In September we have a chance to catch all five of the naked-eye planets, even if the only one out during mid-evening is Saturn. We have a supermoon on Sept. 27-28, although we just miss the lunar eclipse that will go along with that moon for all of the Americas.
While we have up to four planets in the mid-summer mid-evening sky, in September we go down to just one, Saturn. At the start of September, Saturn is halfway up in the southwest at dusk, and sets in the west by 11:15 p.m. By the end of the month, it’s only about a third of the way up in the southeast at dusk, and sets around 9:15 p.m.
The planet has a white color, tinged ever so slightly with yellow. Bishop Museum’s September sky map (which is good for 10 p.m. in early September and 8 p.m. in late September) shows Saturn in front of Scorpius the Scorpion, as the planet nears the southwest horizon.
Mercury has been hanging out low in the western sky at dusk throughout August. From here in the tropics, Mercury still manages to hang through the first week of September. You have a mere half-hour to see Mercury: from 7:30 p.m. when it gets dark enough to see it until 8 p.m. when it sets.
Mercury will be about 5 degrees above the western horizon as it gets dark. Mercury is quite bright, so you might have a good chance of spotting this elusive inner planet if you have a clear, flat western horizon.
After the first week, Mercury will be lost in the light of the sun.
Venus, our evening companion for the earlier part of the summer, has pulled a quick switcharoo and is now in the morning sky. In early September, the sky’s brightest dot rises in the east at 4:40 a.m. and is about 20 degrees (the width of two of your palms at arm’s length) at daybreak. By the end of the month, Venus comes up by 3:20 a.m. and is a third of the way up the eastern sky at daybreak. Venus just passed between the Earth and the sun in late August; it is pretty close to Earth, and thus even brighter than usual.
Mars finally returned to our sky in mid-August after a four-month absence. It’s also in the morning sky, rising at 4:40 a.m. in early September. Finding Mars in early September is easy, for it has a brilliant companion: blazing Venus will be to the right of Mars, which will be about 100 times dimmer than its companion.
By the end of September, Mars rises at 4 a.m. and is no longer side-by-side with Venus but rather about 10 degrees below Venus (the width of your palm at arm’s length). At the end of the month, look east to see orange Mars and the whitish Regulus shining at close to the same brightness, in between the much brighter dots of Venus above and Jupiter below. This sight should be quite striking at 5 a.m. during the last days of the month.
By mid-September Jupiter will appear in the morning sky with Venus. Around Sept. 15, look for Jupiter rising in the east at 5:30 a.m., well below Venus. By Sept. 30, Jupiter comes up at 4:40 a.m. and is 20 degrees above the eastern horizon at daybreak. Jupiter is in the opposite situation as Venus. Venus has just passed between Earth and the sun, is close to us and thus is bright. Jupiter, on the other hand, is just coming around from the far side of the sun. The king of the planets is almost 600 million miles from us this September, which means that Jupiter does not shine quite as brightly as normal but still brighter still than any star.
Supermoon
The full moon on the night of Sept. 27-28 has been referred to as a "supermoon," a recent term that refers to a full moon that occurs when the moon is closer to the Earth than usual during the moon’s slightly oval path around our planet.
Since the moon’s path is oval, or elliptical, the moon can be as close as 225,600 miles from us or as far as 252,000 miles. When the moon is at the closest point to earth in its monthly path around the earth it is said to be at "perigee." A supermoon is a simply a full moon that occurs on the same day that the moon is at perigee. Since this Sept. 27-28 full moon occurs when the moon is a little closer to Earth than usual, the moon appears a little larger than a "normal" full moon.
Lunar eclipses can only occur during full moons, when Earth is in just the right place to block the sun’s light from falling upon the moon. Half of Earth will in fact see a total lunar eclipse on the "supermoon" evening of Sept. 27-28, including all of North, Central and South America.
However, while the Hawaiian Islands had a great view of the last three total lunar eclipses, our luck runs out on this one. We will just miss the lunar eclipse that ends around 6:30 p.m. Sept. 27 in Hawaii, just as the moon rises here that night.
September star map
Bishop Museum’s September star map, which is set for Oahu’s latitude, shows the sky at 10 p.m. in early September and at 8 p.m. in late September. Note that there is no Big Dipper. The Dipper never sets for any place north of Los Angeles or Tokyo. At our lower latitude in Hawaii, we lose the dipper from the evening sky every fall.
The trade-off is that the southern stars are higher here in Hawaii, and we see stars that never even rise above the horizon farther north.
A good example on the September map is Grus the Crane, in the south. Grus is clear in Hawaii’s skies, especially as it is in a part of the sky whose stars are otherwise dim.
Mike Shanahan is director of Education, Exhibits and Planetarium. Visit bishopmuseum.org/planetarium.html.
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