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Wednesday, Sep. 2, 2015

They'll only look like they're close together

Thursday, February 16, 2012

Not much happening astronomically speaking this week. Venus and Jupiter are still the brightest things in the southwestern sky after sunset, and the moon is setting near sunrise.

Next week tiny Mercury will be joining the evening crowd with a short appearance and brief conjunction with our old friend Uranus.

Uranus is one of the outer gas-giant planets. Its location has been shown to us over the last few weeks by Venus and the moon and now Mercury will have a turn at showing us where to look.

Understand that the two planets will not really be close to each other, they will line up along the same line of sight so that they will only look close to each other.

Speaking of which, that brings up another e-mail which showed up in my in-box this past week.

The writer asked about the three stars that appear to form an almost straight line in the eastern sky just after sunset.

In my answer I explained that the stars are the belt of Orion and look to be equally spaced from each other in an almost straight line, looking like a belt around Orion's middle.

Actually the organization of the belt stars only appears to be equally spaced and in a line. They are in what is what is called "optical alignment."

In reality the three stars are nowhere near each other.

From left to right the stars are Alnitak, Alnilam, and Mintaka. Alnitak is 826 light years from us, Alnilam is 1,359 light years away, and Mintaka is 919 light years away.

Even worse, the Orion Nebula -- the center star in the Sword of Orion -- is about 1,600 light years away.

To put this in perspective, keep in mind that a light year is about six trillion miles.

One thing we must come to understand, the sky, like Earth, is not flat. In reality, the stars making up what we see as the familiar shapes of the constellations often are very far away from each other. We must start thinking of the sky in three-dimensional terms.

The organization of the sky into the familiar constellations are only in our mind. If we were to travel a bazillion miles into space, the constellations we know now would not be there when we looked at the sky because the alignment will be totally different.

That is one of the curious things about the human mind, we tend to see patterns in everything we look at, and constellations were some of the first patterns that we, as thinking beings, formed.

Another place this seeming alignment comes into play are with what appear to be double-stars, or stars that seem to be very close to each other.

Some double-stars are truly double, but many others are not. They are only lined up along the same line of sight from our perspective and appear to be close to each other.

SKY WATCH: Fourth quarter moon was Tuesday, Feb. 14. Fifty years ago on Feb. 20, John Glenn was the first American astronaut to orbit Earth. Tuesday, Feb. 21 begin your Mercury watch. The tiny planet will appear in the west just after sunset and move higher each day. It will be near a very slender, one-day old moon on Wednesday, Feb. 22. Look about 45-minutes after sunset. Binoculars will be essential, just be sure the sun is below the horizon before any observation is attempted.

NEXT WEEK: More astronomical blathering.


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Vernon Whetstone
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