This Week’s Sky at a Glance, February 23 – March 3


Moon, Aldebaran, Orion on Feb, 22, 23, 24, 2018

As Moon waxes past first quarter it steps past Aldebaran, as it always does in February. Think why! Hint: the quarter Moon is always 90° from the Sun.

Friday, February 23

• First-quarter Moon (exact at 3:09 a.m. on this date EST). For North America this evening, the Moon shines left or upper left of Aldebaran, and farther upper right of Orion, as shown here.

The Moon occults Aldebaran in daylight or twilight for northern and western Europe, and in darkness for much of Russia; map and timetables.

Saturday, February 24

• The Moon shines over Orion after dark, as shown here.

• Algol should be at minimum brightness, magnitude 3.4 instead of its usual 2.1, for a couple hours centered on 10:05 p.m. EST (7:05 p.m. PST).

Sunday, February 25

• Have you ever seen Canopus, the second-brightest star after Sirius? In one of the many interesting coincidences that devoted skywatchers know about, Canopus lies almost due south of Sirius: by 36°. That's far enough south that it never appears above your horizon unless you're below latitude 37° N (southern Virginia, southern Missouri, central California). And there, you'll need a very flat southern horizon. Canopus crosses the south point on the horizon just 21 minutes before Sirius does.

When to look? Canopus is due south when Beta Canis Majoris — Mirzam the Announcer, the star about three finger-widths to the right of Sirius — is at its highest point due south (roughly 8:00 p.m. now, depending on how far east or west you are in your time zone). Look straight down from Mirzam then.

Monday, February 26

• The Big Dipper standing upright in the northeast means that Bootes is about to rise. The Dipper's handle famously arcs down and around toward Arcturus, Bootes's brightest star — and the arc crosses Bootes for most of the way. The whole constellation is above the east-northeast horizon by 9 or 10 p.m. now. Spring approaches.

Moon, Regulus, and Sickle of Leo, Feb. 27 to March 1, 2018

During the night of the 28th, watch the just-short-of-full Moon creep up on Regulus. As always, the moon symbols here are drawn three times the Moon's actual apparent size. Their centers are plotted exact for latitude 40° N, longitude 90° W, near the population center of North America.

Venus and Mercury, March 2, 2018

Use binoculars to help catch Venus and Mercury very low in bright twilight on Friday evening March 2. . .

Venus and Mercury, March 3, 2018

. . . and even closer on Saturday evening.

Tuesday, February 27

• After dinnertime at this time of year, five carnivore constellations are rising upright in a row from the northeast to south. They're all seen in profile with their noses pointed up and their feet (if any) to the right. These are Ursa Major the Big Bear in the northeast with the Big Dipper as its brightest part, Leo the Lion in the east (with the bright Moon tonight!), dim Hydra the Sea Serpent in the southeast, Canis Minor the Little Dog higher in the south-southeast, and bright Canis Major the Big Dog in the south.

Wednesday, February 28

• Follow the almost-full Moon as it begins the night by leading Regulus upward. Watch as the gap between them decreases hour by hour. The Moon's very thin dark limb will then occult Regulus for much of Maine and northeastern Canada; map and timetables.

Thursday, March 1

• Full Moon (exact at 7:51 p.m. EST). The Moon shines under the Sickle of Leo in early evening, as shown here.

• This is the time of year when Orion stands straight upright due south as the stars come out. Later in the night, and later in the month, he begins his long tilt down toward the west.

Friday, March 2

• If you're in the longitudes of North America, check in on Jupiter's unusually red Great Red Spot with your telescope before dawn tomorrow morning. The GRS should cross Jupiter's central meridian around 6:12 a.m. EST (3:12 a.m. PST) tomorrow morning. Features on Jupiter remain closer to the planet's central meridian than to the limb for nearly an hour before and after they transit.

You'll also find Ganymede's tiny black shadow crossing Jupiter's face from 4:29 to 6:15 a.m. EST (1:19 to 3:15 a.m. PST) tomorrow morning.

All of the Great Red Spot's transit times in February and March (they happen about every 10 hours) are listed on page 50 of the February and March Sky & Telescopes. Facing those pages are timetables of all the phenomena of Jupiter's moons.

Saturday, March 3

• Soon after sunset, use binoculars to start looking for Venus and Mercury together just above the west horizon, as shown here. This is the evening when they appear closest together. They'll still appear almost as close tomorrow evening.

• Now that it's early March, the Big Dipper rises as high in the northeast as Cassiopeia has descended to in the northwest quite soon after dark. Midway between them, as always, is Polaris.


Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6, and hundreds of telescopic galaxies, star clusters, and nebulae among them. Shown above is the Jumbo Edition for easier reading in the night. Larger view. Sample chart.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5; nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup

Jupiter with Great Red Spot on Feb. 26, 2018

On the morning of February 26th, Christopher Go took these images 22 minutes apart. South is up. "The Great Red Spot has a deep red color!" he comments. "It is now interacting with the South Tropical Disturbance [the thin gray mess just above it and to its upper left]. There are some outbreaks and rifts showing up on the North Equatorial Belt."

Mercury (about magnitude –1.4) is emerging from deep in the sunset. Late in the week, use binoculars to find it close to Venus. On March 3rd and 4th the two planets will appear closest, with Mercury 1.1° to Venus's right. Mark your calendar.

Venus is emerging into view low in the afterglow of sunset. Look for it just above the horizon nearly due west about 20 minutes after sunset. Binoculars help. Venus is beginning an "Evening Star" apparition that will continue through next summer.

Mars (magnitude +0.8, in the feet of Ophiuchus) rises around 2 a.m., some 25° to the lower left of Jupiter. Don't confuse Mars with twinklier Antares, which is about 10° to Mars's left or upper left in the early-morning hours. By dawn, Mars and Antares are approaching the meridian in the south and are at very nearly the same height.

Jupiter (magnitude –2.2, in Libra) rises around midnight to shine as the brightest point in the early-morning sky. Jupiter poses for telescopes highest in the south shortly before the beginning of dawn.

Saturn (magnitude +0.6, in Sagittarius above the Teapot) is also a pre-dawn planet but lower in the southeast: about 15° or 20° lower left of Mars.

Uranus (magnitude 5.9, in Pisces) is still up in the west after nightfall.

Neptune is hidden in conjunction with the Sun.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Standard Time (EST) is Universal Time (also called UT, UTC, GMT, or Z time) minus 5 hours.


"The dangers of not thinking clearly are much greater now than ever before. It's not that there's something new in our way of thinking, it's that credulous and confused thinking can be much more lethal in ways it was never before."
— Carl Sagan, 1996


"Objective reality exists. Facts are often determinable. Vaccines save lives. Carbon dioxide warms the globe. Bacteria evolve to thwart antibiotics, because evolution. Science and reason are not a liberal conspiracy. They are how we determine facts. Civilization's survival depends on our ability, and willingness, to use them."
— Alan MacRobert, your Sky at a Glance editor


"Facts are stubborn things."
— John Adams, 1770


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