Astronomical Distances Distances in astronomy are huge The Moon is 240,000 miles away The Sun is 93, 000,000 miles away Neptune is 2,810,687,500 miles.

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Astronomical Distances Distances in astronomy are huge The Moon is 240,000 miles away The Sun is 93, 000,000 miles away Neptune is 2,810,687,500 miles away

Proxima Centauri, the next closest star, is 25,300,000,000,000 miles away The center of our Milky Way Galaxy is 16,500,000,000,000,000 miles away Andromeda, the next closest galaxy is 17,000,000,000,000,000,000 miles away The Universe is 166,000,000,000,000,000,000,000 miles across

Miles and kilometers are too small of a unit to measure such huge distances Astronomers use the following units: Astronomical Unit (AU), the average distance of the Sun to the Earth, 1 AU = 93,000,000 miles Light-year (ly), the distance light travels in one year, 1 ly = 5,900,000,000,000 miles Parsec (pc), the distance when parallax equals 1 sec of arc, 1 pc = 19,000,000,000,000 miles

To measure distances to nearby stars, “parallax” is used. The angle of movement a star makes in a 6 month period across the sky is measured. This gives you the angle of a right triangle, you already know the opposite side (distance to the Sun), so the distance to the star can be calculated (1 AU / tan  ). Because the angle gets extremely small to measure farther and farther stars, distance can only be determined out to about 150 ly (the nearest 5900 stars).

The closest star, besides the Sun is Proxima Centaui. It has a parallax of.76 seconds of arc. One degree 60 minutes in 1 degree 60 seconds in 1 minute

Astronomers can also determine the distance to stars by comparing how bright it looks, to how bright it would appear at some standard distance. A car headlight in the distance appears dimmer than one close by. If you know how bright a headlight actually is, you can calculate the distance to a distant one.

Color is an indication of energy Higher frequencies have more energy Usually, red stars give off less energy than blue stars, so you calculate its actual brightness by its color So, you can measure how bright it appears, calculate how bright it should be, and calculate the distance to the star by its color

Certain stars regularly change their brightness and are called “variable stars”. One kind are called Cepheid Variables. Cepheids pulsate in direct relation to how bright they are. If you time the period of pulsation, you know their true brightness, and thus, distance.

When stars end their lives in an explosion, it is called a supernova A type II supernova is when a giant star blows up. They have hydrogen visible in their spectra and widely different brightness of their explosions Type I supernovas were first predicted in 1930, and happen when the dead core of a medium star like the Sun (white dwarf) explode. They have no hydrogen in their spectra and always explode with the exact same brightness. So distances to other galaxies can be calculated.

Most galaxies are moving away from us. The farther away they are, the faster they are moving. Because they are moving away from us, the light they give off is shifted to the red end of the color spectrum. The faster it is going, the more the “redshift”. You can calculate distance by measuring the redshift of a galaxy.

Ways to find distance 1.parallax 2.comparing brightness 3.measuring color 4.Cepheid Variables 5.type I supernovas 6.galactic redshift

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