Triangles in the Sky
Early morning observing continues to attract me. This morning I observe some favorites, as well as watch the Sunrise breach the Eastern horizon as billows of clouds roll in from the West to change the sky from clear to 95 percent cloudy.
Location
Central Kentucky, USA
Time
Local: October 11, 6:30-8:00 a.m. (EDT).
UT: 10:30-12:00
Observing conditions
Sky Quality Meter (SQM): 19.60, 19.72
Clear Sky Clock
Cloud cover: clear
Transparency: average
Seeing: Poor 2/5
Darkness: 5.8
Weather
Temperature: 40°F, 4°C
Humidity: 82%
Dew point: 35°F, 2°C
Wind: calm, 0 mph
Pressure: 29.89, falling
Visibility: 10.0 miles, 16.1 km
Ceiling: 40,000 ft, 7.5 mi., 12.2 km, unlimited
Equipment
Swift Audubon 820ED 8.5x44 binoculars (hand held)
Sky Quality Meter (SQM)
Planets: Rising / Setting times
Moon: new moon 1:01 a.m., 8:10 a.m. / 7:06 p.m.
Sun: 7:44 a.m. / 7:08 p.m.
Mercury: 9:38 a.m. / 7:46 p.m.
Venus: 4:06 a.m. / 5:07 p.m.
Mars: 11:31 p.m. / 2:09 p.m.
Jupiter: 12:35 p.m. / 10:09 p.m.
Saturn: 4:11 a.m. / 5:26 p.m.
Uranus: 5:49 p.m. / 5:16 a.m.
Neptune: 4:38 p.m. / 3:07 a.m.
Pluto: 1:02 p.m. / 11:16 p.m.
Observations
6:30 a.m.
The early morning sky is very dark—the best I have noticed since I began star observing nine months ago. There are many more stars than last month’s early morning observation (Sept. 23). This morning, I can only observe for a few minutes, but what a show.
The constellation Orion is very prominent in the South (185° azimuth, 50° altitude) with the constellation Canis Major (170° azimuth, 30° altitude) close by and Sirius (Alpha CMa) burning brightly at magnitude -1.5 or more. An excellent binocular object this morning is the Great Orion Nebula (M42, NGC 1976), magnitude 4.0, in Orion’s Sword. M42 is the brightest diffuse nebula in the sky, with apparent dimensions measuring 85 x 60 arc minutes. As the day dawns, I wonder what stars may be dawning inside the Great Orion Nebula.
Close to zenith, the planet Mars is positioned 1° away from Mu Gem, the magnitude 2.9 star that traditionally is claimed for two constellations: Castor’s foot in Gemini and the tip of the club in Orion’s raised arm. Close to Mars are several open clusters: Collinder 89 (1° away), M35 (3° away), and M37 (11° away).
Mars, magnitude -0.1, also forms a nice color triangle with the bright orange stars Betelgeuse (Alpha Ori), magnitude 0.9, and Aldebaran (Alpha Tau), magnitude 0.4. Not a perfect Isosceles triangle, the sides of this morning’s color triangle measure Mars --> Betelgeuse 17.5°, Mars --> Aldebaran 26°, and Betelgeuse --> Aldebaran 21°. Despite being lopsided, the color triangle is still a beautiful naked eye sight in this last hour before dawn.
Another bright sight this morning is the planet Venus, reaching magnitude -4.7 during early October, according to Astronomy magazine. Venus is extremely bright to the naked eye and far too bright for viewing with binoculars at this time.
Venus (100° azimuth, 25° altitude) has some close neighbors this morning in the Eastern sky—the planet Saturn, magnitude 0.8, and the star Regulus (Alpha Leo), magnitude 1.4. In fact, the three objects form another Isosceles triangle with the sides measuring Venus --> Saturn 4°, Venus --> Regulus 4.5°, and Saturn --> Regulus 4.7°. The size of the triangle is perfect for binoculars with a wide field of view (FOV).
I study Saturn for a few minutes with my 8.5x44 binoculars. Saturn is a peach color and I can discern the rings, a thin line protruding from both sides of the planet.
7:15 a.m.
I go back outside. Now is the last 30 minutes before Sunrise and the sky is beautiful light blue graduating to pale amber in the Eastern horizon. Only two objects remain visible in the sky—Venus and Sirius (Alpha CMa). Venus does not appear as bright as she did earlier, so I study this lovely for a few minutes with the binoculars. I look to the West and notice billows of clouds starting to roll in.
7:45 a.m.
The Sun is breaching the horizon. A grey blanket of stratocumulus clouds covers 95 percent of the sky. The 5 percent of the sky still clear is a slender rim in the Eastern horizon above the rising Sun. The effect is a bright gold lining on the edge of the cloud blanket. The Western horizon also displays some color, however, the color in that direction is more pink than gold.
Reflection
I have been measuring sky darkness with the Sky Quality Meter (SQM)—a neat instrument made by Unihedron, a Canadian company. SQM has become my first measure for observing conditions. Although most folks like to factor in other variables, such as specific stars observed with the naked eye, Clear Sky Clock readings, and weather reports (e.g., relative humidity and visibility)—I find SQM is my best “quick read” of what I will be able to see with either my naked eye or binoculars. The higher the SQM reading, the more I see.
This morning’s SQM reading of 19.72 is the best I have recorded since I purchased the instrument two months ago. There is a big difference in what I can observe when I go from a 19.14 sky (September 23) to this morning's predawn 19.72 sky.
I wish I had the conversion formula for converting SQM readings to the Bortle Scale (1.0-9.0). Someone posted a conversion formula in another Cloudy Nights forum. However, from what I remember, this person said the formula needed tweaking. Anyway, I enjoy the convenience and consistency of using SQM readings.
References
Accuweather.com. (2007, Oct. 11, 6:30 a.m.). Current conditions. Retrieved October 11, 2007, from http://www.accuweather.com.
Burnett, J. (2007, Oct. 11). Rise and set. Dublin, NH: Yankee Publishing. Retrieved October 11, 2007, from http://www.almanac.com.
Crinklaw, G. (2003). SkyTools 2 [software]. Cloudcroft, NM: Skyhound.
Crossen, C., & Tirion, W. (1992). Binocular astronomy. Richmond, VA: Willmann-Bell.
Dunlop, S. (2002). The weather identification handbook. Guilford, CT: The Lyons Press, an imprint of The Globe Pequot Press.
Eicher, D. J. (Ed.). (2007). The sky this month. Astronomy, 35(10), pp. 44-51.
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