The new moon was four days ago, on January 16. The synodic period (the amount of time between full moons, or new moons or whatever) is 29 days, 12 hours, and about 44 minutes. The sidereal orbit (the orbit around the earth without regard to the relative position of the sun) is a little more than two days shorter than that, of course. In the time it takes the moon to circle the earth, the earth has moved almost one twelfth of the way around the sun and it takes the moon that extra two-plus days to get back into the same position relative to the sun and the earth. During the first quarter of the cycle, the moon is a growing (waxing) crescent (less than half visible). The second quarter it is waxing gibbous (more than half visible).
Tagged With: Moon
As you probably learned in school, the moon’s orbit around the earth is not circular but elliptical. On average, the moon is 385,000 kilometers (239,000 miles) from earth but tonight is was at perigee, that is at the closest point in its orbit to the earth, and 357,492 km (222,135 miles) from earth. It’s also near syzygy, which is when the moon, earth, and sun all line up (which is when there is a lunar or solar eclipse). Because it’s not exactly at syzygy, it’s just a bigger than normal full moon. George loaned me his telescope a while back and I got it out this evening to see if I could get anything worth while. I bought a t-ring adapter and this is my first chance to use it.
The moon is just past full and with the clear skies we’ve had lately, the moonrise has been wonderful to see. Here is the waning gibbous moon as it rose this evening.