If you go out late this evening and your south-eastern horizon is clear, you will see a nearly full moon rising, and above it the red star Antares.
See the end note about enlarging illustrations
The moon again passed close enough to get in front of this star, as happens 13 times this year (Jan 8, Feb 5, Mar 3, Mar 30, Apr 26, May 24, Jun 20, Jul 17, Aug 14, Sep 10, Oct 7, Nov 4, Dec 28), the main reason why 2024 can boast of an unusually large number (48) of lunar occultations of bright planets and stars.
But the encounter with Antares happened about 7 hours before the time of our scene. So this part of the sky was still below the horizon for America and Europe, as shown on page 105 in the “Occultations” section of Astronomical Calendar 2024.
Please scroll back up to take another look at our horizon scene! There are a few things to remark on.
As usual in these diagrams, the moon is exaggerated 4 times in apparent size, and its position is corrected for our northerly location, but the arrows showing its flight from day to day are as seen from the center of the Earth, so that you can sense the difference of about a degree made by parallax.
The moon may or may not look yellowish when low to the horizon, but the reason I’ve taken to using yellow for it and its labels is to make it easier to distinguish them from the background details.
Something else is noticeable. The Moon is moving rightward (westward) as it rises after Antares. But it is moving leftward (eastward), according to the arrows of its travel from day to day!
Of course. The westward movement is what we see from minute to minute as the planet we are standing on rotates; the eastward travel is that of the Moon itself in its orbit around us.
It’s the difference between the Apparent and the Real – a matter so much prerequisite to keeping descriptions clear that we are making it into the first chapter of the upcoming edition of The Astronomical Companion.
And one thing more. You’ve been wanting to scream “Which is it, moon or Moon? Make up your mind!” We’re trying to.
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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” or ”Open image in new tab”, 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.
Moon is Moon. It is our Moon.
It occurs to me in viewing the drawing of the Moon’s occultation of Antares across the night side of the Earth that, if we take that star to be a point source of light and at infinite distance (neither true of course, but for all practical purposes …) then the two parallel lines of the diagram actually represent parallel planes cutting a spherical segment of the Earth, the height of which will exactly equal the diameter of the Moon.
Yes. That solid is a first approximation to the segment that would be cut out by the actual north and south limits of the shadow.
Which is one way of expressing why the lines on the surface of the planet differ from the exact north and south limits of the path of the occultation.
My days are not complete without these very descriptive essays with peerless graphics. I never fail to learn new things or re-appreciate the old. Tip of the fedora to Guy.
I posted a long comment on this post a few days ago, but I don’t see it.
I’ve been struggling to solve this problem, which several people said they experienced, and thgought I had succeeded. I remember seeing a long comment by you followed by a shorter one, but don’t remember where it was. Could you remind me of the subject of the post you were commenting on>
Same problem here, just today.
I commented on “And next: the 2026 eclipse. As soon as I said I didn’t see it, it showed up. The internet is a weird place.
The Moon is always capitalized. It’s not just any old moon. It’s our Moon! Show some respect. :-)
A new edition of The Astronomical Companion! Yay! (I have many astronomical companions, but there is only one Astronomical Companion.)
For what it’s worth, I always capitalize the name of a specific object, but not a type of object. For example, I capitalize the name of the Moon but, not the moons of the planets. For further clarification, Jupiter’s Galilean moons are Io, Europa, Ganymede and Callisto. I consider our Moon to be a proper name as opposed to the general term moon referring to unspecified satellites of planets.