Diana, the Moon, nods to Venus, queen of planets, in the morning sky of Saturday, August 15 –
– which also happens to be the birthday of a goddess who does not wish to be named.
See the end note about enlarging illustrations.
The Moon, in the picture, is exaggerated 2 times in size, and Venus 150 times, so as to show that their bright crescents face toward the Sun – which we also show (at twice size) below the horizon. So the Moon and Venus are not as close to each other as the picture makes them appear. The closest they get is 4°, though this is as seen from the center of the Earth; for our northern latitudes they are closer. This happens at 14 hours by Universal Time, which is 5 or more hours earlier by American clocks, and about 4 hours after the time of our mid-USA picture.
The parallax, or angular difference caused by shifted viewpoint, is illustrated by the arrows showing the Moon’s travel from day to day. They are uncorrected for parallax: in other words, they are along the Moon’s path as it would be seen from the center of the Earth. Venus is a nearby planet, so its position is also parallax-shifted, but by an angle much too small for the scale of such a picture, yet far larger, relatively, than the parallaxes of the nearest stars.
You can see that Venus must now be about as far away from us as the Sun, because its crescent is fatter than the Moon’s. In fact it was at dichotomy -D-shaped – on August 12; but something about the planet’s cloudy surface makes dichotomy seem to happen up to about 6 days after the date when it geometrically should happen (as explained in the “Dichotomy” section of our new book about Venus). So now and the next few mornings might be a good time for judging how close to a straight line Venus’s terminator – the line between its day and night – looks in your telescope.
There may still be a few Perseid meteors to be seen, flying from their radiant point which is not far above Capella.
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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.
I would guess that it’s Matilda’s b-day.
When I was around seven years old, over sixty-three turns ago of the Earth round Sol, my daddy pointed to the Moon and told me I had the same name as the Roman Moon Goddess, sparking a life-long love of astronomy, skywatching, space exploration, and an on-going interest in how mythologies and anthropomorphisms are the ways a particular human culture attempts to explain what life means to its members. Six months after Apollo 15 astronauts visited lunar soil, I married my sweetie, who by lucky happenstance allowed me to bestow on myself the name of the landing site. Every quarter phase of the Moon I have the opportunity to identify roughly the location of Hadley Rille (about a 1/3 of the way down the terminator from the lunar north pole), where I once hoped would be where I would retire. Some 35 years ago I was introduced to your absolutely magical calendars and astronomical publications, covering so many of the topics I love. I have thanked you before, Guy, but I just have to thank you again — especially as I first thought you were addressing me directly when the initial line of this post popped up in my email!