A grouping in today’s midsummer evening sky
See the end note about enlarging illustrations.
The Moon passes north of Venus (closest June 22, 4 hours Universal Time) and Mars (15 UT). The tightest grouping of all three – a “trio,” fitting within circle of diameter 4.95° – happens June 22 8 UT. This will be in daylight for America and Europe, so June 21 is the nearest evening.
At the time and location of our picture, this grouping is about 20° above the horizon.
Arrows through the moving bodies (including the Sun) show their movement from 2 days before to 2 days after, in relation to the starry background. You can see that Venus is gradually overtaking more distant Mars; this will not happen till July 1. Meanwhile the slender 4-day-old Moon passes them both.
The Moon is shown as seen from the picture location, shifted a degree or so southward by parallax because it is so near to us. The arrows showing the Moon’s flight from day to day are as seen from the center of the Earth, so that you can sense the difference made by parallax.
The Moon is exaggerated 3 times in size, Venus 150 times, so that you can see its shape, like a tiny crescent Moon.
The “antapex of Earth’s motion” – the point away from which we are traveling at this time in our orbit – is at the place ecliptic and celestial equator cross, 90° from the Sun, where the Sun will be at the March equinox.
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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.
I’m looking forward to the illustration.
Thank you Guy. I think two corrections are needed:
Venus will not overtake Mars during their current apparitions. Venus will get to about three and a half degrees west of Mars on July 1. At that point Venus’ eastward motion along the ecliptic will have slowed enough that Mars will be traveling eastward faster than Venus, so Venus will sink more rapidly toward the sunset horizon while Mars lingers higher in evening twilight. Venus stations retrograde July 23.
The Sun will cross the celestial equator from north to south at the September equinox.
Yes, the July 1 event is a quasi-conjunction. I’ll be doing a diagram of it.