Bright Venus hangs low in the west at dusk all month, as we lose its companion Jupiter. Saturn and Mars also start the month together, but separate by September’s end. As autumn stats we lose the Big Dipper, as we do every September in the islands. Elsewhere, all of Africa, and Africa alone, experiences a solar eclipse.
Planets in September
Venus and Jupiter gather in the dusk
On Sunday August 28 (the day this article runs in the Star Advertiser), look for Venus and Jupiter, the sky’s brightest dots, appearing close together, very low in the western sky at dusk. As it gets dark enough the see the planets, about 7:15 p.m., the two planets are about ten degrees above the west horizon, or the width of a fist. Venus will be slightly to the upper left of Jupiter. Venus is the brighter of the pair; at minus 3.88 magnitude, it shines over six times brighter than minus 1.67 magnitude Jupiter.
For the next ten days or so, it remains possible to see both planets. Venus will continue to be about ten degrees above the west horizon as it gets dark, and will continue to set just before 8 p.m.; Venus’s behavior is remarkably unchanged through the month, emerging at twilight and setting just before 8 p.m. All the change occurs with Jupiter. Night after night in early September, Jupiter appears a little lower, and sets earlier and earlier. By the first of September, Jupiter is only five degrees above the western horizon as it comes out at dusk, and is now five degrees below Venus. By the 10th, Jupiter barely emerges from the twilight at 7:00 p.m. before it sets at 7:10. After that, Jupiter is lost in the light of the sun, and Venus hovers all alone in the western skies of early evening.
Jupiter passes on the far side of the sun on September 26 and then appears in the eastern predawn sky by late October.
On the night of September 2, if you have very clear skies and a flat west horizon, you might be able to catch a very slender crescent moon between the planets Jupiter and Venus. On September 3, it should be easy to spot the crescent moon, now above Venus.
Mars, Saturn and Antares: the triangle continues
As Venus sets in the west, you have good views still of Saturn and Mars in the southwest, as shown on the September 2016 star map. Saturn, Mars and the bright star Antares in the Scorpion have formed an ever-evolving triangle all summer.
In early September, look for the triangle of Saturn, Mars and Antares about halfway up in the west at dusk. In early September the three dots make triangle that’s roughly equal on all sides, each dot of light about six degrees (three fingers at arm’s length) distant from the other dots. Mars and Saturn stand side by side, and Antares lies below the two planets. At magnitude minus 0.3, orange Mars is still be brightest of the three dots, several times brighter that the orange star Antares, five degrees to its lower left. At 0.48 Saturn outshines Antares but is dimmer than Mars. In early September the triangle sets just after 11 p.m.
Throughout the month, Saturn and Antares pretty much maintain their relation with each other, at six degrees of separation. However, Mars is moving quickly. By mid-September the red planet will be more than 12 degrees (thicker than a fist at arm’s length) to the left of Saturn and Antares, twice as far as it was on the first of September. By Sept 30, the red planet is over 20 degrees (two fists) to the left of Saturn and Antares, and the triangle is now too stretched out to look much like a triangle anymore. By month’s end, Saturn and Antares are about 1/4th of the way up in the west at dusk and set by 9:30 p.m.; Mars, by 11 p.m.
Look for the moon, around its first-quarter phase, next to Saturn, Mars and Antares on September 7 and 8.
Mercury has its best morning appearance of the year in late September. For the last week of the month, look for Mercury rising in the east at 5:15 a.m., shining brilliantly at 0.6 magnitude. The planet gets lost in the dawn glow by 6:00 a.m.
Other sky events in September
Annular solar eclipse occurs over Africa; not visible in the Hawaiian Islands
An annular solar eclipse occurs when the moon moves in front of the sun when the moon is at a point in the moon’s orbit where the moon is further than average from the earth. Being a little further away than normal, the moon is a little smaller than normal, and not large enough to block out the sun’s disc even when the moon is dead-center in the middle of the sun’s disc. So, a ring of sunlight shines around the moon (‘annulus’ comes from the Latin word for ‘ring’).
As long as any sunlight shows around the moon, there is not the awesome sense of the earth going dark in the middle of the day; in fact, an annular eclipse can occur overhead without people noticing it.
The path of this annular eclipse moves over south-central Africa. Nations in the path of annularity include Gabon, the Congo, the Democratic Republic of Congo, Tanzania, and Mozambique. It will also pass over the islands of Madagascar and Reunion.
As with a total solar eclipse, the areas for thousands of miles on each side of the annular eclipse will see a partial eclipse. Unique to this eclipse: only Africa will see any portion of this eclipse, and all of Africa will see some degree of a partial eclipse.
The peak of the annular eclipse occurs at 9:06 Universal Time on September 1, which is 11:06 p.m. on August 31 Hawai‘i Standard Time; but again this event will not be visible at all in the Hawaiian Islands, since it occurs when it’s the middle of the night in the islands.
Penumbral Lunar Eclipse on Sept 16; not visible in Hawai‘i (or anywhere for that matter)
In what continues to be a poor year for lunar eclipses, the second lunar eclipse of 2016 is, like the one back in March, a “penumbral” eclipse. This one occurs over the Indian Ocean; the peak time is 18:54 Universal Time on September 16. This is 8:54 a.m. on the 16th Hawaii Standard Time, which means we won’t see this penumbral eclipse for two reasons: 1): it occurs during the day in Hawai‘i when the moon is below the horizon. 2): you can’t see penumbral eclipses anyway.
Total and partial lunar eclipses are beautiful sights. In a total eclipse of the moon, the entire moon goes into the earth’s dark inner shadow (the “umbra”), and the moon turns black or dark red. In a partial eclipse of the moon, part of the moon is in the umbra, and it looks like a bite has been taken out of the full moon.
In a penumbral eclipse, on the other hand, no part of the moon goes into the dark inner shadow of the earth. The moon moves only into the outer shadow of the earth, missing the dark inner shadow of the earth entirely. This outer shadow, called the “penumbra,” gives it name to this flavor of lunar eclipse. During a penumbral eclipse, a viewer sees no change in the moon’s brightness; the outer shadow of the earth is too faint to darken the lunar disc.
Autumn begins on September 22
Autumn begins at 4:22 a.m. on September 22 Hawai‘i Standard Time (14:22 Universal Time on September 22.)
September Star Map
Like all of our monthly maps, this one is good for 10 p.m. on the first day of the month, 9 p.m. for the middle of the month, and for 8 p.m. at the end.
The Scorpion (“Maui’s Fishhook” in the Hawaiian Islands) is prominent in the southwest on the map, and is visited by both Mars and Saturn.
The summer triangle – three stars pulled from three different constellations – is in the very top of the sky, with the second-brightest of the three, Deneb, nearly overhead.
The Big Dipper is gone by the time of our September star map; from our more southerly locale, the Big Dipper rises and sets in the Hawaiian Islands. You can catch the Big Dipper low in the northwest in the early evening during the first weeks of September; it starts to set at 9 p.m. on September 1, for example. By the 30th, though, the Dipper sets before it gets dark, and day breaks before it returns to the morning sky; in fact late September and early October are the only times it’s impossible to catch the Big Dipper at all from our island skies.
Among the other constellations missing from the evening sky are the Southern Cross, which is visible in the islands only from December through June; and Orion, which comes up in September in the early morning.
Moon phases (Hawaiian Time zone):
New: August 31, September 30
First Quarter: Sept 9
Full: Sept 16
Third Quarter: Sept 22