Mercury Transit, November 11, 2019

Looks a lot closer to the Sun than 36 million miles...the Sun must really be huge....It's hard to believe there are stars that make the Sun look small...I mean how big is big...

The sun's diameter is about 864,000 miles while Mercury's is 3000 miles, a ratio of about 290:1, but since Mercury is 2/3 as far away, it would make the apparent ratio closer to 200:1.

But those really big guys don't live long, maybe a few million years before they blow through their hydrogen, then helium, etc., to iron, collapse and explode. If what's left is massive enough, it becomes a neutron star or a black hole.

https://www.skyandtelescope.com/astronomy-resources/how-long-do-stars-live-stars-die/#:~:targetText=A%20star's%20life%20expectancy%20depends,few%20million%20years%20of%20fusion.

I didn't know that was general about the big ones. I guess the 'limited lifespan' of millions or billions of years is long enough from a human perspective, to seem really permanent anyway.

We had some rare clear nights recently, and what a treat it is to see all the visible stars instead of the select few.

The luminosity of a star is proportional to the 3.5 power of the mass:

The lifetime of a star is approximately inversely proportional to the 2.5 power of the mass:

http://hyperphysics.phy-astr.gsu.edu/hbase/Astro/startime.html#:~:targetText=The%20lifetime%20of%20a%20star,lifetime%20of%20a%20given%20star.

Get some 7x50 binoculars for the next clear night and you'll see a lot more stars. The 50mm objectives capture a lot of light.

The Pleiades star cluster is awesome.

..."When asked how many stars they see in the cluster, beginning observers will usually say five. That's what most of us see at a glance, and it makes sense because the five brightest Pleiades — Alcyone, Atlas, Electra, Maia, and Merope — range from magnitude 2.9 to 4.2, well within the grasp of most observers from a reasonably dark sky site."...

..."Luminosity is also referred to as the absolute magnitude or absolute brightness of an object. It is the real brightness of a celestial object. The apparent magnitude or apparent brightness of an object is a measure of how bright an object appears to be to an observer."...

http://coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/luminosity.html

Break out those eclipse glasses!

I'm still set up with the filters from the 2017 eclipse. Fortunately, this time the window is about 4 1/2 hours, not 1 or two minutes, so here is hoping the weather cooperates!

There it is...

(Camera: Canon SX50-HS with ND-100000 filter.)

Interestingly, I couldn't see it at all on the camera viewscreen and only found it when I looked at the files on the computer. It was smaller than a pixel on the viewscreen

I've only seen Mercury once before, just after sunset, a very tiny but very bright point of light, visible for just a couple minutes before setting.

Watch it live...now