Andromeda M31 Geology 360/Physics 360 Addendum to Galaxies

Andromeda Galaxy (Hubble Telescope) 2.5 million LY away

The Future Fate of the Milky Way Galaxy - Collision Scenario for the Milky Way and Andromeda Galaxies The Milky Way and the Andromeda galaxy are approaching each other with a speed of 300,000 miles per hour. It's not certain yet whether we're in store for a head-on collision or a simple sideswiping by the massive galaxy, which is a near twin to the Milky Way. Astronomers will first need to use powerful new telescopes to precisely measure Andromeda's tangential motion across the sky. (Just as a baseball outfielder estimates whether a ball is heading directly toward him or is going to miss him by determining whether the ball is moving sideways.) A direct collision would lead to a grand merger between the two behemoths, and the Milky Way would no longer be the pinwheel spiral we are familiar with, but would evolve into a huge elliptical galaxy. It would happen no sooner than five billion years in the future. By then the Sun may have burned out, and the Earth reduced to a frigid, lifeless cinder. It's impossible to predict if there would be any vestige of humanity colonized among the stars, not to mention extraterrestrial civilizations around to witness this great collision. The collision will take several billion years to fully run its course, so it will be hard for any one civilization, like ours, to fully understand the vast scale - both in time and space — of the collision.

Measuring the distance to galaxies Cephid Variables (are a million solar luminosities) Identify the luminosity of the Cephid Variable by measuring its period. Knowing the luminosity using the candlepower equation find the distance to the cephid variable within the galaxy. Using V = H d is also another way to measure the distance to galaxies. You have to measure the recessional velocity of the galaxy. The faster a galaxy recedes the farther away it is. (H is 70 kilometers per second per megaparsec) To measure the diameter of a galaxy, we treat it just as we would measure the diameter of the moon knowing its distance. D (diameter) = 2 Pi A d/360 where A is the angular size in the sky in degrees.

From Stardate.org April 23 Vanishing Orion Orion, the hunter, is bowing out of the evening sky. He's low in the west at nightfall, and his stars begin dropping from view not long afterward. The constellation will be pretty much lost from sight by the middle of May. Like the hour hands on a giant celestial clock, all the stars loop from the morning sky to the evening sky and back again once a year. That motion is caused by Earth's motion around the Sun. Earth rotates on its axis once every 23 hours and 56 minutes. That means that every star returns to the same position in the sky at that same interval -- except one: the Sun. The difference is our orbit around the Sun. Each day, Earth moves about 1.6 million miles along its orbital path. So our planet has to rotate a little longer for the Sun to return to the same position in the sky as the day before: four minutes. That means the other stars rise and set four minutes earlier each day, so they loop around the sky during the year. Back around Thanksgiving, for example, Orion was just climbing into view in the east as night fell. Now, it's on the opposite side of the sky, just sinking into the sunset. But it'll return to view in midsummer -- this time in the morning, as it begins yet another cycle across the sky. For now, look for Orion low in the west beginning not long after sunset. His "belt" of three bright stars runs parallel to the horizon, with bright orange Betelgeuse above the belt, and blue-white Rigel below it.