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Why Variable Stars Are Worth Targeting

Why target variable stars? It helps to improve your ability to distinguish faint objects when you target variable stars when out stargazing. Variable stars are high on the scale of star magnitude and practicing to observe these increases the sensitivity of your eyes to detect differences in brightness.

There are books on the subject, like this one by Percy. But what makes them interesting night sky targets to hone in with your home telescope is that there are many types and you can challenge yourself to find them in the pursuit of helping astronomy. Read on…

Understanding Variable Stars

Title on the subject of variable stars
available at Amazon

About variable stars

Variable stars are stars that vary in brightness for an assortment of reasons. Unlike our Sun, which remains fairly stable, the output of light from these varies. They include stars that are shifting from one stage of their evolution to another, some are in the process of dying.

But there are several reasons for their varying brightness, which makes them interesting targets for backyard stargazers.

Understanding all the different variable stars helps astronomy in that it can reveal processes in the evolution of stars and the death of a star.

It’s easier to sight variable stars than other targets in the night sky of light polluted areas such as cities. And you can become part of a bigger mission to observe variables to monitor their brightness and so add to astronomical knowledge.

Types of variable stars

Two main types: extrinsic (or external) where the brightness is due to an external driver and intrinsic (or internal) where brightness is driven internally.

Intrinsic subtypes:

  1. Pulsating variables, include LPVs and Cepheids, long period variables (LPVs) that include periodic types such as Mira and semi-regular and irregular variables, which are an assortment of random types.
  2. Eruptive or Cataclysmic stars, which include the novas — which stand-out since their outer layer explode and the rare Supernovas, which is when the star dies
Capture by MarcelC

Extrinsic subtypes:

  1. Eclipsing binaries of the Algol class includes the multiple stars of Beta Persei, Beta Lyrae, and BL Telescopium
  2. Rotation variables
Examples of variable stars in a classification tree
Source: CSIRO

They include:

  1. Pulsating variables, such as the long-period ones (LPVs) and the Cepheids, such as Delta Cephei, that are regular and predictable and so can serve as yardsticks to measure distances to galaxies beyond the Milky Way.
    The periodic LPVs include the red giants within the Mira variables, e.g. Mira (Omicron Ceti).
  2. Eruptive types, which include the Novas and rare Supernovas and R Coronea Borealis.
  3. Eclipsing binaries (EB), which have equal brightness, but due to change in their orbit that creates an eclipse, the brightness of one will vary.
  4. Rotating variables, which show minor variation in light emitted as a result of star spots — dark or bright spots, or patches on their surfaces. 

What are examples of variable stars?

Examples of variable stars include the eclipsing variables of Algol: Beta Persei, Beta Lyrae, and BL Telescopium, which are multiple stars.

Look for the supergiant BL Telescopium in Telescopium, a southern hemisphere constellation best seen from latitudes south of 33º during June to August. Its visible brightness is max 7.1–min 9.1, which means it’s outside naked eye viewing, at –6, but within the range for astronomy binoculars.

Another southern hemisphere example: The Eruptive variable of BV Centauri, a dwarf nova in the constellation of Centaurus. With an apparent magnitude of 10.7 to 14.0, you’ll need a telescope.

Examples of Mira variable stars:

  • R Pegasus
  • Omicron Ceti
  • R Horologii
  • L2 Puppis
  • R Carinae
  • L Carinae
  • R Leonis
  • S Carinae
  • T Centaurii
  • RS Scorpii
  • RR Scorpii

How many variable are there to see?

  • With the naked eye there are about a dozen or so you can pick up with good conditions at the right time. An example: the Delta Cepheid, L Car, which has a brightness 3.3–4.2. Also Mira (Omicron Ceti ) with a brightness of 2.

Help monitor variable stars

American Association of Variable Star Observers (aavso.org) is the place to log your information and they have manuals to download to help you do this to advance the science of variable stars.

The aavso.org site offers variable star lists and charts to print. For beginners, look for the Getting Started dropdown for the Manual for Visual Observing of Variable Stars.

If this is something you would like to get into, AAVSO have a list of easy stars to begin with.

Resources

To find out more about identifying and monitoring variable stars, check out these sites:

AAVSO| Australian National Telescope Facility | Variable Stars South