The autumn equinox, which marks the start of fall, occurs at 5:45 a.m. in Hawai'i on Sept. 22 (the vernal equinox, marking the start of spring, occurred this year on March 19).

"Equinox" comes from the Latin phrase for "equal night." On these two days, no matter where you are on Earth, the sun rises roughly at 6 a.m. and sets roughly at 6 p.m. In Honolulu sunrise occurs at 6:20 a.m. on Sept. 22 and sunset occurs at 6:28 p.m.

CONSTELLATIONS IN SEPTEMBER

Due to requests, we are now showing the Milky Way on our star maps again. Please be aware, however, that you need very dark skies to see the Milky Way. It is getting increasingly hard to see the Milky Way on O'ahu, though it is still visible in dark areas on the island. Residents of the Neighbor Islands should have an easier time spotting it. Honolulu residents should abandon all hope of seeing the Milky Way "live" and instead come to the Watumull Planetarium at Bishop Museum, where it is visible at three shows daily.

On the monthly map, the constellation of Scorpius the Scorpion is visible in the southwestern sky. To find Scorpius, look for Antares, the star that marks the heart of the Scorpion. It is a first-magnitude star and has a mildly reddish-orange hue. Scorpius has a very distinctive shape, made up of about a dozen stars in the second-magnitude range.

Scorpius also really looks like Maui's Fishhook, the hook that Maui used the pull the Hawaiian Islands from the bottom of the ocean. You hear this constellation referred to as "Maui's Fishhook" in other parts of Polynesia as well.

Almost due south on our map, and directly below Jupiter, is Sagittarius the Centaur. Sagittarius is not as bright and distinctive as Scorpius, so it's very helpful that we have Jupiter to mark Sagittarius this year. Look just below the blazing light of Jupiter. Eight stars, mainly second magnitude, form the core of the constellation.

PLANETS IN SEPTEMBER

MERCURY

Mercury is in the sunset sky in early September. It starts off the month at zero magnitude. It's quite bright, even though you have to contend with twilight to see the planet. For the first several weeks of September, Venus can be your guide to find the more elusive Mercury. Look for blazing Venus low in the west around 7:15 p.m., and then look just to the left of Venus to see Mercury.

VENUS

The second rock from the sun is back as an evening star, although it is still low in the western sky at dusk. It is the brightest thing in the sky except for the sun and the moon, shining at minus 3.8 magnitude. Throughout the month of September it sets right around 8 p.m. Try to catch this brilliant spot of light from about 7:15 p.m. onward. Find a clear sky and look low in the west, near the place where the sun went down.

MARS

Our neighboring planet in the western sky at dusk. Mars is only at 1.7 magnitude; it's a little hard to tell when it's faint like this, but Mars does have a slight orange color. On Sept. 10 and 11, Mars appears very close to Venus; the two planets will set together by 8 p.m. By the end of September, Mars is lost in the twilight and will not be visible again until it emerges in the morning sky at the very end of 2008.

JUPITER

Jupiter remains the king of the night sky, shining brightly in the south at dusk. As it gets fully dark, look for it about halfway up in the southern sky. At minus 2.5 magnitude, it is brighter than any other night object except for the moon and Venus. It sets around 2 a.m. at the start of the month and around midnight at the end of September.

SATURN

Saturn starts off September at solar conjunction, on the opposite side of the Earth from the sun and thus not visible. However, it will emerge in the morning sky by the end of September. Saturn rises just before 5 a.m. at the end of the month, shining at first magnitude. Look for it just a little north of due east.

PLANET GATHERINGS IN SEPTEMBER

While you have to contend with the light of the sunset, and the fact that we sometimes get cloudy horizons here in the islands, there are some lovely gatherings of Venus, Mercury and Mars in the west for the first few weeks of September. Make sure you have a clear, flat horizon (looking over water, for instance), and the view on a clear night should be really nice. Look for the three planets from around 7 p.m., as it starts to get dark enough to see the planets, and 7:30-7:45 p.m. (when the planets head for the horizon).

Sept. 1-4:

Look west at about 7:15 p.m. Venus will be extremely bright, and about 8 degrees above the horizon. (Hold your hand out at arm's length, with your fingers parallel to the horizon. Venus will be about two finger widths above the horizon.)

Then look for Mercury about three degrees (one finger's width) to the left of Venus. Look the same distance again, 3 degrees, and try to find the slender crescent of the moon, just past its new moon phase.

Then look for Mars, about 6 degrees (two fingers) above Mercury, and much fainter.

The crescent moon will be next to Mercury tomorrow, and about 11 degrees (three fingers) left of Mars on Tuesday.

Sept. 5-10:

The view remains much the same for Venus and Mercury, with Venus about 8 degrees above the horizon (two fingers) at 7:15 p.m. and Mercury about three degrees to Venus's left. What changes is their relationship with Mars. Night by night Mars seems to get closer to the two brighter planets. Look for Mars about 3 degrees above Venus on Friday. Mars will seem to get closer to Venus each evening. By Sept. 10, the pale red planet will be less than a half-degree to the left of Venus.

Sept. 11-20:

For this period Mars and Mercury are now below Venus. Looks for the planets around 7 p.m. (Mercury and Mars set less than a half-hour later). At 7 p.m. on Sept. 11, Mercury is 3 degrees (one finger width) to the lower left of Venus, and Mars is tucked just below Venus. Over the next 10 days, Mercury and Mars hang below Venus, with brighter Mercury on the left and dimmer Mars on the right. By Sept. 20, Mercury is almost 6 degrees (two finger widths) below Venus. By the 20th, Mercury and Mars form a nice triangle with Spica, the bluish star just above Mercury; the triangle seems to hang from Venus. These lower planets in the grouping will set by 7:20 p.m., so you don't have a long time to catch the sight — roughly from 7 to 7:20 p.m.

After Sept. 20 or so, it will be harder and harder to catch Mercury and Mars in the sunset; by the end of the month, Venus will be blazing away alone in the western sunset sky.