Author Archives: Alan MacRobert

About Alan MacRobert

Sky & Telescope senior editor Alan MacRobert has been covering all aspects of astronomy since 1982.

This Week's Sky at a Glance

This Week’s Sky at a Glance, October 24 – November 1

Some daily sky sights among the ever-changing stars and planets The monster sunspot continues in view; see "This Week's Planet Roundup" below. Friday, October 24 As the stars come out, Deneb is nearly straight overhead for skywatchers at mid-northern latitudes. Brighter Vega is west of the zenith. Altair is farther from the zenith toward...

This Week's Sky at a Glance

This Week’s Sky at a Glance, October 17 – 25

Some daily sky sights among the ever-changing stars and planets Monster sunspot alert — see "This Week's Planet Roundup" below. Friday, October 17 Before dawn Saturday morning, Jupiter shines above the waning Moon, as shown at right. Although they look rather close together, Jupiter is 2,100 times farther in the background — it's at...

This Week's Sky at a Glance

This Week’s Sky at a Glance, October 3 – 11

Some daily celestial sights among the ever-changing stars and planets Friday, October 3 As evening twilight fades away, look very far to the lower left of the Moon for Fomalhaut, the Autumn Star, already climbing up from the southeast horizon. Saturday, October 4 The W pattern of Cassiopeia stands vertically (on its dimmer end)...

Mutual Events of Jupiter’s Satellites in 2014–15

A full season of mutual events for Jupiter's four largest satellites As Jupiter shines brightly down from the sky during its 2014–15 apparition, quite often Jupiter's four big Galilean moons will occult and cast their shadows on each other. A "mutual events season" like this happens about every 6 years, when Earth and Sun...

Planck temperature map of universe

What’s Next for Inflation Cosmology – New Updates

Our July 2014 cover story was the apparent discovery of gravitational waves from the instant of inflation when the Big Bang took shape. Just as the article was printed, a serious challenge to the discovery appeared: the researchers had underestimated the amount of interstellar dust that could be contaminating their data. Here are more...

This Week's Sky at a Glance

This Week’s Sky at a Glance, September 5 – 13

Friday, September 5 Saturn, Mars, Delta (δ) Scorpii, and Antares form an equally-spaced ragged line in the southwest at dusk, as shown at right. Delta Scorpii used to be a bit dimmer than Beta above it. Then in July 2000 it doubled in brightness. It has remained bright, with slow fluctuations, ever since. Look...

This Week's Sky at a Glance

This Week’s Sky at a Glance, August 22 – 30

Friday, August 22 Altair is the brightest star shining halfway up the southeastern sky after nightfall. Look to its left, by a little more than a fist at arm's length, for the dim but distinctive constellation Delphinus, the Dolphin. He's leaping leftward, just below the Milky Way. In Saturday's dawn, the thin waning crescent...

This Week's Sky at a Glance

This Week’s Sky at a Glance, August 8 – 16;

Friday, August 8 Already you may see an occasional Perseid meteor if you keep an eye on the night sky. The shower's peak night is predicted for next Tuesday (August 12–13), but moonlight will compromise the view all week. Look northeast as the stars come out for W-shaped Cassiopeia. It's still not quite as...

This Week's Sky at a Glance

This Week’s Sky at a Glance, August 1 – 9

Friday, August 1 At dusk this evening, the Moon forms the lower-right end of a very long, curving line of celestial objects. Counting to the Moon's upper left, these are Spica, Mars, and Saturn, as shown here. Today is Lammas Day or Lughnasadh, one of the four traditional "cross-quarter" days midway between the solstices...

This Week's Sky at a Glance

This Week’s Sky at a Glance, July 25 – August 2

Friday, July 25 Mars and Spica shine in the southwest at nightfall. Mars keeps pulling farther away from Spica; they're now 6° apart. Saturn glows pale yellow to their upper left. Arcturus sparkles high to their upper right. Saturday, July 26 New Moon (exact at 6:42 p.m. EDT). Summer is hardly more than a...

This Week's Sky at a Glance

This Week’s Sky at a Glance, July 11 – 19

Friday, July 11 Mars and Spica form a striking pair in the southwestern sky at dusk! They're now just under 2° apart. On Sunday evening they'll be at their minimum separation, 1.3°. Watch them change day by day. Full Moon tonight and Saturday night (exactly full at 7:25 a.m. Saturday morning Eastern Daylight Time.)...

This Week's Sky at a Glance

This Week’s Sky at a Glance, July 4-12

Friday, July 4 Out to watch fireworks? As you're waiting for twilight to end, spot the Moon in the west-southwest with Mars and Spica off to its left, as shown for July 4 here. High above them all shines brighter Arcturus. Saturn is farther left (off the left edge of this illustration). Point them...

This Week's Sky at a Glance

This Week’s Sky at a Glance, June 27 – July 5

Friday, June 27 This is the time of year when, at the end of dusk, the dim Little Dipper floats straight upward from Polaris (the end of its handle) — like a helium balloon on a string, escaped from some summer evening party. Look due north. (Through light pollution, all that you may see...

This Week's Sky at a Glance

This Week’s Sky at a Glance, June 13 – 21

Friday, June 13 Vega is the brightest star shining in the east after dusk. It's currently the top star of the big Summer Triangle. The brightest star to Vega's lower left is Deneb. Look farther to Vega's lower right for Altair. The Summer Triangle will climb higher in early evening all through the summer,...