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07/17/2023 – Ephemeris – Arcturus, a look at the Sun’s future

July 17, 2023 Comments off

This is Ephemeris for Monday, July 17th. Today the Sun will be up for 15 hours and 11 minutes, setting at 9:24, and it will rise tomorrow at 6:14. The Moon is new today, and won’t be visible.

Arcturus, a red giant star, is about two thirds the way up the sky in the southwest at 10:30 or 11 p.m. It’s one of the earliest stars to appear in twilight, being nearly tied in brightness with Vega, a white star about as high in the east. A pointer to Arcturus is the handle of the Big Dipper, following the arc of the handle to Arcturus. Though only 37 light years away, it’s not from around here. It’s passing through the galactic disk from north to south. Arcturus is about 7 billion years old, and is about 8% more massive than our Sun. It appears to be starting its red giant phase, after running out of hydrogen to fuse into helium in its core, and is beginning to fuse the helium. It’s 25 times the size of the Sun and 170 times brighter, and a preview of our Sun when it gets that old.

The astronomical event times given are for the Traverse City/Interlochen area of Michigan (EDT, UT –4 hours). They may be different for your location.

Addendum

The whole dome of the sky is shown at 11 pm, or about an hour and a half after sunset. The two brightest stars are Arcturus and Vega. Arcturus can otherwise be found by following the arc of the handle of the Big Dipper. It looks like Saturn is about to rise, as its label is partially visible on the east-southeastern horizon. If needed, click or tap on the image to enlarge or show the complete image. Created using Stellarium.
The evolutionary track of a sun-like star as seen on this Hertzsprung- Russell diagram. The temperature is the temperature of the star’s surface or photosphere, which can be determined from the star’s color. Stars on the sloping line called the main sequence is where a star spends the vast majority of its lifetime. A star’s placement on the main sequence is determined by its mass. More massive stars are seen to the upper left of the Sun, Left massive stars appear to the lower right. If needed, click or tap on the image to enlarge or show the complete image. Credit: Sloan Digital Sky Survey (SDSS) website.

Categories: Ephemeris Program, Stars Tags: , ,