Event Date: October 11th
Time: 7:26(.57) PM
Brief
If you remember when we started seeing the Summer Triangle's stars during late spring evenings, the later Sunsets meant that we had to wait about a minute later on average, to see them. That, coupled with them rising four minutes earlier each evening, meant that we saw them high in the east after only about a month, depending exactly when we first saw the stars. Now, since the Sun has been setting at its fastest rate earlier, being shortly after the September equinox, we are still able to see the Triangle at about transit time for several weeks, when the stars come out.
Here is the Triangle at transit time. I included the meridian this time, to further show where the center is vertically. Remember, if a line is drawn from each star, bisecting each opposite "side", they all meet at a common point within the triangle shape; that is the center.
Time: 7:26(.57) PM
Brief
If you remember when we started seeing the Summer Triangle's stars during late spring evenings, the later Sunsets meant that we had to wait about a minute later on average, to see them. That, coupled with them rising four minutes earlier each evening, meant that we saw them high in the east after only about a month, depending exactly when we first saw the stars. Now, since the Sun has been setting at its fastest rate earlier, being shortly after the September equinox, we are still able to see the Triangle at about transit time for several weeks, when the stars come out.
Here is the Triangle at transit time. I included the meridian this time, to further show where the center is vertically. Remember, if a line is drawn from each star, bisecting each opposite "side", they all meet at a common point within the triangle shape; that is the center.
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| click on image to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp. |
Detailed
We have a good view of the stars all evening long, up to about midnight when Altair and Vega get low. Deneb takes a little longer than Vega to set, being a little further north. Even though it is not completely dark yet, the triangle's stars are easily visible during nautical twilight, while bright(est) Vega can even be seen with the eye alone a little earlier, during the end of civil twilight. Deneb and Altair take a little longer, with the latter a little brighter, being much closer. Altair is only 17 light years away, while Deneb is estimated to be as many as 3,000 light years away!
Considering that we can see Deneb, that means that it is not only a huge, hot star; it is an extremely luminous one, at approximately 300,000 times that of the Sun. If Deneb was half the distance it is from us, it would likely exceed all other stars in apparent magnitude-- even Sirius, which is nearly -1.5. Vega and Altair on the other hand, are much less luminous, at 61 and 12 times that of our Sun respectively. Therefore, even though Vega is 8 light years further away than Altair, we see it first, as the sky gets dark.
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