The Ellensburg, WA sky for the week of September 20, 2025

Saturday: Saturn is in opposition tonight. That doesn’t mean that Saturn is stubborn. Opposition means that Saturn is on the opposite side of the Earth as the Sun. When an object is in opposition, it is at its highest point in the sky during the darkest time of the day. Thus, opposition is typically the best time to observe a planet. Saturn is about three and a half fists held upright and at arm’s length above due south at 1:00 a.m. It is nearly two fists above due southeast at 10:00 p.m. Careful readers of this column may recall that Saturn is in opposition about 12 days later each year: July 21, 2020, August 1, 2021, August 14, 2022, August 26, 2023, and September 7, 2024. An outer planet is in opposition when Earth passes it up as both orbit the Sun. The farther out a planet is, the less it has moved along its orbit, and the closer it is to exactly one year from one Earth passing to the next. For comparison, it is about 18 months between successive oppositions for Mars. Saturn is three fists above due southeast at 10:30 p.m. tonight.

Sunday: Tonight’s moon phase is new. Typically, that is pretty boring. Tonight, in the South Pacific and New Zealand it will be pretty exciting because there will be a partial solar eclipse visible from there. For more information so share with your New Zealand friends, go to https://www.timeanddate.com/eclipse/solar/2025-september-21

Monday: At 10:30 a.m. PDT, the center of the Sun crosses the celestial equator and passes into the southern sky. The celestial equator is an imaginary line that divides the sky into a northern and southern half. When the Sun is in the southern half of the sky, it appears to take a shorter path from rising to setting. It also does not get as high in the sky at noon. This leads to shorter days and longer nights. Since the Sun crosses the celestial equator today, there is an instant when it is equally in the northern and southern sky, called the north and south celestial hemispheres. This so-called “equal night” is given by the Latin word equinox. Thus, today is known as the Autumnal Equinox. However, the day and night are not of equal duration today. The sun rises at 6:49 a.m. and sets at 6:58 p.m. in the northern latitudes of the United States.

Tuesday: Mars is right above the west-southwestern horizon at 7:30 p.m.

Wednesday: To the people of Ancient Greece, the stars that are about five and a half fists above the northeastern and eastern horizons, respectively, at 10:30 p.m. were known as Cassiopeia and Andromeda, a mythological queen and her daughter. But not all cultures imagined the same pictures in the sky. To the people of Polynesia, the stars of Cassiopeia and Andromeda represented a dolphin, called Kwu. Cassiopeia formed its tail, the brightest stars of Andromeda formed its fins, and its fainter stars outlined the dolphin’s body.

Thursday: Ask someone which day in September has the same duration day and night. Go ahead, ask someone. Why are you still reading this? I can wait. If that person says the first day of autumn, they are wrong. Today, three days after the first day of autumn, is the date on which day and night are closest in duration. There are two main reasons for this. First, the atmosphere acts like a lens, bending light from the Sun above the horizon when the Sun is actually below the horizon. This makes the Sun appear to rise before it actually rises and appear to set after it actually sets. Second, fall starts when the center of the Sun passes through the point called the autumnal equinox. But the Sun is not a point. The upper edge of the Sun rises about a minute before the center of the Sun and the lower edge sets a minute after the center of the Sun. Thus, even if we didn’t have an atmosphere that bends the sunlight, daytime on the first day of autumn would still be longer than 12 hours.

Friday: At 6:00 a.m., Venus is a little more than a fist above due east. At this time, Jupiter is five fists above the southeastern horizon.

The positional information in this column about stars and planets is typically accurate for the entire week. For up-to-date information about the night sky, go to https://nightsky.jpl.nasa.gov/planner.cfm. All times are Pacific Time unless noted.