The seasons are again changing on Earth, which is being reflected in the heavens above. We have had an excellent summer and are now preparing for autumn as the nights are slowly getting longer and cooler. This is usually a great month to get outside under the vast canopy of the sky and marvel at what the stars and objects that we can glimpse really are, and how we are connected to them.

Autumn begins for us in the northern hemisphere at 10:29 p.m. on Monday the 22nd. This moment is further defined as the instant that the path of the sun on the ecliptic crosses over the celestial equator on a downward path.

The days and nights will be of equal length everywhere except at the poles within a few days of that day. The sun will also rise due east and set due west on that day. The only other day that will happen is at the vernal equinox, which will happen six months later.

Right now the sun still rises north of east and sets north of west. By the time we get to the winter solstice in three more months, the sun will rise at its farthest south of east and also set far south of west, only tracing a very low arc through our sky.

The main highlight this month will be Mars catching up with its rival, Antares, and passing just 3 degrees above it on Sept. 27 and 28.

The red planet already caught up with Saturn last month, and now it continues to race farther east of the ringed planet as it is rapidly catching up with its archrival in Scorpius, named Antares.

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Antares, whose very name means “rival of Mars,” is a first magnitude red super giant star similar to Betelgeuse in Orion. It is also about the same distance from us, which is 600 light years. That means that the light you will be looking at when you see Antares this month will have left that star just before Gutenberg invented the printing press, which essentially revolutionized the way information was disseminated and helped start the Industrial Revolution. Computers and the Internet are the new revolution, which are only possible because of our knowledge of quantum mechanics and the true nature of the atom. As this knowledge continues to grow, you will see that we are only in our infancy as far as true communication capability goes.

Antares is about 15 times the mass of our sun and about 50,000 times its luminosity, which is the fourth power of a star’s mass. Antares is about 700 times the diameter of our sun, which means that if it were placed where our sun currently is, it would engulf Earth and Mars all the way out to the asteroid belt, which is halfway to Jupiter from Mars.

Antares is one of the four Royal Stars of Persia, also known as the Guardians of the Heavens. The other three are Aldebaran in Taurus, Regulus in Leo and Fomalhaut in Piscis Austrinus. At only 25 light years away, Fomalhaut is a very interesting star because the first exoplanet that was seen in visible light was discovered orbiting around it in 2008.

If you could photograph the region of the sky where Antares is located, you would see the brilliant and colorful Rho Ophiuchi complex emerge. This complex of stars and dust emits light in every wavelength from gamma ray to radio waves. The blue light is reflected light off the nebula and the reds, and yellows are caused by emission of atomic and molecular gas. There are also two nice globular star clusters embedded in this complex, named M4 just below Antares and M80 just above it. They are each about 30,000 light years away, and they each contain hundreds of thousands of older stars loosely held together by their mutual gravitational attraction. They are part of about 150 similar globular star clusters that form a halo around the center of our Milky Way Galaxy.

As you enjoy these two amazing objects low in our southwestern sky shortly after sunset, carefully compare the orange-gold hues of the pair. Notice that Mars is still a little brighter than Antares, but that Mars is slowly getting dimmer this month as Earth continues to leave it farther behind in our respective orbits around the sun.

Jupiter passed very close to Venus during the middle of August and is now rising higher in the sky even as Venus sinks lower into our eastern morning sky one hour before sunrise. Venus will look full all month long through a telescope because it is near superior conjunction, when it is farthest away and dimmest, and smallest in the sky, even though it is nearly fully lit by the sun. Venus will pass less than 1 degree above Regulus 30 minutes before sunrise on the morning of Friday the 5th. So two of our bright planets will be seen very close to two of the four Royal Stars of Persia this month.

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A very interesting event that is unfolding now is the spacecraft Rosetta’s recent arrival at Comet Churyumov-Gerasimenko. Launched in March 2004, this spacecraft just arrived at this comet last month and it will soon drop a lander onto the surface of this comet. Named Philae, after an island in the Nile where an obelisk was found and used to help decipher Egyptian hieroglyphics along with the famous Rosetta stone, this lander will be the first time humans in their 100,000-year history will have performed a controlled landing of a spacecraft on a comet. This is a very strange comet, as it looks like two comets that smashed together. Just as the original Rosetta stone helped us understand ancient Egyptian literature and civilization, the new Rosetta spacecraft will help us understand the origin and composition of this primordial comet, which has been roaming the desolate depths of cold space basically unchanged for 4.6 billion years.

SEPTEMBER HIGHLIGHTS

Sept. 2: First-quarter moon is at 7:11 a.m.

Sept. 3: On this day in 1976, Viking 2 landed on Mars. This was only the second mission humans have ever landed on Mars. The first one was Viking 1 only a few weeks earlier. These early Viking missions gave us a much better sense of what it is really like to live and work on Mars, which some humans may actually be doing in as little as 10 years.

Sept. 5: Venus and Regulus will be less than 1 degree apart low in the eastern sky this morning a half-hour before sunrise. Notice that Jupiter is now 15 degrees above the pair.

Sept. 8: Full moon is at 9:38 p.m. This is the third and last of three consecutive super moons we enjoyed this summer. This is also the famous Harvest moon. This moon rises only about 25 minutes later each evening, thereby giving more consistent light to farmers harvesting their crops. That is because of the shallow angle that the ecliptic makes with our horizon at this time of year. Farther north, the full moon would rise only a few minutes later each evening.

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Sept. 11: On this day in 1985, the International Cometary Explorercompleted its first comet fly-by. In March 1986 it also flew close to Halley’s Comet, studying its interaction with the solar wind. ICE was the first spacecraft to be placed in an orbit within a Lagrangian point, which is an area within which gravitational fields are balanced and suspended.

Sept. 15: Last-quarter moon is at 10:05 p.m.

Sept. 17: On this day in 1789, William Herschel discovered Mimas, the smallest and innermost of Saturn’s seven largest moons. At about 250 miles in diameter, it has a giant impact crater that covers one-third of its surface and has a central peak four miles high.

Sept. 20: The waning crescent moon will be just to the right and below Jupiter one hour before sunrise this morning low in the eastern sky.

Sept. 22: Autumn begins at exactly 10:29 p.m.

Sept. 23: On this day in 1846, J. Galle discovered Neptune close to where it was predicted.

Sept. 27: The moon will be just below Saturn one hour after sunset in the southwestern sky. Mars and Antares will be only 3 degrees apart for several evenings.

Sept. 28: The asteroid Vesta will be just half a degree south of the moon this evening.


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