OBSERVERS CHALLENGE May 2023
by Glenn Chaple
NGC 4088 Galaxy in Ursa Major (Magnitude 11.2, Size 5.8’ X 2.2’)
On the evening of March 9, 1788, William Herschel came across a nebulous object which he described as “Bright, considerably large, extended 55 degrees, little brighter in the middle.” He entered it in his Catalogue of Nebulae and Clusters of Stars as H I-206 (H2061), his 206th Class I (Bright Nebulae) object. Its modern-day New General Catalog designation is NGC 4088.
Categorized as a grand design spiral galaxy, NGC 4088 is located at the 2000.0 coordinates 12h5m34.2s RA and +50o32’21” dec. It’s a 3½o star-hop from Phecda (gamma [γ] Ursae Majoris), as shown in the accompanying finder charts. Despite this relatively star-poor journey, I had little trouble locating NGC 4088 with a 10-inch f/5 reflector. At 80X, the galaxy was readily seen. A magnitude 5 limiting magnitude made it difficult to detect any detail, although I sensed a mottled appearance.
I was unable to spot NGC 4085, a 12th magnitude nearly edge-on spiral 12 arc-minutes south of NGC 4088. Herschel missed it on the night he discovered NGC 4088, but picked it up during another sweep the next year. Though it’s fainter and smaller than NGC 4088, he still categorized it as a Class I object, giving it the designation H I-224. The two galaxies apparently form a physical pair and are part of a galaxy group that includes Messier 109.
Distance calculations to NGC 4088 range between 37 and 55 million light years. Assuming a middle value, the Universe Guide website calculates that NGC 4088 would have a true diameter of some 74.3 million light years – about ¾ the size of the Milky Way. If we were to freeze the expansion of space, the Universe Guide figures that a non-stop 4 mile per hour stroll to NGC 4088 would take some 7.6 quadrillion years
Chart from AAVSO Variable Star Plotter (VSP). The magnitude 2.4 star near upper right is gamma (γ) Ursae Majoris. Stars shown to 10th magnitude in this 7 by 4 degree field.
Image by Mario Motta