The cover of the September issue of S&T. Four large radio dishes sit out on a desert plateau with a pink and blue sunset in the back ground. The overlying text reads "ALMA Radio Array Retrofit."
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Radio Array Retrofit, Swimming with Delphinus, and the Great Comet of 1680

In the September 2025 issue of Sky & Telescope, we feature the Atacama Large Millimeter/submillimeter Array (ALMA)’s new face lift. This update will allow the radio array to observe at even more wavelengths and record more data. Meanwhile, the Euclid space telescope has released its first images with many more to come as it prepares to complete a gigantic 3D map of the universe’s structure. Back here on Earth, we’re taking a peek at the deep-sky objects hidden in a very small portion of the sky: Delphinus, the Dolphin. Or if you’re more of a daytime observer, we have a DIY project that’s right up your alley: Richard Schrantz guides us on how to build our own spectroheliograph at home.

FEATURE ARTICLES:

Cosmic Mapper Extraordinaire

Europe’s Euclid space telescope is mapping the cosmos to investigate dark matter and dark energy.

By Javier Barbuzano

A Deep Dive with the Dolphin

There are plenty of visual treasures to explore in the waters of Delphinus.

By Steve Gottlieb

Newton, Halley, and the Great Comet of 1680

How one celestial visitor changed the course of astronomy.

By Douglas MacDougal

ALMA’s Face Lift

Extensive upgrades to the prolific observatory will propel its prowess back to the cutting edge.

By Paige Cromley

How to Build a Spectroheliograph

This project lets you record full-disk images of the Sun at any wavelength.

By Richard Schrantz

Beyond the Printed Page:

Tidal Tails

Check out this map of lost members of the Hyades cluster.

Sol’ex 2.0

Build your own spectroheliograph.

Saturn’s Moons

Use our tool to locate Saturn’s moons.

Variable Star Plotter

Track the magnitudes of variable stars with this tool from the AAVSO.

ALSO IN THIS ISSUE:

Job’s Coffin: A Stellar Mystery

Could this coffin be afloat in a bowl of tears?

By Stephen James O’Meara

Two Planet Oppositions

Saturn and Neptune are visible from dusk to dawn.

By Bob King

A Lunar Eye Chart

Use the Moon’s features to test your vision

By Thomas A. Dobbins

Night of the Lizard

Lacerta may be a small constellation, but it offers big rewards for deep-sky treasure seekers.

By Ken Hewitt-White

Table of Contents

See what else September’s issue has to offer.

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