Today in 1839, Scottish astronomer Thomas Henderson was the first to measure

Today in 1839, Scottish astronomer Thomas Henderson was the first to measure the distance to a star while stationed at the Cape of Good Hope. Using geometrical parallax, Alpha Centauri became the first stellar standard other than our own Sun. Although Henderson began as a lawyer’s clerk, his impressive list of 60,000 star positions led to his appointment as the first Astronomer Royal in Scotland. With the Moon absent during the early evening, our goal for tonight is Iota Orionis. Known to the Arabs as “the Bright One of the Sword,” we know it as the
southern-most star in its asterism’s namesake. Iota is estimated to be around 2000 light-years away and is about 20,000 times brighter than our own Sun. In the small telescope you will find Iota to be an easy and charming triple star. The bluish B star is relatively close at 11” in separation, but a bright 6.9 in magnitude. Much more distant at 50” is the disparate, magnitude 11 reddish C star. Iota itself is a spectroscopic binary and you will note another “white” double(Struve 747) unrelated to Iota about 8’ to the southwest. Staying at high power, the reason I ask you to look here tonight is to conquer a Herschel 400 object and study a region of the sky that would be far more impressive if it weren’t for its alluring neighbor. If you look closely, you will see that Iota is involved in a region of the emission nebula known as NGC 1980, along with a small open cluster known as H 31. To be sure, the area is vague, as are all low surface brightness nebulae, but do look to the east of Iota where a much brighter, roundish area makes an unmistakable appearance! The next objects require the use of high magnification. The reason I ask you to look in this area tonight is to conquer a Herschel 400 object—and to study a region of
the sky that would be far more impressive if it weren’t for its alluring neighbor, Iota. If you look closely, you will see the star is surrounded by a region of the emission nebula
known as NGC 1980...
Jan9
TUE SDAY
NGC 1980
Credit: Palomar Observatory, courtesy of Caltech