Archive
08/31/2012 – Ephemeris – Once in a blue moon
Ephemeris for Friday, August 31st. The sun will rise at 7:04. It’ll be up for 13 hours and 15 minutes, setting at 8:19. The moon, at full today, will rise at 8:01 this evening.
Tonight’s moon has been dubbed by some to be a Blue Moon. No the color of the moon isn’t really blue. But it is as rare as a blue moon. Let me try to explain. Currently the label blue Moon is given to the second full moon in a month. August’s first full moon was on the first. This blue moon rule wasn’t always the case. Early American almanacs apparently gave the title of blue moon to the 4th full moon in a season. So could the moon ever appear blue? Yes it can. If seen through a lot of dust in a dust storm. A totally eclipsed moon can appear very dark and even have a blue tinge if there’s a lot of volcanic ash in the atmosphere. I’ve seen two of these eclipses and the moon didn’t appear blue to my eyes, but it was so dim the I could barely make it out without binoculars.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
07/26/2012 – Ephemeris – Why is a half illuminated moon called a quarter moon?
Ephemeris for Thursday, July 26th. The sun rises at 6:22. It’ll be up for 14 hours and 51 minutes, setting at 9:14. The moon, at first quarter today, will set at 12:56 tomorrow morning.
The moon was at the exact first quarter a few hours ago. By tonight the sunlit side of the moon will be a bit fuller, but might be at the half moon phase to the casual eye. So why do we call the half illuminated moon a quarter moon? The moon is a quarter the way around the earth from new moon. When it goes half way around the earth from new, we ave a fully illuminated moon from our vantage point, Another quarter the way around we have a half illuminated moon from our vantage point, but the moon is at third quarter position or last quarter. Another quarter way around and the moon is new again. The ancients unlike astronomers today called the first sighting of the moon’s crescent in the west after sunset new moon.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
Lunar phase diagram. From Wikimedia Commons.
The arrows in the diagram is light from the sun far off to the distant right.
05/24/2012 – Ephemeris – Phases and shadows on the moon
Ephemeris for Thursday, May 24th. Today the sun will be up for 15 hours and 8 minutes, setting at 9:13. The moon, half way from new to first quarter, will set at 12:11 tomorrow morning. Tomorrow the sun will rise at 6:04.
The fat crescent moon tonight is like the crescent Venus, with the sun shining on mostly the far side. I notice that some folks think that the earth is casting its shadow on the moon to cause the crescent. That isn’t correct. The earth does cast its shadow on the moon sometimes, but only at full moon, but only about one in 6 full moons, and we usually don’t see many of these. The phases of the moon are simply the light and shadow of a ball in the sunlight. In fact, if before sunset you can see the moon, and you are in sunlight also. Hold the ball up next to the moon. You will see that the ball will have the same phase as the moon. This is because the moon is close to the earth.
10/11/11 – Ephemeris – The Hunters Moon and libration
Tuesday, October 11th. The sun will rise at 7:52. It’ll be up for 11 hours and 13 minutes, setting at 7:05. The moon, at full today, will rise at 6:34 this evening.
Tonight’s full moon is the hunter’s moon, and it has some of the characteristics of last month’s Harvest Moon. That is the moon rises less than the average 50 minutes later each night. Tomorrow the moon will rose 26 minutes later than tonight. The moon rotates in the same time that it orbits the earth. Only the moon’s rotation is constant, but its orbit around the earth is elliptical, and is not at a constant speed. That causes the moon to wobble a bit. Tonight the south end of the moon is tilted a bit toward is as is the east or left edge. This tilt is called libration. I usually track libration by checking out the position of the small gray sea at the moon’s upper right quadrant called the Sea of Crises. It’s distance from the moon’s limb or edge is a good indicator of this libration.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
07/11/11 – Ephemeris – The moon’s Oceanus Procellarum
Monday, July 11th. Today the sun will be up for 15 hours and 19 minutes, setting at 9:27. The moon, 3 days past first quarter, will set at 3:25 tomorrow morning. Tomorrow the sun will rise at 6:08.
The moon tonight is a big fat gibbous phase. The terminator, now before full moon is the sunrise line that creates tonight’s phase. It’s crossing the large sea called Oceanus Procellarum or the Ocean of Storms. It is the moon’s largest sea, though really a lava basin. This is easily seen with the unaided eye and binoculars. The moon has never had oceans or seas of water. That impression was in the eyes of early telescopic observers of the moon , who even thought there was life on the moon. Oceanus is huge, by lunar standards, 434 by 303 miles with indistinct walls. Lunar seas are actually huge craters with an age over 3 billion years.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Addendum
The moon's Oceanus Procellarum. Image from the Virtual Moon Atlas.
07/07/11 – Ephemeris – Demonstrate for yourself the phases of the moon
Thursday, July 7th. Today the sun will be up for 15 hours and 24 minutes, setting at 9:29. The moon, 1 day before first quarter, will set at 12:43 tomorrow morning. Tomorrow the sun will rise at 6:05.
The moon changes its phase daily as it orbits the earth. Some still think that it has to do with the earth’s shadow. Now that does happen for a few hours during a lunar eclipse at some full moons. However the moon’s phase is simply the moon in sunlight, the same sunlight that falls on the earth. The dark part of the moon is simply the night side of the moon. It changes because the moon orbits the earth and the farther it appears from the sun, the fuller it appears. This can be proven with a small ball. When the moon’s out in the day time, like it is now before sunset, go out in the sunshine and hold or toss the ball up in the direction of the moon. The ball will have the same phase as the moon.
* Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.
Bob Moler's Ephemeris Blog 