The cover of the October 2021 issue

Evolution of Venus, Extinction of the Dinosaurs, and Gegenshein

In the October 2021 issue of Sky & Telescope, we’re taking a look into some age-old mysteries. Planetary scientists suspect that Venus may have had liquid water oceans in the past. So what happened? We’re also searching for clues to a prehistoric murder case: the extinction of the dinosaurs. We have two suspects: an asteroid strike or volcanic eruptions. But without a smoking gun, scientists can’t agree which is the culprit. Next, we’re hunting down the pieces of the Sagittarius Dwarf Spheroidal Galaxy, one of the many small galaxies that the Milky Way has ripped apart over the eons. And while several sources credit Esprit Pezenas with first noting the Gegenschein in 1730, his account in the Journal de Trévoux leads Don Olson to believe that what Pezenas actually saw was an aurora. So we’re combing through history for the true discoverer of this phenomenon.


Venus: Inevitability or Catastrophe?

Studying Venus can help us understand how large, rocky worlds evolve — and whether the hellish surface conditions on the second planet forebode a similar fate for Earth.

By Paul Byrne

The Case of the Dead Dinosaurs

Scientists can’t agree on whether an asteroid strike or volcanic eruptions caused the downfall of the dinosaurs.

By Shannon Hall

Meet the Neighbors — The Sagittarius Dwarf Spheroidal Family

Our Milky Way has torn a nearby galaxy to shreds. Find out how you can observe its remnants.

By Steve Gottlieb

Who Discovered the Gegenschein?

It’s time to set the record straight and finally give credit where credit is due.

By Donald W. Olson

Flying into Annularity

Sky & Telescope’s June solar-eclipse flight was an event worth losing sleep for.

By Bob King

A Remote Experience

Astrophotography with remotely operated telescopes is easier than you might think.

By Ted Wolfe

Beyond the Printed Page:

Lunar Rilles

Enjoy this comprehensive survey of sinuous rilles on the Moon.

Remnants of the Sagittarius Dwarf Spheroidal Galaxy

Use these finder charts to locate the objects associated with the Sagittarius Dwarf Spheroidal Galaxy’s remnant core.

Solar Wind

Know exactly when an aurora is about to appear with NOAA’s Real Time Solar Wind live feed.

Peculiar Galaxies

Check out Halton Arp’s Atlas of Peculiar Galaxies.


Capricious Capricornus

This strange zodiacal constellation offers more than first meets the eye.

By Fred Schaaf

Aurora Season Arrives

October is one of the most rewarding times of the year to monitor the midnight sky.

By Bob King

Hot and Cold Lunar Rilles

Understanding the origins of these fine Moon features can enhance your observing experience.

By Charles A. Wood

Mastering Polar Alignment

Setting up your mount correctly is an important first step in creating great astrophotos.

By Tony Puerzer

Table of Contents

See what else October's issue has to offer.


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