Perspective on the night sky

Michael P.C. Watts Impattern Solutions

Michael P.C. Watts Copy write 2015

Earth’s position within the Milky Way The night sky by season The night sky during the night Best viewing of key objects

•Earth’s orbit (ecliptic) is tilted at 63 degrees to plane of Milky Way.•NOT to scale !

•Distance of sun to center of Milky Way = 10 9 times the diameter of earth’ orbit = 1 “giga” orbits or 30,000 light years.

Michael P.C. Watts Copy write 2015

63 degrees

View point of Milky way from perpendicular to plane of ecliptic

•The midwinter and midsummer positions of the earth are in the sun / black hole axis.

•Spring and fall positions are at the high and low points of the earth’s orbit out of the galactic plane.

Milky way from perpendicular to plane of ecliptic

Michael P.C. Watts Copy write 2015

Milky Way from plane of ecliptic, perpendicular to Earth – Sun axis

• Shows the midsummer and midwinter locations of earth in earth’s orbital plane (ecliptic)• The earth’s axis tilts 23 degrees away from the galaxy center so in the northern hemisphere, in mid-

summer the daytime sun is high in the sky, and at night the center of the Milky Way is low in the sky. • The midsummer, midnight view shows the center of the Milky Way.• The midwinter midnight view shows the outer edge of the Milky Way.• The pole star sits above the plane of the Milky Way slightly further out from the center of the Milky Way ,

aligned to the earths’ rotation axis Michael P.C. Watts Copy write 2015

Polaris Pole Star

Midsummer, midnight – Milky Way low in the night sky Midwinter, midnight – Milky Way high in sky

Polaris Pole Star

Center of the midnight view from 30 deg N (Austin TX) looking “up” on a galactic projection of the night sky from the sun

Dec Nov Oct Sept Aug Jul Jun May April Mar Feb Jan

• In winter and summer, the earth is located in the plane of the Milky Way .• The tilt of earths rotation means that in spring, with the earth above the Milk Way plane, the midnight view in

northern hemisphere is well above the Milky Way. • In Fall, the same tilt moves the midnight view close to the Milky Way plane. • The sky view spins around the Pole Star.

Michael P.C. Watts Copy write 2015

360 degree view from the sun through the Milky Way Example of a “Mollweide” or homolographic projection, an equal area projection of a sphere onto a flat plane. Invented in 1805.

Patch of the night sky that cannot be seen from 30 degrees North

Mid –summer and Mid –winter midnight Southern horizons define the segment of the Milky Way that cannot be seen from 30

degrees North

Best view of Milky Way core is from 23 degrees South of the Equator, midsummer midnight. This offsets the earth’s tilt.

Mid –summer midnight Southern horizon at 30

degrees north

• Every night, the view to the East at dusk through to the West at dawn, scans 360 degree through the night sky.

• A view point in the Southern Hemisphere needed to see the full Milky Way

• Mid –summer South and Mid –winter South define the segment of the Milky Way that cannot be seen from the Northern Hemisphere. From Austin TX 30 degree N, that is a 45 degree segment

Michael P.C. Watts Copy write 2015

East view at Dawn

West view at Dusk

Midnight

Path through the night sky from West at Dusk to East at Dawn

April 1

July 1

Oct 1

The line shows the path though the night sky from

East at Dusk to West at Dawn.

The spots shows the center of the view “up” at

midnight, 6PM 12AM 6AM

The section of the night sky not seen from the Northern

Hemisphere

Jan 1

SPRING mid-night Showing Polaris or North Star low in the North sky MID-SUMMER mid-night view to the south

Sagittarius center of the Milky Way (Black hole )

Example views. • The spring mid-night view shows the Pole Star low in the sky • The midsummer, midnight view to the South shows the center

of the Milky Way. • The midwinter, midnight, “up” view shows the Pliades at the• The fall midnight, “up” view shows • Pliades and Andromeda are roughly the same size, around 1.5

degrees, or about 3x the size of the moon at around 0.5 degrees.

Michael P.C. Watts Copy write 2015

FALL mid-nightAndromeda Galaxy

MID- WINTER mid-night Pliades

Fall at Dusk, facing East – highest path of Milky Way in the night sky