Mercury greatest elongation

Greatest elongations

Mercury and Venus are closer to the sun than Earth. So they don’t go through opposition. The point at which either planet appears to be farthest from the sun before turning around is called i

Jupiter and Io

Jupiter moon events

Many astronomers with big enough telescopes like to watch Jupiter’s moon cast shadows on the planet, transit the planet’s disk, disappear into its shadow (an eclipse), or pass behind th

Solar eclipse image


There are four eclipses in 2017. Two are lunar and two are solar. Penumbral lunar eclipse February 10-11

Solar conjunctions of planets

When a planet is closest to the sun–in terms of where we see it in the sky, not where it is in orbit–it is in solar conjunction. Sometimes, astronomers shorten the description to simply


The moon is passing in front of stars all the time. Sometimes it passes in front of planets and asteroids. Many astronomers like to watch the brighters stars, planets, and asteroids disappear and r

Moon at ascending and descending node

Ascending node and descending node don’t mean much to the casual astronomer. But some experienced astronomers like to know when the moon is crossing the ecliptic. That’s the line the su

Moon on equator 2

Moon at lunistice and equator crossings

Like the sun, the moon appears to travel northward, then southward, then northward again as it makes it circuit. The sun does this because the earth’s axis is tipped compared to the plane in

Moon perigee and apogee

Perigee is when an object orbiting Earth is closest to the planet. Apogee is when it’s farthest away. Because of the gravitational interactions of the sun, earth, and moon on each other, the

Gibbous moon

Moon phases

Full moon phase dates and times for 2017 are given here in Universal Time. First they are ordered by phase. Farther down the page, you’ll find them ordered by date.

Planet trail 3

Direct and retrograde motion

When a planet is moving eastward compared to the stars behind it, it is said to be in direct motion. When it’s moving westward, it’s said to be in retrograde motion. Around the time i