A Facebook follower asks what it means when the moon is at ascending node or descending node. Continue reading →
¡SkyCaramba! Weekly astronomy blog for the week ending February 8, 2014
If you look at the pages of an almanac, you’ll occasionally see that the moon is at ascending node or descending node. Julie Threadgill, who saw such a message following SkyCaramba via Facebook, asks what that means. It means the moon is crossing a line in the sky that the sun travels on over the course of a year.
You can probably make a good guess where the celestial equator is. During the day, the sun crosses the sky somewhat close to it. But actually only twice per year, at the equinoxes, is the sun exactly on it. For six months after the March equinox, the sun is north of the celestial equator. Then for six months after the September equinox, the sun is south of it. The line the sun actually rides throughout the year is called the ecliptic.
As the sun slowly moves north or south of the equator during the year, it’s also moving slowly eastward against a background of stars we don’t see during the ...