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Astro Mark's Astro Alert: Jupiter Brings It In Tight


Greetings Fellow Stargazer!

Oh, so that’s not an airplane?

I know you are a person who “looks up” at the night sky, so certainly you’ve seen the beacon of light rising in the southeastern horizon a couple of hours after sunset. It’s big and it’s bright, and since you are a keen observer you quickly surmise, it’s not moving; so it can’t be an airplane.


That bluish white spotlight beaming down on you, my friend, is Jupiter. The Greek god of the sky, and king of the gods in ancient Roman mythology. Interestingly, the deity Jupiter is the king of the gods for the Romans, and is equivalent to Zeus, the head of the gods in Greek mythology. Jupiter, by any other name, is found in many cultural mythologies throughout history. With all that said, Jupiter is top banana, and now it is big and bright, and will be super-duper biggest and brightest on Monday night! In what way is it super-duper? Here’s how…Jupiter’s apparent diameter on Monday night will be 49.9”. In fact, the greatest possible apparent diameter Jupiter can ever achieve is 50.1”.


Jupiter at Opposition, Closest to Earth in 60 Years: September 26th

Let’s review: Jupiter is the largest planet in our solar system. It is also a gas giant, because it is composed mostly of hydrogen, helium, and a mix of heavier elements. All together those gases make up about an eighth of Jupiter’s mass. When Jupiter is at opposition (meaning, the Earth is between the Sun and Jupiter), it rises in the southeast, as the sun sets in the west, and is visible all night – because it is directly opposite of the Sun. Ah, makes sense now! On September 26th, Jupiter will be a mere 367.3 million miles away from Earth. To put that into context, the average distance of Jupiter’s orbit from the Earth is 444 million miles. Here’s a moment of “nearness” for you.

Can you See Ganymede?


It may be an urban legend. Or, it could possibly be true; could be possible. There have been hushed whispers at star parties, and from sharp-eyed observers at dark sites, that when Jupiter is in opposition, and the conditions are just right, you can see Jupiter’s largest moon, Ganymede. Chinese astronomical records report that in 365 BC, Gan De, detected what might have been a moon of Jupiter, probably Ganymede, with the naked eye. This seems plausible as Ganymede is the largest and most massive of all the moons in our solar system. Give it a go! Try to slightly squint your eyes and look for Ganymede at the left side of Jupiter. Look for a slight bump attached to the outermost edge of the planet. Then, move your focus off Jupiter for a second, and then look back to Jupiter. In the flash of an instance, when you move your focus off and then back on to Jupiter, there’s your best chance to catch Ganymede. Try it tomorrow night! If you see it, let me know.

(And don’t sweat it if you missed Jupiter tomorrow night, the god of the sky’s reign shines brilliantly upon you well into December.)

Clear skies to you!


Credits: Starry Night 8, Astronomy Magazine, Wikipedia, Sky and Telescope Magazine,, and SkyatNight