The dance of the 5 visible planets in the western sky has just about concluded now, however, Jupiter and Venus are moving provocatively closer. By the 31st, they'll be 3.2 degrees apart, and by early next week, they'll only be about the width of a finger, when held at arm's length, from each other (less than 2 degrees). The spring constellations of Virgo (the Virgin), Bootes (the Hunter) and Leo (the Lion) reign over the night sky now, while high overhead the Big Dipper appears to be scooping up stars. To the east, the summer triangle, consisting of the bright stars Deneb (in the Northern Cross), Altair (in Aquilla the Eagle), and Vega (in Lyra the Lyrist), is coming into view.

The Moon was full last week and is currently in the waning gibbous phase, meaning it rises after sunset but before midnight, and it sets after dawn but before noon. On most nights the Moon rises about 50 minutes later from one night to the next. If it were in the same position at the same time each night, it would just be a stationary satellite. Our Moon appears to be migrating through our night sky in the opposite direction from how we're moving, but actually, like us, it's orbiting and rotating in a counterclockwise direction. The speed of the Earth's rotation accounts for 95% of the movement of the Moon across the night sky, the remaining 5% is due to the motion of the Moon itself.

When the Moon is out at night, regardless of the phase, it's bright enough to dominate the night sky. The full Moon has a magnitude of -12.5 compared to a magnitude of about -4 for the next brightest object we can see at night, Venus. Thus, the full Moon appears about 1,600 times brighter than the brilliant Venus. However, compared to the Sun, the Moon's light is extremely feeble. Actually, the Moon is a fairly dark object, reflecting only about 10% of the sunlight that falls on its surface.

If you have the chance sometime in the next week, take a look at the Moon during the morning. As I write this, about 80% of the Moon's disk is visible, but you likely won't be able to find it right away. Not only is it vastly overmatched by the brightness of the Sun, but even nearby clouds look brighter. Although the light of the full Moon is bright enough so that we can read by it, moonlight is still woefully dim compared to sunlight. At noon, a dull dark color in full sunlight is as much as 4,000 times brighter than a piece of white paper in the light of the full Moon!

Our Moon is by far the most written and sung about celestial body, but with few exceptions, the Moon is rarely alluded to in song or verse as a daylight object. However, the verse below by William Wordsworth, may have been written about the daytime Moon.

With how sad steps, O Moon, thou climb'st the sky,
How silently, and with how wan a face!
Where art thou? Thou so often seen on high.

{from "With How Sad Steps, O Moon Thos Climb'st The Sky" (1806)}

Also, the 1976 song "Moonlight Feels Right" by Starbuck has a lyric that mentions this.

We'll see the Sun come up on Sunday morning
and watch it fade the moon away.

Watching the full Moon rise is something most of us have enjoyed numerous times. However, the reason the rising Moon is so spectacular is because the Sun has departed. The "Moon Illusion" gives the false impression that the Moon, as it's rising, is much larger than it is when it's high in the sky. However, the Moon, like the Sun, subtends an angle of 1/2 degree of arc whether at the horizon or at the zenith. Nonetheless, when it's seen looming above the eastern horizon just as the Sun has set, it makes a lasting impression. But how many of you have ever seen the Moon set?

While watching the Sun set or rise is a common if not a nearly everyday experience, not many of us can say they we have actually seen the Moon disappear below the western horizon. As mentioned above, the Sun and Moon appear to be the same size to us - that's why total solar and lunar eclipses can be observed on occasion from the Earth's surface. However, despite the fact that the Moon can bedazzle us during the nighttime, it often escapes our notice as is sinks toward the western horizon when the Sun is up in the east.

This is particularly so when it sets in the spring and summer (for the Northern Hemisphere). At these times, the Moon's path is more diagonal to the horizon than it is in the autumn, and as a consequence, it sets more slowly. Because it traverses through a longer portion of the Earth's atmosphere as it sets, quite a bit of its light is attenuated, just as the Sun's light is dimmed and reddened by our atmosphere as it sets. As a result, the already weak light of the Moon becomes even fainter as it approaches the horizon. Only when the atmosphere is very dry, and free of pollution and haze, can we detect it on the western horizon, looking more like a cloud fragment than the familiar glowing orb that punctuates the night sky.

For more about this see the US Naval Observatory http://aa.usno.navy.mil/data/docs/RS_OneDay.html
and the Physical Moon and its History
http://www.moonlightsys.com/themoon/phases.html