My first Magazine Sky & Telescope - 02.2019 | Page 37

Holy cow, there it is — and blinking with Dan Gray’s chopper — WOOHOO!!! The Crab pulsar, PSR B0531+21 p LOCATION OF THE PULSAR Left: The 16th-magnitude pulsar, PSR B0531+21, and the very slightly brighter fi eld star that appears next to it, are exaggerated in brightness in this sketch so they’re easily visible. Right: The author’s sketch from the night of April 12, 2010, shows how the ampli- tude of the Crab Pulsar’s brightness changed using Dan Gray’s “chopper.” The minimum to maximum frequency was about 2 seconds as seen using 1210× on the 90-inch Bok telescope at Kitt Peak. The pulsar is the star on the right. “Holy cow, there it is — and blinking with Dan Gray’s chopper — WOOHOO!!! It was best seen with averted vision and was quite obvious once I caught the beat of the 2-ish second ampli- tude. Once I got the beat I watched for about 10 beats before Dan pushed me away from the eyepiece for his turn. This is a dead- solid awesome sight!” This observation will always be one of the most exciting things I’ve seen through a telescope. My exclamations at the eyepiece immediately brought all the other observers rushing to the observing platform as Dan was good-naturedly, but fi rmly, pushing me aside for his turn. I can’t say we saw a difference between the primary and slightly fainter interpulse, but that wasn’t the point — we saw the Crab pulsar’s brightness change with our own eyes. We understood the special nature of this observation, so everyone took several turns at the eyepiece. We may or may not be the only ten people to have ever seen the Crab pulsar change in brightness visually, but we count ourselves excep- tionally fortunate to have done so. It’s one thing to know that it rotates at 30 times per second, but it’s an utterly breathtak- ing experience to see that it actually does. ¢ Nearly nine years later Contributing Editor HOWARD BAN- ICH is still enthralled by this observation — he sincerely thanks his good friend Dan Gray for making the “chopper.” Howard can be reached at [email protected]. +30° ` magnitudes changes in the pulsar’s brightness, the precise rate Dan had chosen for the shutter made the pulsar smoothly change in brightness, from maximum to invisibility and back again over approximately 2 seconds. It was like a lighthouse beacon on a foggy night: AURIGA Elnath TAURUS +25° M1 f Hyades ¡ Cool animations 2. To get an idea of what we saw, check out: https://is.gd/crabmovie1 See the Crab Nebula expansion over 10 years at: https://is.gd/crabmovie2 This is a short animation made by Detleff Hartmann using images he took with his homemade 17.5-inch telescope. 2 3 4 5 6 Crab Nebula +20° c 1. 1 Aldebaran +15° _ a k 1 ORION 5 h 30 m k 2 5 h 00 m 4 h 30 m sk yandtele scope.com • FE B RUA RY 2 019 35