised at the intense brightness of the diamond when it reappeared. I thought it would be more subtle.

    What stars and planets did you see?

    1. Rick, your interest in the “edge phenomena” is so high that I suggest that in 2024 you consider positoning yourself only about three miles inside the southern edge of the path of totality. See the third paragraph of the “Further aspects of the 1991 eclipse” section in Under-Standing of Eclipses. It worked very well in 1991: we saw the red chromosphere wrapping all around the southern curve of the (eclipsed) sun. Being so far from the centerline reduces the length of totality much less than you might expect.

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