The closest Cepheid variable stars

It has long been thought that the two closest Cepheid variable stars were Polaris (Alpha Ursae Minoris) and Delta Cephei, the prototype for this class.  However, recent parallax data from the Gaia Space Observatory suggests that another Cepheid, Eta Aquilae, might actually be slightly closer than Delta Cephei.  Eta Aquilae and Delta Cephei were the first two Cepheid variable stars identified, in 1784, by English astronomers Edward Pigott and John Goodricke, respectively. 

The current status of the closest three Cepheids is summarized in this table: 

Closest Cepheid variables

name	parallax (mas)	distance (ly)	source
Polaris	7.292 ± 0.028	447 ± 2	1
Eta Aquilae	3.711 ± 0.194	879 ± 46	2
Delta Cephei	3.578 ± 0.148	912 ± 38	2
1) Scott G. Engle et al, 2018 Res. Notes AAS 2 126
2) Kayla A. Owens et al., Astrophys.J. 927 (2022)1,8

According to the analysis of the Gaia data in Ref. 2, Eta Aquilae and Delta Cephei are at essentially the same distance, within measurement uncertainty (4–5%).  [note: distance is obtained from the measured parallax by d = 3261 ly/P, where P is the parallax in milliarcsec (mas)]

 Here is a finder chart showing the location of Eta Aquilae (η Aqi):

credit: SkySafariAstronomy.com

On Sunday night (27 July) the sky was remarkably dark, with sqml=21.71 to 21.78. That is almost as good as it gets here in Creede.  These images were obtained with an Olympus E-M1iii + 17mm f/1.8 lens.
 

Eta Aquilae is circled.  Sparkle-6 filter.

The bright star left of center is Altair (Alpha Aquilae, α Aqi).

A closer look.  Softon filter.

Silent Sky

 "Silent Sky" is the name of a play by Lauren Gunderson that tells the somewhat fictionalized story of the life of Henrietta Swan Leavitt.  The play is currently being performed this season at the Creede Repertory Theatre.  

Leavitt worked at the Harvard College Observatory in the early 1900s and is famous for discovering the correlation between the intrinsic brightness and the pulsation period of a type of variable star known as Cepheids.  This relationship was the key toward understanding the size of our galaxy, the distance to other galaxies, and the size of the universe.  Leavitt would have been a strong contender for the Nobel prize had she not died of cancer at the age of 53.

Put  simply, if two Cepheid variables with the same pulsation period are observed and one is four times fainter than the other, then the inverse-square law says that the fainter star must be twice as far away.  If the distance to the nearer star can be determined, then the distance to the further star is also known.  By measuring the apparent brightness and pulsation period of Cepheids in other galaxies and comparing them to those in our galaxy, we can determine the distance to the other galaxies.  This was first accomplished by Edwin Hubble in 1924.

 The two closest Cepheid variables are Polaris, the North Star, and Delta Cephei, from which the type-name "Cepheid" is derived.  The distance to both have now been measured via parallax to an accuracy of about 0.4% for Polaris and 4% for Delta Cephei.  Polaris is 447 ly distant, and the distance to Delta Cephei is about 912 ly.

 

The Little Dipper (left) and the constellation Cepheus (right).  Polaris and Delta Cephei are marked by circles.

Without the constellation lines.  Olympus 17mm f/1.8 lens, Sparke-6 filter.

These images were obtained on 25 July, the first clear night after a prolonged stretch of rainy weather.  The night was breathlessly calm and very dark, with a measured sky brightness of sqml = 21.66 to 21.71 mpsas.

 

The Summer Triangle

The Big Dipper over Bristol Head.

The moon reappears in the evening sky

 

2.3-d moon setting over Bristol Head

Saturday evening, 26 July

Masuyama MOP and Meade Super Plössl eyepieces

Two highly-regarded telescope-eyepiece series are the original Meade Super Plössl and the Masuyama eyepieces from Ohi Optical Manufacturing company of Japan. 

