Australian Sky & Telescope — November-December 2017

64 AUSTRALIAN SKY & TELESCOPE November | December 2017

RICK JOHNSON

distractedbytheview.Stevehasanimpressivefolderfullof

observingtargetsandwriteshisnotesdirectlyonitspages.

Isoakedintheviewandthenquicklyreturnedtotheguest

observingtabletosketchwhatIsaw.Ithinkittookthree

trips up the ladder to make my drawing.

Whatasight!Eventhoughwecouldn’tseethetidaltails,

theviewwasmemorable.NGC7715lookedlikeaperfectly

edge-on galaxy and appeared much brighter than it had

throughmy0.7-mreflector,butNGC7714hadtakenona

muchmoredetailedshape.Itsportedalong,curvedcentral

barwithastubbyspiralarmcomingoffeachend.Isaw

both galactic arms distinctly, but the southern one was a bit

brighterthanthenorthern,withabrightspotrightatitstip.

Thebendsinbotharmsgavethegalaxyashapereminiscent

ofaseahorse.Theroundcorewasthebrightestpartofthe

galaxy overall but wasn’t particularly concentrated. On the

sidefacingNGC7715,afaintarcofgalacticfuzzconnected

tothecentralbar,almostlookinglikeablurofmotion.

Severalfaintstarswerescatteredaroundthefieldofview.

SFINELY SPACED TRIO Magnitude-5.7 star 16 Piscium shines at the top centre of this image. Arp 284, comprised of the two interacting galaxies

NGC 7714 and NGC 7715, lies north of the F6 star. In the unimaginably distant background shines the quasar 2333+019, seen here as a light-

blue, starlike object (arrowed) below the west end of NGC 7715. Why doesn’t the quasar appear red? Quasars peak in their energy output at 1000

angstroms. For a z = 1.87 quasar, this peak will shift redward to 2870 angstroms, making 2333+019 appear blue. The quasar would have to be much

farther away or surrounded by dust to appear red. South is up, west is to the right.

While I was working on my sketch and Steve was looking

through the eyepiece, the direction of our observation

suddenly changed. Jimi sat at his wonderfully shielded laptop,

examining the DSS image of Arp 284 loaded into MegaStar,

looking for anything interesting nearby we could observe

next. That’s when he saw a star-like object labeled 2333+019

just a few arcminutes off the northwest end of NGC 7715.

With a name like that, just a right ascension and declination,

it could be anything. It turned out to be a quasar.

The unexpected quasar

Jimi clicked on the image in front of him and an info box

popped up to show us a redshift of 1.871. (An object’s

redshift, noted as z, is a measure of its distance; the larger

the number, the longer it takes for the object’s light to

travel to us.) He excitedly told us the number, and we were

suddenly re-energised. Steve was trying to figure out the

light-travel time in his head while Jimi looked it up on an

online cosmological calculator. Meanwhile, I was trying to

DEEP DISCOVERY