How long an exposure would a photographer need to photograph star trails that are complete circles? Why?
The star Sirius is 4.3 light years from Earth. Determine the distance to Sirius in km and in astronomical units.
THe moon's average distance from Earth is about 380,000 km. How long does it take moonlight to reach Earth? HELP!!!!!!
To photograph star trails that form complete circles in the sky, the exposure time will depend on a few factors:
1. The rotation of the Earth: The Earth rotates 360 degrees in approximately 24 hours, which means it moves about 15 degrees per hour. To capture complete circles, you would need an exposure time slightly longer than the time it takes for the stars to move 360 degrees across the frame. Let's assume you want to capture a complete circle in a 24mm lens, which has a field of view of about 84 degrees diagonally. The exposure time would be approximately (360/15) x (24/84) = 8 hours.
However, keep in mind that this is a rough estimate, and the actual exposure time may vary based on various conditions like the latitude, the focal length of the lens, the desired effect, and the level of light pollution.
Now let's move on to the other questions:
1. The distance to Sirius in km:
Since light travels at a speed of approximately 300,000 km/s, and Sirius is 4.3 light-years away, you can calculate the distance in km by multiplying the speed of light by the number of seconds in a year (365.25 days) and then by 4.3. The approximate distance to Sirius would be 300,000 km/s * (365.25 days * 24 hours * 60 minutes * 60 seconds) * 4.3.
2. The distance to Sirius in astronomical units (AU):
One astronomical unit (AU) is the average distance between the Earth and the Sun, which is approximately 150 million km. To convert the distance to Sirius into AU, you would divide the distance in km by 150 million km/AU.
For the moonlight question, we can determine the time it takes for moonlight to reach Earth by dividing the average distance between the Earth and the moon (380,000 km) by the speed of light (300,000 km/s). The time would be approximately 1.27 seconds.
To photograph star trails that form complete circles, a photographer would need to take a long exposure shot. Let's break down the process of calculating the exposure time required:
1. Determine the desired length of the star trails circle: This depends on the photographer's artistic vision and the desired size of the circle. Let's assume the photographer wants an image with a radius of 10 degrees, which is roughly the size of a closed hand with fingers extended.
2. Calculate the apparent motion of the stars: The stars appear to move across the sky due to Earth's rotation. The apparent motion of stars depends on the location and the observer's latitude.
3. Formula to calculate exposure time: The exposure time can be determined using the following formula:
Exposure time (in seconds) = 360 degrees / apparent motion of stars (in degrees per hour)
4. Use the appropriate conversion factors: Ensure that the degrees and degrees per hour are in the same units, either degrees/minute or degrees/second, for correct calculation.
By following these steps, the photographer can determine the exposure time needed to capture star trails forming complete circles.
Moving on to the second question, let's calculate the distance to Sirius:
1. Given information: Sirius is 4.3 light years away from Earth.
2. Conversion from light years to kilometers: Since light travels at approximately 299,792 kilometers per second in a vacuum, we can calculate the distance using the following equation:
Distance (in kilometers) = 4.3 light years × (9.461 × 10^12 kilometers per light year)
3. Therefore, the distance to Sirius is approximately 40.7236 × 10^12 kilometers.
Lastly, let's determine how long it takes for moonlight to reach Earth:
1. Given information: The moon's average distance from Earth is about 380,000 kilometers.
2. Speed of light: As mentioned earlier, light travels at approximately 299,792 kilometers per second in a vacuum.
3. Time calculation: Divide the distance by the speed of light to determine the time it takes:
Time = Distance / Speed of light
4. Therefore, the time it takes for moonlight to reach Earth is approximately 380,000 kilometers / 299,792 kilometers per second, resulting in about 1.27 seconds.
Remember, calculations may vary slightly due to rounding or different conversion values used.