I always intend to keep these newsletters brief, but every time I sit down to write one of these things, I find more and more that I want to say. In this issue, I wanted to draw your attention primarily to a couple of upcoming eclipses. There's a partial solar eclipse in about a week for those of you in Europe, and a total lunar eclipse a fortnight later for those of you in Asia and the Americas. But I also want to mention a couple of bright stars currently in the evening skies. So I've decided to discuss the stars and the solar eclipse today, and I'll save the lunar eclipse for another issue in about a week, when we are closer to the actual event. If you want further information immediately regarding either eclipse, including visibility and scheduling for your particular location, I recommend the Time and Date website. Clicking on the foregoing links will take you there.
In recent evenings, perhaps you've noticed an exceptionally bright star rising in the east after the sun goes down in the west. This “star” is much brighter than any proper star ought to be. If you compare it to the constellations nearby, you may discover that it moves very gradually day-by-day, and thus it does not belong to any constellation itself. What you are watching is the second-brightest “wandering star” … also known as a “planet.” The brightest wandering star is trapped near the sun and can only be seen over sunrises and sunsets, but this other bright one can rise high into the night sky, like an imperious god looking down over the world from Mount Olympus. This is Jupiter. Try looking at it through binoculars and see if you can see its moons. If you have a large enough telescope, maybe you can even see the beautiful colored bands of clouds swirling across the surface.
Incidentally, the slowest wandering star is also visible at the same time. Around 8 pm in the United States (or similar latitudes) it will be somewhat to the right of Jupiter, about the same height above the horizon in the south. If you look at that one through a telescope, you may see some beautiful rings.
Notice where Jupiter is in the sky compared to the Sun. It rises in the east after the sun has set in the west, just like a full moon does. Like a full moon, Jupiter is currently on the opposite side of us from the sun. Planets usually get brighter when they are “at opposition,” and this is part of the reason Jupiter is so noticeable right now. (The exact date of Jupiter's opposition was September 26, but it doesn't move very quickly, so it's still in the same general area.)
You can see why planets become brighter at opposition if you think about the arrangement in space. When Jupiter and the Sun are on opposite sides in the sky, they must also be on opposite sides of us in space as well. We are all in a row, with the Earth in between the Sun and Jupiter. Assuming that the Earth and Jupiter move in concentric circles around the Sun, then we will all line up like this when the Earth and Jupiter are on the same side of the sun, lined up in our orbits. It is as if the Earth is passing Jupiter in the inner lane of a racetrack. Opposition happens whenever the Earth “laps” another planet in their race around the sun. And when this happens, the two racers are closer together than when they are in different positions around the racetrack. Planets are brightest in the sky (and most beautiful in telescopes) when they are at opposition from the Sun, because this is when they are closest to the Earth. (This applies to the outer planets Mars, Jupiter, and Saturn. Mercury and Venus are never at opposition, and follow different rules.)
You may have heard some brouhaha in the media recently about Jupiter being closer than ever in 70 years. Jupiter comes nearly this close whenever it reaches opposition, which it does every 13 months or so. But during some oppositions Jupiter comes a little bit closer than usual, and in other oppositions it doesn't approach quite so close. This year we had an unusually close opposition, sometimes called a “great opposition.” Google tells me that the distance at closest approach this time was 367 million miles. If you subtract the average radius of the Earth's orbit from the average radius of Jupiter's orbit, you find an average separation at opposition of about 391 million miles. That's more of a difference than I thought it would be, but still not huge, considering that when Jupiter is not at opposition, we can be as much as 577 million miles apart. If you are interested, I also found this image comparing the view through a telescope for two different oppositions.
By the way, when Jupiter reaches opposition, it grows a little brighter than usual, but there is another wandering star — a red one — that grows much brighter when it reaches opposition, like a god of war flaring up in anger. Mars currently rises a bit before midnight, and it is fairly dim. But keep your eyes on it — it will rise earlier and earlier, and it will reach opposition in December, growing so bright that it rivals Jupiter. (When this happens, it will be where Jupiter is now, so you will be able go out in the evenings after the sun sets in the west, enjoy the sunset colors for a while, then turn around and find Mars rising in the east.) Just as a side note, I began this newsletter in October of 2020 by discussing an opposition of Mars. Jupiter passes through opposition almost once a year, but Mars takes about 2½ years between oppositions. In December, this newsletter will have existed through one complete “synodic cycle” of Mars, from opposition to opposition.
