by Bill Pellerin, GuideStar editor
Object: V473 Lyr, (SAO 87008)
Class: Classic Cepheid Variable
Constallation: Lyra
Magnitude: 5.99—6.35
Period: 1.49078 days
R.A.: 19 h 15 m 59.5 s (2000 coordinates)
Dec: 27 deg 55 min 34.7 sec
Size/Spectral: F6
Distance: 1,681 ly
Optics needed: Small telescope
Many HAS members will be attending the Silent Sky play at the Main Street Theater this month. The play is about Henrietta Swan Leavitt who identified the luminosity (intrinsic brightness) / period relationship in Cepheid variable stars. The prototype star is Delta Cep, which was the object of the month way back in September, 2006.
Eta Aql, another Cepheid is the object of the month in the June, 2015 GuideStar. Generally speaking, Cepheid stars are short period, low amplitude variables. Their light doesn’t change much, and the cycle of variability is short. V473 Lyr’s period is only about 1.5 days. The period and the amplitude of variation is, itself, variable so any results you obtain through your own observations may, well, vary.
The AAVSO has limited data on this star, and you can print a finder chart by visiting AAVSO.org. If you print a chart, make sure the orientation of the stars in the chart match the orientation of stars you’d see in your eyepiece. Join the AAVSO and submit your observations at AAVSO.org.
So, how did Miss Leavitt discover this relationship? She was tasked with getting data from photographic plates of the Large Magellanic Cloud. The stars in the cloud are approximately the same distance from us so the brightness of these stars could be compared. In her report she wrote, “It is worthy of notice (that) the brighter variables have longer periods” (From the book Miss Leavitt’s Stars.) Needless to say this was a great understatement of her discovery, but she was a cautious person and only had a limited number of examples of variable stars to work with.
The problem came to be the ‘calibration’ of the Cepheid variable stars. Once the distance to any one Cepheid star could be determined, the distance to all others could be determined using the inverse square law, which simply says that stars that are farther away are dimmer.
By the time Edwin Hubble discovered a Cepheid variable in the Andromeda Galaxy the ‘calibration’ was not very good. This resulted in his estimate of distance to the Andromeda Galaxy of 1,000,000 light years. As astronomers established better information on the Cepheid variables, the distance estimate changed to the better value of 2.1 million light years.
After a brief hiatus (life seems to intrude on my astronomy) this installment of Astrophotography Corner concerns one of the two important mechanical requirements for getting good image data, polar alignment. Next to autoguiding (which we cover in the next installment), getting your mount well polar aligned is essential.
Why this object is interesting.
October is here, and that means the weather should start to be a little cooler (maybe), night time comes a little earlier, and more importantly, fall star party season is upon us! As I write this message, the UBarU star party was held just a few weeks ago, the Okie-Tex Star Party is happening this upcoming week, and in a month, the Eldorado Star Party will be in full swing. For many of us, it’s a great time to get away under dark skies with many other kindred spirits to observe, take astrophotographs, enjoy great speakers, and otherwise enjoy the time away from the hustle-and-bustle of the big city.
You can observe the Moon whenever it's up, day or night! While binoculars and telescopes certainly reveal incredible details of our neighbor’s surface, bringing out dark seas, bright craters, and numerous odd fissures and cracks, these tools are not the only way to observe details about our Moon. There are more ways to observe the Moon than you might expect, just using common household materials.
