APOD
Astronomy Picture of the Day
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.


Equinox: Analemma over the Callanish Stones
Explanation: Does the Sun return to the same spot on the sky every day at the same time? No. A more visual answer to that question is an analemma , a composite image taken from the same spot at the same time over the course of a year. The featured analemma was composed from images taken every few days at noon near the village of Callanish in the Outer Hebrides in Scotland , UK . In the foreground are the Callanish Stones , a stone circle built around 2700 BC during humanity's Bronze Age . It is not known if the placement of the Callanish Stones has or had astronomical significance. The ultimate causes for the figure-8 shape of this and all analemmas are the tilt of the Earth axis and the ellipticity of the Earth's orbit around the Sun . At the solstice s, the Sun will appear at the top or bottom of an analemma. Equinox es, however, correspond to analemma middle points -- not the intersection point. Today at 1:54 am ( UT ) is the equinox (“equal night”), when day and night are equal over all of planet Earth. Many cultures celebrate a change of season at an equinox .
| Date | September 23, 2018 |
|---|---|
| Credit | Image Credit & Copyright: Giuseppe Petricca |
| Authors & editors: | Robert Nemiroff (MTU) & Jerry Bonnell (UMCP) |
| A service of: |
ASD at NASA / GSFC, NASA Science Activation & Michigan Tech. U. |


