September 2004 night skies
Most professional astronomers, when asked to name the twelve moons of Earth, might be inclined to gently correct the questioner. Our planet has just one Moon, not a dozen! But ask any farmer and they'll explain that there are indeed twelve, including the Strawberry Moon, the Buck Moon, the Pink Moon, and every now and then a Blue Moon! They're really all the same Moon, but long before the advent of modern calendars people named the full Moons of a year to keep track of time. This month, during last week of September, we can enjoy one of the most famous moons, the Harvest Moon.
By loose definition, the Harvest Moon is the full Moon nearest the autumn equinox. Most years, the title goes to the full Moon in September, since the equinox occurs around September 22. However, the Harvest Moon can occur as early as September 8 (as in 1976) or as late as October 7 (as in 1987).
The Moon officially turns full when it reaches a spot exactly opposite to the Sun in the sky, with Earth in the middle. This year, the official Harvest Moon turns full on September 28 at 7:09 pm MDT. The official full Moon only lasts an instant, but the Moon will look full on the September 27 and 29.
The Harvest Moon is no ordinary full Moon: it behaves in a special way. Throughout the year the Moon generally rises about fifty minutes later each day. But near the autumn equinox, the daily difference in the time of Moonrise is only thirty minutes. The Moon will rise around sunset on September 28, and not long after sunset for the next few evenings. That comes in handy for northern farmers who are working long days to harvest their crops before autumn. The extra dose of lighting afforded by the full Moon closest to the equinox is what gives the Harvest Moon its name. In the southern hemisphere, this full Moon behaves in exactly the opposite way. South of the equator, there will be an extra long time between moonrises from one evening to the next.
We have all noticed how the Moon seems larger when it hangs over the horizon and how it takes on an orange glow. The apparent size difference is an optical illusion. You can prove this by taking a dime and holding it at armís length over the Moon. By comparing the size of the dime and the size of the Moon on the horizon and overhead, you will see that the size of the Moon does not change. Another test is to bend over and view the rising or setting Moon upside-down between your legs.
The color of the Moon is due to the amount of atmosphere you are looking through, and that is highly dependent on local weather conditions. When the Moon is low in the sky, you're seeing it through air filled with all kinds of junk. It will look even more orange after a dust storm or during wildfires that blow smoke into your skies. The dust and smoke scatter the blue light much better than the red light reflecting from the Moon. So, more of the red light shines through the air when the Moon is low than when it is overhead with only a little bit of atmosphere and junk to filter the light. Overhead, you will see the Moon take on more of a blue color.
So, go outside in September and enjoy the rising of the big orange Harvest Moon!
It will be worth getting up extra early on September 9 and 10. About 5:30 a.m., look outside to see the Moon hanging near Saturn and Venus in the eastern dawn. Mercury will be very low on the eastern horizon. Next to Mercury is the star Regulus. You may need binoculars to see Regulus in the twilight.
Note that all times are approximate and are valid for mid-month.
- Mercury rises around 5:20 a.m. in the eastern sky.
- Venus rises in the east about 3:30 a.m.
- Mars sets about 7:30 p.m. in the west.
- Jupiter sets in the west about 7:30 p.m.
- Saturn rises around 2 a.m. in the western sky.
- The Moon is new on September 14, and full on September 28.
- Fall begins at 10:30 p.m. on September 22.
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Stargazing in the Manzanos concludes
The Albuquerque Astronomical Society and the Sandia Ranger District will cohost their final star party of the season on Saturday, September 4, at Oak Flat Picnic Area. This free family event is open to the public.
The dark skies of the East Mountains and the large telescopes of TAAS astronomers allow for great views of moon craters, as well as numerous deep-sky galaxies, nebulae, and star clusters not usually visible near the glare of city lights.
Observing begins at sunset, weather permitting, and is suitable for all ages. Picnic facilities are available for those who would like to come early, and parking is available. Alcoholic beverages and pets are not allowed in the telescope viewing area.
To get there, take NM Highway 337 nine miles south of Tijeras, and follow the signs to Oak Flat and Juniper Loop. For information and a map, visit www.taas.org or call 254-TAAS.