Mira

[glenc]

The variable star Mira is bright now. I estimate it to be about magnitude 3. It has a maximum every 332 days.
The attached map is from SkyMapPro. Mira is marked by circles.
This map is from the AAVSO http://www.aavso.org/charts/CET/OMI_CET/OMICET-A.GIF

http://en.wikipedia.org/wiki/Mira
"Evidence that the variability of Mira was known in ancient China (http://en.wikipedia.org/wiki/History_of_China), Babylon (http://en.wikipedia.org/wiki/Babylon) or Greece (http://en.wikipedia.org/wiki/Ancient_Greece) is at best only circumstantial.[7] (http://en.wikipedia.org/wiki/Mira#cite_note-6) What is certain is that the variability of Mira was recorded by the astronomer David Fabricius (http://en.wikipedia.org/wiki/David_Fabricius) beginning on August 3 (http://en.wikipedia.org/wiki/August_3), 1596 (http://en.wikipedia.org/wiki/1596). Observing the planet Mercury (http://en.wikipedia.org/wiki/Mercury_%28planet%29), he needed a reference star for comparing positions and picked a previously unremarked third-magnitude star nearby. By August 21 (http://en.wikipedia.org/wiki/August_21), however, it had increased in brightness by one magnitude (http://en.wikipedia.org/wiki/Apparent_magnitude), then by October had faded from view. Fabricius assumed it was a nova, but then saw it again on February 16 (http://en.wikipedia.org/wiki/February_16), 1609 (http://en.wikipedia.org/wiki/1609) [8] (http://en.wikipedia.org/wiki/Mira#cite_note-7).
In 1638 Johannes Holwarda (http://en.wikipedia.org/wiki/Johann_Holwarda) determined a period of the star's reappearances, eleven months; he is often credited with the discovery of Mira's variability. Johannes Hevelius (http://en.wikipedia.org/wiki/Johannes_Hevelius) was observing it at the same time and named it "Mira" (meaning "wonderful" or "astonishing," in Latin) in 1662's Historiola Mirae Stellae, for it acted like no other known star. Ismail Bouillaud (http://en.wikipedia.org/wiki/Ismail_Bouillaud) then estimated its period at 333 days, less than one day off the modern value of 332 days (and perfectly forgivable, as Mira is known to vary slightly in period, and may even be slowly changing over time)."

[sheeny]

Thanks Glen. I had showers and storms here last night but I'd like to get a spectrum of Mira while its bright, so weather permitting maybe this weekend!

Al.

[Robh]

Al, excuse my ignorance. I understand the spectral class for Mira is M7.
If the star increases in luminosity, does the spectrum change and does this mean the spectral class changes also?

Regards, Rob.

[seanliddelow]

It was discovered by David Fabricus on the 13th of August 1596 but he thought it was a nova.
In 1603 Bayer put it in his atlas at 4th magnitude, not aware of its variability.
In 1779 it rose to nearly 1st magnitude and almost equal to Aldebaran.

Mira can sometimes reach the 2nd magnitude in brightness.
Its minimum is 9th magnitude.
With an average period of 331 days.
At minimum Mira is one of the coolest known stars with a temprature of 1900k and a spectral type M9.
At maximum the temp rises to 2500k and a spectral type of M6e.
The highest temp is reached after the star cools.
It has strong spectral bands of titanium oxide.
Mira has a bright blue companion with a density of 3300 times that of the Sun.

Heres a link for an image of Mira and its companion:
http://hubblesite.org/newscenter/archive/releases/star/1997/26/

[Robh]

Sean. Thanks for that. You've answered my question.

Regards, Rob

[sheeny]

As I understand it, the spectral class should change - depending on the degree of variation. Change in brightness usually means a change in temperature, which therefore means a change in spectrum. So small brightness variations, may not means a change of class, but bigger variations would.

Al.

[seanliddelow]

The information I used was from Burnhams Celestial Handbook Volume 1 it is 30 years old but I would imagine in would be fairly accurate as Mira is a well known star.

Sean

[Saturnine]

Hi All

Re - Mira observations

Observed Mira last Sunday night and estimated that its current magnitude is approx 3.7, using the nearby stars Delta, mag 4.1 and Gamma, mag 3.5 as references. It was definitely brighter than Delta but fainter than Gamma, will be fascinating to watch for the next few months.

Regards

Jeff

[seanliddelow]

I saw Mira a month ago when it was 4th or 5th magnitude.
It was probably 4.5