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Milky Way hiding along the horizon on May evenings

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Tonight for May 3, 2014

The two brightest celestial bodies to adorn the evening sky - the moon and the planet Jupiter - beam in the west at dusk and nightfall.

The two brightest celestial bodies to adorn the evening sky – the moon and the planet Jupiter – beam in the west at dusk and nightfall.

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

Click here to expand image of Milky Way

Where is the starlit band of the Milky Way on these May evenings? That luminous band of stars crossing the dome of sky is nowhere to be seen during the evening hours in May. Why?

The disk of our Milky Way galaxy is shaped like a pancake. On May evenings, the plane of the pancake-shaped galactic disk coincides with the plane of the horizon. Because the Milky Way rims the horizon in every direction in the evening in May, we can’t see this roadway of stars until later at night right now.

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, 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.

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.

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.

Click here to expand image above