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Evan Hazard: Norhland Stargazing — June planets and two bright reddish stars

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Just past midnight June 21, at 00:04 CDT, Sol will reach its northernmost point on the Ecliptic, the night will be the shortest of the year, and astronomical summer will begin. That’s before midnight June 20 MDT and PDT. That’s why astronomical summer sometimes begins on June 20 or 22. It depends on the time zone you’re in then. Mosquitoes and ticks are already abundant, time zone or not.

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Mercury has its best apparition of the year, reaching greatest elongation after sunset 12 June. It is visible in the WNW 45 minutes after sundown from now into late June. Since Venus is in the same part of the sky, it provides a place to start searching for dimmer Mercury. June 7 Mercury is above and left of Venus and works its way down toward the horizon, passing Venus the third week in June. June 9-11, thin crescent Luna cruises up past the two inner planets.

Jupiter, on the far side of Sol, is visible after sunset June 1, but disappears into Sol’s glare by June 3. Saturn is high in the south at nightfall, and remains the brightest planet after Venus sets. Dim Mars is a difficult pre-dawn object June 1, but by June 30 is visible in binocs 7??above the eastern horizon. Luna is full June 23 and will degrade stargazing the latter half month.

Before that, find a clear evening for summer stargazing. The bright reddish star overhead is the orange giant Arcturus, in Boötes, the 4th brightest true star in the night sky. It is relatively nearby (37 light years), somewhat more massive than Sol, and probably about 7 billion years (BY) old. It has fused most of its hydrogen into helium, and is now fusing helium into carbon. It will eventually collapse and become a white dwarf.

Above the SSE horizon is another reddish star, not quite so bright, Antares (named in contrast to Ares, Greek name for Mars, god of war). It is a red supergiant, probably only 11-12 million years (MY) old. Much larger than Arcturus, its diameter is greater than the orbit of Mars. It is also much more massive than Arcturus, containing some 17 solar masses.

Why is Antares dimmer than Arcturus? At 550 light years away, it’s 15 times more distant. The larger a newborn star is, the hotter its center is, and the faster it fuses hydrogen. So, in only 11 MY, it has reached the same stage of helium fusion that Arcturus reached in 7 BY. Antares is actually part of an association of thousands of stars in Scorpius, averaging 11 MY old, all condensed from one cloud of gas and dust. As one of the largest, it has gone through its life cycle rapidly, and will end its red giant stage in about a million years as a supernova and then become a neutron star or black hole. For more, go to: https :// en.wikipedia.org/wiki/Arcturus and http :// en.wikipedia.org/wiki/Antares .

EVAN HAZARD also writes "Threescore and Ten" for The Pioneer’s "Prime Time."

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