Mars will be at opposition, the mid-point of the best time for seeing it, on October 13. The more exact time of the event is 13h Universal Time, which is 5 or more hours earlier in America – in daylight. So our scene is for the evening before.
See the end note about enlarging illustrations.
At the time and place of the picture, Mars is climbing into view; it is about 10° up. By midnight, it will be highest, in the south (on the meridian of the sky).
The arrow through the planet shows its movement over 5 days. You can see that it will by tomorrow have passed the “anti-Sun,” my name for the point opposite to the Sun, which is moving eastward.
And that Mars will pass a few degrees south of that point. It is in the half of its slightly tilted orbit that lies south of the ecliptic plane.
About 90° over to the west are Jupiter and Saturn, which passed through their oppositions on July 14 and 20.
Here is the map of the part of the sky where Mars is, as shown in the October band of our Zodiac Wavy Chart for 2020. (The Zodiac Wavy Chart for 2021 is now available.)
In a sense, the opposition is, for Mars, a slight anticlimax, because it was nearest to Earth a week earlier, on Oct. 6. This is because Mars has an orbit that is not only quite inclined (tilted) but quite eccentric (elliptical), and the planet is now in the part that curves outward.
Mars at this opposition is distant from us by about 0.42 of an astronomical unit (Sun-Earth distance), appears 22 seconds wide, and shines at magnitude -2.6. It is in this part of the sky and has that distance, size, and brightness because of where it is, this year, in its orbit: the southerly part, but the inner part. It was at perihelion, the nearest point to the Sun, on Aug. 23, so we are overtaking it only 71 days after that.
In this spatial view, from a viewpoint 6 astronomical units from the Sun and 35° north of the ecliptic plane, the planet globes, at one-month intervals, are exaggerated 700 times in size; the Sun 5 times.
I am going to put more about Mars’s cycle of oppositions into another added page to the “Astronomical Calendar Any-Year” (see the menu of links at the top). Maybe not till after supper, or after some sleep. So take another look tomorrow.
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ILLUSTRATIONS in these posts are made with precision but have to be inserted in another format. You may be able to enlarge them on your monitor. One way: right-click, and choose “View image”, then enlarge. Or choose “Copy image”, then put it on your desktop, then open it. On an iPad or phone, use the finger gesture that enlarges (spreading with two fingers, or tapping and dragging with three fingers). Other methods have been suggested, such as dragging the image to the desktop and opening it in other ways.
Sometimes I make improvements or corrections to a post after positing it. If you click on the title, rather than on ‘Read more’, I think you are sure to see the latest version.
This weblog maintains its right to be about astronomy or anything under the sun.
Thank you for the excellent diagrams of Mars’ position in 3D ~ they are always the best visual descriptors of what is really happening! My image of Mars on October 7 (one day after closest approach):
http://www.starvergnuegen.com/astropix/mars_2020_10_07_1.jpg
then again the next night on the 8th:
http://www.starvergnuegen.com/astropix/2020_10_08_mars_1.jpg
and then another image on the night of opposition:
http://www.starvergnuegen.com/astropix/2020_10_13_mars_1.jpg
The sequence clearly shows the motion of Mars away from mu Piscium
Hello Guy,
i’ve been intrigued by your invention of the “ante-Sun”.
Another way of considering that half-degree-wide circle is that its center locates the apices of both the Earth’s umbra and its antumbra. Indeed, a year-long sweep of that point superimposed on the sky could be an alternate definition of the ecliptic.
While our conical umbra has a fixed base (about 8,000 mi.), height (about 850,000 mi) and volume (about 14 trillion cu. mi) our antumbra is infinite in all three of those parameters. Infinite though the antumbra is, from our viewpoint it is nevertheless confined within that aforementioned half-degree circle. “Viewpoint” implies that there is something antumbral out there for us to view. But of course we don’t see the antumbra. Perhaps it is more apt to say that anyone in a stellar (or galactic!) system within the confines of that antumbral circle who happens to look our way would see us transiting our sun once a year.
The first exoplanets discovered by the Kepler mission revealed themselves to us as their antumbras swept our way. We are constantly returning the favor by sweeping our antumbra, our tiny annular eclipse, across whomever may be under-standing that half-degree wide ecliptic band in our sky.
We are their exoplanet.
Kenneth A. Heisler, M.D.
That’s all correct, of course. The axis of Earth’s shadow travels along the ecliptic, as does the Sun in the opposite direction, and any extraterrestrial inside the widening cone of the antumbra sees Earth transiting the Sun. You’re pretty clever to compute the volume of the umbra!
After starting to plot my anti-Sun in these pictures, I sometimes mentioned that it might also be called the shadow of the Earth though becoming visible only when encountering the Moon (or a nearer object such as an artificial satellite); I think I sometimes marked it as “or Earth-shadow”. The decision is what size to give it in the picture, since it is a cross-section of the umbra and the umbra tapers outward. I see that I gave it a sort of arbitrary average size, but if it encounters the Moon I enlarge it by the same factor as enlarges the Moon.