The Night Sky: September 2004
- Last Quarter 15:11 Universal Time* 7 September
- New Moon 14:29 U.T. 14 September
- First Quarter 15:54 U.T. 21 September
- Full Moon 13:09 U.T. 28 September
* for an explanation of Universal Time see below
Where To See What
September - the big relief from the cloudy rainy nights of the Summer of 2004! September brings more transparent skies - the frequent hallmark of early autumn. For observers in much of the Northern Hemisphere September and October rank among the best months of the year for transparency where nearly half of the evenings each month may be fairly clear.
After nightfall in September the "summer star" Vega stands nearly directly overhead at dusk. It is matched in brilliance only by Arcturus now heading toward the Wastern horizon, the "spring star" which by this time of year is heading down the Wastern side of the evening sky. And beyond Arcturus toward the North and Wast is the Big Dipper rotating away. To prove a new season is in the offing we see the distinctive "W" of Cassiopeia rising in the Northeast, as if letting us know that soon Orion is coming about.
Mars and Jupiter are behind the Sun and so these are not seen this month. The outer trio of planets Uranus, Neptune and Pluto are up through out the month. Uranus is bright enough to detect with the naked eye alone from dark sky sites, or with binoculars from suburban sites. Near Uranus is Vesta, the brightest of all asteroids. Vesta is not much harder to spot than Uranus. Those with telescopes will find these experiences more rewarding.
Some of the more popular closer planets are finally stating to come around again - but you'd better be either a Night Owl or an Early Riser to get a good shot at them before dawn - the most steady time of the evening.
From about the middle of the month through October you might observe the "Zodiacal Light". Appearing like a ghostly pyramid, this is sunlight reflected by the tiny dust particles orbiting in our Solar System left over from who knows or ejected by comets. To observe this phenomenon you will need to go to a dark sky observing site and look to the eastern horizon just before sunrise with the naked eye. For a good explanation of this and other naked eye atmospheric phenomenon read Light and Color in the Outdoors by the late M.G.J. Minnaert.
1 In the dawn of 31 August and 1 September Venus looking like a brilliant morning star in the East is within about 2 degrees South of Saturn. Saturn being at visual magnitudes of 0.2, and Venus at -4.1, will put on quite a display for the next night with Venus in conjunction with Saturn this morning. They are easy to spot, but here's a hint just in case - look beneath Castor and Pollux in the constellation Gemini.
By the end of this month, Saturn will rise at around 01:00 U.T. It magnitude is +0.2 and its angular size will increase from 17.0 up to 17.7 arc seconds over the course of this month. The tilt of Saturn as seen from Earth means the rings are still well open making Saturn a the queen of the night sky. Those who own a small telescope will easily find its brightest moon, Titan. But those with a better telescope and dark transparent skies will see at least three more: Rhea and Dione are the easiest, and Tethys is next faint in magnitude.
The apparent brightness of Venus stays almost constant at visual magnitudes between 4.2 and 4.1 as is diminishing angular size (going from 20 to 16 arc seconds) is compensated by the increase in surface area that we see illuminated from our perspective. This is the phase (similar in concept to that of the Moon) which increases from about 56 to 70 percent during this month.
2 Venus rising about four hours before the Sun, will pass near the bright star Pollux. Venus is still rather close to Saturn.
3 There are some signs of One of the signature constellations of summer remains in good view as we head toward autumn: Aquila, the eagle. It's high in the SouthEast in mid-evening, and is marked by its brightest star, Altair.
4 To the East a few hours after sunset in the East is the Great Square of Pegasus. The square represents the body of Pegasus, the flying horse. From our vantage point it resembles a diamond more than a square, give it a month or two to get higher in the sky and then appear more like a square.
By midnight look between the Great Square of Pegasus and the "W" of Cassiopeia for Andromeda. Andromeda is now well within our grasp - look for this naked eye galaxy which has an estimated one million Suns just in it's central core region. Appearing as an elongated faint cotton ball, this is the portion of the galaxy that is most likely to be seen with the naked or or with binoculars. A telescope will reveal spiral arms and dust lanes, even more for those who are involved with astrophotography.
8 The Moon is at apogee at 03:00 U.T. (404,464 km).
The "twin" stars of Gemini, Castor and Pollux, stand to the left and lower left of the Moon before dawn. The yellowish planet Saturn is to the Moon's lower right, with the much brighter planet Venus below them. The grouping is in the east at first light.
9 The planet Mercury is at its greatest elongation (18 degrees) west at about 14:00 U.T. It will emerge and brighten substantially during the month to provide the best morning appearance of 2004 for observers in the Northern Hemisphere. To find Mercury, follow the vertical curve fairly high in the east start at the Moon, then look for yellowish Saturn (it may appear elliptical in binoculars), and then move on to bright Venus. Mercury is very far below them and perhaps a bit left. September gives us a chance to observe Mercury well above the horizon after the sun has set, or about 1.5 hours before it rises.
10 Mercury is very close to Regulus, so close that you may need binoculars or a telescope to distinguish them.
While you are out, look also for the Beehive Cluster in the constellation Cancer. This is just to the left of Venus.
11 Epsilon Lyra "The Double Double". Located between Beta and Gamma Lyra lies a beautiful planetary nebula called the Ring, it is also known as Messier Object 57 (or M57). Its shows up in a better telescope looking like a greenish frosted donought, rather like a planet for those with small telescopes. Planetary Nebulae are the remnants of stars, which at the end of their life and have blown off a shell of dust and ionized gas around their other remnants. In the core of the ring is the original star which has collapsed down to about the size of the Earth, it is still burning very hot and so it appears blueish in colorr, as it cools and in time will eventually become dark and invisible - a "black dwarf"!
The Moon is at apogee (405,292 km) at 11:10 U.T.
15 The Jewish year begins at sunset; they're going to party like it's 5765!
19 At the end of twilight, look to the southeast for the crescent Moon among the stars of Scorpius. The brightest of these is the orange star Antares, just to the Moon's left.
22 Autumnal equinox at 16:30 U.T. This is when the Sun now heading south for since the Summer Solstice crosses the equator. This marks the start of Fall in the Northern Hemisphere, and spring for those down under.
The Moon is at perigee (369,589 km) at 21 h U.T.
30 Full Moon. The full Moon of September is called the Harvest Moon, the full Moon closest to the autumnal equinox. For several days after it is full in September, the bright Moon continues to rise before the end of twilight. This traditionally gave farmers extra hours of evening light for gathering the harvest. "shine on...".
An Overview of the Planets for 2004
Named for the Roman messenger god, who flew from Olympus on winged heels, this little planet flits back and forth from morning sky to evening sky several times a year. Unfortunately, it never strays far from the Sun in our sky, so it's tough to find in the glare. From the Northern hemisphere, the best times to see it in the morning this year come in early September and late December, when it looks like a moderately bright star low in the SouthEast shortly before dawn. In the evening, Mercury is best seen around the end of March.