The Night Sky This Week

Each Monday, I pick out North America’s celestial highlights for the week ahead (which also applies to northern hemisphere mid-northern latitudes). Check my main feed for more in-depth articles on stargazing, astronomy, eclipses and more.

The Night Sky This Week: March 17-23, 2025

Spring is almost here in the Northern Hemisphere. With the vernal equinox on March 20 — a way-marker in our planet’s journey around the sun — it’s time to say goodbye to the winter stars, with the likes of Orion now visibly sinking into the western horizon after dark. Rising in the east — to the left of, an beneath, the planet Mars — and becoming dominant are a bevy of stars and constellations, including Leo, Boötes and Virgo.

It’s also potentially a great week for aurora borealis/the Northern Lights because around equinox the Earth’s axis is side-on to the sun. The magnetic fields of Earth and the solar wind are briefly aligned, according to the Russell-McPherron Effect, leading to cracks through which charged particles can accelerate, causing more intense displays of aurora.

Here’s everything you need to know about stargazing and astronomy this week:

Monday, March 17: Spring Triangle

Is spring really coming? If you want celestial evidence, locate the “spring triangle” asterism in the night sky. This equilateral triangle connects three brilliant stars — Arcturus in Boötes, Spica in Virgo and Denebola in Leo, all of them fixtures of the spring night sky in the Northern Hemisphere.

Thursday, March 20: Vernal Equinox

The northward equinox occurs at precisely 09:00 UTC (4:00 a.m. EDT) today as the the sun crosses the celestial equator. It brings an equal day and night to the entire planet and marks the start of spring in the Northern Hemisphere and autumn (fall) in the Southern Hemisphere.

Saturday, March 22: Last Quarter Moon

The moon reaching its last quarter phase is a reason to celebrate for sky-watchers and astrophotographers because it clears the way for 10 or so nights of dark, moonlight-free evenings. The moon, now 50%-lit from Earth’s point of view, is today in Sagittarius. In the coming mornings, a crescent moon will be visible in the pre-sunrise hours.

Constellation of the Week: Ursa Major

This constellation, whose name means the Great Bear, is visible throughout the year in the northern hemisphere since it’s circumpolar — it goes around Polaris, the North Star, to which Earth’s northern axis points. Although Ursa Major is well known, few stargazers can go beyond the core asterism — the Big Dipper. Find this asterism’s seven bright star, which are high in the north after sunset, with the bear upside-down.

The times and dates given apply to mid-northern latitudes. For the most accurate location-specific information, consult online planetariums like Stellarium and use a sunrise and sunset calculator for where you are.

Wishing you clear skies and wide eyes.