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What's Up...Look for the “false dawn” PDF Print E-mail

The days are getting shorter, the Sun is shining through that south-facing window where it hasn’t been all summer and the nighttime temperatures are getting cooler.

Sound familiar? Well, you guessed it, autumn is coming, and will officially arrive at 9:09 p.m. MDT, Sept. 22. That is the date of the Autumnal equinox when the sun crosses the celestial equator on its journey back south. More about that later as we get closer to the date.

We have been observing some really great passes of the International Space Station (ISS) recently. In the early part of August they occurred in the early morning, but toward the end of the month–due to orbital mechanics–they moved to the early evening.

Even managed to work in a few Iridium flares–a glancing glare of sunlight off the surfaces of one of the numerous Iridium communication satellites in low Earth orbit.

Predictions for both these events can be found at, all you have to do is register as a member and find your geographic location (longitude and latitude) and you are all set.

The Summer Triangle of Lyra, Deneb, and Altair have all moved into position directly overhead in the early evening sky but the autumn constellations are pushing up from the east into a position of prominence.

The autumn constellation Pegasus, the Flying Horse, is clear of the eastern horizon by 9:30 p.m. MDT. The  “Great Square of Pegasus” is tipped up on one corner and looks currently like a giant diamond hovering over the eastern horizon. 

The two arms of the constellation Andromeda reach out from the northeast corner star of the square to the north, left, toward her hero, Perseus, who won’t be in view for another two hours. 

The next two weeks are a great time to observe the Zodiacal Light in the early morning eastern sky. The Zodiacal Light is sunlight reflected off the zillions of dust particles drifting in  the galactic plain. It is often called a “false dawn” as it gives the appearance of sunrise.

Each autumn this horizontal plain is almost vertical to the horizon and can be seen as a faint, glowing light above the eastern horizon before twilight begins to lighten the horizon with the real sunrise.

I had been looking for the Zodiacal Light for some time and finally got a glimpse of it last spring when this same phenomenon occurs in the evening skies. 

It takes the form a cone of light extending from a broad base at the horizon extending to a point up into the zodiac, hence the name.

If you can see the Milky Way from your location, or your favorite dark-sky location, you should be able to see this false dawn.

SKY WATCH: New Moon Sept. 8. The Moon is left of the Pleiades star cluster, M45, after midnight tonight. Mars, Venus and Spica make a close conjunction for the next week. Very dim and sinking Saturn to the group’s far right. The Jupiter/Uranus pair rise in the east after 9 p.m. MDT and make a nice binocular target.