I hope you had an opportunity to be outside on the evenings of April 20 and 21 to see the conjunction of the Moon and the planet Venus. It was a wonderful sight especially since earthshine was very prominent on the lunar surface.

Earthshine can be seen whenever there is a crescent Moon close to the horizon at sunset. It is the ghostly image of a full Moon between the horns of the lit crescent Moon.

Earthshine is sunlight reflected off of the earth and onto the Moon. The full, round shape of the Moon is obvious with bright sunlight illuminating a small crescent shape for the just-past new Moon. It is often called the "old Moon in the new Moon's arms."

The mystery of this ashen glow on the surface of the Moon, now known as earthshine, was solved by no less a personage than Leonardo Da Vinci in the 1500s. He wrote about the Moon in a publication called Codex Leicester in about 1510. In it he said he believed the Moon was a good reflector of light because of the oceans that were there. He also believed the Moon had an atmosphere. Then he said the "ghostly glow" came from sunlight bouncing off the Earth's oceans onto the surface of the Moon.

Well, he was partly right, the Moon does not have oceans or an atmosphere, and the reflected sunlight comes from the Earth's clouds, not the surface of its oceans, but he had it in principle.

In a few years when NASA sends astronauts back to the Moon they will be spending a lot more time there than the Apollo astronauts did. In Apollo the stay was only a few hours, or days in come cases.

When the new astronauts go back they will be spending weeks or months there and will experience lunar night. The lunar day is 29.5 Earth-days long. They will have 15 Earth-days of light followed by 15 Earth-days of night and will get a chance to experience earthshine.

Well, that isn't what I wanted to talk about this week, so we will put the bears of Ursa Major and Ursa Minor on the back burner for next week.

SKY WATCH: Venus still rules the western sky just after sunset. The bright planet is often confused with airplane landing lights it is so bright. In the southern evening sky look for bright Saturn near Regulus in Leo the Lion. In the morning southern sky is bright Jupiter, the king of the planets. At present it is between Scorpius on the right and Sagittarius on the left. You might note, both are summer constellations. Starting at about 9 p.m. MST, on Thursday, April 26, look in the southern sky for a close conjunction of the Moon and the star Regulus. As the hours wear on look for the Moon to get closer to the star. If we had more sky and less horizon we would be able to watch the Moon cover the star in an event called an occultation, or covering. On Thursday, April 26, look just above the eastern horizon about an hour before sunrise for a faint planet Mars. Mars is just coming around from being on the far side of the Sun. Also with the planet Mars will be the planet Uranus. It will be to the left of the red planet. Watch over the next few days as Mars moves closer to Uranus for a close conjunction on Sunday morning, April 29. The pair will fit inside a viewing field of a pair of binoculars. Look for a bright Iridium flare on Wednesday, April 25, at 10:52 p.m. CDT in the ENE. Also on Thursday, April 26 at 10:46 p.m. in the ENE. More times for Iridium flares can be found at www.heavens-above.com