Measuring the Universe: How Astronomers Learned to Measure Celestial Distances Explained with Animation

Have you ever won­dered how astronomers fig­ure out the mind-bog­gling dis­tances between the Earth and var­i­ous astro­nom­i­cal objects? In this infor­ma­tive ani­mat­ed video from the Roy­al Obser­va­to­ry at Green­wich, we learn the fun­da­men­tals of the Cos­mic Dis­tance Lad­der, the suc­ces­sion of meth­ods used to deter­mine those dis­tances.

The video was made for “Mea­sur­ing the Uni­verse: from the tran­sit of Venus to the edge of the cos­mos,” an exhib­it that will be on dis­play at the obser­va­to­ry through Sep­tem­ber 2. The exhib­it is timed to coin­cide with this year’s rare tran­sit of Venus, which will be vis­i­ble from Earth on June 5 and 6 and won’t hap­pen again until 2117. The tran­sit of Venus played a key role in the his­to­ry of astrom­e­try. In 1663 the Scot­tish math­e­mati­cian and astronomer James Gre­go­ry pro­posed a method of tim­ing the move­ment of Venus across the Sun from two wide­ly sep­a­rat­ed points on the Earth and using the dif­fer­en­tial to cal­cu­late the sun’s mean equa­to­r­i­al par­al­lax and, by tri­an­gu­la­tion, the Sun’s dis­tance from the Earth.

Know­ing the dis­tance from the Earth to the Sun, we can then fig­ure out the dis­tances of some stars using the same method of trigono­met­ric par­al­lax. But as astronomer Olivia John­son explains in the video, that tech­nique can only be used to mea­sure the clos­est stars. For dis­tances greater than 500 light years, oth­er meth­ods are required. When the objects in ques­tion have a known luminosity–in oth­er words, when they are “stan­dard can­dles”–the inverse square law of light can be used to cal­cu­late dis­tances. Those mea­sure­ments, along with Hub­ble’s Law and the Doppler Effect, enable even fur­ther cal­cu­la­tions extend­ing to the edge of the known cos­mos.

“What’s most incred­i­ble to me,” says John­son, “is how all these mea­sure­ments build on each oth­er. It’s only by know­ing the scale of our Solar System–the dis­tance between the Earth and Sun–that we’re able to mea­sure dis­tances to near­by stars using par­al­lax. If we can learn how far it is to some near­by stan­dard can­dles using par­al­lax, we can then use com­par­isons between stan­dard can­dles to mea­sure the dis­tances to far­ther stars and galax­ies. Final­ly, by study­ing the motions of galax­ies with stan­dard can­dles, we learn we can use red­shift to mea­sure dis­tances through­out our expand­ing Uni­verse.”

via Devour

Relat­ed Con­tent:

The Hig­gs Boson, AKA the God Par­ti­cle, Explained with Ani­ma­tion