Recent Astronomy Articles at Cosmic Pursuits

Newtonian Reflectors and Dobsonian Telescopes

May 26, 2020 by Brian Ventrudo Filed Under: Astronomy Equipment

A Newtonian reflector telescope on an equatorial mount (credit: Skywatcher).

Reflecting telescopes (or reflectors) collect light using a curved mirror at the rear of the main tube rather than a lens at the front end. Isaac Newton gets credit for inventing the first reflecting telescope in the late 17^th century. He used a second small diagonal mirror to direct light out the side of the telescope to an eyepiece. His immensely practical design, now called the Newtonian reflector, is the main type of purely reflecting telescope in use today by amateur astronomers [Read more…] about Newtonian Reflectors and Dobsonian Telescopes

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Supernova in Messier 61

May 20, 2020 by Brian Ventrudo Filed Under: Celestial Events

The Type II supernova SN2020jfo in the face-on spiral galaxy Messier 61 in the constellation Virgo. Captured on May 19, 2020 with a TV85 refractor, TRF-2008 0.8x focal reducer, and ASI290MM camera. Stack of 20x10s images.

The galaxy M61 has done it again: it’s produced another supernova, the eighth such event since 1926. That makes this lovely face-on spiral galaxy in the Virgo cluster one of the most prolific supernova producers of the past century.

The supernova, cataloged as SN2020jfo, was discovered on May 6, 2020 at the Zwicky Transient Facility at Palomar Observatory near San Diego. Upon discovery, the exploding star was magnitude 14.7. It’s since brightened to about 14.3. To see it visually requires at least a 10″ telescope, but it is relatively easy to take a snapshot with an astronomy camera and a much smaller scope. I took the 20x10s stack of images at the top with an 85mm Tele Vue refractor, an 0.8x focal reducer, and an inexpensive ZWO ASI290MM camera.

One of the more prominent members of the Virgo cluster, Messier 61 is a lovely barred spiral with winding arms knotted with star-forming nebula and clouds of blue-white stars. It’s a starburst galaxy, one wracked with prodigious star formation which explains why so many supernovae have been seen here. With lots of massive, fast-burning young stars forming, it’s inevitable that they reach their spectacular end as a Type II supernova during which the star, as it runs out of fuel, collapses and snaps back in a spectacular explosion. It releases as much energy in a few weeks as our Sun releases in its entire 10 billion year life span.

The face-on spiral galaxy Messier 61 in the constellation Virgo. Image courtesy of the European Southern Observatory (ESO).

M61 is about the same size as our Milky Way and lies about 52 million light years away, so the progenitor star detonated when Earth was in the Eocene period back when Australia and Antarctica were still connected and most of the planet was covered in lush forest.

And since astronomy is not just a matter of contemplating space but also time, keep in mind that the light from thousands more supernovae from M61 are on the way to us now, events to be detected by generations of Earth-bound astronomers yet to be born.

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Schmidt-Cassegrain Telescopes

May 14, 2020 by Brian Ventrudo Filed Under: Astronomy Equipment

A Schmidt-Cassegrain telescope (credit: Celestron)

In the most recent article on telescopes, you had a look at Newtonian reflectors, the oldest type of mirror-based telescope for astronomy. Newtonians, as you learned, have one big drawback: they are big. Because they use a single primary mirror to direct light back to a flat secondary mirror, which in turn reflects light to the eyepiece at the side of the tube, the physical length of a Newtonian is roughly equal to its focal length. So a 12″ aperture f/6 Newtonian, for example, is at least six feet long and more than a foot wide. But in 1672, shortly after Issac Newton developed his famous design, an obscure French Catholic priest named Laurent Cassegrain invented a reflector that used two mirrors to fold a long optical path into a much shorter tube. Now many reflectors, and nearly all professional astronomy telescopes, use some variation of the Cassegrain design [Read more…] about Schmidt-Cassegrain Telescopes

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A Primer on Telescope Mounts

May 3, 2020 by Brian Ventrudo Filed Under: Astronomy Equipment

A professional-grade German equatorial telescope mount (credit: Bisque.com)

Even the most expensive and carefully crafted telescope isn’t worth much if it’s not on a solid and stable mount that lets you accurately point it anywhere in the sky. A good telescope mount is as important as the optics of a telescope, and it must be sufficiently solid and stable such that if you give the telescope tube a good tap on the side, the mount should damp down vibrations in less than 5 seconds (max), and faster if you’re planning on astrophotography. Most telescopes, especially scopes aimed at beginners, include a mount when you buy them. Smaller telescopes, especially high-end refractors, may just have mounting rings or plates which allows them to be attached to a mount which you buy separately. And if you are contemplating astrophotography, a solid mount is a must-have.

All telescope mounts can be classified as one of two types: alt-azimuth or equatorial. Let’s have look at each [Read more…] about A Primer on Telescope Mounts

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Edge-On Spirals Galaxies in the Northern Spring Sky

April 30, 2020 by Brian Ventrudo Filed Under: Deep Sky

A close-up of NGC 4565 (the Flying Saucer Galaxy), an edge-on spiral in Coma Berenices. Image credit: ESO.

The great amateur astronomer Leslie Peltier once suggested a cure for many of the world’s problems is simply “one gentle dose of starlight to be taken each night just before retiring”. If you feel the need for a little starlight these days, there is no better bang for your buck than looking at galaxies. Northern spring is the perfect time for observing these immense collections of billions of stars, hundreds of which lie within easy reach of a small telescope (thousands if you’re using a camera instead of an eyepiece) [Read more…] about Edge-On Spirals Galaxies in the Northern Spring Sky

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