Matt’s World of Weather: Big Dogs and Satellite Radio

Orion’s belt is one of the easier star clusters to find, and one of the more familiar features we can use to hop around the night sky. Watch the video and see for yourself how simple it is to locate Sirius. Below you’ll find additional information about Sirius and other helpful stargazing tidbits.

A Tad More Sirius:
All the bad puns aside, Sirius is responsible for the saying “Dog Days of Summer”. As mentioned in the video, Sirius is located in the constellation Canis Major or Big Dog. Accordingly, Sirius has been known as the Dog Star. The constellation is visible most of the year, but during the summer months, Sirius actually rises with the sun*. Thus, when Sirius (Dog Star) rises along with the sun, we can refer to those days as the “Dog Days of Summer”. They just happen to come during the hottest days of the year! Also, don’t forget about Sirius’s little pup. It’s a binary star system and the Big Dog (Sirius A) outshines the Pup (Sirius B) 10,000 to 1.

Numbers game:
The apparent magnitude number is very useful when deciding if trying to find an object at night is even worth it. The number alone will let you know, yes or no, if an object is visible with the naked eye. I say “object” because even the International Space Station is given a magnitude when it crosses overhead. The number is useful by itself and is often included in the location data for a star/object.

In our case Sirius has a magnitude –1.46. Basically that negative means it is a bright object and should be pretty easy to see at night. Initially you would think big number, bright star, but it’s actually the opposite, big number, very faint star…who knew a negative could really be a positive? Any star that has a magnitude between –1 and 6 can be seen without a telescope. Anything bigger than 6 means it is very faint and needs a telescope or binoculars. Can you see these objects with the naked eye?

Mercury at its brightest: -2.45 (Yes)
Sirius: -1.46 (Yes)
Saturn at its brightest: -.49 (Yes)
Andromeda Galaxy: 3.44 (Yes)
Neptune at its brightest: 7.78 (No)
Pluto at its brightest: 16.65 (No Way)
Venus in January: -4.3 (Yes Way)

Not only can this number save you time in the evening, but it will also give you a good sense of how bright one object is compared to another!

*This has changed through the years because of the Earth's rotation on its axis

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  • by David McGowan Location: Greenville, NC on May 4, 2011 at 04:44 PM
    I really enjoy these astrometry updates.

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