How Many Galaxies Will Rubin See?
Look deeper into the Cosmic Treasure Chest image to estimate the total number of galaxies in the observable Universe by estimating the total number of galaxies in one Rubin field of view.
Teacher Notes
The Cosmic Treasure Chest image in Skyviewer is measured in “Rubin‘s field of view”. One Rubin field of view shows the amount of the observable Universe that Rubin Observatory captures each time an image is created by pointing the telescope at the night sky. It is equivalent to approximately 10 square degrees.
The fully zoomed-out Cosmic Treasure Chest image is approximately 24 square degrees.
The Legacy Survey of Space and Time will extend for ten years and over that period, each area of the main survey is expected to be visited about 800 times.
Previous estimates for the total number of galaxies in the observable Universe were 200-300 billion galaxies. But recent research suggests that the number is more likely to be around two trillion galaxies.
For a variation in Step 6, have each student report their galaxy counts and develop a class average. This could be used to do the remaining calculations.
Prerequisites/ Starting Points
If students do not understand the concept of a degree, first introduce that there are 360 degrees in a circle.
Stars are mapped in a similar way that the Earth is mapped, but instead of using longitude (the imaginary lines that run from the North Pole to the South Pole on maps), celestial maps use right ascension, or RA, for short. Instead of using latitude (the lines that parallel the Equator), celestial maps use declination, or Dec. Like longitude and latitude, RA and Dec are measured in degrees.
When calculating an area on a celestial map, multiplying the measured change in declination by the measured change in right ascension produces an area in square degrees.