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FAQs

What are star trails? How can I capture them?

A two-hour-and-15-minute star trail image from March 21, 2014.  Our friend Ken Christison in North Carolina captured this image.  He wrote,

A two-hour-and-15-minute star trail image from March 21, 2014. Our friend Ken Christison in North Carolina captured this image.

What are star trails? They are the continuous paths created by stars, produced during long time exposure photographs, as shown on this page. In other words, the camera doesn’t track along with the stars’ apparent motion as night passes (actually caused by Earth’s spin under the sky). Instead, the camera stays fixed, while, as the hours pass, the stars move. The resulting photos show the nightly movement of stars on the sky’s dome.

How often does a solar eclipse happen on the March equinox?

Composite total solar eclipse Aug. 1999 by Fred Espenak.

A total solar eclipse is nature’s grandest spectacle. This composite image is by eclipse master Fred Espenak.

There’s a total solar eclipse coming up at this month’s equinox. When is the next one after this, and how often do we get an equinox-eclipse?

What makes a halo around the sun or moon?

A moon halo in Mandan, North Dakota by Marshall Lipp. February, 2015.

A moon halo in Mandan, North Dakota by Marshall Lipp. February, 2015.

Your Friday FAQ! Here’s what causes those rings of light around the sun or moon … plus lots of cool photos.

What’s the birthstone for March?

Photo credit:

Photo credit: Wikimedia

Happy birthday to all you March babies! March has two birthstones – aquamarine and bloodstone.

Are a star’s brightness and luminosity the same thing?

Image credit: NASA

Image credit: NASA

When we talk about the luminosity of a star, we are referring to the star’s intrinsic brightness. We are not talking about the star’s apparent magnitude – its brightness as it appears from Earth. For instance, most every star that you see with the unaided eye is larger and more luminous than our sun. The stars that we see at night are millions – even hundreds of millions – of times farther away than the sun. Regardless, you can still see these distant suns because many of them are hundreds or thousands of times more luminous than our local star.

What makes Venus the brightest planet?

Venus (brighter) and Mars (above) on February 15, 2015, submitted to EarthSky by Marsha Kircshbaum.  She got this shot as Point Reyes National Seashore in California.  Thank you, Marsha.

Venus (brighter) and Mars (above) on February 15, 2015, by Marsha Kircshbaum. She got this shot as Point Reyes National Seashore in California. Thank you, Marsha.

Venus is much brighter than any other planet viewed in Earth’s sky. It’s the third-brightest object in the sky, after the sun and moon. Click the links below to learn more about why Venus is so bright and when to see it as its brightest

How big are the biggest monster stars?

UY Scuti compared to our sun

UY Scuti compared to our sun. Image by Philip Park via Jillian Scudder

How big can stars get? And how do these monster stars get so big? When speaking of bigness among stars, you have to define your terms. The heaviest star is thought to be R136a1. It’s 265 times more massive than our sun – nearly twice as massive as what astronomers thought was possible. It’s the most massive star known at this time (February 2015). But there are more ways than one to measure stars’ bigness. In terms of sheer physical size, another exceedingly large star is UY Scuti. It’s only 30 times the sun’s mass, but has a radius more than 1,700 greater than the sun. Follow the links inside to learn more about these monster stars.

What are circumpolar stars?

482px-Circumpolar_AZ81

Circumpolar stars always reside above the horizon, and for that reason, never rise or set. All the stars at the Earth’s North and South Poles are circumpolar. Meanwhile, no star is circumpolar at the Earth’s equator. And in between?

What’s the birthstone for February?

Hey February babies! Happy birthday! Your birthstone, the amethyst, was the stone of royalty, representing power.

What do you know about the Yellowstone supervolcano?

Echinus Geyser, Yellowstone National Park. Image Credit: National Park Service.

Echinus Geyser, Yellowstone National Park. Image Credit: National Park Service.

Beneath Yellowstone National Park in the western United States, lies a hot, upwelling plume of mantle. Heat from the mantle melts the overlying rocks and the resulting magma pools close to Earth’s surface. Areas such as these are known as volcanic hotspots.