Moon and Venus adorn the morning September 13 to 15

On the mornings of September 13, 14 and 15, 2020, look for the waning crescent moon and dazzling planet Venus in the east before sunrise. If you have very good vision, you might even glimpse these bright beauties after sunrise, in a blue daytime sky. After all, the moon and Venus rank as the second- and third-brightest bodies to light up the sky (after the sun).

As you can see from the chart above, the moon will appear closer to the sunrise horizon each morning. And, each morning, the moon will appear as a thinner crescent. By the morning of September 15 – although Venus will still be easy to spot in the east before sunrise – the moon will be a very thin crescent indeed, rising only shortly before the sun.

On September 15, if you’re up for a challenge, try your luck spotting the star Regulus near the moon. Regulus is the brightest star in the constellation Leo the Lion. It’s one of the brightest stars in the sky. But the sun and Regulus were in conjunction on August 23; on that day, this star rose and set when the sun did. Now, this star is returning to the east at dawn, and so – if you see it at all – Regulus will appear faint against a bright twilight background.

Very thin waning crescent moon and star Regulus below Venus near almost vertical line of ecliptic.

Venus will be easy on September 15, 2020. For a challenge, try your luck at spotting Regulus – the Lion’s Heart – near the moon. Binoculars will be helpful. Can’t see it? Keep watching in the coming mornings. One morning soon, it’ll pop into view.

Like Earth’s moon, Venus displays the full range of phases in Earth’s sky. Unlike the moon, you need a telescope to observe Venus’ changing phases. Given that the moon and Venus are nearly at the same place on the sky’s dome on September 14, you might expect the moon and Venus to display a similar phase. But they don’t.

From North America, the waning crescent moon will be only about 12% illuminated by sunlight on the morning of September 14. To know more specifically how much of the lunar disk is illuminated right now or at a given time, check out Heavens-Above or The Moon Tonight.

On the other hand – on September 14, 2020 – Venus will be exhibiting a waxing gibbous phase, with its disk 65% illuminated. To know how much of the Venusian disk is illuminated by sunshine, go to Astropixels.com and look under the column Phase illumination.

Why are the phases of the moon and Venus so wildly different now?

Half-lit Earth and moon, showing 8 labeled positions of moon around Earth.

Moon’s orbit around Earth, seen from above. The moon’s dark side faces Earth at new moon, and its illuminated side faces Earth at full moon. At the quarter moons, we see 1/2 of the moon’s daytime side and 1/2 of its nighttime side. Read more: Understanding moon phases

The reason, of course, is that Venus orbits the sun, while the moon orbits Earth. The moon is now about to pass between us and the sun. Most of its daylight side is turned away from our direction in space. Venus, meanwhile, passed between us and the sun in June. It’s now speeding ahead of us in its smaller, faster orbit. The chart below, from Fourmilab, shows Venus with respect to Earth on September 14, 2020.

And by the way … it takes our moon about 29.5 Earth-days to complete its cycle of phases (new moon to new moon, or full moon to full moon), whereas it takes Venus about 1.6 Earth-years to complete its cycle of phases (new Venus to new Venus, or full Venus to full Venus).

Chart showing the inner planets in positions on their orbits in respect to one another.

Here’s the inner solar system on September 14, 2020. The moon isn’t shown. Earth is blue, and Venus is white. You can see that, from our earthly perspective, we’re gazing at Venus now to one side of the sun, and thus we see a 65%-illuminated phase. Image via Fourmilab.

Diagram showing labeled phases of Venus in oblique view of Earth and Venus orbits.

Venus is at full phase at superior conjunction, on the far side of the sun from us. We see it at the new phase at inferior conjunction, when it’s passing between us and the sun. That happened last on June 3, 2020. The cycle of Venus’ phases happens over a period of 584 Earth-days (1.6 Earth-years). Image via UCLA.

Venus rises sooner before before the sun at northerly latitudes than at southerly latitudes. We give you Venus’ approximate rising time for the next several days for 60 degrees north, 40 degrees north, equator (0 degrees), and 35 degrees south:

60 degrees north latitude
Venus rises 4 2/3 hours before the sun

40 degrees north latitude
Venus rises 3 1/2 hours before the sun

Equator (0 degrees latitude)
Venus rises 2 3/4 hours before the sun

35 degrees south latitude
Venus rises 2 hours before the sun

Live in the U.S. or Canada? Click on Old Farmer’s Almanac for Venus’ rising time.

For virtually anywhere worldwide, visit TimeandDate.com for Venus’ rising time.

Horizon, with two examples of ecliptic, one shallow, the other nearly vertical.

At sunrise on the autumn equinox, the ecliptic – pathway of the sun, moon and planets – hits the sunrise horizon at its steepest angle of the year. But at sunrise on the spring equinox, the ecliptic hits the sunrise horizon at its shallowest angle. Therefore, in September 2020, Venus rises sooner before sunrise at more northerly latitudes, and closer to the sunrise at more southerly latitudes. Image via Dominick Ford.

Venus comes up sooner before sunrise in the Northern Hemisphere because September is a late summer/early autumn month for the northern half of the world. In the Southern Hemisphere, Venus rises closer to sunrise because September is a later winter/early spring month to the south of the equator. From either the Northern or Southern Hemisphere, the ecliptic – pathway of the planets – hits the sunrise horizon at its steepest angle of the year on autumn equinox, yet at its shallowest angle on the spring equinox. (The green line on our charts, by the way, depicts the ecliptic.)

The upcoming September equinox is the Northern Hemisphere’s autumn equinox, and the Southern Hemisphere’s spring equinox. Therefore, the ecliptic now hits the sunrise horizon at a steep angle in the Northern Hemisphere, and a at shallow angle in the Southern Hemisphere.

The steep tilt of the ecliptic in the morning sky also makes September an especially a good month for catching the normally elusive zodiacal light (false dawn) from mid-northern latitudes. Don’t know which way to look for the mysterious zodiacal light? Simply look for Venus. This cone of light, if it’s visible, will be pointing right at Venus.

Read More: Hazy light pyramid in east? False dawn

Bottom line: On the mornings of September 13, 14 and 15, 2020, look for the waning crescent moon and dazzling planet Venus in the eastern sky before sunrise. From all of Earth, they will beautify the early morning tableau.

Bruce McClure