September 1998

by Steve Stefanik

The summer sky gives way to September’s changing of the seasons. Officially this happens on September 23rd at 1:53 EDT (Eastern Daylight Time) but all one needs to do is look up at the harbingers of the sky. Foremost is the fact that the sun is rising later each morning and farther to the south than a couple of months ago. Conversely it sets about and hour earlier and also farther to the south. The "Summer Triangle" which consists of the three bright stars Altair, Deneb, and Vega are directly overhead as night falls and enter the western sky by late evening. The bright orange star Arcturus in the constellation Bootes which was predominant in the early Spring is now low in the west by mid-evening. The "birds of Summer" the constellations Aquilla and Cygnus, are winging their way west while the "water bearers" of the constellations Capricorn, Aquarius, and Pisces are rising in the east. The "Great Square" of the constellation Pegasus the mythological flying horse is winging its way upward. All are sure signs of Fall. Taurus rises by mid-night, a depressing thought to many because its a winter constellation. If you’re up by 5:00 a.m. on the morning of the 12th you could witness the occultation of its brightest star Aldebaran by the last quarter moon.

If you are an early riser or just getting in, you will be in for a spectacular show by the planets Mercury and Venus with the constellation Leo’s brightest star Regulus. The three form a tight little triangle less than three degrees apart low on the eastern horizon just before sun-up the first couple of weeks of the month. This will be Mercury’s best apparation (appearance) of the year. Venus is the brightest of the three at -3.9. Mercury is an impressive -1.3 magnitude making it even brighter than the first magnitude star which will be less than 1 degree to the lower right of Venus with Mercury above them early this morning. If you missed them this morning don’t despair, you can catch them tommorrow morning with Mercury and Venus about 1.2 degrees to the left of Regulus and again on Tuesday morning with Regulus about 1.2 degrees to the right of them.

The planet Mars is also in the east before sunrise. Its higher and to the right of Venus and Mercury. Its dim +1.7 magnitude and small 3.9 arc second disc makes it very difficult to make out any surface detail because it is to far away at this point.

If you’re not a morning person you can catch the planet Jupiter just above the full moon tonight! You can’t miss the brilliant -2.9 beacon, its huge at 49.7 arc seconds which is almost 1/60 of a degree. It will reach opposition directly opposite from the sun on the night of the 15-16th. Not only will it be at its brightest then but it will also be at its closest because it will be at perihelion (closet to the sun) during this year’s apparition. If you get the opportunity to view it through a telescope you can see its four biggest moons glide in front it casting their shadows onto the brightly colored swirls and bands of its atmosphere or disappear behind its massive disk.

The other spectacular sight is the planet Saturn which rises right behind Jupiter about two hours later. Though not as big or as bright as Jupiter, its still a respectable +0.2 in magnitude and 19.4 arc seconds in size. What makes it spectacular of course is its rings. Through a telescope you may be able to make out the subtle colored bands of its atmosphere and spot its largest satellite, Titan.

Uranus and Neptune are still visible through a telescope among the stars of Capricorn at magnitudes +5.9 and +7.9 respectively due south at night-fall.