On April 25, 1990, the Hubble Space Telescope was put into orbit after being launched the day before on the Space Shuttle Discovery. To celebrate that event’s 27th anniversary representing a milestone in the history of astronomy, one of the many breathtaking photographs that accompanied Hubble’s activity was published, which in this case portrays two galaxies together, NGC 4302 and NGC 4298.
This pair of galaxies is part of Virgo Cluster, which includes about 2,000 galaxies. They’re both spiral galaxies, like the Milky Way, and were discovered in 1784 by the astronomer William Herschel. They’re about 55 million light years away from Earth so Herschel classified them as spiral nebulaes because of the instruments of the time’s limits. Only in the 20th century it was possible to understand their nature thanks to Edwin Hubble’s studies, one more reason reason to choose their photo to celebrate the telescope named after him.
The NGC 4302 galaxy has a 90° tilt from our point of view so it’s exactly edge on. It has a diameter of about 87,000 light years, about 60% of that of the Milky Way, but has a total mass that is only a tenth. The blue spot in its lower part is probably an area where a star formation process is in progress that gives it a color different from the remaining visible part.
The NGC 4302 galaxy has an 70° tilt from our point of view so we can see its “face”. Its size is relatively small with a diameter of about 45,000 light years with a total mass of less than 2% of that of the Milky Way being estimated at about 17 billion solar masses. Its spiral structure is visible but not very pronounced in comparison with other galaxies of this type.
After its launch in orbit, the Hubble Space Telescope has been upgraded in various service missions with new instruments that still make it one of the most extraordinary telescopes available to astronomers around the world. This celebratory photo was taken with one of the last instruments installed, the Wide Field Camera 3 (WFC3) installed in 2009, in three visible light bands.
In 2016, a further extension of the Hubble Space Telescope mission was approved until 2021 but with a bit of luck this wonderful product of human ingenuity could keep on working for several years. In fact, it wonn’t be replaced by the James Webb Space Telescope but the two of them will independently and sometimes maybe will complement each other.