How Far Can You See?

Richard

The most distant object observable with the unaided eye is visible in our current night time sky. It is the Great Galaxy in Andromeda, M31. There are many ways to find this object. I prefer to use the constellation Cassiopeia.

Cassiopeia was the Queen of Ethiopia. She is commonly depicted as a lady on a throne, upside down for part of the year. From our latitude (northern Utah), the constellation is circumpolar, meaning that it never sets. It is close enough to the north celestial pole that, if we could hide the Sun, we would see Cassiopeia simply circling the north star over a 24-hour period.

10 pm, MDT, from Salt Lake City, image credit: Starry Night Pro software

10 pm, MDT, from Salt Lake City, image credit: Starry Night Pro software

It may be difficult to see a lady on a throne in the stars, so I see Cassiopeia as a lazy ‘w’ shape, currently in the northeastern sky at 10 pm, MDT. Using the image below, we can find the ‘w’ shape on its side, about 1/3 of the way up the sky from the northeastern horizon. The distance between the  two end points of the ‘w’ is about 15 degrees. The distance from the bottom of the ‘w’ to Andromeda is also about 15 degrees.

Use the 'w' of Cassiopeia to find M31, the Andromeda Galaxy

Use the 'w' of Cassiopeia to find M31, the Andromeda Galaxy

M31 is difficult to see from a city or suburb–the darker the sky, the better. Nevertheless, it can be seen without the aid of binoculars or a telescope. This galaxy contains around one trillion stars and is about 5 times the size of our Milky Way galaxy. It is over 2.5 million light years away.

Most of the stars you can see individually in the night sky are all pretty close to us–within a couple thousand light years. The Milky Way, that streak of cloudy light we see across the sky, is a few thousand to a few tens of thousands of light years away. Our entire Milky Way galaxy, containing around 200 billion stars, is probably 100,000 light years across. The Andromeda Galaxy, the nearest major galaxy to us, is over 2.5 million light years away, and there is a lot of nothing between us and it.

Space is a great big empty…

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One thought on “How Far Can You See?

  1. I was Surfing for something completely different, but got your page How Far Can You See? « Clark Planetarium and found it Interesting.Nice Post on city light…Thanks.

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