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Where is the Milky Way on May evenings?

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Tonight for May 16, 2015

Starlit band of the Milky Way. Photo by Larry Landolfi via NASA

Tonight – if you’re in a dark location, at northern temperate latitudes – you might be searching for one of the sky’s most spectacular sights, the starlit band of the Milky Way. You won’t find it in the early part of the night. That luminous band of stars crossing the dome of sky is nowhere to be seen as evening falls in May. Where is the the Milky Way at nightfall this month?

For starters, remember that the disk of our Milky Way galaxy is flat, like a pancake. At northern temperate latitudes, as evening falls in the month of May, the plane of the pancake-shaped galactic disk pretty much coincides with the plane of your horizon.

Because the Milky Way rims the horizon in every direction at nightfall and early evening, we can’t see this roadway of stars until late at night.

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An all-sky plot of the 25,000 brightest, whitest stars shows how these stars are concentrated along the Milky Way. This map shows our limited, inside view of the Milky Way galaxy. The large, dark patch near the middle of the picture is due to nearby dark nebulae, or clouds of gas and dust, which obscure the stars. Via altasoftheuniverse.com.

The galactic disk most closely aligns with the horizon at about 30 degrees North latitude – the latitude of St. Augustine, Florida. Appreciably north of this latitude, the galactic disk tilts a bit upward of the northern horizon. Appreciably south of 30 degrees north latitude, the galactic disk tilts a bit above the southern horizon.

Even so, no matter where you are on Earth, the Milky Way is pretty much out of sight in our Northern Hemisphere sky during the evening hours in May.

Like the sun, the stars rise in the east and set in the west. If you stay up until late night – near midnight – you’ll begin to see the the stars of the Summer Triangle – Deneb, Vega, and Altair – rising above your eastern horizon.

In a dark country sky, the Milky Way’s band of stars becomes visible as well, for the Milky Way passes right through the Summer Triangle. Watch for it, if you’re up late this month.

Bottom line: The Milky Way’s softly-glowing band of luminescence hides behind the horizon at nightfall and early evening in the month of May. But if you stay up until around midnight, you’ll begin to see the starlit band of the Milky Way rising in the eastern sky.

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