In the evenings in the Northern Hemisphere, there is another bright star, a little orangish, hanging above the horizon opposite to Jupiter. Maybe you can think of the pair of them like a pair of lanterns hanging over opposite sides of the horizon. (This northwest star will be fairly low, however, and will continue to sink as Jupiter continues to rise, so you won't be able to find it if you go out long after sunset, or if you have a cluttered western horizon.) The Big Dipper should be a little to the right of this star in the northeastern sky. If you follow the arc of the handle of the Dipper and keep going, you should land on this star. You have just followed the “Arc to Arcturus.” In October evenings, Arcturus stands in the sky in very nearly the same place that the sun stood a few months ago at the same time of day. As the days grow shorter and the air becomes chilly, we can keep the memory of warmer, sunnier times by finding this “Ghost of Summer Suns” in the evening sky. (If you live in the Southern Hemisphere, you can still enjoy brilliant Jupiter in the northeastern sky, but Arcturus will be below your horizon.)
There won't be any dramatic meteor showers for awhile, but we are entering the season of the Taurids, a weak but two-month-long meteor shower. Don't worry about trying to catch it on the peak day, because it doesn't really have one. Just keep your eyes open for meteors while you are stargazing, and you may see a few per hour on any given night. (The Taurids are not numerous, but they can occasionally be spectacular. Sometimes a Taurid meteor will explode and give us a “Halloween Fireball.”)
Solar Eclipse (October 25)
Unfortunately, not much of the world will be able to see this eclipse, and it is only a partial eclipse. Darkness will never fall and nobody will get to see the sun disappear from the sky. I'm pretty sure that nobody on this mailing list lives in Kazakhstan or Siberia, but if you did you might notice a slight dimming of the world around mid-day on October 25th. Elsewhere in Europe, you probably won't notice anything unusual on that day unless you can take a careful look at the sun. If you do, you may discover that it has a strange shape.
So if you live in central or eastern Europe, try looking at the sun around mid-day on October 25th. If you have clear weather, there will probably be too much glare for you to get a good look at the shape of the sun directly, just as there would be on any other day. If you have the right kind of weather, you may be able to see the shape of the sun behind a thin cloud. Normal sunglasses aren't strong enough to help you see the sun, but you can get a great view of the shape of the sun using “eclipse glasses”, which are like sunglasses except much, much darker. (Warning: According to what I've read, looking at the sun through “normal” sunglasses is not only useless, it could even be dangerous. If they are the wrong material or color, they can trick your eyes into thinking the world is darker, thus reducing your natural ocular defenses, while still allowing the harmful UV rays into your eyes at full strength.)
Another way to see the shape of the sun would be to make a pinhole projector. If you make a small hole in a large piece of paper or cardboard, and then hold it in the sunshine, you may notice the dot of sunlight in the shadow of your card. You can make this dot brighter by making the hole larger (up to a point), and you can make the dot larger (but dimmer) by holding it higher above the ground. You may also want to shine the dot into a deep dark box of some kind to make the faint light spot easier to see. If you try this on a normal day, you will see the normal “circle of sunlight.” (Try making the holes in different shapes. As long as they are not too large, you will find that the light spot is always a circle, for some strange reason.) But if you try this during an eclipse, you may discover that the circle is not a circle. It looks like a circle with a piece missing. (For small holes and large distances, the shape of the spot is determined by the shape of the sun, rather than the shape of the hole.)
You know those overlapping circles of dappled sunlight you sometimes see underneath trees or in the shadow of high bushes or vine trellises? Watch what happens to them during a solar eclipse. Those circles are actually images of the sun, and a partial eclipse is a great time to discover this, because then they will turn from circles into crescent shapes. Perforated shade-trees are just like natural pinhole projectors with many pinholes.
In any case, if you can get a good look at the sun during a partial eclipse, you will see the normal circle of the sun with a circular piece subtracted from it, as if someone took a bite out of a cookie. In Europe on October 25th, this ”bite“ or missing portion will grow, reach a maximum, and then shrink away to nothing again. (If this were a total eclipse, there would be a moment in the middle when all of the sun disappeared, but that won't happen this time.) How much of the sun will disappear? In France and the UK, the ”bite“ will ultimately reach across about one-quarter of the sun's diameter, blocking around 10-15% of the sun's circular area and thus eliminating around 10-15% of the sunshine. If you didn't know there was an eclipse, you probably wouldn't be able to tell that it wasn't a normal day. A little farther east, in Scandinavia and Poland, the ”bite" will ultimately eat up about half of the sun's diameter, and obscure around 40% of the area and the sunshine.
What is causing the sun to take on these strange shapes? It looks as if a round solid object is passing between us and the sun, and blocking a portion of our view of it. What is this object? One important clue is that it has the same size and shape as the moon. Another important clue is that we only see solar eclipses at the time of the New Moon, when we know the moon is passing by the sun in the sky anyway. That dark object must be the moon. (We can confirm this during total eclipses, because when all of the sunshine goes away, we can still see a faint glow and recognize ... the face of the moon! In effect, the sun turns into the moon in that moment of darkness.)
As I noted above, you can find more details about this eclipse, including specifics for your location, at Time and Date.
That's all for today. Happy Viewing!