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Earthsky Tonight - Oct 01 2009
Arcturus shines in west on October evenings
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The very bright object in the southeast to southern sky on these October 2009 evenings is the planet Jupiter. But many have asked about a bright star – not as bright as Jupiter, but still very bright and twinkling very actively – in the west after sunset. Jim wrote, When I looked at it through my binoculars it flashed brilliant red, brilliant blue and bright white. I live in Indiana and called my cousin in Wisconsin, who also could see it. It was quite beautiful. Do you know what it was that I was looking at?
Jim, every year at this time, we get questions about three different stars that are flashing different colors. One is Capella in the constellation Auriga the Charioteer, which is now in the northeast in mid-evening. One is Sirius in the constellation Canis Major the Greater Dog, which is now in the south before dawn.
And the third is the one you’re asking about, Jim, in the west to northwest after sunset. This star is Arcturus in the constellation Bootes the Herdsman. It’s flashing colors for the same reason Sirius and Capella are . . . because all three of these stars are bright and, at this time of year, noticeably low in the sky. When you see an object low in the sky, you’re seeing it through a greater thickness of atmosphere than when it’s overhead. The atmosphere refracts or splits the stars’ light to cause the colorful flashing you observed, Jim.
Written by Deborah Byrd
Comments (8)
at 06.11 am on 09-29-2009 Al
We can see this awesome star in deep south texas. We can't take our eyes off it. Who needs cable and digital when u can go outside and view all these beautiful sights. Last night we witnessed again the ISS flying over our home. SPECTACULAR SIGHT
Replyat 07.51 am on 10-01-2009 Kent Hunter
I am curious. If Arcturus was located where our sun is, how far into our solar system would it extend (as far as the earth?)
Replyat 11.14 am on 10-01-2009 Bruce McClure
Kent,
According to the star expert Jim Kaler, the diameter of Arcturus is about 25 times that of the sun. If Arcturus were to take the place of the sun, the surface of this giant star would extend about 1/4 to 1/3 the way to the orbit of Mercury, the solar system's innermost planet.
at 09.36 am on 10-01-2009 Lou
Regarding Jupiter, is it possible that I can discern the moons with my naked eye? What I mean to say is, last night (9-30-09) I thought that from my central New Jersey latitude that I could make out some sort of satellite at the 4 o'clock position of Jupiter. Does this correlate with the actual data?
Replyat 12.42 pm on 10-01-2009 Bruce McClure
Lou,
There was a fairly dim star (Iota Caprcorni) about 1/2 degree to the east of Jupiter on September 30, at about the 9 o'clock position. In fact, this star and Jupiter will remain close together all through October 2009. As for seeing a moon of Jupiter with the unaided eye, I have my doubts - especially since the bright moon last night (September 30) would have made the task all the more difficult. Do you have a good pair of binoculars that you can hold steadily? Or a telescope? If so, there's a good chance of seeing some of Jupiter's moons tonight (October 1). The 4 moons will be in a straight line, with one moon on one side of Jupiter and the other 3 moons on the other side. Good luck!
at 10.46 am on 10-01-2009 Orion
Roughly when should we next expect to be able to see Mars or Saturn again?
Replyat 05.17 am on 10-02-2009 Bruce McClure
Orion,
To see Mars, you have to stay up late or wake up early. Mars rises into the east-northeast sky at midnight or later, and is close to the summit of sky by daybreak. Are you familiar with the constellation Gemini's brightest stars, Castor and Pollux? Mars is quite close to Pollux right now. If all else fails, you can use the moon to find Mars on the nights of October 10-11 and October 11-12. You can go to the upper right of this page to scroll to our October 10th show for more on the moon and Mars.
As for Saturn, you can catch this planet low in the east at morning dawn. Be sure to read our October 7th show about the Saturn/Mercury conjunction on the morning of October 8.
Good luck!
Bruce
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at 06.11 am on 09-29-2009 Al
We can see this awesome star in deep south texas. We can't take our eyes off it. Who needs cable and digital when u can go outside and view all these beautiful sights. Last night we witnessed again the ISS flying over our home. SPECTACULAR SIGHT
Replyat 07.51 am on 10-01-2009 Kent Hunter
I am curious. If Arcturus was located where our sun is, how far into our solar system would it extend (as far as the earth?)
Replyat 11.14 am on 10-01-2009 Bruce McClure
Kent,
According to the star expert Jim Kaler, the diameter of Arcturus is about 25 times that of the sun. If Arcturus were to take the place of the sun, the surface of this giant star would extend about 1/4 to 1/3 the way to the orbit of Mercury, the solar system's innermost planet.
at 09.36 am on 10-01-2009 Lou
Regarding Jupiter, is it possible that I can discern the moons with my naked eye? What I mean to say is, last night (9-30-09) I thought that from my central New Jersey latitude that I could make out some sort of satellite at the 4 o'clock position of Jupiter. Does this correlate with the actual data?
Replyat 12.42 pm on 10-01-2009 Bruce McClure
Lou,
There was a fairly dim star (Iota Caprcorni) about 1/2 degree to the east of Jupiter on September 30, at about the 9 o'clock position. In fact, this star and Jupiter will remain close together all through October 2009. As for seeing a moon of Jupiter with the unaided eye, I have my doubts - especially since the bright moon last night (September 30) would have made the task all the more difficult. Do you have a good pair of binoculars that you can hold steadily? Or a telescope? If so, there's a good chance of seeing some of Jupiter's moons tonight (October 1). The 4 moons will be in a straight line, with one moon on one side of Jupiter and the other 3 moons on the other side. Good luck!
at 10.46 am on 10-01-2009 Orion
Roughly when should we next expect to be able to see Mars or Saturn again?
Replyat 05.17 am on 10-02-2009 Bruce McClure
Orion,
To see Mars, you have to stay up late or wake up early. Mars rises into the east-northeast sky at midnight or later, and is close to the summit of sky by daybreak. Are you familiar with the constellation Gemini's brightest stars, Castor and Pollux? Mars is quite close to Pollux right now. If all else fails, you can use the moon to find Mars on the nights of October 10-11 and October 11-12. You can go to the upper right of this page to scroll to our October 10th show for more on the moon and Mars.
As for Saturn, you can catch this planet low in the east at morning dawn. Be sure to read our October 7th show about the Saturn/Mercury conjunction on the morning of October 8.
Good luck!
Bruce