This sequence of images taken with NASA's Hubble Space Telescope chronicles the rhythmic changes in a rare class of variable star (located in the center of each image) in the spiral galaxy M100. This class of pulsating star is called a Cepheid Variable. The Cepheid in this Hubble picture doubles in brightness (24.5 to 25.3 apparent magnitude) over a period of 51.3 days.
The interval it takes for the Cepheid to complete one pulsation is a direct indication of the stars's intrinsic brightness. This value can be used to make a precise measurement of the galaxy's distance, which turns out to be 56 million light-years from Earth.
Cosmic distance measurements as accurate as this are needed to calculate the rate at which the universe is expanding. This value, called the Hubble Constant, is used to estimate the age and size of the universe.
Though M100 is the most distant galaxy in which Cepheid variables have been discovered, HST must find Cepheids in a larger sample of galaxies before a definitive number can be agreed upon for the size and age of the universe
Hubble Space Telescope was used to image repeatedly a region of M100 in order to pick out the flickering Cepheid candidates from normal stars. Twelve one-hour exposures, timed carefully in a two-month observing window, resulted in the discovery of 20 Cepheid variable stars.
Technical Information:
The Hubble Space Telescope images were taken on (from left to right) April 23, May 4, 9, 16, 20, 31, 1994 with the Wide Field Planetary Camera 2 (WFPC 2) This black and white picture was take at visible light wavelengths.
Credits
Dr. Wendy L. Freedman, Observatories of the Carnegie Institution of Washington, and NASA| About The Object | |
|---|---|
| Object Name | M100 |
| R.A. Position | 12h 22m 54.94s |
| Dec. Position | 15° 49' 19.49" |
| About The Object | |
|---|---|
| Object Name | A name or catalog number that astronomers use to identify an astronomical object. |
| Object Description | The type of astronomical object. |
| R.A. Position | Right ascension – analogous to longitude – is one component of an object's position. |
| Dec. Position | Declination – analogous to latitude – is one component of an object's position. |
| Constellation | One of 88 recognized regions of the celestial sphere in which the object appears. |
| Distance | The physical distance from Earth to the astronomical object. Distances within our solar system are usually measured in Astronomical Units (AU). Distances between stars are usually measured in light-years. Interstellar distances can also be measured in parsecs. |
| Dimensions | The physical size of the object or the apparent angle it subtends on the sky. |
| About The Data | |
| Data Description |
|
| Instrument | The science instrument used to produce the data. |
| Exposure Dates | The date(s) that the telescope made its observations and the total exposure time. |
| Filters | The camera filters that were used in the science observations. |
| About The Image | |
| Image Credit | The primary individuals and institutions responsible for the content. |
| Publication Date | The date and time the release content became public. |
| Color Info | A brief description of the methods used to convert telescope data into the color image being presented. |
| Orientation | The rotation of the image on the sky with respect to the north pole of the celestial sphere. |
