Venus Butts Up Against The “linking Star” Tonight

Venus and El Nath, a star officially belonging to Taurus but shared by Auriga, will be closest tonight. They'll still be close the next few nights. Maps created with Stellarium

If you look to the west at nightfall tonight you’ll notice that Venus has a close companion, the star El Nath. El Nath sits at the tip of Taurus the Bull’s northern horn; its name comes from the Arabic “al nath” meaning “the butting one”. Fitting for a bull, I’d say.

Over the past week or so, Venus and the star have been closing in toward each other. Tonight the two will be closest at only 0.8 degrees apart.

El Nath and Alpheratz are shared by dual constellations. Each helps complete the outline of both.

El Nath is one of only two “linking stars” in the sky. Linking stars officially belong to one constellation but do double duty filling out the outline of another. El Nath, also called Beta Tauri, completes the familiar pentagonal outline of Auriga the Charioteer directly above Taurus. The other one, Alpheratz (AL-fer-ratz), is Andromeda’s brightest star and completes the well known diamond-shaped Great Square of Pegasus. Without Alpheratz, the Square would collapse into an ordinary triangle.

Venus shines as a brilliant crescent on May 2 seen from Dayton, Ohio through a 10-inch telescope. Credit: John Chumack

El Nath is also known as Beta Tauri – the second brightest star in Taurus – and shines a bright second magnitude. That hardly compares to Venus’ brilliance. If we could somehow be transported to an imaginary planet orbiting El Nath, we’d be taken aback. Blazing before our eyes would be a star 4.6 times the size of the sun and shining 700 times brighter.

Its true brilliance is masked by the 130 light years that separate us. Venus wins out by proximity at a trifling 38 million miles.

Astronomers use the different viewpoints provided by the Earth's location at either end of its orbit to measure a nearby star’s shift in position (parallax) against the more distant background stars. Click to see a great animation of parallax. Illustration: Bob King

Determining whether a star is bright because it’s closer or because it’s intrinsically brighter has been one of astronomy’s key questions since the invention of the telescope. How do you tell the difference?

We had to wait until 1838 before astronomers had the precision telescopes needed to measure a star’s parallax or shift against the more distant background stars.  From that shift, the nearby star’s distance could from Earth could be determined (top). Parallax allowed us to extend our reach to about a 100 light years. Stars beyond that were compared to similar-type stars with known distances to extend the distance scale even further.

In 1908, Henrietta Leavitt discovered that variable stars called Cepheids could be used as “yardsticks” to measure distances as far as neighboring galaxies. Thanks to these efforts and others, nowadays we know which stars are truly bright and which are truly faint.

If you’d like to learn more about how astronomers probed distances across the universe, please check out my previous blog on parallax and this one on Cepheids.

6 Responses

      1. Nath Gallagher

        I just wanted to express the joy I have found this evening* Finding out things that I didn’t know about my name. The star is most interesting, Taurus is my lil brothers sign. That makes it extra special to me. I also have an international Order named ofter me, even though it is a eastern Indian thing, I have many shared views. Very excited right now *!

  1. gene

    hi bob. i Observed the super moon in high def and noticed a “picture”? You posted a shot of the moon in 2008 that shows it very clearly. The face of a “native” is the lunersea. he is looking left tword the sky. There is a burning pipe/alter in front of him. The smoke “rises” and is funeled into the “mouth” of a seperate face. the bridge of the nose and cheek bones are un deniable on the second “man” on the moon. What do you think? Am i seeing

    1. astrobob

      Hi Gene,
      You have a great imagination. I think I can see the head of the person you refer to but not the whole figure. You’re free of course to see lots of things in the dark and light lunar patches. Your interpretation is as good as the rabbit, the woman or whatever might be up there. Thanks for sharing your impression.

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