This Week’s Sky at a Glance

With your telescope, do you ever observe the lunar landscape when the Moon is waning before dawn and the terminator is lunar sunset rather than sunrise? Get up early this week and have a look at familiar features in this new light.
Alan MacRobert

Friday, April 26

  • Around the end of twilight, the Moon rises below Saturn. With binoculars, look closer below Saturn for the wide double star Alpha2 and Alpha1 Librae, magnitudes 2.8 and 5.2 respectively. (They're numbered in order of their westward progression across the sky, not in order of brightness).

    Saturday, April 27

  • Saturn is at opposition tonight: opposite the Sun as seen from Earth. See more under "This Week's Planet Roundup" below.

  • The waning gibbous Moon rises in the southeast very late this evening, with the red supergiant Antares sparkling to its right. By early dawn Sunday morning Antares is below the Moon in the southwest, as shown above.

    Sunday, April 28

  • The classic small-scope binary star Gamma Virginis, or Porrima, shines upper right of Spica, 14° from it (about a fist and a half at arm's length) these evenings. Porrima's two equal components were almost unresolvably close together for much of the last decade, but this spring they've widened to 2 arcseconds apart. Use high power. (An orbit diagram is in the May Sky & Telescope, page 51.)

    Monday, April 29

  • It's almost May, yet the winter star Sirius still twinkles low above the west-southwest horizon in late twilight. How much later into the spring can you keep it in view?

    Tuesday, April 30

  • The small but distinctive constellation Corvus, the Crow, is an icon of spring evenings (in the Northern Hemisphere). Look for its four-star quadrilateral in the south-southeast after dark, to the right of Saturn and Spica.

    Watch for Venus beginning to creep up into view shortly after sunset.

    Wednesday, May 1

  • Have you ever really explored the richest 1° field of the Virgo Galaxy Cluster? How deeply into it can your scope go? Use the charts and guide in Alan Whitman's "Going Deep" column in the May Sky & Telescope, page 61.

    Thursday, May 2

  • Last-quarter Moon. The Moon, between dim Capricornus and Aquarius, rises around the middle of the night (far below Altair). By daybreak Friday morning it's high in the south.

    Friday, May 3

  • As soon as it's fully dark, look for the Big Dipper very high in the north-northeast. It's upside down, with its handle to the right and its bowl to the left. It's "dumping water" onto the much dimmer Little Dipper down below.

    Saturday, May 4

  • The three brightest stars of the May dusk are all zero magnitude: Capella in the northwest, Vega lower in the northeast, and Arcturus high in the east. (Jupiter, far lower left of Capella, is brighter but doesn't count.)


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

    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. Or download our free Getting Started in Astronomy booklet (which only has bimonthly maps).

    The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but that's less than one star in an entire telescopic field of view, on average. By comparison, Sky Atlas 2000.0 plots 81,312 stars to magnitude 8.5, typically one or two stars per telescopic field. Both atlases include many hundreds of deep-sky targets — galaxies, star clusters, and nebulae — to hunt among the stars.
    Sky & Telescope

    Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The standards are the little Pocket Sky Atlas, which shows stars to magnitude 7.6; the larger and deeper Sky Atlas 2000.0 (stars to magnitude 8.5); and 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, the bigger Night Sky Observer's Guide by Kepple and Sanner, or the beloved if dated Burnham's Celestial Handbook.

    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 (able to point with better than 0.2° repeatability). As Terence Dickinson and Alan Dyer say in their invaluable 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's non-Red-Spot side on April 22nd. The dwindling giant planet appears only 70% as large now as it did at opposition last December. But that's still enough for many amateur scopes to show the color difference between the broad South and North Equatorial Belts, and the presence of the thinner North Temperate Belt compared to the absence of its southern equivalent. South is up.

    Mercury is lost in the glow of dawn.

    Venus (magnitude –3.9) is just beginning an evening apparition that will continue for the rest of the year. How soon can you first pick it up? Use binoculars to look for Venus a mere 15 or 20 minutes after sunset, barely above the west-northwest horizon. It's far to the lower right of Jupiter for viewers at mid-northern latitudes.

    Mars remains hidden in the glare of the Sun. Not until summer will it emerge in the dawn.

    Jupiter (magnitude –2.0, in Taurus) is the first "star" to come out in the west after sunset, a little lower every day. It descends in the evening and sets around 10 or 11 p.m. Below Jupiter twinkles orange Aldebaran, and a similar distance above Jupiter is El Nath (Beta Tauri). Bright Capella shines to the upper right from there. In a telescope, Jupiter has shrunk to a disappointing 34 arcseconds wide.

    The Seeliger effect: Christopher Go took these images of Saturn on March 2nd (top) and April 24th. Notice how the rings brightened with respect to the globe. And on the 24th, Saturn was still three days from opposition.

    Saturn (magnitude +0.1, in Libra) is at opposition Saturday night April 27th. All week it glows low in the east-southeast as twilight fades (to the lower left of Spica and farther lower right of Arcturus). It rises it higher all evening and shines highest in the south in the middle of the night.

    Carefully note the brightness of the rings with respect to the globe. The rings always brighten for several days around opposition due to the Seeliger effect. The solid, very irregular particles of the rings preferentially reflect sunlight back in the direction it came from more than Saturn's cloudtops do. Watch as the rings dim back down later in the week, as Saturn moves away from the opposition point in Earth's sky.

    Got a telescope? See our guide "Scrutinizing Saturn" in the May Sky & Telescope, page 50, or the shorter version online. And identify Saturn's many moons with our SaturnMoons utility or handier app.

    Uranus is hidden in the dawn.

    Neptune (magnitude 7.9, in Aquarius) is low in the east-southeast just before dawn.


    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 Daylight Time (EDT) equals Universal Time (also known as UT, UTC, or GMT) minus 4 hours.


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