This week I’m tackling the subject of our Sun’s motion through the Milky Way Galaxy and approximately how long one orbit is.
The Milky Way Galaxy has two major spiral arms, named the Perseus Arm and the Scutum-Centaurus Arm. There are also smaller less pronounced arms, including the Sagittarius Arm, the Norma Arm, The Local Arm (aka the Orion Spur) and the Outer Arm. Our solar system resides in the Orion Spur (Local Arm), branching off from the larger Perseus Arm. During the summer months in the northern hemisphere, we predominantly observe the Sagittarius Arm, including the galactic center, which appears as steam from the Tea Pot asterism in the constellation Sagittarius. (Gaherty, 2016) Over the winter, we’re looking away from the galactic center and through the Perseus Arm. (Comins, 396)
Tonight is my first night this year as a volunteer of the Astronomical Society of Kansas City in our public outreach efforts to introduce astronomical observing to the public. Every Saturday night in May and through the end of October, we open up Powell Observatory to the public and provide education programs, solar observing, binocular observing and of course telescopic observing (weather and cloud cover permitting). The weather forecast for this evening couldn’t be better. See for yourself as we have our own weather station and sky cam broadcasting 24-hours a day.
• The Moon moves approximately 13° eastward relative to the starry background every 24 hours, and its motion carries it near Jupiter this evening. From North America, the two appear within 5° of each other all night. They will be in conjunction at 6 a.m. EDT tomorrow morning, when our satellite passes 2° due south of the planet. Although the best views of the pair come with the naked eye or binoculars, don’t pass up the opportunity to observe Jupiter through a telescope. The giant planet’s disk currently spans 39″ and displays a wealth of atmospheric detail. All this week, Jupiter appears high in the south as darkness falls and doesn’t set until nearly 3 a.m. local daylight time. It shines at magnitude –2.2 — brighter than any other point of light in the night sky — against the backdrop of southern Leo.
While Sky and Telescope Sky at a Glance expands on: The two brightest things in the evening sky, the Moon and Jupiter, shine high just a few degrees apart this evening, as shown here. Third brightest is Mars, low in the southeast after dark.
So for a great time this evening, head south of Kansas City down US-69 to Louisburg and join me and several hundred other people as we take in the wonders of the night sky.
I don’t remember seeing Esther (the author of the above article) at last Saturday evening’s ASKC meeting and Dr. Feldman’s lecture on Dark Matter and Dark Energy … but I’ve seen that graph very recently.