This Week's Sky at a Glance, May 7–15 [Mercury, Venus, Mars, thin crescent Moon, LOW in West at sunset]

Greet Mercury and Venus low in the west-northwest in the fading afterglow of sunset. You may first spot Venus, bright at magnitude –3.9, very low exactly west-northwest.

As the sky darkens further, Mercury will come into view some 9° above Venus as shown below. Mercury fades from magnitude 0.0 to +0.5 this week.

Much higher to their upper left, in the west as night falls, is little [currently very distant] Mars. [Mars is currently on the other side of the Sun, many millions of miles more distant than where it is on the same side as Earth]

Venus and a super-thin crescent Moon pair up very low in the west-northwest in early twilight. Bring binoculars; the Moon is only 1% illuminated, just a few hours more than one day old (the Moon was new at 3:00 p.m. yesterday Eastern Daylight Time). The circumstances of this pairing will depend on where you are, but for much of North America they will be less than 1° apart. Mercury looks on from above.

Now comes the crescent Moon back to the evening sky, higher and bolder in the western twilight each evening. Watch it pair with Venus, then Mercury, then skip a beat, then Mars.

The Moon is these scenes is, as always, drawn about three times its actual apparent size. Positions are exact for an observer at latitude 40° N, longitude 90° W, near the population center of North America. And remember, the visibility of faint little objects in bright twilight is exaggerated.

This evening the crescent Moon, less thin and less low in twilight, bestows its company on Mercury after partnering with Venus yesterday. See above. And with those binoculars, can you pull out Betelgeuse some 20° to their left?

After full dark, the fine galaxies M81 and M82 are among the most-sought telescopic targets when the bowl of the Big Dipper is high. But have you ever tried for the two lesser galaxies in their vicinity, and the four double stars here for amateur scopes? Two of those are easy to resolve; two are challenging. See Ken Hewitt-White’s Suburban Stargazer column in the May Sky & Telescope, page 54.

In early twilight, spot the crescent Moon in the west-northwest as shown above. Upper left of it by about 13° (for North America) is little Mars. About the same distance lower right of the Moon is Mercury, and farther to the Moon’s lower left is Betelgeuse, the last bright star of Orion to depart as spring advances.

And now the crescent Moon shines with faint, far-distant Mars, which is nearly on the opposite side of its orbit from us. Mars is currently 18 light-minutes away, compared to the Moon’s 1.3 light-seconds.

Three zero-magnitude stars shine after dark in May: Arcturus high in the southeast, Vega much lower in the northeast, and Capella in the northwest. They appear so bright because each is at least 60 times as luminous as the Sun, and because they’re all relatively nearby: 37, 25, and 42 light-years from us, respectively.

The following sky map is to be viewed as if it is pasted onto the inside of a large dome hanging above you, such that North (at the top of the map) is BEHIND you and South (bottom of the map) in FRONT. East is therefore on the left side of map, west on the right. Like the Sun and Moon, planets rise in the east and set in the west.

That said, all 5 of the currently visible planets are depicted as they appear in the sky this morning (May 8). Of course they cannot be seen in the daytime sky. I present the map only to show their current positions relative to the Sun. If they are east of the Sun they will set after the Sun. If they are west of the Sun they will rise before it.

Note that, in its ~monthly orbit around the Earth, the Moon moves about 15 degrees to the east (left on map) every day. And so, by May 12, it will have moved alongside Venus (VERY LOW on the western horizon), near Mercury on May 13, then Mars on May 15.

The map is from a website called Heavens-Above.com. Look under Sky Map (old version) to find a link to the customizable/updateable map. The site also includes various other useful info for amateur astronomers and sky watchers, including a schedule of naked-eye-visible passes of the International Space Station, abbreviated at the site as "ISS". You will need to provide your general location in order to get a useful schedule for your area. Note that the LOWER the "Magnitude" of a given pass the BRIGHTER it will be. Negative numbers are brighter than positive ones. The system is based on an old one that, as far as I know, was never revised.

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