07/23/2015 – Ephemeris – Altair, the nearest star of the Summer Triangle
Thursday, July 23rd. Today the Sun will be up for 14 hours and 59 minutes, setting at 9:18. The Moon, 1 day before first quarter, will set at 12:57 tomorrow morning. Tomorrow the Sun will rise at 6:20.
The southernmost star of the Summer Triangle is Altair, high in the south. The other two stars of the triangle are Vega nearly overhead, and Deneb high in the east. Altair is the closest of the three at a distance of 16.7 light years away. One light year is nearly 6 trillion miles. Altair is 10 times the brightness of the sun. If seen at Altair’s distance, the sun would only be as bright as one of the two stars that flank it. What is rather different about Altair is its rapid rotation. While it’s almost twice the sun’s diameter, it rotates once in only 8.9 hours, The CHARA Interferometer at Mt. Wilson has actually imaged its squashed disk in the infrared. Our sun’s a slow poke, taking nearly a month to rotate once.
Times are for the Traverse City/Interlochen area of Michigan. They may be different for your location.