In the mid 1980s, Ohi Optical released a Masuyama-branded  series of telescope eyepieces.  Masuyama is the name of the designer and the founder of Ohi Optical. These eyepieces were a 5-element, 3-group 2-1-2 configuration, and are believed to be implementations or derivatives of the Zeiss Astroplanokular design.   These eyepieces were well received and similar designs soon appeared on the market, notably Meade 5-element "Super Plössl" eyepieces manufactured by the Japanese company Kowa.  The Meade eyepieces and similar offerings under other brands became known as "pseudo-Masuyamas".

The Meade eyepieces eventually devolved into a more traditional 4-element 2-group 2-2 Plössl configuration, while retaining the now-meaningless "Super Plössl" designation.  Manufacturing was first shifted from Japan to Taiwan, then to mainland China.  Meade Corporation is now defunct.  The original Japanese 5-element versions are considered to be collectibles.

In late 2023 Ohi Optical released a new series of 5-element eyepieces designated as Masuyama MOP. There was much initial speculation about the meaning of the "MOP" acronym, but the Ohi Optical website now clearly states that it means "Masuyama Ortho Plössl".   

The Masuyama nomenclature is confounding for at least two reasons.  First, the original Plössl design comprises two achromatic doublets with four elements total, not five.  Second, the MOP eyepieces are advertised as having an apparent field of view (AFOV) of 53°.  A true orthoscopic eyepiece is limited to an AFOV of about 44°, beyond which distortion becomes evident.  The MOP eyepieces are neither orthoscopic nor Plössls.  Marketing, as usual, is not deterred by engineering facts.

Regardless of the naming peculiarities, the MOP eyepieces have received excellent reviews.  I have three of the new MOP line as well as three of the original Meade eyepieces, which were purchased in 1988.  Together they form a set spanning focal lengths from 6.4 mm to 26 mm. 

 

The Masuyama MOP eyepieces are advertised as having a 53° AFOV, but my measurements (using the flashlight test) put this at 51°.  In the table below, the effective eye relief (EER) is the distance measured from the lip of the folded down eyecup.

Masuyama MOP eyepieces

FL (mm)	mass* (g)	field stop* (mm)	AFOV* (deg)	EER* (mm)
10	77.8	8.7	51	5
15	100.9	13	51	7
20	116.2	17.5	51	11
*measured

 

Meade.  Engraved "Japan" imprint.

Meade Super Plössl eyepieces (1988)

FL (mm)	mass* (g)	field stop* (mm)	AFOV* (deg)	EER* (mm)
6.4	43.8	5.3	50	3
12.4	69.8	10.4	52	7
26	100.3	26	50	16
*measured

 

The combined set

Milky Way through the clouds

 There was just enough time to get the star-tracker aligned before the clouds in the northern sky covered Polaris.  I was able to get two shots of the the Milky Way in the southern sky.  There has been a lot of haze from wildfire smoke, so the current rainy weather should help to clear the air.

Both images: Olympus E-M1iii + 12mm f/2 lens, ISO 1600, 30 sec.

with Hoya Softon filter

 

with Hoya Sparkle-6 filter

Another large prominence on the sun

Hydrogen-alpha, false-color.  Lunt LS50THa double-stacked. 

full disk, 11 July.

Thick wildfire smoke this morning.  This was shot through very obvious smoky haze. The large prominence on the NE limb extends about 57,000 mi (93,000 km) above the sun's surface.

 

July 4 moon

 

1st-quarter moon over McCall Gulch, 02 July

4th of July.  Celestron C8, Sony A7iii.

Northern region.  Celestron C8, Olympus E-M5iii + 2x Barlow.

The Moon last night. The Sun today.

 There was a clear view of the 6.7-d moon last night, just before some late-evening clouds moved in.

Celestron C8, Sony A7iii.

 

The crater with the central peak is named Theophilus.

 

There were more massive prominences on the sun today (02 July).

 

double-stacked Lunt LS50THa + ASI 178mm camera.

false color, masked to emphasize the prominences.